wcdma ran planning and optimization (book1 wrnpo basics)

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WCDMA RAN Fundamental


Objectives

Upon completion of this course, you will be able to:

Describe the development of 3G

Outline the advantage of CDMA principle

Characterize code sequence

Outline the fundamentals of RAN

Describe feature of wireless propagation


Contents

1. 3G Overview

2. CDMA Principle

3. WCDMA Network Architecture and protocol structure

4. WCDMA Wireless Fundamental


Different Service, Different Technology

AMPS

TACS

NMT

Others

1G 1980sAnalog

GSMGSM

CDMA CDMA IS-95IS-95

TDMATDMAIS-136IS-136

PDCPDC

2G 1990sDigital

Technologies drive

3G IMT-2000

UMTSUMTSWCDMAWCDMA

cdmacdma20002000

Demands drive

TD-SCDMA

TD-SCDMA

3G provides compositive services for both operators and subscribers

The first generation is the analog cellular mobile communication network in the time period from the middle of 1970s to the middle of 1980s. The most important breakthrough in this period is the concept of cellular networks put forward by the Bell Labs in the 1970s, as compared to the former mobile communication systems. The cellular network system is based on cells to implement frequency reuse and thus greatly enhances the system capacity.

The typical examples of the first generation mobile communication systems are the AMPS system and the later enhanced TACS of USA, the NMT and the others. The AMPS (Advanced Mobile Phone System) uses the 800 MHz band of the analog cellular transmission system and it is widely applied in North America, South America and some Circum-Pacific countries. The TACS (Total Access Communication System) uses the 900 MHz band. It is widely applied in Britain, Japan and some Asian countries.

The main feature of the first generation mobile communication systems is that they use the frequency reuse technology, adopt analog modulation for voice signals and provide an analog subscriber channel every other 30 kHz/25 kHz.

However, their defects are also obvious:

Low utilization of the frequency spectrum

Limited types of services

No high-speed data services

Poor confidentiality and high vulnerability to interception and number embezzlement

High equipment cost

To solve these fundamental technical defects of the analog systems, the digital mobile communication technologies emerged and the second generation mobile communication systems represented by GSM and IS-95 came into being in the middle of 1980s. The typical examples of the second generation cellular mobile communication systems are the DAMPS of USA, the IS-95 and the European GSM system.

The GSM (Global System for Mobile Communications) is originated from Europe. Designed as the TDMA standard for mobile digital cellular communications, it supports the 64 kbps data rate and can interconnect with the ISDN. It uses the 900 MHz band while the DCS1800 system uses the 1800 MHz band. The GSM system uses the FDD and TDMA modes and each carrier supports eight channels with the signal bandwidth of 200 kHz.

The DAMPS (Digital Advanced Mobile Phone System) is also called the IS-54 (North America Digital Cellular System). Using the 800 MHz bandwidth, it is the earlier of the two North America digital cellular standards and specifies the use of the TDMA mode.

The IS-95 standard is another digital cellular standard of North America. Using the 800 MHz or 1900 MHz band, it specifies the use of the CDMA mode and has already become the first choice among the technologies of American PCS (Personal Communication System) networks.

Since the 2G mobile communication systems focus on the transmission of voice and low-speed data services, the 2.5G mobile communication systems emerged in 1996 to address the medium-rate data transmission needs. These systems include GPRS and IS-95B.

The CDMA system has a very large capacity that is equivalent to ten or even twenty times that of the analog systems. But the narrowband CDMA technologies come into maturity at a time later than the GSM technologies, their application far lags behind the GSM ones and currently they have only found large-scale commercial applications in North America, Korea and China. The major services of mobile communications are currently still voice services and low-speed data services.

With the development of networks, data and multimedia communications have also witnessed rapid development; therefore, the target of the 3G mobile communication is to implement broadband multimedia communication.

The 3G mobile communication systems are a kind of communication system that can provide multiple kinds of high quality multimedia services and implement global seamless coverage and global roaming. They are compatible with the fixed networks and can implement any kind of communication at any time and any place with portable terminals.


3G Evolution

Proposal of 3G

IMT-2000: the general name of third generation mobile

communication system

The third generation mobile communication was first proposed

in 1985，and was renamed as IMT-2000 in the year of 1996

Commercialization: around the year of 2000

Work band : around 2000MHz

The highest service rate :up to 2000Kbps

Put forward in 1985 by the ITU (International Telecommunication Union), the 3G mobile communication system was called the FPLMTS (Future Public Land Mobile Telecommunication System) and was later renamed as IMT-2000 (International Mobile Telecommunication-2000). The major systems include WCDMA, cdma2000 and UWC-136. On November 5, 1999, the 18th conference of ITU-R TG8/1 passed the Recommended Specification of Radio Interfaces of IMT-2000 and the TD-SCDMA technologies put forward by China were incorporated into the IMT-2000 CDMA TDD part of the technical specification. This showed that the work of the TG8/1 in formulating the technical specifications of radio interfaces in 3G mobile communication systems had basically come into an end and the development and application of the 3G mobile communication systems would enter a new and essential phase.

The 3GPP is an organization that develops specifications for a 3G system based on the UTRA radio interface and on the enhanced GSM core network.

The 3GPP2 initiative is the other major 3G standardization organization. It promotes the CDMA2000 system, which is also based on a form of WCDMA technology. In the world of IMT-2000, this proposal is known as IMT-MC. The major difference between the 3GPP and the 3GPP2 approaches into the air interface specification development is that 3GPP has specified a completely new air interface without any constraints from the past, whereas 3GPP2 has specified a system that is backward compatible with IS-95 systems.


3G Spectrum Allocation

ITU has allocated 230 MHz frequency for the 3G mobile communication system IMT-2000: 1885 ~ 2025MHz in the uplink and 2110~ 2200 MHz in the downlink. Of them, the frequency range of 1980 MHz ~ 2010 MHz (uplink) and that of 2170 MHz ~ 2200 MHz (downlink) are used for mobile satellite services. As the uplink and the downlink bands are asymmetrical, the use of dual-frequency FDD mode or the single-frequency TDD mode may be considered. This plan was passed in WRC92 and new additional bands were approved on the basis of the WRC-92 in the WRC2000 conference in the year 2000: 806 MHz ~ 960 MHz, 1710 MHz ~ 1885 MHz and 2500 MHz ~ 2690 MHz.


Bands WCDMA UsedMain bands

1920 ~ 1980MHz / 2110 ~ 2170MHz

Supplementary bands: different country maybe different1850 ~ 1910 MHz / 1930 MHz ~ 1990 MHz (USA)

1710 ~ 1785MHz / 1805 ~ 1880MHz (Japan)

890 ~ 915MHz / 935 ~ 960MHz (Australia)

. . .

Frequency channel number＝central frequency×5, for main band:

UL frequency channel number ：9612～9888

DL frequency channel number : 10562～10838

The WCDMA system uses the following frequency spectrum (bands other than those specified by 3GPP may also be used): Uplink 1920 MHz ~ 1980 MHz and downlink 2110 MHz ~ 2170 MHz. Each carrier frequency has the 5M band and the duplex spacing is 190 MHz. In America, the used frequency spectrum is 1850 MHz ~ 1910 MHz in the uplink and 1930 MHz ~ 1990 MHz in the downlink and the duplex spacing is 80 MHz.


3G Application Service

Time Delay

Error Ratio

background

conversational

streaming

interactive

Compatible with abundant services and applications of 2G, 3G system has an open integrated service platform to provide a wide prospect for various 3G services.

Features of 3G Services

3G services are inherited from 2G services. In a new architecture, new service capabilities are generated, and more service types are available. Service characteristics vary greatly, so each service features differently. Generally, there are several features as follows:

Compatible backward with all the services provided by GSM.

The real-time services (conversational) such as voice service generally have the QoS requirement.

The concept of multimedia service (streaming, interactive, background) is introduced.


The Core technology of 3G: CDMA

CDMA

WCDMAWCDMACN: based on MAP and GPRS

RTT: WCDMA

TD-SCDMACN: based on MAP and GPRS

RTT: TD-SCDMA

cdma2000CN: based on ANSI 41 and MIP

RTT: cdma2000

Formulated by the European standardization organization 3GPP, the core network evolves on the basis of GSM/GPRS and can thus be compatible with the existing GSM/GPRS networks. It can be based on the TDM, ATM and IP technologies to evolve towards the all-IP network architecture. Based on the ATM technology, the UTRAN uniformly processes voice and packet services and evolves towards the IP network architecture.

The cdma2000 system is a 3G standard put forward on the basis of the IS-95 standard. Its standardization work is currently undertaken by 3GPP2. Circuit Switched (CS) domain is adapted from the 2G IS95 CDMA network, Packet Switched (PS) domain is A packet network based on the Mobile IP technology. Radio Access Network (RAN) is based on the ATM switch platform, it provides abundant adaptation layer interfaces.

The TD-SCDMA standard is put forward by the Chinese Wireless Telecommunication Standard (CWTS) Group and now it has been merged into the specifications related to the WCDMA-TDD of 3GPP. The core network evolves on the basis of GSM/GPRS. The air interface adopts the TD-SCDMA mode.


Contents

1. 3G Overview

2. CDMA Principle




Multiple Access and Duplex Technology

Multiple Access Technology

Frequency division multiple access (FDMA)

Time division multiple access (TDMA)

Code division multiple access (CDMA)

In mobile communication systems, GSM adopts TDMA; WCDMA, cdma2000 and TD-SCDMA adopt CDMA.


Multiple Access Technology

Frequency

Time

Power

FDMA

FrequencyTime

Power

TDMA

Power

Time

CDMA

Frequency

Frequency Division Multiple Access means dividing the whole available spectrum into many single radio channels (transmit/receive carrier pair). Each channel can transmit one-way voice or control information. Analog cellular system is a typical example of FDMA structure.

Time Division Multiple Access means that the wireless carrier of one bandwidth is divided into multiple time division channels in terms of time (or called timeslot). Each user occupies a timeslot and receives/transmits signals within this specified timeslot. Therefore, it is called time division multiple access. This multiple access mode is adopted in both digital cellular system and GSM.

CDMA is a multiple access mode implemented by Spreading Modulation. Unlike FDMA and TDMA, both of which separate the user information in terms of time and frequency, CDMA can transmit the information of multiple users on a channel at the same time. The key is that every information before transmission should be modulated by different Spreading Code to broadband signal, then all the signals should be mixed and send. The mixed signal would be demodulated by different Spreading Code at the different receiver. Because all the Spreading Code is orthogonal, only the information that was be demodulated by same Spreading Code can be reverted in mixed signal.


Multiple Access and Duplex Technology

Duplex Technology

Frequency division duplex (FDD)

Time division duplex (TDD)

In third generation mobile communication systems, WCDMA and cdma2000 adopt frequency division duplex (FDD), TD-SCDMA adopts time division duplex (TDD).


Duplex Technology

Time

Frequency

Power

TDD

USER 2

USER 1

DLUL

DLDL

UL

FDD

Time

Frequency

Power

UL DL

USER 2

USER 1


Contents

1. 3G Overview

2. CDMA Principle




WCDMA Network Architecture

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B Node B

Iu-CS Iu-PS

Iur

Iub IubIub Iub

CN

UTRAN

UEUu

CS PS

Iu-CSIu-PS

CSPS

WCDMA including the RAN (Radio Access Network) and the CN (Core Network). The RAN is used to process all the radio-related functions, while the CN is used to process all voice calls and data connections within the UMTS system, and implements the function of external network switching and routing.

Logically, the CN is divided into the CS (Circuit Switched) Domain and the PS (Packet Switched) Domain. UTRAN, CN and UE (User Equipment) together constitute the whole UMTS system

A RNS is composed of one RNC and one or several Node Bs. The Iu interface is used between RNC and CN while the Iub interface is adopted between RNC and Node B. Within UTRAN, RNCs connect with one another through the Iur interface. The Iur interface can connect RNCs via the direct physical connections among them or connect them through the transport network. RNC is used to allocate and control the radio resources of the connected or related Node B. However, Node B serves to convert the data flows between the Iub interface and the Uu interface, and at the same time, it also participates in part of radio resource management.


WCDMA Network Version Evolution

3GPP Rel993GPP Rel4

3GPP Rel5

2000 2001 2002

GSM/GPRS CNWCDMA RTT

IMSHSDPA 3GPP Rel6

MBMSHSUPA

2005

CS domain change to NGN

WCDMA RTT

The overall structure of the WCDMA network is defined in 3GPP TS 23.002. Now, there are the following three versions: R99, R4, R5.

3GPP began to formulate 3G specifications at the end of 1998 and beginning of 1999. As scheduled, the R99 version would be completed at the end of 1999, but in fact it was not completed until March, 2000. To guarantee the investment benefits of operators, the CS domain of R99 version do not fundamentally change., so as to support the smooth transition of GSM/GPRS/3G.

After R99, the version was no longer named by the year. At the same time, the functions of R2000 are implemented by the following two phases: R4 and R5. In the R4 network, MSC as the CS domain of the CN is divided into the MSC Server and the MGW, at the same time, a SGW is added, and HLR can be replaced by HSS (not explicitly specified in the specification).

In the R5 network, the end-to-end VOIP is supported and the core network adopts plentiful new function entities, which have thus changed the original call procedures. With IMS (IP Multimedia Subsystem), the network can use HSS instead of HLR. In the R5 network, HSDPA (High Speed Downlink Packet Access) is also supported, it can support high speed data service.

In the R6 network, the HSUPA is supported which can provide UL service rate up to 5.76Mbps. And MBMS (MultiMedia Broadcast Multicast Service) is also supported.


WCDMA Network Version Evolution

Features of R6

MBMS is introduced

HSUPA is introduced to achieve the service rate up to 5.76Mbps

Features of R7

HSPA+ is introduced, which adopts higher order modulation and MIMO

Max DL rate: 28Mbps, Max UL rate:11Mbps

Features of R8

WCDMA LTE (Long term evolution) is introduced

OFDMA is adopted instead of CDMA

Max DL rate: 50Mbps, Max UL rate: 100Mbps (with 20MHz bandwidth)


Contents

1. 3G Overview

2. CDMA Principle




Processing Procedure of WCDMA System

SourceCoding

Channel Coding& Interleaving Spreading Modulation

SourceDecoding

Channel Decoding& Deinterleaving Despreading Demodulation

Transmission

Reception

chip modulated signalbit symbol

ServiceSignal

Radio Channel

ServiceSignal

Receiver

Source coding can increase the transmitting efficiency.

Channel coding can make the transmission more reliable.

Spreading can increase the capability of overcoming interference.

Through the modulation, the signals will transfer to radio signals from digital signals.

Bit, Symbol, Chip

Bit : data after source coding

Symbol: data after channel coding and interleaving

Chip: data after spreading


WCDMA Source Coding

AMR (Adaptive Multi-Rate) Speech

A integrated speech codec with 8 source rates

The AMR bit rates can be controlled by the RAN depending on the system load and quality of the speech connections

Video Phone ServiceH.324 is used for VP Service in CS domain

Includes: video codec, speech codec, data protocols, multiplexing and etc.

5.15AMR_5.15

4.75AMR_4.75

5.9AMR_5.90

6.7 (PDC EFR)AMR_6.70

7.4 (TDMA EFR)AMR_7.40

7.95AMR_7.95

10.2AMR_10.20

12.2 (GSM EFR)AMR_12.20

Bit Rate (kbps)CODEC

AMR is compatible with current mobile communication system (GSM, IS-95, PDC and so on), thus, it will make multi-mode terminal design easier.

The AMR codec offers the possibility to adapt the coding scheme to the radio channel conditions. The most robust codec mode is selected in bad propagation conditions. The codec mode providing the highest source rate is selected in good propagation conditions.

During an AMR communication, the receiver measures the radio link quality and must return to the transmitter either the quality measurements or the actual codec mode the transmitter should use during the next frame. That exchange has to be done as fast as possible in order to better follow the evolution of the channel’s quality.



Transmitter

SourceCoding


SourceDecoding


Transmission

Reception


ServiceSignal

Radio Channel

ServiceSignal

Receiver




Scrambling can make transmission in security.


Bit, Symbol, Chip





WCDMA Block Coding - CRC

Block coding is used to detect if there are any uncorrected

errors left after error correction.

The cyclic redundancy check (CRC) is a common method of

block coding.

Adding the CRC bits is done before the channel encoding

and they are checked after the channel decoding.

During the transmission, there are many interferences and fading. To guarantee reliable transmission, system should overcome these influence through the channel coding which includes block coding, channel coding and interleaving.

Block coding: The encoder adds some redundant bits to the block of bits and the decoder uses them to determine whether an error has occurred during the transmission. This is used to calculate Block Error Ratio (BLER) used in the outer loop power control.

The CRC (Cyclic Redundancy Check) is used for error checking of the transport blocks at the receiving end. The CRC length that can be inserted has four different values: 0, 8, 12, 16 and 24 bits. The more bits the CRC contains, the lower is the probability of an undetected error in the transport block in the receiver.

Note that certain types of block codes can also be used for error correction, although these are not used in WCDMA.


WCDMA Channel Coding

Effect

Enhance the correlation among symbols so as to recover the signal when interference occurs

Provides better error correction at receiver, but brings increment of the delay

Types

No Coding

Convolutional Coding (1/2, 1/3)

Turbo Coding (1/3)

Code Block of N Bits

No Coding

1/2 Convolutional Coding

1/3 Convolutional Coding

1/3 Turbo Coding

Uncoded N bits

Coded 2N+16 bits

Coded 3N+24 bits

Coded 3N+12 bits

UTRAN employs two FEC schemes: convolutional codes and turbo codes. The idea is to add redundancy to the transmitted bit stream, sO that occasional bit errors can be corrected in the receiving entity.

The first is convolution that is used for anti-interference. Through the technology, many redundant bits will be inserted in original information. When error code is caused by interference, the redundant bits can be used to recover the original information. Convolutional codes are typically used when the timing constraints are tight. The coded data must contain enough redundant information to make it possible to correct some of the detected errors without asking for repeats.

Turbo codes are found to be very efficient because they can perform close to the theoretical limit set by the Shannon’s Law. Their efficiency is best with high data rate services, but poor on low rate services. At higher bit rates, turbo coding is more efficient than convolutional coding.

In WCDMA network, both Convolution code and Turbo code are used. Convolution code applies to voice service while Turbo code applies to high rate data service.

Note that both block codes and channel codes are used in the UTRAN. The idea behind this arrangement is that the channel decoder (either a convolutional or turbo decoder) tries to correct as many errors as possible, and then the block decoder (CRC check) offers its judgment on whether the resulting information is good enough to be used in the higher layers.


WCDMA Interleaving

Effect

Interleaving is used to reduce the probability of consecutive bits error

Longer interleaving periods have better data protection with more delay

⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢

⎣

⎡

11101........................0000100

0 0 1 0 0 0 0 . . . 1 0 1 1 1

⎥⎥⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢⎢⎢

⎣

⎡

11101........................0000010

0 0 … 0 1 0 … 1 0 0 … 1 0 … 1 1 Inter-column permutation

Output bits

Input bits

Interleaving periods: 20, 40, or 80 ms

Channel coding works well against random errors, but it is quite vulnerable to bursts of errors, which are typical in mobile radio systems. The especially fast moving UE in CDMA systems can cause consecutive errors if the power control is not fast enough to manage the interference. Most coding schemes perform better on random data errors than on blocks of errors. This problem can be eased with interleaving, which spreads the erroneous bits over a longer period of time. By interleaving, no two adjacent bits are transmitted near to each other, and the data errors are randomized.

The longer the interleaving period, the better the protection provided by the time diversity. However, longer interleaving increases transmission delays and a balance must be found between the error resistance capabilities and the delay introduced.



SourceCoding


SourceDecoding


Transmission

Reception


ServiceSignal

Radio Channel

ServiceSignal

Receiver






Bit, Symbol, Chip





Correlation

Correlation measures similarity between any two arbitrary signals.

Identical and Orthogonal signals:

Correlation = 0Orthogonal signals

-1 1 -1 1⊗

-1 1 -1 1

1 1 1 1

+1

-1+1

-1

+1

-1

+1

-1

Correlation = 1Identical signals

-1 1 -1 1⊗

1 1 1 1

-1 1 -1 1

C1

C2+1

+1

C1

C2

Correlation is used to measure similarity of any two arbitrary signals. It is computed by multiplying the two signals and then summing (integrating) the result over a defined time windows. The two signals of figure (a) are identical and therefore their correlation is 1 or 100 percent. In figure (b) , however, the two signals are uncorrelated, and therefore knowing one of them does not provide any information on the other.


Orthogonal Code Usage - Coding

UE1: ＋1 －1

UE2: －1 ＋1

C1 : －1 ＋1 －1 ＋1 －1 ＋1 －1 ＋1

C2 : ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1

UE1×c1：－1 ＋1 －1 ＋1 ＋1 －1 ＋1 －1

UE2×c2：－1 －1 －1 －1 ＋1 ＋1 ＋1 ＋1

UE1×c1＋ UE2×c2：－2 0 －2 0 ＋2 0 ＋2 0

UE1: ＋1 －1

UE2: －1 ＋1

C1 : －1 ＋1 －1 ＋1 －1 ＋1 －1 ＋1

C2 : ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1

UE1×c1：－1 ＋1 －1 ＋1 ＋1 －1 ＋1 －1

UE2×c2：－1 －1 －1 －1 ＋1 ＋1 ＋1 ＋1

UE1×c1＋ UE2×c2：－2 0 －2 0 ＋2 0 ＋2 0

By spreading, each symbol is multiplied with all the chips in the orthogonal sequence assigned to the user. The resulting sequence is processed and is then transmitted over the physical channel along with other spread symbols. In this figure, 4-digit codes are used. The product of the user symbols and the spreading code is a sequence of digits that must be transmitted at 4 times the rate of the original encoded binary signal.


Orthogonal Code Usage - Decoding

UE1×C1＋ UE2×C2: －2 0 －2 0 ＋2 0 ＋2 0

UE1 Dispreading by c1: －1 ＋1 －1 ＋1 －1 ＋1 －1 ＋1

Dispreading result: ＋2 0 ＋2 0 －2 0 －2 0

Integral judgment: ＋4 (means＋1) －4 (means－1)

UE2 Dispreading by c2: ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1

Dispreading result: －2 0 －2 0 ＋2 0 ＋2 0

Integral judgment: －4 (means－1) ＋4 (means＋1)

UE1×C1＋ UE2×C2: －2 0 －2 0 ＋2 0 ＋2 0

UE1 Dispreading by c1: －1 ＋1 －1 ＋1 －1 ＋1 －1 ＋1

Dispreading result: ＋2 0 ＋2 0 －2 0 －2 0

Integral judgment: ＋4 (means＋1) －4 (means－1)

UE2 Dispreading by c2: ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1 ＋1

Dispreading result: －2 0 －2 0 ＋2 0 ＋2 0

Integral judgment: －4 (means－1) ＋4 (means＋1)

The receiver dispreads the chips by using the same code used in the transmitter. Notice that under no-noise conditions, the symbols or digits are completely recoveredwithout any error. In reality, the channel is not noise-free, but CDMA system employ Forward Error Correction techniques to combat the effects of noise and enhance the performance of the system.

When the wrong code is used for dispreading, the resulting correlation yields an average of zero. This is a clear demonstration of the advantage of the orthogonal property of the codes. Whether the wrong code is mistakenly used by the target user or other users attempting to decode the received signal, the resulting correlation is always zero because of the orthogonal property of codes.


Spectrum Analysis of Spreading & Dispreading

Spreading code

Spreading code

Signal Combination

Narrowband signalf

P(f)

Broadband signal

P(f)

f

Noise & Other Signal

P(f)

f

Noise+Broadband signal

P(f)

f

Recovered signal P(f)

f

Traditional radio communication systems transmit data using the minimum bandwidth required to carry it as a narrowband signal. CDMA system mix their input data with a fast spreading sequence and transmit a wideband signal. The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data. The dispreading gives substantial gain proportional to the bandwidth of the spread-spectrum signal. The gain can be used to increase system performance and range, or allow multiple coded users, or both. A digital bit stream sent over a radio link requires a definite bandwidth to be successfully transmitted and received.


Spectrum Analysis of Spreading & Dispreading

Max allowed interference

Eb/No Requirement

Power

Max interference caused by UE and others

Processing Gain

Ebit

Interference from other UE Echip

Eb / No = Ec / No ×PG


Process Gain

Process Gain

Process gain differs for each service.

If the service bit rate is greater, the process gain is smaller, UE needs more power for this service, then the coverage of this service will be smaller, vice versa.

)rate bitrate chiplog(10Gain ocessPr =

For common services, the bit rate of voice call is 12.2kbps, the bit rate of video phone is 64kbps, and the highest packet service bit rate is 384kbps(R99). After the spreading, the chip rate of different service all become 3.84Mcps.


Spreading Technology

Spreading consists of 2 steps:

Channelization operation, which transforms data symbols into chips

Scrambling operation is applied to the spreading signal

scramblingchannelization

Data symbol

Chips after spreading

Spreading means increasing the bandwidth of the signal beyond the bandwidth normally required to accommodate the information. The spreading process in UTRAN consists of two separate operations: channelization and scrambling.

The first operation is the channelization operation, which transforms every data symbol into a number of chips, thus increasing the bandwidth of the signal. The number of chips per data symbol is called the Spreading Factor (SF). Channelizationcodes are orthogonal codes, meaning that in ideal environment they do not interfere each other.

The second operation is the scrambling operation. Scrambling is used on top of spreading, so it does not change the signal bandwidth but only makes the signals from different sources separable from each other. As the chip rate is already achieved in channelization by the channelization codes, the chip rate is not affected by the scrambling.


WCDMA Channelization Code

OVSF Code (Orthogonal Variable Spreading Factor) is used as

channelization code

SF = 8SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1, -1)

Cch,4,0 = (1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)

Cch,8,0 = (1,1,1,1,1,1,1,1)

Cch,8,1 = (1,1,1,1,-1,-1,-1,-1)

Cch,8,2 = (1,1,-1,-1,1,1,-1,-1)

Cch,8,3 = (1,1,-1,-1,-1,-1,1,1)

Cch,8,4 = (1,-1,1,-1,1,-1,1,-1)

Cch,8,5 = (1,-1,1,-1,-1,1,-1,1)

Cch,8,6 = (1,-1,-1,1,1,-1,-1,1)

Cch,8,7 = (1,-1,-1,1,-1,1,1,-1)

……

Orthogonal codes are easily generated by starting with a seed of 1, repeating the 1 horizontally and vertically, and then complementing the -1 diagonally. This process is to be continued with the newly generated block until the desired codes with the proper length are generated. Sequences created in this way are referred as “Walsh” code.

Channelization uses OVSF code, for keeping the orthogonality of different subscriber physical channels. OVSF can be defined as the code tree illustrated in the following diagram.

Channelization code is defined as Cch SF, k,, where, SF is the spreading factor of the code, and k is the sequence of code, 0≤k≤SF-1. Each level definition length of code tree is SF channelization code, and the left most value of each spreading code character is corresponding to the chip which is transmitted earliest.


WCDMA Channelization Code

SF = chip rate / symbol rate

High data rates → low SF code

Low data rates → high SF code

16Data 128 kbps DL8Data 128 kbps UL




128Speech 12.2 DL64Speech 12.2 UL

SFRadio bearerSFRadio bearer

The channelization codes are Orthogonal Variable Spreading Factor (OVSF)codes. They are used to preserve orthogonality between different physical channels. They also increase the clock rate to 3.84 Mcps. The OVSF codes are defined using a code tree.

In the code tree, the channelization codes are individually described by Cch,SF,k, where SF is the Spreading Factor of the code and k the code number, 0 ≤ k ≤ SF-1.

A channelization sequence modulates one user’s bit. Because the chip rate is constant, the different lengths of codes enable to have different user data rates. Low SFs are reserved for high rate services while high SFs are for low rate services.

The length of an OVSF code is an even number of chips and the number of codes (for one SF) is equal to the number of chips and to the SF value.

The generated codes within the same layer constitute a set of orthogonal codes. Furthermore, any two codes of different layers are orthogonal except when one of the two codes is a mother code of the other. For example C4,3 is not orthogonal with C1,0and C2,1, but is orthogonal with C2,0.

SF in uplink is from 4 to 256.

SF in downlink is from 4 to 512.


Purpose of Channelization Code

Channelization code is used to distinguish different physical

channels of one transmitter

For downlink, channelization code ( OVSF code ) is used to

separate different physical channels of one cell

For uplink, channelization code ( OVSF code ) is used to

separate different physical channels of one UE

For voice service (AMR), downlink SF is 128, it means there are 128 voice services maximum can be supported in one WCDMA carrier;

For Video Phone (64k packet data) service, downlink SF is 32, it means there are 32 voice services maximum can be supported in one WCDMA carrier.


Purpose of Scrambling Code

Scrambling code is used to distinguish different transmitters

For downlink, scrambling code is used to separate different

cells in one carrier

For uplink, scrambling code is used to separate different UEs

in one carrier

In addition to spreading, part of the process in the transmitter is the scrambling operation. This is needed to separate terminals or base stations from each other.


Scrambling Code

Scrambling code: GOLD sequence.

There are 224 long uplink scrambling codes which are used for

scrambling of the uplink signals. Uplink scrambling codes are

assigned by RNC.

For downlink, 512 primary scrambling codes are used.

Different scrambling codes will be planned to different cells in downlink.

Different scrambling codes will be allocated to different UEs in uplink.

The scrambling code is always applied to one 10 ms frame.

In UMTS, Gold codes are chosen for their very low peak cross-correlation.


Primary Scrambling Code Group

Primary scrambling codes for downlink physical channels

Group 0

…

Primary scrambling code 0

……

Primary scrambling code

8*63

……

Primary scrambling code

8*63 +7512 primary scrambling

codes

……

……

Group 1

Group 63



64 primary scrambling code

groupsEach group consists of 8

primary scrambling codes

There are totally 512 primary scrambling codes defined by 3GPP. They are further divided into 64 primary scrambling code groups. There are 8 primary scrambling codes in every group. Each cell is allocated with only one primary scrambling code.


Code Multiplexing

Downlink Transmission on a Cell Level

Scrambling code

Channelization code 1



User 1 signal

User 2 signal

User 3 signal

NodeB


Code Multiplexing

Uplink Transmission on a Cell Level

NodeB

Scrambling code 3

User 3 signalChannelization code

Scrambling code 2

User 2 signal

Channelization code

Scrambling code 1

User 1 signal

Channelization code



SourceCoding


SourceDecoding


Transmission

Reception


ServiceSignal

Radio Channel

ServiceSignal

Receiver






Bit, Symbol, Chip





Modulation Overview

1 00 1

time

Basic steady radio wave:

carrier = A.cos(2πFt+φ)

Amplitude Shift Keying:

A.cos(2πFt+φ)

Frequency Shift Keying:

A.cos(2πFt+φ)

Phase Shift Keying:A.cos(2πFt+φ)

Data to be transmitted:Digital Input

A data-modulation scheme defines how the data bits are mixed with the carrier signal, which is always a sine wave. There are three basic ways to modulate a carrier signal in a digital sense: amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK).

In ASK the amplitude of the carrier signal is modified by the digital signal.

In FSK the frequency of the carrier signal is modified by the digital signal.

The PSK family is the most widely used modulation scheme in modern cellularsystems. There are many variants in this family, and only a few of them are mentioned here.


Modulation Overview

Digital Modulation - BPSK

1

t

1 10

1

t-1

NRZ coding

fo

BPSKModulated

BPSK signal

Carrier

Information signal

φ=0 φ=π φ=0

1 102 3 4 9875 6

1 102 3 4 9875 6

Digital Input

High FrequencyCarrier

BPSK Waveform

In binary phase shift keying (BPSK) modulation, each data bit is transformed into a separate data symbol. The mapping rule is 1 −> + 1 and 0 − > − 1. There are only two possible phase shifts in BPSK, 0 and π radians.

NRZ means none return zero.


Modulation Overview

Digital Modulation - QPSK

-1 -1

1 102 3 4 9875 6

1 102 3 4 9875 6

NRZ Input

I di-Bit Stream

Q di-Bit Stream

IComponent

QComponent

QPSK Waveform

1

1

-1

1

-1

1

1

-1

-1

-1

1 1 -1 1 -1 1 1 -1

The quadrature phase shift keying (QPSK) modulation has four phases: 0, π/2, π, and 3π/2 radians. Two data bits are transformed into one complex data symbol; A symbol is any change (keying) of the carrier.


Modulation Overview

NRZ coding

90o

NRZ coding

QPSK

Q(t)

I(t)

fo

±A

±A ±Acos(ωot)

±Acos(ωot + π/2)

φ

1 1 π/41 -1 7π/4-1 1 3π/4-1 -1 5π/4

)cos(2: φω +oAQPSK


Demodulation

QPSK Constellation Diagram

1 102 3 4 9875 6

QPSK Waveform

1,1

-1,-1

-1,1

1,-1

1 -11 -1 1 -1-11-1 1

-1,1

NRZ Output


WCDMA Modulation

Different modulation methods corresponding to different

transmitting abilities in air interface

HSDPA: QPSK or 16QAMR99/R4: QPSK

The UTRAN air interface uses QPSK modulation in the downlink, although HSDPA may also employ 16 Quadrature Amplitude Modulation (16QAM). 16QAM requires good radio conditions to work well. As seen, with 16QAM also the amplitude of the signal matters.

As explained, in QPSK one symbol carries two data bits; in 16QAM each symbol includes four bits. Thus, a QPSK system with a chip rate of 3.84Mcps could theoretically transfer 2 × 3.84 = 7.68 Mbps, and a 16QAM system could transfer 4 ×3.84 Mbps = 15.36 Mbps. In 3GPP also the usage of 64QAM with HSDPA has been studied.



SourceCoding

ChannelCoding Spreading Modulation

SourceDecoding

ChannelDecoding Despreading Demodulation

Transmission

Reception


ServiceSignal

Radio Channel

ServiceSignal

Transmitter

Receiver






Bit, Symbol, Chip





Wireless Propagation

ReceivedSignal

TransmittedSignal

Transmission Loss:Path Loss + Multi-path Fading

Time

Amplitude

A mobile communication channel is a multi-path fading channel and any transmitted signal reaches a receive end by means of multiple transmission paths, such as direct transmission, reflection, scatter, etc.


Propagation of Radio SignalSignal at Transmitter

Signal at Receiver

-40-35-30-25-20-15-10-5

dB

0

0

dBm

-20-15-10-5

5101520

Fading


Fading Categories

Fading Categories

Slow Fading

Fast Fading

Furthermore, with the moving of a mobile station, the signal amplitude, delay and phase on various transmission paths vary with time and place. Therefore, the levels of received signals are fluctuating and unstable and these multi-path signals, if overlaid, will lead to fast fading. Fast fading conforms to Rayleigh distribution. The mid-value field strength of fast fading has relatively gentle change and is called “slow fading”. Slow fading conforms to lognormal distribution.


Diversity Technique

Diversity technique is used to obtain uncorrelated signals for combining

Reduce the effects of fadingFast fading caused by multi-path

Slow fading caused by shadowing

Improve the reliability of communication

Increase the coverage and capacity

Diversity technology means that after receiving two or more input signals with mutually uncorrelated fading at the same time, the system demodulates these signals and adds them up. Thus, the system can receive more useful signals and overcome fading.


Diversity

Time diversity

Channel coding, Block interleaving

Frequency diversity

The user signal is distributed on the whole bandwidth

frequency spectrum

Space diversity

Polarization diversity

Diversity technology is an effective way to overcome overlaid fading. Because it can be selected in terms of frequency, time and space, diversity technology includes frequency diversity, time diversity and space diversity.

Time diversity: Channel coding

Frequency diversity: WCDMA is a kind of frequency diversity. The signal energy is distributed on the whole bandwidth.

Space diversity: using two antennas


Principle of RAKE Receiver

Receive set

Correlator 1

Correlator 2

Correlator 3

Searcher correlator Calculate the time delay and signal strength

CombinerThe

combined signal

tt

s(t) s(t)

RAKE receiver help to overcome on the multi-path fading and enhance the receive performance of the system

The RAKE receiver is a technique which uses several baseband correlators to individually process multipath signal components. The outputs from the different correlators are combined to achieve improved reliability and performance.

When WCDMA system is designed for cellular system, the inherent wide-bandwidth signals with their orthogonal Walsh functions were natural for implementing a RAKE receiver. In WCDMA system, the bandwidth is wider than the coherence bandwidth of the cellular. Thus, when the multi-path components are resolved in the receiver, the signals from different paths are uncorrelated with each other. The receiver can then combine them using some combining schemes. So with RAKE receiver WCDMA system can use the multi-path characteristics of the channel to get signal with better quality.


Summary

In this course, we have discussed basic concepts of WCDMA:

Spreading / Despreading principle

UTRAN Voice Coding

UTRAN Channel Coding

UTRAN Spreading Code

UTRAN Scrambling Code

UTRAN Modulation

UTRAN Transmission/Receiving

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WCDMA Radio Interface Physical Layer


Foreword

The physical layer offers data transport services to higher layers.

The physical layer is expected to perform the following functions in

order to provide the data transport service, for example: spreading,

modulation and demodulation, despreading, Inner-loop power

control and etc.


Objectives


Outline radio interface protocol Architecture

Describe structure and functions of different physical channels

Describe UMTS physical layer procedures


Contents

1. Physical Layer Overview

2. Physical Channels

3. Physical Layer Procedure


UTRAN Network Structure

RNS

RNC

RNS

RNC

Core Network

NodeB NodeB NodeB NodeB

Iu-CS Iu-PS

Iur

Iub IubIub Iub

CN

UTRAN

UEUu

CS PS

Iu-CSIu-PS

CSPS

UTRAN: UMTS Terrestrial Radio Access Network.

The UTRAN consists of a set of Radio Network Subsystems connected to the Core Network through the Iu interface.

A RNS consists of a Radio Network Controller and one or more NodeBs. A NodeB is connected to the RNC through the Iub interface.

Inside the UTRAN, the RNCs of the RNS can be interconnected together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over direct physical connection between RNCs or virtual networks using any suitable transport network.


Uu Interface Protocol Structure

L3co

ntro

l

cont

rol

cont

rol

cont

rol

C-plane signaling U-plane information

PHY

L2/MAC

L1

RLC

DCNtGC

L2/RLC

MAC

RLCRLCRLC

Duplication avoidance

UuS boundary

L2/BMC

control

PDCPPDCP L2/PDCP

DCNtGC

RRC

RLCRLCRLCRLC

BMC

radio bearer

logical channel

transport channel

The layer 1 supports all functions required for the transmission of bit streams on the physical medium. It is also in charge of measurements function consisting in indicating to higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power, transmit power, … It is basically composed of a “layer 1 management” entity, a “transport channel” entity, and a “physical channel” entity.

The layer 2 protocol is responsible for providing functions such as mapping, ciphering, retransmission and segmentation. It is made of four sub-layers: MAC (Medium Access Control), RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol) and BMC (Broadcast/Multicast Control).

The layer 3 is split into 2 parts: the access stratum and the non access stratum. The access stratum part is made of “RRC (Radio Resource Control)” entity and “duplication avoidance” entity. “duplication avoidance” terminates in the CN but is part of the Access Stratum. The higher layer signalling such as Mobility Management (MM) and Call Control (CC) is assumed to belong to the non-access stratum, and therefore not in the scope of 3GPP TSG RAN. In the C-plane, the interface between 'Duplication avoidance' and higher L3 sub-layers (CC, MM) is defined by the General Control (GC), Notification (Nt) and Dedicated Control (DC) SAPs.

Not shown on the figure are connections between RRC and all the other protocol layers (RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services.

The protocol layers are located in the UE and the peer entities are in the NodeB or the RNC.

Many functions are managed by the RRC layer. Here is the list of the most important:

Establishment, re-establishment, maintenance and release of an RRC connection between the UE and UTRAN: it includes an optional cell re-selection, an admission control, and a layer 2 signaling link establishment. When a RNC is in charge of a specific connection towards a UE, it acts as the Serving RNC.

Establishment, reconfiguration and release of Radio Bearers: a number of Radio Bearers can be established for a UE at the same time. These bearers are configured depending on the requested QoS. The RNC is also in charge of ensuring that the requested QoS can be met.

Assignment, reconfiguration and release of radio resources for the RRC connection: it handles the assignment of radio resources (e.g. codes, shared channels). RRC communicates with the UE to indicate new resources allocation when handovers are managed.

Paging/Notification: it broadcasts paging information from network to UEs.

Broadcasting of information provided by the non-access stratum (Core Network) or access Stratum. This corresponds to “system information” regularly repeated.

UE measurement reporting and control of the reporting: RRC indicates what to measure, when and how to report.

Outer loop power control: controls setting of the target values.

Control of ciphering: provides procedures for setting of ciphering.

The RRC layer is defined in the 25.331 specification from 3GPP.

The RLC’s main function is the transfer of data from either the user or the control plane over the Radio interface. Two different transfer modes are used: transparentand non-transparent. In non-transparent mode, 2 sub-modes are used: acknowledged or unacknowledged.

RLC provides services to upper layers:

data transfer (transparent, acknowledged and unacknowledged modes).

QoS setting: the retransmission protocol (for AM only) shall be configurable by layer 3 to provide different QoS.

notification of unrecoverable errors: RLC notifies the upper layers of errors that cannot be resolved by RLC.

The RLC functions are:

mapping between higher layer PDUs and logical channels.

ciphering: prevents unauthorized acquisition of data; performed in RLC layer for non-transparent RLC mode.

segmentation/reassembly: this function performs segmentation/reassembly of variable-length higher layer PDUs into/from smaller RLC Payload Units. The RLC size is adjustable to the actual set of transport formats (decided when service is established). Concatenation and padding may also be used.

error correction: done by retransmission (acknowledged data transfer mode only).

flow control: allows the RLC receiver to control the rate at which the peer RLC transmitting entity may send information.

MAC services include:

Data transfer: service providing unacknowledged transfer of MAC SDUsbetween peer MAC entities.

Reallocation of radio resources and MAC parameters: reconfiguration of MAC functions such as change of identity of UE. Requested by the RRC layer.

Reporting of measurements: local measurements such as traffic volume and quality indication are reported to the RRC layer.

The functions accomplished by the MAC sub-layer are listed above. Here’s a quick explanation for some of them:

Priority handling between the data flows of one UE: since UMTS is multimedia, a user may activate several services at the same time, having possibly different profiles (priority, QoS parameters...). Priority handlingconsists in setting the right transport format for a high bit rate service and for a low bit rate service.

Priority handling between UEs: use for efficient spectrum resources utilization for bursty transfers on common and shared channels.

Ciphering: to prevent unauthorized acquisition of data. Performed in the MAC layer for transparent RLC mode.

Access Service Class (ACS) selection for RACH transmission: the RACH resources are divided between different ACSs in order to provide different priorities on a random access procedure.

PDCP

UMTS supports several network layer protocols providing protocol transparency for the users of the service.

Using these protocols (and new ones) shall be possible without any changes to UTRAN protocols. In order to perform this requirement, the PDCP layer has been introduced. Then, functions related to transfer of packets from higher layers shall be carried out in a transparent way by the UTRAN network entities.

PDCP shall also be responsible for implementing different kinds of optimization methods. The currently known methods are standardized IETF (Internet Engineering Task Force) header compression algorithms.

Algorithm types and their parameters are negotiated by RRC and indicated toPDCP.

Header compression and decompression are specific for each network layer protocol type.

In order to know which compression method is used, an identifier (PID: Packet Identifier) is inserted. Compression algorithms exist for TCP/IP, RTP/UDP/IP, …

Another function of PDCP is to provide numbering of PDUs. This is done if lossless SRNS relocation is required.

To accomplish this function, each PDCP-SDUs (UL and DL) is buffered and numbered. Numbering is done after header compression. SDUs are kept until information of successful transmission of PDCP-PDU has been received from RLC. PDCP sequence number ranges from 0 to 65,535.

BMC (broadcast/multicast control protocol)

The main function of BMC protocol are:

Storage of cell broadcast message. the BMC in RNC stores the cell broadcast message received over the CBC-RNC interface for scheduled transmission.

Traffic volume monitoring and radio resource request for CBS. On the UTRAN side, the BMC calculates the required transmission rate for the cell broadcast service based on the messages received over the CBC-RNC interface, and requests appropriate .CTCH/FACH resources from from RRC

Scheduling of BMC message. The BMC receives scheduling information together with each cell broadcast message over the CBC-RNC interface. Based on this scheduling information, on the UTRAN side the BMC generates schedule message and schedules BMC message sequences accordingly. On the UE side ,the BMC evaluates the schedule messages and indicates scheduling parameters to RRC, which are used by RRC to configure the lower layers for CBS discontinuous reception.

Transmission of BMC message to UE. The function transmits the BMC messages according to the schedule

Delivery of cell broadcast messages to the upper layer. This UE function delivers the received non-corrupted cell broadcast messages to the upper layer

The layer 1 (physical layer) is used to transmit information under the form of electrical signals corresponding to bits, between the network and the mobile user. This information can be voice, circuit or packet data, and network signaling.

The UMTS layer 1 offers data transport services to higher layers. The access to these services is through the use of transport channels via the MAC sub-layer.

These services are provided by radio links which are established by signaling procedures. These links are managed by the layer 1 management entity. One radio link is made of one or several transport channels, and one physical channel.

The UMTS layer 1 is divided into two sub-layers: the transport and the physical sub-layers. All the processing (channel coding, interleaving, etc.) is done by the transport sub-layer in order to provide different services and their associated QoS. The physical sub-layer is responsible for the modulation, which corresponds to the association of bits (coming from the transport sub-layer) to electrical signals that can be carried over the air interface. The spreading operation is also done by the physical sub-layer.

These two parts of layer 1 are controlled by the layer 1 management (L1M) entity. It is made of several units located in each equipment, which exchange information through the use of control channels.


RAB, RB and RL

RAB

RB

RLNodeB

RNC CNUE

UTRAN

RAB: The service that the access stratum provides to the non-access stratum for transfer of user data between User Equipment and CN.

RB: The service provided by the layer 2 for transfer of user data between User Equipment and Serving RNC.

RL: A "radio link" is a logical association between single User Equipment and a single UTRAN access point. Its physical realization comprises one or more radio bearer transmissions.


Contents





Contents


2.1 Physical Channel Structure and Functions

2.2 Channel Mapping


WCDMA Radio Interface Channel Definition

Logical Channel = information container

Defined by <What type of information> is transferred

Transport Channel = characteristics of transmission

Described by <How> and with <What characteristics> data is transmitted over the radio interface

Physical Channel = specification of the information global content

providing the real transmission resource, maybe a frequency , a specific set of codes and phase

In terms of protocol layer, the WCDMA radio interface has three types of channels: physical channel, transport channel and logical channel.

Logical channel: Carrying user services directly. According to the types of the carried services, it is divided into two types: control channel and service channel.

Transport channel: It is the interface between radio interface layer 2 and layer 1, and it is the service provided for MAC layer by the physical layer. According to whether the information transported is dedicated information for a user or common information for all users, it is divided into dedicated channel and common channel.

Physical channel: It is the ultimate embodiment of all kinds of information when they are transmitted on radio interface. Each channel which uses dedicated carrier frequency, code (spreading code and scramble) and carrier phase (I or Q) can be regarded as a physical channel.


Logical Channel

Control channel

Traffic channelDedicated traffic channel (DTCH)

Common traffic channel (CTCH)

Broadcast control channel (BCCH)

Paging control channel (PCCH)

Dedicate control channel (DCCH)

Common control channel (CCCH)

As in GSM, UMTS uses the concept of logical channels.A logical channel is characterized by the type of information that is transferred.As in GSM, logical channels can be divided into two groups: control channels for control plane information and traffic channel for user plane information.The traffic channels are:

Dedicated Traffic Channel (DTCH): a point-to-point bi-directional channel, that transmits dedicated user information between a UE and the network. That information can be speech, circuit switched data or packet switched data. The payload bits on this channel come from a higher layer application (the AMR codec for example). Control bits can be added by the RLC (protocol information) in case of a non transparent transfer. The MAC sub-layer will also add a header to the RLC PDU. Common Traffic Channel (CTCH): a point-to-multipoint downlink channel for transfer of dedicated user information for all or a group of specified UEs. This channel is used to broadcast BMC messages. These messages can either be cell broadcast data from higher layers or schedule messages for support of Discontinuous Reception (DRX) of cell broadcast data at the UE. Cell broadcast messages are services offered by the operator, like indication of weather, traffic, location or rate information.


Logical Channel

Control channel

Traffic channelDedicated traffic channel (DTCH)

Common traffic channel (CTCH)

Broadcast control channel (BCCH)

Paging control channel (PCCH)

Dedicate control channel (DCCH)

Common control channel (CCCH)

The control channels are:

Broadcast Control Channel (BCCH): a downlink channel that broadcasts all system information types (except type 14 that is only used in TDD). For example, system information type 3 gives the cell identity. UEs decode system information on the BCH except when in Cell_DCH mode. In that case, they can decode system information type 10 on the FACH and other important signaling is sent on a DCCH.

Paging Control Channel (PCCH): a downlink channel that transfers paging information. It is used to reach a UE (or several UEs) in idle mode or in connected mode (Cell_PCH or URA_PCH state). The paging type 1 message is sent on the PCCH. When a UE receives a page on the PCCH in connected mode, it shall enter Cell_FACH state and make a cell update procedure.

Dedicated Control Channel (DCCH): a point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. This channel is used for dedicated signaling after a RRC connection has been done. For example, it is used for inter-frequency handover procedure, for dedicated paging, for the active set update procedure and for the control and report of measurements.

Common Control Channel (CCCH): a bi-directional channel for transmitting control information between network and UEs. It is used to send messages related to RRC connection, cell update and URA update. This channel is a bit like the DCCH, but will be used when the UE has not yet been identified by the network (or by the new cell). For example, it is used to send the RRC connection request message, which is the first message sent by the UE to get into connected mode. The network will respond on the same channel, and will send him its temporary identities (cell and UTRAN identities). After these initial messages, the DCCH will be used.


Transport Channel

Dedicated Channel (DCH)

Broadcast channel (BCH)

Forward access channel (FACH)

Paging channel (PCH)

Random access channel (RACH)

High-speed downlink shared channel (HS-DSCH)

Common transport channel

Dedicated transport channel

In order to carry logical channels, several transport channels are defined. They are:

Broadcast Channel (BCH): a downlink channel used for broadcast of system information into the entire cell.

Paging Channel (PCH): a downlink channel used for broadcast of control information into the entire cell, such as paging.

Random Access Channel (RACH): a contention based uplink channel used for initial access or for transmission of relatively small amounts of data (non real-time dedicated control or traffic data).

Forward Access Channel (FACH): a common downlink channel used for dedicated signaling (answer to a RACH typically), or for transmission of relatively small amounts of data.

Dedicated Channel (DCH): a channel dedicated to one UE used in uplink ordownlink.


Physical Channel

A physical channel is defined by a specific carrier frequency, code (scrambling code, spreading code) and relative phase.

In UMTS system, the different code (scrambling code or spreadingcode) can distinguish the channels.

Most channels consist of radio frames and time slots, and each radio frame consists of 15 time slots.

Two types of physical channel: UL and DL

Physical Channel

Frequency, Code, Phase

Now we will begin to discuss the physical channel. Physical channel is the most important and complex channel, and a physical channel is defined by a specific carrier frequency, code and relative phase. In CDMA system, the different code (scrambling code or spreading code) can distinguish the channel. Most channels consist of radio frames and time slots, and each radio frame consists of 15 time slots. There are two types of physical channel: UL and DL.


Downlink Physical ChannelDownlink Dedicated Physical Channel (DL DPCH)

Downlink Common Physical Channel

Primary Common Control Physical Channel (P-CCPCH)

Secondary Common Control Physical Channel (S-CCPCH)

Synchronization Channel (SCH)

Paging Indicator Channel (PICH)

Acquisition Indicator Channel (AICH)

Common Pilot Channel (CPICH)

High-Speed Physical Downlink Shared Channel (HS-PDSCH)

High-Speed Shared Control Channel (HS-SCCH)

The different physical channels are: Synchronization Channel (SCH): used for cell search procedure. There is the primary and the secondary SCHs.Common Control Physical Channel (CCPCH): used to carry common control information such as the scrambling code used in DL (there is a primary CCPCH and additional secondary CCPCH).Common Pilot Channels (P-CPICH and S-CPICH): used for coherent detection of common channels. They indicate the phase reference.Dedicated Physical Data Channel (DPDCH): used to carry dedicated data coming from layer 2 and above (coming from DCH).Dedicated Physical Control Channel (DPCCH): used to carry dedicated control information generated in layer 1 (such as pilot, TPC and TFCI bits).Page Indicator Channel (PICH): carries indication to inform the UE that paging information is available on the S-CCPCH.Acquisition Indicator Channel (AICH): it is used to inform a UE that the network has received its access request.High Speed Physical Downlink Shared Channel (HS-PDSCH): it is used to carry subscribers BE service data (mapping on HSDPA) coming from layer 2.High Speed Shared Control Channel (HS-SCCH): it is used to carry control message to HS-PDSCH such as modulation scheme, UE ID etc.


Uplink Physical Channel

Uplink Dedicated Physical Channel

Uplink Dedicated Physical Data Channel (Uplink DPDCH)

Uplink Dedicated Physical Control Channel (Uplink DPCCH)

High-Speed Dedicated Physical Channel (HS-DPCCH)

Uplink Common Physical Channel

Physical Random Access Channel (PRACH)

The different physical channels are:

Dedicated Physical Data Channel (DPDCH): used to carry dedicated data coming from layer 2 and above (coming from DCH).

Dedicated Physical Control Channel (DPCCH): used to carry dedicated control information generated in layer 1 (such as pilot, TPC and TFCI bits).

Physical Random Access Channel (PRACH): used to carry random access information when a UE wants to access the network.

High Speed Dedicated Physical Control Channel (HS-DPCCH): it is used to carry feedback message to HS-PDSCH such CQI,ACK/NACK.


Function of Physical Channel

NodeB UE

P-CCPCH-Primary Common Control Physical ChannelP-CCPCH-Primary Common Control Physical Channel

P-CPICH--Primary Common Pilot ChannelSCH--Synchronisation ChannelP-CPICH--Primary Common Pilot ChannelSCH--Synchronisation Channel

Cell Search Channels

DPDCH--Dedicated Physical Data ChannelDPDCH--Dedicated Physical Data Channel

DPCCH--Dedicated Physical Control ChannelDPCCH--Dedicated Physical Control Channel

Dedicated Channels

Paging ChannelsPICH--Paging Indicator ChannelPICH--Paging Indicator Channel

SCCPCH--Secondary Common Control Physical ChannelSCCPCH--Secondary Common Control Physical Channel

PRACH--Physical Random Access ChannelPRACH--Physical Random Access ChannelAICH--Acquisition Indicator ChannelAICH--Acquisition Indicator Channel

Random Access Channels

HS-DPCCH--High Speed Dedicated Physical Control ChannelHS-DPCCH--High Speed Dedicated Physical Control Channel

HS-SCCH--High Speed Share Control ChannelHS-SCCH--High Speed Share Control Channel

HS-PDSCH--High Speed Physical Downlink Share ChannelHS-PDSCH--High Speed Physical Downlink Share Channel

High Speed Downlink Share Channels


Synchronization Channels (P-SCH & S-SCH)

Used for cell search

Two sub channels: P-SCH and S-SCH

SCH is transmitted at the first 256 chips of every time slot

Primary synchronization code is transmitted repeatedly in each time slot

Secondary synchronization code specifies the scrambling code groups of the cell

Primary SCH

Secondary SCH

Slot #0 Slot #1 Slot #14

acsi,0

pac pac pac

acsi,1 acs

i,14

256 chips2560 chips

One 10 ms SCH radio frame

When a UE is turned on, the first thing it does is to scan the UMTS spectrum and find a UMTS cell. After that, it has to find the primary scrambling code used by that cell in order to be able to decode the BCCH (for system information). This is done with the help of the Synchronization Channel.

Each cell of a NodeB has its own SCH timing, so that there is no overlapping.

The SCH is a pure downlink physical channel broadcasted over the entire cell. It is transmitted unscrambled during the first 256 chips of each time slot, in time multiplex with the P-CCPCH. It is the only channel that is not spread over the entire radio frame. The SCH provides the primary scrambling code group (one out of 64 groups), as well as the radio frame and time slot synchronization.

The SCH consists of two sub-channels, the primary and secondary SCH. These sub-channels are sent in parallel using code division during the first 256 chips of each time slot. P-SCH always transmits primary synchronization code. S-SCH transmits secondary synchronization codes.

The primary synchronization code is repeated at the beginning of each time slot. The same code is used by all the cells and enables the mobiles to detect the existence of the UMTS cell and to synchronize itself on the time slot boundaries. This is normally done with a single matched filter or any similar device. The slot timing of the cell is obtained by detecting peaks in the matched filter output.

This is the first step of the cell search procedure. The second step is done using the secondary synchronization channel.


Secondary Synchronization Channel (S-SCH)

slot number Scrambling Code Group #0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14

Group 0 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16 Group 1 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10 Group 2 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12 Group 3 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7 Group 4 1 2 16 6 6 11 15 5 12 1 15 12 16 11 2

… Group 61 9 10 13 10 11 15 15 9 16 12 14 13 16 14 11 Group 62 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16 Group 63 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10

……..acp

Slot # ?

P-SCH acp

Slot #?

16 6S-SCH

acp

Slot #?

11 Group 2Slot 7, 8, 9

256 chips

The S-SCH also consists of a code, the Secondary Synchronization Code (SSC) that indicates which of the 64 scrambling code groups the cell’s downlink scrambling code belongs to. 16 different SSCs are defined. Each SSC is a 256 chip long sequence.

There is one specific SSC transmitted in each time slot, giving us a sequence of 15 SSCs. There is a total of 64 different sequences of 15 SSCs, corresponding to the 64 primary scrambling code groups. These 64 sequences are constructed so that one sequence is different from any other one, and different from any rotated version of any sequence. The UE correlates the received signal with the 16 SSCs and identifies the maximum correlation value.

The S-SCH provides the information required to find the frame boundaries and the downlink scrambling code group (one out of 64 groups). The scrambling code (one out of 8) can be determined afterwards by decoding the P-CPICH. The mobile will then be able to decode the BCH.


Primary Common Pilot Channel (PCPICH)

Primary PCPICH

Carrying pre-defined sequence

Fixed channel code: Cch, 256, 0, Fixed rate 30Kbps

Scrambled by the primary scrambling code

Broadcast over the entire cell

A phase reference for SCH, Primary CCPCH, AICH, PICH and downlink DPCH, Only one PCPICH per cell

Pre-defined symbol sequence

Slot #0 Slot #1 Slot # i Slot #14

Tslot = 2560 chips , 20 bits

1 radio frame: Tr = 10 ms

The Common Pilot Channel (CPICH) is a pure physical control channel broadcasted over the entire cell. It is not linked to any transport channel. It consists of a sequence of known bits that are transmitted in parallel with the primary and secondary CCPCH.

The PCPICH is used by the mobile to determine which of the 8 possible primary scrambling codes is used by the cell, and to provide the phase reference for common channels.

Finding the primary scrambling code is done during the cell search procedure through a symbol-by-symbol correlation with all the codes within the code group. After the primary scrambling code has been identified, the UE can decode system information on the P-CCPCH.

The P-CPICH is the phase reference for the SCH, P-CCPCH, AICH and PICH. It is broadcasted over the entire cell. The channelization code used to spread the P-CPICH is always Cch,256,0 (all ones). Thus, the P-CPICH is a fixed rate channel. Also, it is always scrambled with the primary scrambling code of the cell.


Primary Common Control Physical Channel (PCCPCH)

Carrying BCH transport channel

Fixed rate, fixed OVSF code (30kbps，Cch, 256, 1)

The PCCPCH is not transmitted during the first 256 chips of eachtime slot

PCCPCH Data18 bits

Slot #0

1 radio frame: T f = 10 ms

Slot #1 Slot #i

256 chips

Slot #14

T slot = 2560 chips,20 bits

SCH

The Primary Common Control Physical Channel (P-CCPCH) is a fixed rate (SF=256) downlink physical channel used to carry the BCH transport channel. It is broadcasted continuously over the entire cell like the P-CPICH.

The figure above shows the frame structure of the P-CCPCH. The frame structure is special because it does not contain any layer 1 control bits. The P-CCPCH only hasone fix predefined transport format combination, and the only bits transmitted are data bits from the BCH transport channel. It is important to note that the P-CCPCH is not transmitted during the first 256 chips of the slot. In fact, another physical channel (SCH) is transmitted during that period of time. Thus, the SCH and the P-CCPCH are time multiplexed on every time slot.

Channelization code Cch,256,1 is always used to spread the P-CCPCH.


Paging Indicator Channel (PICH)

Carrying Paging Indicators (PI)

Fixed rate (30kbps), SF = 256

N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72, or 144

One radio frame (10 ms)

b1b0

288 bits for paging indication 12 bits (undefined)

b287 b288 b299

The Page Indicator Channel (PICH) is a fixed rate (30kbps, SF=256) physical channel used by the NodeB to inform a UE (or a group of UEs) that a paging information will soon be transmitted on the PCH. Thus, the mobile only decodes the S-CCPCH when it is informed to do so by the PICH. This enables to do other processing and to save the mobiles’ battery.

The PICH carries Paging Indicators (PI), which are user specific and calculated by higher layers. It is always associated with the S-CCPCH to which the PCH is mapped.

The frame structure of the PICH is illustrated above. It is 10 ms long, and always contains 300 bits (SF=256). 288 of these bits are used to carry paging indicators, while the remaining 12 are not formally part of the PICH and shall not be transmitted. That part of the frame (last 12 bits) is reserved for possible future use.

In order not to waste radio resources, several PIs are multiplexed in time on the PICH. Depending on the configuration of the cell, 18, 36, 72 or 144 paging indicators can be multiplexed on one PICH radio frame. Thus, the number of bits reserved for each PI depends of the number of PIs per radio frame. For example, if there is 72 PIs in one radio frame, there will be 4 (288/72) consecutive bits for each PI. These bits are all identical. If the PI in a certain frame is “1”, it is an indication that the UE associated with that PI should read the corresponding frame of the S-CCPCH.


Secondary Common Control Physical Channel (SCCPCH)

Carrying FACH and PCH, SF = 256 - 4

Pilot: used for demodulation

TFCI: Transport Format Control Indication, used for describe data

format

DataN bits

Slot #0 Slot #1 Slot #i Slot #14

1 radio frame: T f = 10 ms

T slot = 2560 chips,

DataPilot

N bitsPilotN bitsTFCITFCI

20*2 k bits (k=0..6)

The Secondary Common Control Physical Channel (S-CCPCH) is used to carry the FACH and PCH transport channels. Unlike the P-CCPCH, it is not broadcasted continuously. It is only transmitted when there is a PCH or FACH information to transmit. At the mobile side, the mobile only decodes the S-CCPCH when it expects a useful message on the PCH or FACH.

A UE will expect a message on the PCH after indication from the PICH (page indicator channel), and it will expect a message on the FACH after it has transmitted something on the RACH.

The FACH and the PCH can be mapped on the same or on separate S-CCPCHs. If they are mapped on the same S-CCPCH, TFCI bits have to be sent to support multiple transport formats

The figure above shows the frame structure of the S-CCPCH. There are 18 different slot formats determining the exact number of data, pilot and TFCI bits. The data bits correspond to the PCH and/or FACH bits coming from the transport sub-layer. Pilot bit are typically used when beamforming techniques are used.

The SF ranges from 4 to 256. The channelization code is assigned by the RRC layer as is the scrambling code, and they are fixed during the communication. They are sent on the BCCH so that every UE can decode the channel.

As said before, FACH can be used to carry user data. The difference with the dedicated channel is that it cannot use fast power control, nor soft handover. The advantage is that it is a fast access channel.


Physical Random Access Channel (PRACH)

Carrying uplink signaling and data, consist of two parts:

One or several preambles: 16 kinds of available preambles

10 or 20ms message part

Message partPreamble

4096 chips10 ms (one radio frame)

Preamble Preamble

Message partPreamble

4096 chips 20 ms (two radio frames)

Preamble Preamble

The Physical Random Access Channel (PRACH) is used by the UE to access the network and to carry small data packets. It carries the RACH transport channel. The PRACH is an open loop power control channel, with contention resolution mechanisms (ALOHA approach) to enable a random access from several users.

The PRACH is composed of two different parts: the preamble part and the message part that carries the RACH message. The preamble is an identifier which consists of 256 repetitions of a 16 chip long signature (total of 4096 chips). There are 16 possible signatures, basically, the UE randomly selects one of the 16 possible preambles and transmits it at increasing power until it gets a response from the network (on the AICH). That preamble is scrambled before being sent. That is a sign that the power level is high enough and that the UE is authorized to transmit, which it will do after acknowledgment from the network. If the UE doesn’t get a response from the network, it has to select a new signature to transmit.

The message part is 10 or 20 ms long (split into 15 or 30 time slots) and is made of the RACH data and the layer 1 control information.


PRACH Message Structure

PilotN bits

Slot # 0 Slot # 1 Slot # i Slot # 14

Message part radio frame T = 10 ms

Tslot = 2560 chips, 10*2

Pilot

TFCIN bitsTFCI

DataN data bitsData

Control

k bits (k=0..3)

The data and control bits of the message part are processed in parallel. The SF of the data part can be 32, 64, 128 or 256 while the SF of the control part is always 256. The control part consists of 8 pilot bits for channel estimation and 2 TFCI bits to indicate the transport format of the RACH (transport channel), for a total of 10 bits per slot.

The OVSF codes to use (one for RACH data and one for control) depend on the signature that was used for the preamble (for signatures s=0 to s=15: OVSFcontrol= Cch,256,m, where m=16s + 15; OVSFdata= Cch,SF,m, where m=SF*s/16.


PRACH Access Timeslot Structure

#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14

5120 chips

radio frame: 10 ms radio frame: 10 ms

Access slot #0 Random Access Transmission

Access slot #1

Access slot #7

Access slot #14

Random Access Transmission

Random Access Transmission

Random Access TransmissionAccess slot #8

The PRACH transmission is based on the access frame structure. The access frame is access of 15 access slots and lasts 20 ms (2 radio frames). To avoid too many collisions and to limit interference, a UE must wait at least 3 or 4 access slots between two consecutive preambles.The PRACH resources (access slots and preamble signatures) can be divided between different Access Service Classes (ASC) in order to provide different priorities of RACH usage. The ASC number ranges from 0 (highest priority) to 7 (lowest priority).


Acquisition Indicator Channel (AICH)

Carrying the Acquisition Indicators (AI), SF = 256

There are 16 kinds of Signature to generate AI

AS #14 AS #0 AS #1 AS #i AS #14 AS #0

a1 a2a0 a31 a32a30 a33 a38 a39

AI part Unused part

20 ms

The Acquisition Indicator Channel (AICH) is a common downlink channel used to control the uplink random accesses. It carries the Acquisition Indicators (AI), each corresponding to a signature on the PRACH (uplink). When the NodeB receives the random access from a mobile, it sends back the signature of the mobile to grant its access. If the NodeB receives multiple signatures, it can sent all these signatures back by adding the together. At reception, the UE can apply its signature to check if the NodeB sent an acknowledgement (taking advantage of the orthogonality of the signatures).

The AICH consists of a burst of data transmitted regularly every access slot frame. One access slot frame is formed of 15 access slots, and lasts 2 radio frames (20 ms). Each access slot consists of two parts, an acquisition indicator part of 32 real-valued symbols and a long part during which nothing is transmitted to avoid overlapping due to propagation delays.

s (with values 0, +1 and -1, corresponding to the answer from the network to a specific user) and the 32 chip long sequence <bs,j> is given by a predefined table. There are 16 sequences <bs,j>, each corresponding to one PRACH signatures. A maximum of 16 AIs can be sent in each access slot. The user can multiply the received multi-level signal by the signature it used to know if its access was granted.

The SF used is always 256 and the OVSF code used by the cell is indicated in system information type 5.


Uplink Dedicated Physical Channel (DPDCH&DPCCH)

Uplink DPDCH and DPCCH are I/Q code division

multiplexed (CDM) within each radio frame

DPDCH carries data generated at Layer 2 and higher layer,

the OVSF code is Cch,SF,SF/4, where SF is from 256 to 4

DPCCH carries control information generated at Layer 1,

the OVSF code is Cch,256,0

There are two kinds of uplink dedicated physical channels, the Dedicated Physical Data Channel (DPDCH) and the Dedicated Physical Control Channel (DPCCH).The DPDCH is used to carry the DCH transport channel. The DPCCH is used to carry the physical sub-layer control bits.

Each DPCCH time slot consists of Pilot, TFCI，FBI，TPC

Pilot is used to help demodulation

TFCI: transport format control indicator

FBI:used for the FBTD. (feedback TX diversity)

TPC: used to transport power control command.


Uplink Dedicated Physical Channel (DPDCH&DPCCH)

Frame Structure of Uplink DPDCH/DPCCH

PilotNpilot bits

TPCNTPC bits

DataNdata bits


Tslot = 2560 chips, 10*2k bits (k=0..6)

1 radio frame: Tf = 10 ms

DPDCH

DPCCH FBINFBI bits

TFCINTFCI bits

On the figure above, we can see the DPDCH and DPCCH time slot constitution. The parameter k determines the number of symbols per slot. It is related to the spreading factor (SF) of the DPDCH by this simple equation: SF=256/2k. The DPDCH SF ranges from 4 to 256. The SF for the uplink DPCCH is always 256, which gives us 10 bits per slot. The exact number of pilot, TFCI, TPC and FBI bits is configured by higher layers. This configuration is chosen from 12 possible slot formats. It is important to note that symbols are transmitted during all slots for the DPDCH


Downlink Dedicated Physical Channel (DPDCH+DPCCH)

Downlink DPDCH and DPCCH is time division multiplexing

(TDM).

DPDCH carries data generated at Layer 2 and higher layer

DPCCH carries control information generated at Layer 1

SF of downlink DPCH is from 512 to 4

The uplink DPDCH and DPCCH are I/Q code multiplexed. But the downlink DPDCH and DPCCH is time multiplexed. This is main difference.

Basically, there are two types of downlink DPCH. They are distinguished by the use or non use of the TFCI field. TFCI bits are not used for fixed rate services or when the TFC doesn’t change.


Downlink Dedicated Physical Channel (DPDCH+DPCCH)

Frame Structure of Downlink DPCH (DPDCH+DPCCH)

One radio frame, Tf = 10 ms


Tslot = 2560 chips, 20*2k bits (k=-1..6)

Data2Ndata2 bits

DPDCH

TFCINTFCI bits

PilotNpilot bits

Data1Ndata1 bits

DPDCH DPCCH DPCCH

TPCNTPC bits

We have known that the uplink DPDCH and DPCCH are I/Q code multiplexed. But the downlink DPDCH and DPCCH is time multiplexed. This is main difference. The parameter k in the figure above determines the total number of bits per time slot. It is related to the SF, which ranges from 4 to 512. The chips of one slot is also 2560.

Downlink physical channels are used to carry user specific information like speech, data or signaling, as well as layer 1 control bits. Like it was mentioned before, the payload from the DPDCH and the control bits from the DPCCH are time multiplexed on every time slot. The figure above shows how these two channels are multiplexed. There is only one DPCCH in downlink for one user.


High-Speed Physical Downlink Shared Channel (HS-PDSCH)

Bearing service data and layer 2 overhead bits mapped from the transport channel

SF=16, can be configured several channels to increase data service

Slot #0 Slot#1 Slot #2

Tslot = 2560 chips, M*10*2k bits (k=4)

DataNdata1 bits

1 subframe: Tf = 2 ms

HS-PDSCH is a downlink physical channel that carries user data and layer 2 overhead bits mapped from the transport channel: HS-DSCH.

The user data and layer 2 overhead bits from HS-DSCH is mapped onto one or several HS-PDSCH and transferred in 2ms subframe using one or several channelization code with fixed SF=16.


High-Speed Shared Control Channel (HS-SCCH)

Carries physical layer signalling to a single UE ,such as modulation scheme (1 bit) ,channelization code set (7 bit), transport block size (6bit),HARQ process number (3bit), redundancy version (3bit), new data indicator (1bit), UE identity (16bit)

HS-SCCH is a fixed rate (60 kbps, SF=128) downlink physical channelused to carry downlink signalling related to HS-DSCH transmission

Slot #0 Slot#1 Slot #2

Tslot = 2560 chips, 40 bits

DataNdata1 bits

1 subframe: Tf = 2 ms

HS-SCCH uses a SF=128 and has q time structure based on a sub-frame of length 2 ms, i.e. the same length as the HS-DSCH TTI. The timing of HS-SCCH starts two slot prior to the start of the HS-PDSCH subframe.

The following information is carried on the HS-SCCH (7 items)

Modulation scheme(1bit) QPSK or 16QAM

Channelization code set (7bits)

Transport block size ( 6bits)

HARQ process number (3bits)

Redundancy version (3bits)

New Data Indicator (1bit)

UE identity (16 bits)

In each 2 ms interval corresponding to one HS-DSCH TTI , one HS-SCCH carries physical-layer signalling to a single UE. As there should be a possibility for HS-DSCH transmission to multiple users in parallel (code multiplex), multiplex HS-SCCH may be needed in a cell. The specification allows for up to four HS-SCCHs as seen from a UE point of view .i.e. UE must be able to decode four HS-SCCH.


High-Speed Dedicated Physical Control Channel (HS-DPCCH )

Carrying information to acknowledge downlink transport blocks and feedback information to the system for scheduling and link adaptation of transport block

CQI and ACK/NACK

Physical Channel, Uplink, SF=256

Subframe #0 Subframe #i Subframe #n

One HS-DPCCH subframe ( 2ms )

ACK/NACK


CQI

Tslot = 2560 chips 2 × Tslot = 5120 chips

The uplink HS-DPCCH consists of:

Acknowledgements for HARQ

Channel Quality Indicator (CQI)

As the HS-DPCCH uses SF=256, there are a total of 30 channel bits per 2 ms sub frame (3 time slot). The HS-DPCCH information is divided in such a way that the HARQ acknowledgement is transmitted in the first slot of the subframe while the channel quality indication is transmitted in the rest slot.


Contents


2.1 Physical Channel Structure and Functions

2.2 Channel Mapping


Mapping Between ChannelsLogical channels Transport channels Physical channels

BCCH BCH P-CCPCH

FACH S-CCPCH

PCCH PCH S-CCPCH

CCCH RACH PRACH

FACH S-CCPCH

CTCH FACH S-CCPCH

DCCH, DTCH DCH DPDCH

HS-DSCH HS-PDSCH

RACH, FACH PRACH, S-CCPCH

This page indicates how the mapping can be done between logical, transport and physical channels. Not all physical channels are represented because not all physical channels correspond to a transport channel.

The mapping between logical channels and transport channels is done by the MAC sub-layer.

Different connections can be made between logical and transport channels:

BCCH is connected to BCH and may also be connected to FACH;

DTCH can be connected to either RACH and FACH, to RACH and DSCH, to DCH and DSCH, to a DCH or a CPCH;

CTCH is connected to FACH;

DCCH can be connected to either RACH and FACH, to RACH and DSCH, to DCH and DSCH, to a DCH or a CPCH;

PCCH is connected to PCH;

CCCH is connected to RACH and FACH.

These connections depend on the type of information on the logical channels.


Contents





Synchronization Procedure - Cell Search

Frame synchronization & Code Group Identification

Scrambling Code Identification

UE uses SSC to find frame synchronization and identify the code group of the cell found in the first step

UE determines the primary scrambling code through correlation over the PCPICH with all codes within the identified group, and then detects the P-CCPCH and reads BCH information。

Slot Synchronization

UE uses PSC to acquire slot synchronization to a cell

The purpose of the Cell Search Procedure is to give the UE the possibility of finding a cell and of determining the downlink scrambling code and frame synchronization of that cell. This is typically performed in 3 steps:

PSCH (Slot synchronization): The UE uses the SCH’s primary synchronization code to acquire slot synchronization to a cell. The primary synchronization code is used by the UE to detect the existence of a cell and to synchronize the mobile on the TS boundaries. This is typically done with a single filter (or any similar device) matched to the primary synchronization code which is common to all cells. The slot timing of the cell can be obtained by detecting peaks in the matched filter output.

SSCH (Frame synchronization and code-group identification): The secondary synchronization codes provide the information required to find the frame boundaries and the group number. Each group number corresponds to a unique set of 8 primary scrambling codes. The frame boundary and the group number are provided indirectly by selecting a suite of 15 secondary codes. 16 secondary codes have been defined C1, C2, ….C16. 64 possible suites have been defined, each suite corresponds to one of the 64 groups. Each suite of secondary codes is composed of 15 secondary codes (chosen in the set of 16), each of which will be transmitted in one time slot. When the received codes matches one of the possible suites, the UE has both determined the frame boundary and the group number.

PCPICH (Scrambling-code identification): The UE determines the exact primary scrambling code used by the found cell. The primary scrambling code is typically identified through symbol-by-symbol correlation over the PCPICH with all the codes within the code group identified in the second step. After the primary scrambling code has been identified, the Primary CCPCH can be detected and the system- and cell specific BCH information can be read.


Random Access Procedure

START

Choose a RACH sub channel fromavailable ones

Get available signatures

Set Preamble Retrans Max

Set Preamble_Initial_Power

Send a preamble

Check the corresponding AI

Increase message part power by p-m based on preamble power

Set physical status to be RACHmessage transmitted Set physical status to be Nack

on AICH received

Choose a access slot again

Counter> 0 & Preamble power < maximum allowed power

Choose a signature and increase preamble transmit power

Set physical status to be Nackon AICH received

Get negative AI

No AI

Report the physical status to MAC

END

Get positive AI

The counter of preamble retransmit Subtract 1, Commanded preamble power

increased by Power Ramp Step

N

Y

Send the corresponding message part

Physical random access procedure

1. Derive the available uplink access slots, in the next full access slot set, for the set of available RACH sub-channels within the given ASC. Randomly select one access slot among the ones previously determined. If there is no access slot available in the selected set, randomly select one uplink access slot corresponding to the set of available RACH sub-channels within the given ASC from the next access slot set. The random function shall be such that each of the allowed selections is chosen with equal probability ；

2. Randomly select a signature from the set of available signatures within the given ASC. ；

3. Set the Preamble Retransmission Counter to Preamble_ Retrans_ Max

4. Set the parameter Commanded Preamble Power to Preamble_Initial_Power

5. Transmit a preamble using the selected uplink access slot, signature, and preamble transmission power.

6. If no positive or negative acquisition indicator (AI ≠ +1 nor –1) corresponding to the selected signature is detected in the downlink access slot corresponding to the selected uplink access slot:

A: Select the next available access slot in the set of available RACH sub-channels within the given ASC;B: select a signature;C: Increase the Commanded Preamble Power;D: Decrease the Preamble Retransmission Counter by one. If the Preamble Retransmission Counter > 0 then repeat from step 6. Otherwise exit the physical random access procedure.

7. If a negative acquisition indicator corresponding to the selected signature is detected in the downlink access slot corresponding to the selected uplink access slot, exit the physical random access procedure Signature

8. If a positive acquisition indicator corresponding to the selected signature is detected , Transmit the random access message three or four uplink access slots after the uplink access slot of the last transmitted preamble

9. exit the physical random access procedure


Transmit Diversity ModeApplication of Tx diversity modes on downlink physical channel

––applied–AICH

––applied–HS-SCCH

–appliedapplied–HS-PDSCH

––applied–PICH

appliedappliedapplied–DPCH

––applied–S-CCPCH

–––appliedSCH

––applied–P-CCPCH

Mode 2Mode 1STTDTSTD

Closed loop modeOpen loop modePhysical channel type

Transmitter-antenna diversity can be used to generate multi-path diversity in places where it would not otherwise exist. Multi-path diversity is a useful phenomenon, especially if it can be controlled. It can protect the UE against fading and shadowing. TX diversity is designed for downlink usage. Transmitter diversity needs two antennas, which would be an expensive solution for the UEs.

The UTRA specifications divide the transmitter diversity modes into two categories: (1) open-loop mode and (2) closed-loop mode. In the open-loop mode no feedback information from the UE to the NodeB is available. Thus the UTRAN has to determine by itself the appropriate parameters for the TX diversity. In the closed-loop mode the UE sends feedback information up to the NodeB in order to optimize the transmissions from the diversity antennas.

Thus it is quite natural that the open-loop mode is used for the common channels, as they typically do not provide an uplink return channel for the feedback information. Even if there was a feedback channel, the NodeB cannot really optimize its common channel transmissions according to measurements made by one particular UE. Common channels are common for everyone; what is good for one UE may be bad for another. The closed-loop mode is used for dedicated physical channels, as they have an existing uplink channel for feedback information. Note that shared channels can also employ closed loop power control, as they are allocated for only one user at a time, and they also have a return channel in the uplink. There are two specified methods to achieve the transmission diversity in the open-loop mode and two methods in closed-loop mode


Transmit Diversity - STTD

Space time block coding based transmit antenna diversity

(STTD)

4 consecutive bits b0, b1, b2, b3 using STTD coding

b0 b1 b2 b3 Antenna 1

Antenna 2Channel bits

STTD encoded channel bitsfor antenna 1 and antenna 2.

b0 b1 b2 b3

-b2 b3 b0 -b1

The TX diversity methods in the open-loop mode are

space time-block coding-based transmit-antenna diversity (STTD)

time-switched transmit diversity (TSTD).

In STTD the data to be transmitted is divided between two transmission antennas at the base station site and transmitted simultaneously. The channel-coded data is processed in blocks of four bits. The bits are time reversed and complex conjugated, as shown in above slide. The STTD method, in fact, provides two brands of diversity. The physical separation of the antennas provides the space diversity, and the time difference derived from the bit-reversing process provides the time diversity.

These features together make the decoding process in the receiver more reliable. In addition to data signals, pilot signals are also transmitted via both antennas. The normal pilot is sent via the first antenna and the diversity pilot via the second antenna.

The two pilot sequences are orthogonal, which enables the receiving UE to extract the phase information for both antennas.

The STTD encoding is optional in the UTRAN, but its support is mandatory for the UE’s receiver.


Transmit Diversity - TSTD

Time switching transmit diversity (TSTD) is used only on

SCH channel

Antenna 1

Antenna 2

i,0

i,1

acsi,14

Slot #0 Slot #1 Slot #14

i,2

acp

Slot #2

(Tx OFF)

(Tx OFF)

(Tx OFF)

(Tx OFF)

(Tx OFF)

(Tx OFF)

(Tx OFF)

acp acp

acsacs

acp

acs(Tx OFF)

Time-switched transmit diversity (TSTD) can be applied to the SCH. Just like STTD, the support of TSTD is optional in the UTRAN, but mandatory in the UE. The principle of TSTD is to transmit the synchronization channels via the two base station antennas in turn. In even-numbered time slots the SCHs are transmitted via antenna 1, and in odd-numbered slots via antenna 2. This is depicted in above Figure. Note that SCH channels only use the first 256 chips of each time slot (i.e., one-tenth of each slot).


Closed Loop Mode

Used in DPCH and HS-PDSCH

The closed-loop-mode transmit diversity can only be applied to the downlink channel if there is an associated uplink channel. Thus this mode can only be used with dedicated channels. The chief operating principle of the closed loop mode is that the UE can control the transmit diversity in the base station by sending adjustment commands in FBI bits on the uplink DPCCH. The UE uses the base station’s common pilot channels to estimate the channels separately. Based on this estimation, it generates the adjustment information and sends it to the UTRAN to maximize the UE’s received power.

There are actually two modes in the closed-loop method. In mode 1 only the phase can be adjusted; in mode 2 the amplitude is adjustable as well as the phase. Each uplink time slot has one FBI bit for closed-loop-diversity control. In mode 1 each bit forms a separate adjustment command, but in mode 2 four bits are needed to compose a command.

This functions can be configured by LMT command ADD CELLSETUP.


ReferencesTS 25.104 UTRA (BS) FDD Radio Transmission and Reception

TS 25.201 Physical layer-general description

TS 25.211 Physical channels and mapping of transport channels onto physical channels (FDD)

TS 25.212 Multiplexing and channel coding (FDD)

TS 25.213 Spreading and modulation (FDD)

TS 25.214 Physical layer procedures (FDD)

TS 25.308 UTRA High Speed Downlink Packet Access (HSDPA)

TR 25.877 High Speed Downlink Packet Access (HSDPA) - Iub/Iur Protocol Aspects

TR 25.858 Physical layer aspects of UTRA High Speed Downlink Packet Access


This course mainly introduces the basic concept, key

technology and procedures of WCDMA physical layer.

These knowledge is very important for understanding Uu

interface and further study.

Summary

www.huawei.com


WCDMA UTRAN Interface and Signaling Procedure


Objectives


Understand UTRAN interface and structure

Understand the definitions about UTRAN network elements

Understand UTRAN signaling procedure


Contents

1. UTRAN Network Overview

2. Basic Concepts about UTRAN

3. UTRAN Signaling Procedure


UMTS Network Structure

RNS

RNC

RNS

RNC

Core Network

NodeB NodeB NodeB NodeB

Iu-CS Iu-PS

Iur

Iub IubIub Iub

CN

UTRAN

UEUu

CS PS

Iu-CSIu-PS

CSPS

UTRAN (UMTS Terrestrial Radio Access network) structure

The UTRAN consists of one or several Radio Network Subsystem ( RNS ), each containing one RNC and one or several NodeB

Interface

Iu interface: the Iu interface connects the UTRAN to the CN and is split in two parts. The Iu-CS is the interface between the RNC and the circuit switched domain of the CN. The Iu-PS interface is the interface between the RNC and the packet switched domain of the CN.

Uu interface: the Uu interface is the WCDMA radio interface with in UMTS. It is the interface through which the UE accesses the fixed part of the network.

Iub interface: the Iub interface connects the NodeB and the RNC. Contrarily to GSM, this interface is fully open in UMTS and thus more competition is expected.

Iur interface: the RNC-RNC interface was initially designed in order to provide inter RNC soft handover, but more features were added during the development.


Uu Interface

L3co

ntro

l

cont

rol

cont

rol

cont

rol

C-plane signaling U-plane information

PHY

L2/MAC

L1

RLC

DCNtGC

L2/RLC

MAC

RLCRLCRLC


UuS boundary

L2/BMC

control

PDCPPDCP L2/PDCP

DCNtGC

RRC

RLCRLCRLCRLC

BMC

radio bearer

logical channel

transport channel

The layer 1 supports all functions required for the transmission of bit streams on the physical medium. It is also in charge of measurements function consisting in indicating to higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power, transmit power, … It is basically composed of a “layer 1 management” entity, a “transport channel” entity, and a “physical channel” entity.

The layer 2 protocol is responsible for providing functions such as mapping, ciphering, retransmission and segmentation. It is made of four sublayers: MAC (Medium Access Control), RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol) and BMC (Broadcast/Multicast Control).

The layer 3 is split into 2 parts: the access stratum and the non access stratum. The access stratum part is made of “RRC (Radio Resource Control)” entity and “duplication avoidance” entity. The non access stratum part is made of CC, MM parts.

Not shown on the figure are connections between RRC and all the other protocol layers (RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services.

The protocol layers are located in the UE and the peer entities are in the NodeB or the RNC.


General Protocol Mode for UTRAN Terrestrial Interface

The structure is based on the principle that the layers and planes are logically independent of each other.

Application Protocol

Data Stream(s)

ALCAP(s)

Transport Network

Layer

Physical Layer

Signaling Bearer(s)

Control Plane User Plane

Transport NetworkUser Plane

Transport Network Control Plane

Radio Network

Layer

Signaling Bearer(s)

Data Bearer(s)


Protocol structures in UTRAN terrestrial interfaces are designed according to the same general protocol model. This model is shown in above slide. The structure is based on the principle that the layers and planes are logically independent of each other and, if needed, parts of the protocol structure may be changed in the future while other parts remain intact. Horizontal Layers

The protocol structure consists of two main layers, the Radio Network Layer (RNL) and the Transport Network Layer (TNL). All UTRAN-related issues are visible only in the Radio Network Layer, and the Transport Network Layer represents standard transport technology that is selected to be used for UTRAN but without any UTRAN-specific changes.

Vertical Planes

Control Plane

The Control Plane is used for all UMTS-specific control signaling. It includes the Application Protocol (i.e. RANAP in Iu, RNSAP in Iur and NBAP in Iub), and the Signaling Bearer for transporting the Application Protocol messages. The Application Protocol is used, among other things, for setting up bearers to the UE (i.e. the Radio Access Bearer in Iu and subsequently the Radio Link in Iur and Iub). In the three plane structure the bearer parameters in the Application Protocol are not directly tied to the User Plane technology, but rather are general bearer parameters. The Signaling Bearer for the Application Protocol may or may not be of the same type as the Signaling Bearer for the ALCAP. It is always set up by O&M actions.

User Plane

All information sent and received by the user, such as the coded voice in a voice call or the packets in an Internet connection, are transported via the User Plane. The User Plane includes the Data Stream(s), and the Data Bearer (s) for the Data Stream(s). Each Data Stream is characterized by one or more frame protocols specified for that interface.

Transport Network Control Plane

The Transport Network Control Plane is used for all control signaling within the Transport Layer. It does not include any Radio Network Layer information. It includes the ALCAP protocol that is needed to set up the transport bearers (Data Bearer) for the User Plane. It also includes the Signaling Bearer needed for the ALCAP. The Transport Network Control Plane is a plane that acts between the Control Plane and the User Plane. The introduction of the Transport Network Control Plane makes it possible for the Application Protocol in the Radio Network Control Plane to be completely independent of the technology selected for the Data Bearer in the User Plane.

About AAl2 and AAL5

Above the ATM layer we usually find an ATM adaptation layer (AAL). Its function is to process the data from higher layers for ATM transmission.

This means segmenting the data into 48-byte chunks and reassembling the original data frames on the receiving side. There are five different AALs (0, 1, 2, 3/4, and 5). AAL0 means that no adaptation is needed. The other adaptation layers have different properties based on three parameters:

Real-time requirements;

Constant or variable bit rate;

Connection-oriented or connectionless data transfer.

The usage of ATM is promoted by the ATM Forum. The Iu interface uses two AALs: AAL2 and AAL5.

AAL2 is designed for the transmission of connection oriented, real-time data streams with variable bit rates.

AAL5 is designed for the transmission of connectionless data streams with variable bit rates.


RNL Control Plane Application Protocol

NBAP Node B Application Part

RANAP Radio Access Network Application Part

RNSAP Radio Network Subsystem Application Part

RRC Radio Resource Control

NodeB

RNC

CN

UE

RANAP

NBAP

RNSAPRRC RNC

RANAP is the signaling protocol in Iu that contains all the control information specified for the Radio Network Layer.

RNSAP is the signaling protocol in Iur that contains all the control information specified for the Radio Network Layer.

NBAP is the signaling protocol in Iub that contains all the control information specified for the Radio Network Layer.

RRC is the signaling protocol in Uu that locate in the Uu interface layer 3.


Iu-CS Interface

ALCAPALCAP

Control Plane

Transport NetworkControl Plane

User planeRadioNetworkLayer


TransportNetworkLayer

A B

RANAP

AAL2 PATH

ATM

Physical Layer

SAAL NNI

SCCPMTP3-B

Iu UP

SAAL NNI

MTP3-B


Protocol Structure for Iu CS

The Iu CS overall protocol structure is depicted in above slide. The three planes in the Iu interface share a common ATM (Asynchronous Transfer Mode) transport which is used for all planes. The physical layer is the interface to the physical medium: optical fiber, radio link or copper cable. The physical layer implementation can be selected from a variety of standard off-the-shelf transmission technologies, such as SONET, STM1, or E1.

Iu CS Control Plane Protocol Stack

The Control Plane protocol stack consists of RANAP, on top of Broadband (BB) SS7 (Signaling System #7) protocols. The applicable layers are the Signaling Connection Control Part (SCCP), the Message Transfer Part (MTP3-b) and SAAL-NNI (Signaling ATM Adaptation Layer for Network to Network Interfaces).

Iu CS Transport Network Control Plane Protocol Stack

The Transport Network Control Plane protocol stack consists of the Signaling Protocol for setting up AAL2 connections (Q.2630.1 and adaptation layer Q.2150.1), on top of BB SS7 protocols. The applicable BB SS7 are those described above without the SCCP layer.

Iu CS User Plane Protocol Stack

A dedicated AAL2 connection is reserved for each individual CS service.


Iu-PS Interface

Control Plane User planeRadioNetworkLayer

Transport NetworkUser PlaneTransport

NetworkLayer


C

RANAP

ATM

SAAL NNI

SCCP

MTP3-B

Iu UP

AAL Type 5IP

UDP

GTP-U

Physical Layer

Protocol Structure for Iu PS

The Iu PS protocol structure is represented in above slide. Again, a common ATM transport is applied for both User and Control Plane. Also the physical layer is as specified for Iu CS.

Iu PS Control Plane Protocol Stack

The Control Plane protocol stack consists of RANAP, on top of Broadband (BB) SS7 (Signaling System #7) protocols. The applicable layers are the Signaling Connection Control Part (SCCP), the Message Transfer Part (MTP3-b) and SAAL-NNI (Signaling ATM Adaptation Layer for Network to Network Interfaces).

Iu PS Transport Network Control Plane Protocol Stack

The Transport Network Control Plane is not applied to Iu PS. The setting up of the GTP tunnel requires only an identifier for the tunnel, and the IP addresses for both directions, and these are already included in the RANAP RAB Assignment messages.

Iu PS User Plane Protocol Stack

In the Iu PS User Plane, multiple packet data flows are multiplexed on one or several AAL5 PVCs. The GTP-U (User Plane part of the GPRS Tunneling Protocol) is the multiplexing layer that provides identities for individual packet data flow. Each flow uses UDP connectionless transport and IP addressing.


Iub Interface

ALCAPALCAP

Control Plane






NBAP

AAL2 PATH

ATM

Physical Layer

SAAL UNI

Iub FP

SAAL UNI

NCP CCP

The Iub interface is the terrestrial interface between NodeB and RNC. The Radio Network Layer defines procedures related to the operation of the NodeB. The Transport Network Layer defines procedures for establishing physical connections between the NodeB and the RNC.

The Iub application protocol, NodeB application part ( NBAP ) initiates the establishment of a signaling connection over Iub . It is divided into two essential components, CCP and NCP.

NCP is used for signaling that initiates a UE context for a dedicated UE or signals that is not related to specific UE. Example of NBAP-C procedure are cell configuration , handling of common channels and radio link setup

CCP is used for signaling relating to a specific UE context.

SAAL is an ATM Adaptation Layer that supports communication between signaling entities over an ATM link.

The user plane Iub Frame Protocol ( FP ), defined the structure of the frames and the basic in band control procedure for every type of transport channel. There are DCH-FP, RACH-FP, FACH-FP, HS-DSCH FP and PCH FP.


Iur Interface

ALCAPALCAP

Control Plane




A B

RANAP

AAL2 PATH

ATM

Physical Layer

SAAL NNI

SCCPMTP3-B

Iur Data Stream

SAAL NNI

MTP3-B



Iur interface connects two RNCs. The protocol stack for the Iur is shown in above slide.

The RNSAP protocol is the signaling protocol defined for the Iur interface.


Contents





SRNC / DRNC

SRNC and DRNC are concepts for a connected UE.The SRNC handles the connection to one UE, and may borrow radio resources of a certain cell from the DRNC. Drift RNCs support the Serving RNC by providing radio resourcesA UE in connection state has at least one and only one SRNC, but can has 0 or multiple DRNCs

CN

SRNC DRNC

Iu Iur

Inside the UTRAN, the RNCs of the Radio Network Subsystems can be interconnected together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over direct physical connection between RNCs or virtual networks using any suitable transport network .

For each connection between User Equipment and the UTRAN, One RNC is the Serving RNC. When required, Drift RNCs support the Serving RNC by providing radio resources. The role of an RNC (Serving or Drift) is on a per connection basis between a UE and the UTRAN.


RAB, RB and RL

RAB

RB

RLNodeB

RNC CNUE

UTRAN

RAB: The service that the access stratum provides to the non-access stratum for transfer of user data between User Equipment and CN.

RB: The service provided by the layer2 for transfer of user data between User Equipment and Serving RNC.

RL: A "radio link" is a logical association between single User Equipment and a single UTRAN access point. Its physical realization comprises one or more radio bearer transmissions.


UE Working Modes and States

Idle Mode

Connected Mode

CELL_DCH

CELL_FACH

CELL_PCH

URA_PCH

If RRC connection does not exit between UE and RNC, then the UE is in idle mode.

If RRC connection exits between UE and RNC, then the UE is in connected mode.

Based on UE mobility and activity UE in connected mode may be allocated to four different states: CELL_DCH, CELL_FACH, CELL_PCH and URA_PCH.

The UE leaves the connected mode and returns to idle mode when the RRC connection is released or at RRC connection failure.


Idle Mode

The UE has no relation to UTRAN, only to CN. For data

transfer, a signaling connection has to be established.

UE camps on a cell

It enables the UE to receive system information from the PLMN

UE can monitor PICH of a cell for paging

The idle mode tasks can be divided into three processes:

PLMN selection and reselection

Cell selection and reselection

Location registration

When a UE is switched on, a public land mobile network (PLMN) is selected and the UE searches for a suitable cell of this PLMN to camp on.

The UE searches for a suitable cell of the chosen PLMN and chooses that cell to provide available services, and tunes to its control channel. This choosing is known as "camping on the cell". The UE will, if necessary, then register its presence, by means of a NAS registration procedure, in the registration area of the chosen cell.

If the UE finds a more suitable cell, it reselects onto that cell and camps on it. If the new cell is in a different registration area, location registration is performed.


Connected Mode

When UE is in connected mode

The UE position can be known on different levels:

Cell level (CELL_DCH/CELL_FACH/CELL_PCH)

UTRAN Registration Area (URA) level (URA_PCH)

The UE can use different types of channels in connected mode

Dedicated transport channels (CELL_DCH)

Common transport channels (CELL_FACH)

Assuming that there exists an RRC connection, there are two basic families of RRC connection mobility procedures, URA updating and handover. Different families of RRC connection mobility procedures are used in different levels of UE connection (cell level and URA level):

URA updating is a family of procedures that updates the UTRAN registration area of a UE when an RRC connection exists and the position of the UE is known on URA level in the UTRAN;

Handover is a family of procedures that adds or removes one or several radio links between one UE and UTRAN when an RRC connection exists and the position of the UE is known on cell level in the UTRAN.

Which type of transport channel is used by UE in connected mode is decided by RNC according to the UE activity.


Connected Mode

Cell-DCH

In active state

Communicating via its dedicated channels

UTRAN knows which cell UE stays in

If there is huge data to be transmitted, it must allocate dedicated channel. Thus UE will be in Cell-DCH. UE in Cell-DCH state is communicating via DCH (downlink and uplink) with UTRAN.


Connected Mode

Cell-FACH

In active state

Few data to be transmitted both in uplink and in downlink.

There is no need to allocate dedicated channel for this UE

Downlink uses FACH and uplink uses RACH

UE needs to monitor the FACH for its information

UTRAN knows which cell the UE stays in

If there is only few data to be transmitted, there is no need to allocate dedicated channel. Thus UE will be in Cell-FACH. UE in Cell-FACH state is communicating via FACH (downlink) and RACH (uplink) with UTRAN. UE need to monitor the FACH for its relative information because FACH is shared for all users in the cell.


Connected Mode

Cell-PCH

No data to be transmitted or received

Monitor PICH, to receive its paging

UTRAN knows which cell the UE stays in

UTRAN has to update cell information of UE when UE roams

to another cell

Lower the power consumption of UE

If UE has no data to be transmitted or received, UE will be in Cell-PCH or URA-PCH. In these two states, UE needs to monitor PICH,to receive its paging. UTRAN knows which cell or URA UE is now in. The difference between Cell-PCH and URA-PCH is that UTRAN update UE information only after UE which is in URA-PCH state has roamed to other URA.

UTRAN have to update cell information of UE when UE roams to another cell. UE migrates to cell-FACH state to complete the cell update. If there is also no data to be transmitted or received, UE is back to CELL-PCH state after cell update. If the cell update times in a fixed time reach a preset value, UTRAN will let UE migrate to URA-PCH. URA is an area of several cells.


Connected Mode

URA-PCH

No data to be transmitted or received

Monitor PICH, to receive its paging

UTRAN only knows which URA (which consists of multiple cells) that UE stays

UTRAN updates UE information only after UE has roamed to other URA

A better way to reduce the resource occupancy and signaling transmission

It is the same as the CELL-PCH state. UE should migrate to CELL-FACH state to complete the URA update.


UE Working Modes and States

CELL_DCH CELL_FACH

CELL_PCHURA_PCH

IDLE

DEAD - Scan networks (PLMN)- Camp on a cell

- Monitor paging channel- Cell re-selection

- Dedicated channel- Common service, such as voice

- Reduce activity, DTX,and save powerRRC Connection

- Common channel- PS service with few

data to transmit

- Reduce activity further- Avoid unnecessary signaling

This is the UE states figure. These states are significant only for UTRAN and UE. They are transparent to CN. Let’s focus on the switch between the states.


Contents





Contents


3.1 System Information Broadcast

3.2 Paging

3.3 Call Process

3.4 Handover


System Information Broadcast Flow

3. BCCH: System Information

1. System Information Update Request

UE Node B RNC

NBAPNBAP

RRCRRC

4. BCCH: System InformationRRCRRC

5. BCCH: System Information RRCRRC

2. System Information Update ResponseNBAPNBAP


Introduction of System Information

MIB:

PLMN tag

Scheduling information for SB (Scheduling Block)

Scheduling information for SIB (System Information Block)

SB1: scheduling information for SIB

SB2: scheduling information for SIB (extended)



SIB1: System information for NAS and the timer/counter for UE

SIB2: URA information

SIB3: Parameters for cell selection and cell re-selection

SIB4: Parameters for cell selection and cell re-selection while UE is in connected mode

SIB5: Parameters for the common physical channels of the cell

SIB6: Parameters for the common physical channels of the cell while UE is in connected mode



SIB7: uplink interference level and the refreshing timer

SIB8: the CPCH static information

SIB9: the CPCH dynamic information

SIB10: information to be used by UEs having their DCH controlledby a DRAC procedure

SIB11: measurement controlling information

SIB12: measurement controlling information in connected mode



SIB13: ANSI-41 system information

SIB14: the information in TDD mode

SIB15: the position service information

SIB16: the needed pre-configuration information for handover from other RAT to UTRAN

SIB17: the configuration information for TDD

SIB18: the PLMN identities of the neighboring cells to be used in shared networks to help with the cell reselection process


System Information Block Type 1

System information type 1

The NAS system information

CS domain DRX: K=6, then DRX period is 2^k= 2^6= 64TTI=640 ms

PS domain DRX: K=6, then DRX period is 2^k=2^6=64TTI =640 ms



System info type 2

URA information



The references for cell selection and re-selection

Qhyst2s

Sintrasearch

Sintersearch

Sinterratsearch

Qqualmin

Qrxlemin

T reselection

Max Allowed UE TX power



The configuration information for the following physical channels and the counterpart transport channels

PCCPCH

SCCPCH

PICH

AICH

PRACH


System Information Block Type 7 and 11

System info type 7

Including the UL interference level which is used for open loop power control

Including the Expiration Time Factor which is used for refreshing the SIB7 periodically

System info type 11

The neighbor cell information for cell re-selection in IDLE mode


Contents



3.2 Paging

3.3 Call Process

3.4 Handover


Paging Initiation

CN initiated paging

Establish a signaling connection

UTRAN initiated paging

Trigger the cell update procedure

Trigger reading of updated system information

For CN originated paging:

In order to request UTRAN connect to UE, CN initiates the paging procedure, transmits paging message to the UTRAN through Iu interface, and UTRAN transmits the paging message from CN to UE through the paging procedure on Uu interface, which will make the UE initiate a signaling connection setup process with the CN.

For UTRAN originated paging:

UE state transition: In order to trigger UE in the CELL_PCH or URA_PCH state to carry out state transition (for example, transition to the CELL_FACH state), the UTRAN will perform a paging process. Meanwhile, the UE will initiate a cell update or URA update process, as a reply to the paging.

When the cell system message is updated: When system messages change, the UTRAN will trigger paging process in order to inform UE in the idle, CELL_PCH or URA_PCH state to carry out the system message update, so that the UE can read the updated system message.


Paging Type 1

If UE is in CELL_PCH,URA_PCH or IDLE state，the paging message will be transmitted on PCCH with paging type 1

CN RNC1 RNC2 NODEB1.1 NODEB2.1 UE

RANAPRANAP

RANAP RANAP

PCCH: PAGING TYPE 1

PAGING

PAGING

PCCH: PAGING TYPE 1

Paging type 1:

The message is transmitted in one LA or RA according to LAI or RAI.

After calculating the paging time, the paging message will be transmitted at that time

If UE is in CELL_PCH or URA_PCH state, the UTRAN transmits the paging information in PAGING TYPE 1 message to UE. After received paging message, UE performs a cell update procedure to transit state to CELL_FACH.

As shown in the above figure, the CN initiates paging in a location area (LA), which is covered by two RNCs. After receiving a paging message, the RNC searches all the cells corresponding to the LAI, and then calculates the paging time, at which it will send the PAGING TYPE 1 message to these cells through the PCCH.


Paging Type 2

If UE is in CELL_DCH or CELL_FACH state，the paging message will be transmitted on DCCH with paging type 2

CN SRNC UE

RANAPRANAP

PAGING

RRCRRCDCCH: PAGING TYPE 2

Paging type 2:

If UE is in CELL_DCH or CELL_FACH state，the paging message will be transmitted on DCCH with paging type 2

The message will be only transmitted in a cell

As shown in the above figure, if the UE is in the CELL_-DCH or CELL_FACH state, the UTRAN will immediately transmit PAGING TYPE 2 message to the paged UE on DCCH channel.


Contents



3.2 Paging

3.3 Call Process

3.4 Handover


Introduction of Call Process

In WCDMA system, a call process includes the following basic signaling flows:

RRC connection flow

Direct transfer message flow

Authentication flow (optional)

Security flow (optional)

RAB establish flow

Call proceeding

NAS signaling before correlative bearer release

Correlative bearer release


RRC Connection Establishment Flow (CCCH)

UE Serving RNC

RRCRRC

RRCRRC2. CCCH: RRC Connection Set up

RRCRRC3. DCCH: RRC Connection Setup Complete

1. CCCH: RRC Connection Request

In the idle mode, when the non-access layer of the UE requests to establish a signaling connection, the UE will initiate the RRC connection procedure. Each UE has up to one RRC connection only.

When the SRNC receives an RRC CONNECTION REQUEST message from the UE, the Radio Resource Management (RRM) module of the RNC determines whether to accept or reject the RRC connection request according to a specific algorithm. If accepting the request, the RRM module determines whether to set up the RRC connection on a Dedicated Channel (DCH) or on a Common Channel (CCH) according to a specific RRM algorithm.

Description:

The UE sends an RRC CONNECTION REQUEST message to the SRNC through the uplink CCCH, requesting the establishment of an RRC connection.

Based on the RRC connection request cause and the system resource state, the SRNC decides to establish the connection on the common channel.

The SRNC sends an RRC CONNECTION SETUP message to the UE throughthe downlink CCCH. The message contains the information about the CCH.

The UE sends an RRC CONNECTION SETUP COMPLETE message to the SRNC through the uplink CCCH.


RRC Connection Establishment Flow (DCCH)

5. Downlink Synchronization

UE Node B Serving RNC

DCH - FP

Allocate RNTISelect L1 and L2parameters

RRCRRC

NBAPNBAP3. Radio Link Setup Response

NBAPNBAP2. Radio Link Setup Request

RRCRRC7. CCCH: RRC Connection Set up

Start RX

Start TX

4. ALCAP Iub Data Transport Bearer Setup

RRCRRC9. DCCH: RRC Connection Setup Complete

6. Uplink Synchronization

NBAPNBAP8. Radio Link Restore Indication

DCH - FP

DCH - FP

DCH - FP

1. CCCH: RRC Connection Request

Typically, an RRC connection is set up on the DCH.

Description:

The UE sends an RRC Connection Request message via the uplink CCCH to request to establish an RRC connection.

Based on the RRC connection request cause and the system resource state, the SRNC decides to establish the connection on the dedicated channel, and allocates the RNTI and L1 and L2 resources.

The SRNC sends a Radio Link Setup Request message to Node B, requesting the Node B to allocate specific radio link resources required by the RRC connection.

After successfully preparing the resources, the Node B responds to the SRNC with the Radio Link Setup Response message.

The SRNC initiates the establishment of Iub user plane transport bearer with the ALCAP protocol and completes the synchronization between the RNC and the Node B.

The SRNC sends an RRC Connection Setup message to the UE in the downlink CCCH.

The UE sends an RRC Connection Setup Complete message to the SRNC in the uplink DCCH.

DCH_3.4K_SIGNALLINGSpare RRC establishDEFAULTEST

FACHTerminating cause unknownTERMCAUSEUNKNOWN

FACHTerminating Low Priority SignalingTERMLOWPRIORSIGEST

DCH_13.6K_SIGNALLINGTerminating High Priority SignalingTERMHIGHPRIORSIGEST

DCH_3.4K_SIGNALLINGCall re-establishmentCALLREEST

FACHOriginating Low Priority SignalingORIGLOWPRIORSIGEST

DCH_13.6K_SIGNALLINGOriginating High Priority SignalingORIGHIGHPRIORSIGEST

FACHDetachDETACHEST

DCH_13.6K_SIGNALLINGRegistrationREGISTEST

DCH_3.4K_SIGNALLINGInter-RAT cell change orderINTERRATCELLCHGORDEREST

DCH_3.4K_SIGNALLINGInter-RAT cell re-selectionINTERRATCELLRESELEST

DCH_13.6K_SIGNALLINGEmergency Call RRC establish typeEMERGCALLEST

DCH_13.6K_SIGNALLINGTerminating Background CallTERMBKGCALLEST

DCH_13.6K_SIGNALLINGTerminating Interactive CallTERMINTERCALLEST

DCH_13.6K_SIGNALLINGTerminating Streaming CallTERMSTREAMCALLEST

DCH_13.6K_SIGNALLINGTerminating Conversational CallTERMCONVCALLEST

DCH_13.6K_SIGNALLINGOriginating Subscribed traffic CallORIGSUBSTRAFFCALLEST

DCH_13.6K_SIGNALLINGOriginating Background CallORIGBKGCALLEST

DCH_13.6K_SIGNALLINGOriginating Interactive CallORIGINTERCALLEST

DCH_13.6K_SIGNALLINGOriginating Streaming CallORIGSTREAMCALLEST

DCH_13.6K_SIGNALLINGOriginating Conversational CallORIGCONVCALLEST

Recommended valueNameID


Direct Transfer Message Flow

In Iu interface, radio network layer reports the RANAP

information and NAS information. NAS information is

taken as directed message in RANAP information.

UE NodeB RNC CN

RRC RRC

SCCP SCCP

SCCP SCCP

Initial DT

Connect Request

Connect Confirm

RRC

RANAP RANAPInitial UE Message

RANAP RANAPCommon ID

After the RRC connection between the UE and the UTRAN is successfully set up, the UE sets up a signaling connection with the CN via the RNC for NAS information exchange between the UE and the CN, such as authentication, service request and connection setup. This is also called the NAS signaling setup procedure.

For the RNC, the signaling exchanged between the UE and the CN is a direct transfer message. After receiving the first direct transfer message, that is, the Initial Direct Transfer message, the RNC sets up a signaling connection with the CN on the SCCP. The procedure is shown in the above figure:

The specific procedure is given as follows:

After the RRC connection is established, the UE sends the Initial Direct Transfer message to the RNC via the RRC connection. This message carries the NAS information content sent to the CN by the UE.

After receiving the Initial Direct Transfer message from the UE, the RNC sends the SCCP Connection Request (CR) message to the CN via the Iu interface. The message content is the Initial UE Message sent from the RNC to the CN, and carries the message content sent from the UE to the CN.

If the CN is ready to accept the connection request, then it returns the SCCP Connection Confirm (CC) message to the RNC. The SCCP connection is successfully set up. The RNC receives the message and confirms the signaling connection setup success.

If the CN cannot accept the connection request, then it returns the SCCP Connection Reject (CJ) message to the RNC. The SCCP connection setup fails. The RNC receives the message and confirms the signaling connection setup failure. Then it initiates the RRC release procedure.

After the signaling connection is successfully set up, the message sent by the UE to the CN is forwarded to the RNC via the Uplink Direct Transfer message, and the RNC converts it into the Direct Transfer message to send to the CN. The message sent by the CN to the UE is forwarded to the RNC via the Direct Transfer message, and the RNC converts it into the Downlink Direct Transfer to send to the UE.


Common ID


Authentication and Security FlowUE RNC CN

RRC Connection Setup Initial DT Initial UE Message

(CM Service Request)

DL DT (Authentication Request)DL DT (Authentication Request)

DL DT (Authentication Response)DL DT (Authentication Response)

Common ID

Security Mode CommandSecurity Mode Command

Security Mode Command Complete Security Mode Command Complete

RAB Assignment

UL Direct Transfer (Setup) Direct Transfer (Setup)

Direct Transfer (Call Proceeding)DL Direct Transfer (Call Proceeding)

Authentication is used for the validity of CN and UE. Security flow includes the encrypt process and integrity protection.


RAB Establishment FlowNodeBUE CNRNC

RANAPRANAPRAB Ass Req

Q.AAL2 Q.AAL2

Q.AAL2Q.AAL2

NBAPNBAP

AAL2 Setup Req

RL Recfg Prep

AAL2 Setup Rsp

NBAPNBAPRL Recfg Ready

Q.AAL2Q.AAL2 AAL2 Setup Req

Q.AAL2Q.AAL2 AAL2 Setup Rsp

FPFPDL Sync

FPFPUL Sync

RRC RRCRB Setup

NBAPNBAPRL Recfg Commit

RRC RRCRB Setup Complete

RANAPRANAPRAB Ass Rsp

RAB is the carrier which is provided by AS for NAS.

RAB is the carrier in user plane, which is for transferring the voice service, data service or multiple media service between UE and CN.

RAB establishment flow mainly includes the AAL2 PATH establishment of Iu and Iub interface, also includes the reconfiguration process of radio resource.

The RAB refers to the user plane bearer that is used to transfer voice, data and multimedia services between the UE and the CN. The UE needs to complete the RRC connection establishment before setting up the RAB.

The RAB setup is initiated by the CN and executed by the UTRAN. The basic procedure is as follows:

1. First the CN sends the RAB assignment request message to the UTRAN, requesting the UTRAN to establish the RAB.

2. The SRNC in the UTRAN initiates the establishment of the data transport bearer between the Iu interface and the Iub interface (Iur interface).

3. The SRNC sends the RB setup request to the UE.

4. After completing the RB establishment, the UE responds to the SRNC with the RB setup complete message.

5. The SRNC responds to the CN with the RAB assignment response message and the RAB setup procedure ends.

When the RAB is successfully established, a basic call is set up and the UE enters the conversation process.


NAS Signaling (CS)UE MSC

CM Service Request

RRC and NAS signaling Connection Setup

Authentication Request

Authentication Response

Security Mode Command

Security Mode Command Complete

RAB Assignment

SetupCall Proceeding

Alerting

Connect Connect ACKDisconnect

ReleaseRelease Complete

UE Outgoing Call UE Terminating Call

UEMSC

Paging Response

Authentication Request

Authentication Response



RAB Assignment

SetupCall Confirmed

Alerting Connect

Connect ACKDisconnect

ReleaseRelease Complete

Paging


Authentication and security flow are optional.CN does not need to the CM Service Response if the security mode is used.


NAS Signaling (PS)UE SGSN

Service Request


Authenticate and Ciphering Req



RAB Assignment

Service Accept

Activate PDP Context Req

Activate PDP Context Accept

Deactivate PDP Context Req

Deactivate PDP Context Accept

UE Outgoing Call

Authenticate and Ciphering Rsp

UE Terminating Call

UE

Service Request

Authenticate and Ciphering Req



RAB Assignment

Request PDP Context Activation

Activate PDP Context Req

Activate PDP Context Accept

Deactivate PDP Context Req

Deactivate PDP Context Accept

Paging


SGSN

Authenticate and Ciphering Rsp


UE to UE CS Call Process (1)


Activate PDP Context from UE (1)


Activate PDP Context from UE (2)


Activate PDP Context from Network (1)


Activate PDP Context from Network (2)


Contents



3.2 Paging

3.3 Call Process

3.4 Handover


Concepts about Soft Handover

Soft handover: the signals from different NodeBs are

merged in RNC

Softer handover: the signals from different cells, but from

the same NodeB are merged in NodeB

In the WCDMA system, since the intra-frequency exists among neighboring cells, the UE can communicate with the network via multiple radio links, and can select one with good signal quality by comparison when these radio links are merged, thus optimizing the communication quality. The soft handover can be conducted only in the FDD mode. The soft handover falls into the following cases according to the locations of the cells. The first case is the soft handover among difference cells of the Node B. In this case, the radio links can be merged within the Node B or the SRNC. If they are merged within the Node B, it is called softer handover. The second case is the soft handover among different Node Bs within the same RNC and among different RNCs.

An important issue during the soft handover is the merge of multiple radio links. In the WCDMA system, the MACRO DIVERSITY technology is adopted for the merge of the radio links, that is, the system compares the data from different radio links based on certain standards (such as BER), and selects the data with better quality to send to the upper layer.

Soft handover:

Selection combination in uplink

Maximum combination in downlink

Softer handover

Maximum combination in uplink and downlink


Soft Handover Flow (Intra-RNC)

Before Handover After Handover

SRNC

NodeBNodeB

SRNC

NodeBNodeB

SRNC

NodeBNodeB

During Handover

CNCN CN

During the soft handover, two or more radio links are connected with UE, and data in each RL are same.

The following are some key concepts about the neighboring cell in the soft handover:

Active set: The set of cells currently used by the UE. The execution result of the soft handover indicates the increase or decrease of the cells in the active set.

Monitor set: The set of cells that are not in the active set but are being observed by the UE based on the neighboring cell information from the UTRAN. The UE measures the cells in the observation set. When the measurement results satisfy certain conditions, the cells may be added to the active set. Therefore, the observation set sometimes is also called the candidate set.

Detected set: The set of cells that have been detected by the UE but do not belong to the active set or the observation set. The UTRAN can request the UE to report the measurement result of the detected set. Since the cells in the detected set are not listed in the neighboring cell list, this set is also called the unlisted set.


Soft Handover Flow

RNC (SRNC)

AirBridgeAirBridge

AirBridgeAirBridge

AirBridgeAirBridge

Core NetworkCore Network

Node B

It is no handover in this slide, only one radio links is connected with UE.


Soft Handover Flow

RNC (SRNC)

AirBridgeAirBridge

AirBridgeAirBridge

AirBridgeAirBridge

Merged in NodeB


Node B

It is softer handover. During the handover, the cells in active set belong to one NodeB. The NodeB uses the RAKE receiver to combine the data, and the UE also combines the data in RAKE receiver.


Soft Handover Flow

Merged in RNC

RNC (SRNC)

AirBridgeAirBridge

AirBridgeAirBridge

AirBridgeAirBridge


Node B

It is soft handover. During the handover, the cells in active set belong to one RNC, but different NodeBs. So the UE can combine the data in RAKE receiver. But in uplink, the data are combined with selection combination in RNC.


Soft Handover Flow (SRNC-DRNC)

Merged in SRNC

Node B

AirBridgeAirBridge

AirBridgeAirBridge

AirBridgeAirBridge

Serving RNC

Drift RNC


It is soft handover. During the handover, the cells in active set belong to different RNCs. So the UE can combine the data in RAKE receiver. But in uplink, the data are combined with selection combination in SRNC.


Soft Handover Flow (SRNC Relocation)

Node B

AirBridgeAirBridge

AirBridgeAirBridge

AirBridgeAirBridge

Serving RNC

RNC


There is no handover, but the SRNC has been changed.


Typical Soft Handover Flow (L3 Signaling)

Soft handover is triggered by 1A/1B/1C or 1D event

Measurement Report (1A/1B/1C or 1D)

Measurement Control

RRC Connection Setup Procedure

RNCUE

Active Set Update

Active Set Update Complete

Measurement Control

The soft handover procedure comprises the following steps:

Based on the Measurement Control information from the RNC, the UE measures the intra-frequency neighboring cells, and reports the measurement result to the RNC via Measurement Report.

The RNC compares the reported measurement result with the set threshold to decide the cells to be added and deleted.

(If some cells are to be added, the RNC notifies the Node B to get ready. )

The RNC notifies the UE to add and/or delete cells via the Active Set Updatemessage.

After the UE successfully update the active set, UE will send Active Set UpdateComplete to inform RNC.

(if the cells are deleted, the Node B will be notified to release the corresponding resources. )

After the soft handover, perhaps the measurement control information changes, if it is, RNC will send new Measurement Control to UE.

The original communication is not affected during the soft handover procedure so that smooth handover from a cell to another can be successfully completed.


Soft Handover Flow (Add Branch in AS)

For adding a cell into Active Set, RNC will notify NodeB to prepare the new RL before sending Active Set Update.


Soft Handover Flow (Del Branch from AS)

For deleting a cell from Active Set, RNC sends Active Set Update to UE first. After UE deleting the RL successfully, RNC will inform NodeB to delete the RL.


Hard Handover

Before Handover After Handover

Radio Link can not exist simultaneously

SRNC

NodeBNodeB

SRNC

NodeBNodeB

CNCN

It is hard handover. The UE disconnects the original radio link, then connects to the target cell. It happens in intra-frequency, inter-frequency and inter-RAT.


Intra-Frequency Hard Handover

Intra-Frequency hard handover is triggered by 1D event

Measurement Control (Intra-freq)


RNCUE

Measurement Control (Intra-Freq)

Physical Channel Reconfiguration

Physical Channel Reconfiguration Complete

Decision to setup new RL

Measurement Report (1D)


Inter-frequency Handover

Measurement Report(2D)



RNCUE

Measurement Control (Inter-Freq)

Decision to enter compress mode



Measurement Report

Decision to setup new RL

Measurement Control (2D & 2F)




Description:

Step 1 to step 5 is similar with soft handover, the differences are:

The SRNC sends the Physical Channel Reconfiguration message carrying the target cell information to the UE via the downlink DCCH.

After the UE hands over from the source cell to the target cell, the Node B of the source cell detects the radio link communication failure and then sends the Radio Link Failure Indication message to the SRNC, indicating the radio link failure.

After successfully handing over to the target cell, the UE sends the Physical Channel Reconfiguration Complete message to the SRNC via the DCCH, notifying the SRNC that the physical cannel reconfiguration is complete.

The Node B where the source cell is deletes the radio link resources, and then responds to the SRNC with the Radio Link Deletion Response message.

The SRNC adopts the ALCAP protocol to release the Iub interface transport bearer of the SRNC and the Node B where the source cell is.


Inter-RAT Handover Flow (UMTS->GSM)

Measurement Report(2D)



RNCUE

Measurement Control (Inter-RAT)

Decision to enter compress mode



Measurement Report (GSM)Decision to

handover to GSM

Measurement Control (2D & 2F)

Relocation Required

3G MSC3G MSC

Prepare Handover

BSC

Handover Request

Handover Request ACKPrepare Handover

ResponseRelocation Command

Inter-System Handover Command

Handover Complete

Handover CompltetSend END

Signal RequestIu Release Command

Iu Release Complete


Inter-RAT Handover Flow (GSM->UMTS)

www.huawei.com


WCDMA HSDPA Principles


Course Learning ObjectivesReview WCDMA and HSDPA evolution and standards

Define HSDPA protocol stack

Describe new channels for HSDPA

Explain the physical channel processing

HSDPA impact on protocol stack

Identify HSDPA UE categories

Define HSDPA protocols of Mac sub-layer


References3GPP Release 6 Specification References

TS 25.308 HSDPA overall description stage2

TS 25.211 Physical channel and mapping of transport channels onto physical channel (FDD)

TS 25.212 Multiplexing and channel coding (FDD)

TS 25.213 Spreading and modulation (FDD)

TS 25.214 Physical layer procedure (FDD)

TS 25.306 UE radio access capabilities

TS 25.321 Medium Access Control (MAC) protocol specification

TS 25.322 Radio Link Control (RLC) protocol specification

TS 25.331 Radio Resource Control (RRC) protocol specification


Contents1. HSDPA Introduction

2. HSDPA Key Techniques

3. HSDPA Physical Layer Channels

4. HSDPA Physical Layer Processing

5. HSDPA Layer2 Protocol


WCDMA Evolution

14.4Mbps10.0MbpsHSDPA

2.0Mbps384kbpsR99 WCDMA

473kbps120kbpsEDGE

171kbps40kbpsGPRS

9.6kbps9.6kbpsGSM

Downlink Peak Data Rate (Theoretical Maximum)

Downlink Peak Data Rate (Typical Deployment)

GSMGSM GPRSGPRS

EDGEEDGE

WCDMA WCDMA R99R99

HSDPA HSDPA R5R5

HSUPA HSUPA R6R6

WCDMA Evolution

WCDMA evolved from GSM/GPRS, inheriting much of the upper layer functionality directly from those systems. The first commercial deployments of WCDMA are based on a version of the standards called Release 99.

Enhanced Data rates for GSM Evolution (EDGE) is another system in the GSM/GPRS family that some operators have deployed as an intermediate step before deploying WCDMA.

HSDPA was introduced in WCDMA Release 5 to offer higher speed Downlink data services.

Release 6 introduces the Enhanced Uplink (i.e. HSUPA) that will provide faster data services for the Uplink.


High Speed Downlink Packet Access

What are the benefits of HSDPA

Higher Data Rates

Peak data rate up to 14Mbps per user

Higher Capacity

More subscribers and throughput

Further reduces the cost per megabyte

Richer Application

Low latency – improvement for

streaming ,interactive, background

applications

Data Services and High Speed Downlink Packet Access (HSDPA)

Data Services are expected to grow significantly within the next few years. Current 2.5G and 3G operators are already reporting that a significant proportion of usage is now due to data, implying an increasing demand for high-data-rate, content-rich multimedia services. Although current Release 99 WCDMA systems offer a maximum practical data rate of 384 kbps, the 3rd Generation Partnership Project (3GPP) have included in Release 5 of the specifications a new high-speed, low-delay feature referred to as High Speed Downlink Packet Access (HSDPA).

HSDPA provides significant enhancements to the Downlink compared to WCDMA Release 99 in terms of peak data rate, cell throughput, and round trip delay. This is achieved through the implementation of a fast channel control and allocation mechanism that employs such features as Adaptive Modulation and Coding and fast Hybrid Automatic Repeat Request (HARQ). Shorter Physical Layer frames are also employed.


How is Packet Data handled in Release 99 (FDD) ?

DCH ( Dedicated Channel )

Spreading codes assigned per user

Closed loop power control

Soft handover

FACH ( Common Channel )

Common Spreading code

No closed loop power control

No soft handover

Release 99 Packet Data

Node B

Node B

Release 99 Packet Data

There are different techniques defined in the Release 99 specification to enable Downlink packet data. Most commonly, data transmission is supported using either the Dedicated Channel (DCH) or the Forward Access Channel (FACH).

The DCH is the primary means of supporting packet data services. Each user is assigned a unique Orthogonal Variable Spreading Factor (OVSF) code dependent on the required data rate. Fast closed loop Power Control is employed to ensure that a target Signal to Interference Ratio (SIR) is maintained in order to control the block error rate (BLER). Macro Diversity is supported using soft handover.

Data transfer can also be supported on the FACH. This common channel employs a fixed OVSF code. As it needs to be received by all UEs, higher data rates are generally not supported. Macro Diversity is also not supported and the channel operates with a fixed (or slow changing) power allocation. Each data block contains a unique UE identifier that allows a given UE to keep itsown data and discard that belonging to other UEs.


Release 99 Downlink LimitationDedicated Channel Features ( DCH )

Maximum implemented downlink of 384kbps

OVSF code limitation for high data rate users

Rate change according to burst throughput is slow

Outer loop power control responds slowly to channel

Common Channel Features ( FACH )Good for burst data application

Only low data rates supported

Fixed transmit power

Release 99 Downlink Limitations

1. Although WCDMA Release 99 standard allows for maximum data rates of up to 2.0 Mbps, it has only been widely implemented with a maximum data rate of 384 kbps. This data rate is achieved by allocating a dedicated channel to each user. The use of dedicated resources can be a limitation, especially for data applications with burstycharacteristics. Each dedicated channel uses an OVSF code. Shorter codes are used for higher data rates and longer codes for lower data rates. When an OVSF of a particular length is used, all longer OVSF codes derived from that code become unavailable. This limits the number of simultaneous high speed data users in a given cell. The Release 99 standards provide support for a Secondary Scrambling Code, which eases this limitation, but it has not been widely implemented in commercial systems and will likely be removed from future versions of the specification. The data rate of a dedicated channel can be adjusted to accommodate varying requirements of a data service application, but the procedure for doing so is slow and thus inefficient. Capacity is controlled both by the maximum amount of PA power that is available and by the power requirement of each data service. In dedicated mode, fast power control is used so that a target Eb/No is achieved on the Downlink. However, the required Eb/No set point changes at a much slower rate. This can result in wasted resources whereby a better than required Eb/No is achieved for the required BLER.


High Speed Downlink Packet AccessThe differences between HSDPA and R99

Set of high data rate channel

Channels are shared by multiple users

Each user may be assigned all or part of the resource every 2ms

HSDPA user#1HSDPA user#2HSDPA user#3HSDPA user#4

Node B

a set of HS-PDSCHs

Code multiplexing for HSDPA

2ms

“Big shared pipe”

High Speed Downlink Packet Access (HSDPA)

In HSDPA, the NodeB allocates a set of high speed channels. These channels are assigned to a user using a fast scheduling algorithm that allocates the channels every 2 ms. All or part of the channels may be assigned to a given user during any 2 ms period.

The rapid scheduling of HSDPA is well-suited to the bursty nature of packet data. During periods of high activity, a given user may get a larger percentage of thechannel bandwidth, while it gets little or no bandwidth during periods of low activity.


High Speed Downlink Packet AccessHow will HSDPA figure out the limitations of R99

Adaptive modulation and coding

Fast feedback of Channel condition

QPSK and16QAM

Channel coding rate from 1/3 to 1

Multi-code operation

Multiple codes allocated per user

Fixed spreading factor

NodeB fast Scheduling

Physical Layer HARQ ( Hybrid Automatic Repeat reQuest )

HSDPA Basic Concepts

In HSDPA a common channel with fixed power is employed for data transfer. Users are separated in both the time and code domains. A fixed spreading factor is employed but multi codes operation is possible for increased data rates.

Adaptive Modulation and Coding (AMC) replaces the role of power control so that the modulation and coding rate are changed depending on the channel condition.

This is accomplished by locating the scheduling algorithm for channel allocation at the NodeB instead of the RNC in Release 99.


High Speed Downlink Packet Access

Comparison Summary

HighLowMediumData Rate

GoodGoodPoorSuitability for Bursty

Not SupportedNot SupportedSupportedSoft Handover

Fixed Power with link

adaptationNo

Closed Inner Loop at 1500Hz & Closed Outer

Loop

Power Control

SharedSharedDedicatedChannel TypeHSDPAFACHDCHMode

Comparison Summary

DCH and FACH are the two Release 99 channels typically used for packet switched data in practice. The advantages and disadvantages of each approach are apparent. Whereas DCH is suited for medium high data rates (with a maximum rate of 384 kbps), rate switching is slow, making it unsuitable and inefficient for bursty data such as a Web browsing application. By contrast, FACH provides good support for bursty data but is a common channel without power control or other mechanism to account for channel conditions. This makes it unsuitable for higher data rates. Switching from DCH to FACH is slow and inefficient, due in part to the typical timer values used to detect inactivity

HSDPA is suitable to high date rates for a bursty application, though we will see that the absence of soft handover makes it more suitable for stationary or low-mobility users than for highly mobile users. HSDPA typically operates at a fixed power, but feedback from the UE can instruct the NodeB to use lower power when the UE is in good channel conditions. Link adaptation is used to adjust data rate, coding, and modulation to quickly respond to changing channel conditions.


HSDPA Key Techniques

AMC (Adaptive Modulation & Coding)Data rate adapted to radio condition on 2ms

Fast Scheduling based on CQI and fairness

Scheduling of user on 2ms

HARQ（Hybrid ARQ）with Soft combing

Reduce round trip time

16QAM16QAM in complement to QPSK

for higher peak bit rates

SF16, 2ms and CDM/TDMDynamic shared in Time and code domain

3 New Physical Channels

Block 1 Block 2Block 1

Block 1?

Block 1Block 1?

+


Adaptive Modulation and CodingAMC ( Adaptive Modulation and Coding ) in accordance with CQI

( Channel Quality Indicator )

Adjust data rate to compensation channel condition

Good channel condition – higher data rate

Bad channel condition – lower data rate

Adjust channel coding rate to compensation channel condition

Good channel condition – channel coding rate is higher e.g. 3/4

Bad channel condition –channel coding rate is higher e.g. 1/3

Adjust the modulation scheme to compensation channel condition

Good channel condition – high order modulation scheme e.g. 16QAM

Bad channel condition – low order modulation scheme e.g. QPSK


Adaptive Modulation and CodingAMC ( Adaptive Modulation and Coding ) based on CQI ( Channel Quality Indicator )

CQI ( channel quality indicator )

UE measures the channel quality and reports to NodeB every 2ms or more cycle

NodeB selects modulation scheme ,data block size based on CQI

Bad channel condition→ More power Node B Node B

Power Control Rate Adaptation

Good channel condition

Bad channel condition

Good channel condition→ less power

→ low data rate

→ high data rate


CQI mapping table for UE category 10

Out of rangeOut of rangeN/AN/A00

001616--QAMQAM151525558255583030

001616--QAMQAM151524222242222929

001616--QAMQAM151523370233702828

……………………………………………………

001616--QAMQAM55466446641818

001616--QAMQAM55418941891717

001616--QAMQAM55356535651616

00QPSKQPSK55331933191515

00QPSKQPSK44258325831414

00QPSKQPSK44227922791313

……………………………………………………

00QPSKQPSK1117317322

00QPSKQPSK1113713711

Reference power Reference power

adjustment adjustment ΔΔModulationModulation

Number of Number of

HSHS--PDSCHPDSCHTransport Transport

Block SizeBlock SizeCQI valueCQI value

CQI Mapping Table

The CQI table consists of 30 entries, where each entry indicates a different TFRC. Transport Format Resource Combination (TFRC) points to the combination of number of HS-PDSCH channelization codes, modulation scheme, and the HS-DSCH transport block size. The 5-bit CQI reported by a UE is an index into this table containing all possible TFRC combinations for that UE category. The TFRC combinations are different for UEs with different HS-DSCH UE categories because of the differences in the UE capabilities. Along with TFRC, CQI may also indicate a power offset relative to the current HS-PDSCH power. The CQI table shown in the slide is for UE categories supporting up to 15 HS-PDSCH codes (HSDPA terminal category 10)


HSDPA UE Categories

28800363015Category 12

14400363025Category 11

17280027952115Category 10

17280020251115Category 9

13440014411110Category 8

11520014411110Category 7

67200729815Category 6

57600729815Category 5

38400729825Category 4

28800729825Category 3

28800729835Category 2

19200729835Category 1

Total Number of Soft Channel Bits

Maximum Number of Bits of an HS-DSCH Transport

Block Received Within an HS-DSCH TTI

Minimum Inter-TTI Interval

Maximum Number of HS-DSCH Codes

Received

UE Category

HSDPA RF performance depends on UE capability

UE Categories

HSDPA is advertised with data rates up to 14 Mbps. However, the actual HS-DSCH peak data rate depends on the UE’s HS-DSCH category. As shown in the table, only a category 10 UE can achieve the maximum HSDPA throughput of 14 Mbps when using all 15 HS-PDSCHs simultaneously.

Factors that decide the UE’s HS-DSCH category are:

HS-PDSCH codes – Determines the number of simultaneous HS-PDSCH channels that can be decoded by a UE.

Inter-TTI interval – Determines the minimum interval (in terms of HS-DSCH TTI) between two successive HS-PDSCH assignments. The more HARQ processes a UE supports, the shorter the inter-TTI interval. A minimum inter-TTI of 1 requires at least 6 simultaneous HARQ processes.

Transport Block size – Determines the maximum size of transport block that can be sent on HS-DSCH in a TTI. It is dependent on the number of HS-PDSCH codes and the modulation scheme.

IR buffer size – Determines the maximum number of soft bits that can be bufferedby a UE across all simultaneously running HARQ processes.


Hybrid Automatic Repeat reQuestConventional ARQ

In a conventional ARQ scheme, received data blocks that can not be correctly decoded are discarded and retransmitted data blocks are separately decoded

Hybrid ARQ ( HARQ )

In case of Hybrid ARQ with soft combining, received data blocks that can not be correctly decoded are not discarded. Instead the corresponding received signal is buffered and soft combined with later received retransmission of information bits. Decoding is then applied to the combined signal


Hybrid Automatic Repeat reQuestExample for HARQ

The use of HARQ with soft combining increases the effective received

Eb/Io for each retransmission and thus increases the probability for

correct decoding of retransmissions, compare to conventional ARQ

The maximum retransmission amount of HARQ procedure can be set. (NodeB LMT)


Hybrid Automatic Repeat reQuestThere are many different schemes for HARQ with soft combining

These schemes differ in the structure of retransmissions and in the way by which the soft combining is carried out at the receiver

In case of Chase combining ( CC ) each retransmission is an identical copy of the original transmission

In case of Incremental Redundancy ( IR ) each retransmission may add new redundancy

HARQ is a technique that transmitter sends new set of parity bits if the previous transmission failed (NACK) and receiver buffer the failed decodes for soft combining with later retransmission.

Example for Chase Combining ( CC ) Scheme

Example for Incremental Redundancy ( IR ) Scheme


Hybrid Automatic Repeat reQuestEach HSDPA assignment is handled by a HARQ process

HARQ processes run in NodeB and UE

The UE HARQ process is responsible for:

Attempting to decode the data

Deciding whether to send ACK or NACK

Soft combining of retransmitted data

The NodeB HARQ process is responsible for:

Selecting the corrected bits to send according to the selected

retransmission scheme and UE capability

Hybrid Automatic Repeat Request (HARQ)

To support consecutive assignments, HSDPA defines a Hybrid Automatic Repeat Request (HARQ) protocol. This protocol is implemented in both the NodeB and the UE, and consists of procedures implemented in both the MAC-hs sublayer and the Physical Layer. When the NodeB assigns an HSDPA subframe to a UE, it also assigns a HARQ process to handle the data transfer. The UE HARQ process is responsible for

Decoding the initial transmission

Sending an ACK or NACK

Soft-combining retransmissions of the data packet until it is successfully decoded or until NodeB aborts the packet

The maximum number of HARQ processes that a UE supports is a function of its HSDPA category. The minimum number of HARQ processes supported by any UE is 2, which corresponds to a UE that uses an inter-TTI interval of 3.


Short TTI (2ms) Shorter TTI ( Transmission Time Interval ) is to reduce RTT

( round trip time )

Shorter TTI is necessary to benefit from other functionalities

such as AMC, scheduling algorithm and HARQ


In HSDPA, a new DL transport channel is introduced call HS-

DSCH. The idea is that a part of the total downlink code resource

is dynamically shared between HSDPA and Release 99

Shared Channel Transmission

Shared channel transmission implies that a certain amount of radio resource of a cell (code and power) is seem as a common resource that is dynamically shared between users.


In HSDPA, a new DL transport channel is introduced call HS-

DSCH. The idea is that a part of the total downlink power resource

is dynamically shared between HSDPA and Release 99

Shared Channel Transmission

Time

Allowed power for HSDPA

Total Power

DPCH

Power for CCH

Higher power utility efficiency

TimePower margin for DCH power control

Shared channel transmission implies that a certain amount of radio resource of a cell (code and power) is seem as a common resource that is dynamically shared between users.

The NodeB transmit power allocation algorithm is not specified by the standard, but two possible schemes are likely:

� Static – A fixed amount of power is allocated to HSDPA channels (i.e. the HS-PDSCHsand HS-SCCHs). Remaining power is distributed among common channels and power controlled dedicated channels. The overall transmit power fluctuates as a function of the power controlled channels.

� Dynamic – HSDAP( i.e.HS-PDSCH and HS-SCCH ) power is allocated dynamically as a function of the remaining available power, which fluctuates due to the power controlled dedicated channels. The overall transmit power of the cell remains constant.

The above diagram does not consider the Node B’s power margin, whereby the Node B’s power fluctuates. The Node Bpower doesn’t really remain constant, due to the peak-to-average ratio of transmit power.


Shared Channel TransmissionThe codes are assigned to HSDPA user only when they are actually to be used for transmission, which leads to efficient code and power utilization

In HSDPA, the idea is that a part of the total downlink code resource is dynamically shared between a set of HSDPA users

There can be multiple (up to 15) HS-PDSCHs in a serving cell, which enables use of both time division and code division multiple access methods.


Higher-Order Modulation SchemeHSDPA modulation scheme

QPSK

16QAM

WCDMA R99 uses QPSK data modulation for downlink transmission. To support higher data rate, higher order data modulation, such as 16QAM can be used.

Compared to QPSK modulation, higher order modulation is more bandwidth efficient i.e. can carry more bits per Hertz


Fast Scheduling Fast scheduling is about to decided to which terminal the shared

channel transmission should be directed at any given moment

The basic idea of fast scheduling is to transmit at the fading peaks of the channel in order to increase the throughput and to use resource more efficiently. But this might lead to large variations in data rate of the users. The trade-off is between the cell throughput and fairness against users.

There are a number of scheduling algorithms that take into consideration the trade-off between throughput and fairness:

Round Robin (RR): radio resource are allocated to communication links on a sequential basis, not taking into account the instantaneous radio channel conditions experienced by each link.

Max C/I: for maximum cell throughput ,the radio resource should be as much as possible be allocated to communication links with the best instantaneous channel condition.

Proportional Fair (PF): allocates the channel to the user with relatively best channel quality.

Enhanced Proportional Fair (EPF): allocates the channel to the user according to relatively best channel quality, fairness, guarantee bit rate requirement.


HSDPA New Physical Channels


R99 Physical Channels

Release 99 Channels

This diagram shows possible mappings of logical, transport, and physical channels in the control and user planes for UMTS Release 99.

Some channels exist only in Physical Layer (CPICH, SCH, DPCCH, AICH, PICH). These channels carry no upper layer signaling or user data.

Transport channels carry the following types of information:

Broadcast Control Channel (BCH) – Broadcast information that defines overall system configuration.

Paging Channel (PCH) – Paging notification messages. A Paging Indicator Channel (PICH) is associated with a PCH to allow a UE to quickly determine whether it needs to read the PCH during its assigned paging occasion.

Forward Access Channel (FACH) – Common Downlink signaling messages. Also carries dedicated Downlink signaling and user information to a UE operating in Cell_FACH state.

Random Access Channel (RACH) – Common Uplink signaling messages. Also carries dedicated Uplink signaling and user information to a UE operating in Cell_FACH state.

Dedicated Channel (DCH) – Dedicated signaling and user information for a UE operating in the Cell_DCH state. DCH is mapped to a Dedicated Physical Data Channel (DPDCH). An associated Dedicated Physical Control Channel (DPCCH) carries Physical Layer control information, such as power control commands.


HSDPA Physical Layer ChannelsNew HSDPA Channels

High Speed Downlink shared Channel ( HS-DSCH )

Downlink Transport Channel

High Speed Shared Control Channel ( HS-SCCH )

Downlink Control Channel

High Speed Physical Downlink Shared Channel ( HS-PDSCH )

Downlink Physical Channel

High Speed Dedicated Physical Control Channel ( HS-DPCCH )

Uplink Control Channel

HSDPA introduces three new Downlink channels and one new Uplink channel:

High Speed Downlink Shared Channel (HS-DSCH) – A Downlink transport channel shared by several UEs. The HS-DSCH is associated with one or several Shared Control Channels (HS-SCCH). It operates on a 2 ms Transmission Time Interval (TTI).

High Speed Shared Control Channel (HS-SCCH) – A Downlink physical channel used to carry Downlink control information related to HS-DSCH transmission. The UE monitors this channel continuously to determine when to read its data from the HS-DSCH, and the modulation scheme used on the assigned physical channel.

High Speed Physical Downlink Shared Channel (HS-PDSCH) – A Downlink physical channel shared by several UEs. It supports Quadrature Phase Shift Keying (QPSK) and 16-Quadrature Amplitude Modulation (16-QAM) and multi-code transmission. It is allocated to a user at 2 ms intervals.

High Speed Dedicated Physical Control Channel (HS-DPCCH) – An Uplink physical channel that carries feedback from the UE to assist the Node B’s scheduling algorithm. The feedback includes a Channel Quality Indicator (CQI) and a positive or negative acknowledgement (ACK/NACK) of a previous HS-DSCH transmission.


HSDPA Physical Channels

HSDPA Channels (continued)

Only dedicated logical user data channels may be mapped to HS-DSCH. When DTCH is mapped to HS-DSCH, only Unacknowledged Mode (UM) and Acknowledged Mode (AM) channels may be used.

A UE operating in HSDPA mode also has at least one Release 99 dedicated channel (DCH/DPDCH) allocated, to ensure that RRC and NAS signaling can always be sent, even if the UE is not able to receive the high speed channels.

The HS-DPCCH is a Physical Layer control channel. It carries no upper layer information, and therefore has no logical or transport channel mapping.


Physical layer Frame DurationFrame Duration

10ms radio frame, 15 slots

2ms HSDPA sub-frame, 3 slots

1 HS-DSCH Transport Time interval (TTI)

Slot Duration

2560chips per slot

7680 chips per HSDPA sub-frame

Symbol Timing

QPSK: 2bits / symbol

16QAM: 4bits / symbol

R99 radio frame

10ms

HSDPA sub-frame

2ms

Time slot

0.67ms

Physical Layer Frame Timing

A basic WCDMA radio frame is 10 ms long and has 15 slots. HSDPA introduces the notion of sub-frames within a WCDMA radio frame. An HSDPA sub-frame is 2 ms (3 slots) long and all the HS-channels use this sub-frame timing. The sub-frame allows fast user switching where the shared channel can potentially be assigned to a different user every sub-frame. As the HSDPA sub-frame is only 2ms long, it alleviates the need for power control. HS-DSCH has a fixed TTI of 2 ms. Each HS-DSCH transport block is mapped to an HS-PDSCH sub-frame. HS-SCCH and HSDPCCH also use the 2ms sub-frame to transmit control and feedback respectively.

Each HSDPA sub-frame has 3 slots and each slot is comprised of symbols. The number of symbols in a slot depends on the spreading factor used for that channel. HS-PDSCH, HS-SCCH,and HS-DPCCH use SF 16, 128, and 256 respectively, giving number of symbols per slot as 160 (HS-PDSCH), 20 (HS-SCCH), and 10 (HS-DPCCH).

A symbol is made up of 1 or more bits and each bit is spread using SF to an equivalent number of chips. A QPSK symbol consists of two consecutive bits, one bit each mapped onto the I and Q branch. A 16-QAM symbol, on the other hand, has four consecutive bits with two bits on each branch.

HSDPA use 2ms TTI. Shorter TTI mechanism can reduce the latency ,and then increase fast schedule times. Shorter TTI mechanism can better trace the variation of wireless environment


HS-PDSCH sub-frame StructureHS-PDSCH sub-frame structure

3 time slots constituted one TTI (2ms) , only one TB will be sent during one TTI

Fixed spreading factor ( SF=16 )

May use QPSK or 16QAM modulation scheme

Up to 15 HS-PDSCH may be assigned simultaneously

UE capability indicated max. number of codes it supports

All HS-PDSCH used to carry user’s data

UE can be assigned multiple OVSF code ( SF=16 ) based on UE Categories

HS-PDSCH

When the UE decodes the HS-SCCH and determines that there is an HS-DSCH assignment in the next TTI, it decodes the assigned HS-PDSCHs. Each HS-PDSCH uses an OVSF of length 16. If multiple HS-PDSCHs are assigned simultaneously to one UE, they must use consecutive OVSF codes. The HS-SCCH indicates the first OVSF code and the number of codes for each assignment.

The High Speed Physical Downlink Shared Channel (HS- PDSCH) is used to carry the High Speed Downlink Shared Channel (HS-DSCH).

An HS-PDSCH may use QPSK, 16QAM or 64QAM modulation symbols. In above figure, M is the number of bits per modulation symbols i.e. M=2 for QPSK, M=4 for 16QAM and M=6 for 64QAM.

A UE is a member of one of 12 categories, as a function of its hardware capabilities. Each category represents different values of the following parameters:

Number of simultaneous HS-PDSCH codes (5, 10, or 15)

Maximum transport block size

Inter-TTI interval – minimum time between consecutive assignments.

Incremental redundancy buffer size – used to soft-combine symbols from retransmissions.


HS-SCCH sub-frame StructureHS-SCCH sub- frame structure

3 time slots constitutes one TTI ( 2ms )

HS-SCCH SF=128, QPSK only, Fixed rate of 60kbps

HS-SCCH carries the following control messages: Xue, Xccs, Xms, Xrv, Xtbs, Xhap and Xnd

UE demodulates HS-SCCH sub-frame and find out the received data addressed to the UE with Xue. Then UE demodulates HS-PDSCH sub-frame with Xccs, Xms, Xrv, Xhap, Xtbs and Xnd are used for HARQ Process

UE may need to simultaneous monitor up to four HS-SCCHs

Xue [16bits]:UE identity, Multiple UEs may be monitoring the same set of HS-SCCHs. Each UE has an assigned identity called the H-RNTI.

Xccs [7bits]:channelization code set, The HS-SCCH indicates which of the OVSF codes allocated to the HS-PDSCHs will be used. HS-PDSCH uses multi-code transmission, which means that multiple OVSF codes may be assigned to one UE at the same time

Xms [1bit]:modulation scheme, HS-PDSCH uses either QPSK or 16-QAM modulation. This can change from one assignment to the next, and HS-SCCH indicates which method will be used.

Xrv[3bits]:redundancy version, The HARQ protocol supports retransmissions and incremental redundancy. These parameters allow the UE to differentiate new transmissions from retransmissions.

Xtbs [6bits]:transport block size, The HS-SCCH indicates how much data will be sent during the next assignment

Xhap [3bits]:HARQ process number

Xnd [1bit]:new data indicator


HS-DPCCH sub-frame StructureHS-DPCCH sub-frame structure

TTI=2ms ( 3 time slots ), SF=256, Fixed rate of 15kbps, carry 2 types of HSDPA uplink physical layer control message, including ACK/NACK CQI

ACK and NACK notifies NodeB that UE has received correct downlink data or not. The field defines like this: 1-NACK, 0-ACK

CQI reflects physical channel quality indicator based on CPICH strength, and reported by period range from 0 to 160ms ( 0 means no transmission ). Usually the period is 2ms ( one TTI )

ACK/NACK and CQI having different function may be controlled independently by different parameters.

HS-DPCCH

Whenever the UE is operating in HSDPA mode, it uses the HS-DPCCH to give feedback to the serving Node B. This feedback consist of two parts:

ACK/NACK – The UE sends a positive or negative acknowledgement for each HS-DSCH assignment. UTRAN may configure the UE to repeat the ACK/NACK, up to a maximum of 4 transmissions. The first ACK/NACK for a given HS-DSCH assignment is sent 5 ms (7.5 slots) after the end of the HS-DSCH transmission.

Channel Quality Indicator (CQI) – The UE measures the channel quality of the Downlink CPICH and computes a CQI value. The value is an index into a table, and corresponds to the maximum data rate that the UE can decode with an error rate of less than 10%, assuming the channel conditions don’t change. UTRAN may configure the UE to repeat the CQI, up to a maximum of 4 transmissions. UTRAN may also configure the periodicity of CQI reporting, ranging from 2 ms to 160 ms.


Uplink HS-DPCCH preamble and postamble

Transmit Preamble and Postamble on HS-DPCCH around ACK / NACK

Eases the decoding, which allows HS-DPCCH to operate at lower power

The general rule of when N_acknack_transmit > 1

In R5, whether the data is received by UE is judged based on ACK/NACK. Pre/Postamble is introduced since R6. Position is the 1st slot in HS-DPCCH sub-frame, same as ACK/NACK.

Advantage of Pre/PostambleMore coding gain is introduced, since Node B could judge whether the data is received by UE on the basis of more correlative slots If ensuring the same demodulation performance of ACK/NACK, PO (ACK/NACK) could be reduced. Accordingly, UL interference to be reduced

Problem of Pre/PostambleMore decoding complexity is introduced More power is consumed by UE to send Pre/Postamble


Associated physical channel –A -DPCH

﹡Besides 3 physical channels on top. There is another physical channel named DPCH, which is a dedicated channel . DPCH is also called associated

channel used for signalling transmission and power control

﹡ DPCH does not carry service generally, sometimes carry real time (RT) service such as AMR service

UE

HSDPA Serving Cell

HS_DPCCHHS_PDSCH

HS_SCCH Downlink DPDCH&DPCCH (i.e.

associated DPCH)

Uplink DPDCH&DPCCH (i.e. associated DPCH)

When a DL RAB is mapped onto the HS-DSCH, UL DCH is set up regardless of the existence of UL data. UL DCH transmits the UL signaling, UL RLC acknowledgement message and possible UL service data. DL DCH is set up to transmit the DL signaling. These DCHs are called associated DCHs.

When the UE is in soft handover or softer handover, the HS-DSCH data can be transmitted only in the HSDPA serving cell while the DCH data can be transmitted in all the cells in the active set.

﹡ F-DPCH ( Fractional Dedicated Physical Channel ) is a new downlink physical channel in release 6. Release 6 supports mapping the SRB to the HS channels on both the Downlink and the Uplink (provided that HS channels are activated). This results in faster signaling and, for PS-only calls, the DCH (i.e. associated DCHs) is not reserved for signaling. To maintain closed loop power control functionality without the DCH (i.e. associated DCH), a new physical channel is introduced: the F-DPCH (Fractional DPCH).


Fractional Dedicated Physical Channel (F-DPCH)

The F-DPCH is a new physical channel in Release 6

Purpose of F-DPCH introduction is to keep the closed loop power control working for HSDPA users without an assigned DPCH (A-DPCH)

The difference of HSDPA physical channels between Release5 and Release6

The Downlink A-DPCH occupies one code per user in the cell

The F-DPCH is a shared physical channel. It has only TPC bits information

The F-DPCH is a new physical channel in release 6. Huawei RAN10 product support this physical channel

The F-DPCH is a special case of the Downlink DPCCH. It has only TPC bits information; no Pilot or data fields are carried. It multiplexes the TCP bits for a maximum of 10 UEswith different frame offsets. The TPC bits forwarded on the F-DPCH are needed to control the power of the HS-DPCCH (Uplink channel)


Fractional Dedicated Physical Channel (F-DPCH)

The F-DPCH carries control information generated at layer 1 (TPC commands). It is a special case of downlink DPCCH

Following figure shows the frame structure of the F-DPCH

Each frame of length 10ms is split into 15 slots, each of length Tslot = 2560 chips, corresponding to one power-control period, SF=256

Each user occupy one Symbol in one slot to bear TPC command, Pilot and TFCI is not needed

Up to 10 users can be multiplexed on one F-DPCH(Tx OFF) NOFF2 bits


Tslot = 2560 chips


TPC NTPC bits

(Tx OFF) NOFF1 bits

10 users can be multiplexed on one F-DPCH

Advantage of F-DPCH introduction

Code utilization efficiency is improved up to 90%, especially used for large number

of VoIP users

Problem of F-DPCH introduction

Code utilization efficiency could be downgraded in SHO due to the timing restrictions

on when TPC bits can be transmitted to UE’s in SHO zones

TPC

TPC

TPC

TPC

TPC

TPC

TPC

TPC

TPC

TPC

TPC

TPC

TPC

UE1

UE2

UE3

UE4

UE5

UE6

UE7

UE8

UE9

UE10

P-CCPCH frameoffset（256chip）

0

1

2

3

4

5

6

7

8

9


HSDPA Physical Channels TimingStart of HS-SCCH is aligned with the start of PCCPCH

HS-PDSCH, subframe is transmitted two slots after the associated HS-SCCH subframe

H S-SC C H

H S-PD SC H

3 slo ts = 2 m s

D PC H

τD PC H

R adio fram e w ith (SFN m odulo 2) = 0 P -C C PC H

2 slo ts

3 slo ts = 2 m s

S lo t S lot S lot S lo t S lo t S lot S lot S lo t Slot S lot S lot S lo t Slot S lot S lo t

15 slo ts = 10 m s

Subfram e #0 Subfram e #1 Subfram e #2 Subfram e #3 Subfram e #4

R adio fram e w ith (SFN m odulo 2)=1 10 m s

Subfram e #0 Subfram e #1 Subfram e #2 Subfram e #3 Subfram e #4

H S-D PC C H 3 slo ts = 2 m s

~7.5 slo ts

HSPDA Channel Timing

HSDPA channel timing is based on a time interval of 2 ms, or 3 slots

1. The UE measures the Downlink channel quality and sends a CQI report on the HS-DPCCH. An ACK or NACK from a previously received block may also be included in this transmission

2. If the NodeB decides to send data to the UE, it will send information on the HS-SCCH to assign the physical channel and give the UE information about how the data was encoded. The earliest that this assignment can be made is in the sub-frame following the end of CQI report.

3. During the next 2ms HS-DSCH transmission time, one or more HS-PDSCHs carry the UE’s data. The HS-SCCH transmission overlaps the HS-PDSCH transmission

4. After the UE decodes the data, it sends an ACK or NACK on the HS-DPCCH. The UE must send the ACK or NACK 5ms(i.e. 7.5 slots) after the end of the HS-DSCH transmission. If the UE sends a NACK, the NodeBmay send the data again during a later time slot, or may choose not to retransmit the data. A CQI report may also be included in this transmission


Theoretical HSDPA Maximum Data Rate

Theoretical HSDPA Maximum data rate is 14.4Mbps

How do we get to 14.4Mbps ?Multi-code transmission

NodeB must allocate all 15 OVSF codes ( SF =16 ) to one UE

Consecutive assignments using multiple HARQ processNodeB must allocate all time slots to one UE

UE must decode all transmission correctly on the first transmission

Low channel coding gainEffective code rate = 1

Requires very good channel conditions to decode

16QAMRequires very good channel condition

Theoretical HSDPA Maximum Data Rate

The theoretical maximum data rate is 14.4 Mbps. The following techniques are used to achieve this data rate:

Multi-code transmission – Up to 15 HS-PDSCH channels may be assigned to a single UE during one 2 ms TTI.

Consecutive assignments – The HARQ procedure allows the NodeB to send back-to-back assignments at 2 ms intervals.

Lower Coding Gain –Higher data rates can be achieved by puncturing more bits for a higher effective code rate (and thus lower coding gain).

16-QAM – This modulation scheme increases the data rate over QPSK by a factor of 2.


More Data Rate Factors More factors that affect HSDPA data rate

Inter- TTI interval

Retransmission

ACK / NACK Repetition

Assuming

5 OVSF code for HS-PDSCH

Consecutive assignment

QPSK

Turbo code rate =1/3

Retransmission

75% of data block decoded on first transmission

25% of data block decoded on second transmission

Other factors that influence the maximum data rate are:

Inter-TTI Interval – The interval between consecutive assignments is called the inter-TTI interval. If the UE supports an inter-TTI interval of 1, then it is capable of receiving a new HSDPA assignment every 2 ms. Allowed values of the inter-TTI interval are 1, 2, and 3

Retransmissions – If the UE NACKs a transmission, the NodeB may retransmit that data in a subsequent assignment. The retransmission may consist of identical symbols that were sent previously, or may be a different redundancy version of the turbo coded output symbols

ACK/NACK Repetition – The NodeB may configure the UE to send the ACK/NACK transmission up to four times


More Data Rate Factors 5 OVSF code for HS-PDSCH

14.4Mbps / 3 = 4.8Mbps

QPSK

4.8Mbps / 2 = 2.4Mbps

Turbo code rate =1/3

2.4Mbps / 3 = 0.8Mbps

Retransmission

0.8Mbps × 0.8 = 640 kbps

54321

Decoded on 1st transmit Decoded on 2nd transmit


HSDPA Physical Layer Model-Downlink

NodeB PHY UE PHY

HS-PDSCH – carries actual information payload from HS-DSCH

HS-SCCH – carries Physical Layer control information including HARQ

parameters, OVSF codes, and UE ID

HSDPA Physical Layer Model – Downlink

In 3GPP Release 5, two new Downlink physical channels have been introduced to enable HSDPA. In addition, the existing R99 channels are also required for HSDPA operation.

HS-PDSCH – Transmitted by NodeB to send HS-DSCH data to UEs in the HSDPA serving cell. Unlike a dedicated channel, this shared channel is assigned to a user for a 2ms period and may be assigned to another user in the next 2ms period. This fast scheduling rate is well suited for the bursty packet data and helps increase the capacity of a cell. There can be multiple (up to 15) HS-PDSCHs in a serving cell, which enables use of both time division and code

division multiple access methods. HS-PDSCH carries user data and has a transport channel HSDSCH mapped on it.

HS-SCCH – Transmitted by NodeB to signal control information to the users in the HSDPA serving cell. This channel is shared by multiple users and the control information sent on it is masked with a UE ID. The mask allows a UE to identify if there is HS-DSCH data for it in the upcoming HS-PDSCH sub-frame and the control information tells how to decode that data. HS-SCCH does not have a transport channel mapped on it.


HSDPA Physical Layer Model-Uplink

NodeB PHY UE PHY

HS-DPCCH – carries feedback signaling consisting of HARQ acknowledgement and channel quality indicator (CQI)

HSDPA Physical Layer Model – Uplink

In 3GPP Release 5, there is one new Uplink physical channel. The existing R99 channels are required for the HSDPA operation.

HS-DPCCH – Transmitted by the UE to signal feedback information to Node B. The feedback information consists of:

1. acknowledgement of data received by the UE on HS-PDSCH

2. Downlink channel quality indicator (CQI)

NodeB uses this feedback information to send retransmissions and to schedule HS-PDSCH transmissions to UEs. HS-DPCCH doesn’t carry any higher layer control or traffic and doesn’t have a transport channel mapped on it.


Downlink HS-PDSCHHigh Speed Physical Downlink Shared Channel (HS-

PDSCH)

Fixed SF 16 with 3 slots format

Uo to 15 HS-PDSCH under one cell

May use QPSK or 16QAM modulation scheme

DL HS-PDSCH – High Speed Physical Downlink Shared Channel

An HS-PDSCH channel carries the actual user payload to the UE. One HS-PDSCH subframe contains one TTI (2 ms) of HS-DSCH transport channel payload. There is no transport channel multiplexing in HSDPA so the information contained in HS-PDSCH subframe is from a single

HS-DSCH transport channel.

An HS-DSCH serving cell can have as many as 15 channelization codes assigned to HS-PDCH. The HS-PDSCH channels are shared among different users by using time division, code division or a combination of the two multiple access methods. The number of HS-PDSCHs that can be simultaneously decoded by a UE depends on the HS-DSCH UE Category.

The phase reference used for demodulating HS-PDSCH is the same as for the associated DL DPCH. By default, P-CPICH is used as the phase reference.


Downlink HS-PDSCHHS-DSCH Processing chain

New Physical Layer Procedures in

Release 5

Bit Scrambling

Physical Layer HARQ functionality

HS-DSCH interleaving

Constellation re-arrangement for 16QAM

The HS-DSCH channel coding involves a number of other functions performed by the NodeB’s Physical Layer. The main reason for this additional processing is the dynamic size of the transport block transmitted in an HS-DSCH TTI. Other reasons include large HS-DSCH payload size and the possible use of 16-QAM modulation for HS-PDSCH. Comparing the coding chain for the Release 99 channel with the Release 5 HS-DSCH channel, some blocks have been removed and some new blocks have been added.

HS-DSCH coding chain does not require:

1. Concatenation, because there is always only one transport block per HS-DSCH TTI. The transport block size, however, varies from 137 bits to 27952 bits. In case of retransmission, the transport block size remains the same as of the original transmission.

2. First DTX insertion, because HS-DSCH doesn’t support fixed position transport channel and thus Blind Transport Format Detection (BTFD).

3. Second DTX insertion, because there is just one transport channel mapped on to HS-PDSCH.

4. Radio frame segmentation, because HS-DSCH has a fixed TTI of 2 ms, which is equal to the HS-PDSCH sub-frame duration.

5. Transport channel multiplexing, because there is just one transport channel mapped on to HS-PDSCH.


HS-DSCH Channel CodingMac delivers one HS-DSCH TB per TTI to Physical Layer

CRC Attachment

24 bits CRC added per TB

Bit Scrambling

Facilitates uniform distribution of 16- QAM symbols at receiver

Code Block Segmentation

Turbo encoder has a fixed max. code block size of 5114 bits

If bit scrambled data is more than 5114 bits, need to segment into equal code blocks

HS-DSCH Channel Coding

NodeB’s MAC-hs delivers the HS-DSCH transport channel data to the Physical Layer in NodeB. The Physical Layer then performs a number of functions on the HS-DSCH TTI data before the data is finally mapped to one or more HS-PDSCH physical channels.

CRC Attachment – A fixed 24-bit Cyclic Redundancy Check (CRC) is attached to HS-DSCH TTI data. There is only one transport block per HS-DSCH TTI.

Bit Scrambling – Done to avoid non-uniform symbol distribution over 16-QAM constellation at the receiver. A uniform symbol distribution helps the UE efficiently decode the received HS-DSCH bits. Typically, the received symbols are uniformly distributed over the entire constellation. However, certain degenerate HS-DSCH bit sequences (e.g., the all-ones or all-zeroes sequences) could violate this condition, leading to an asymmetric HS-DSCH bit distribution (over {0,1}) and hence a non-uniform 16-QAM symbol distribution at the receiver input. This is true regardless of the use of turbo-encoding on the HS-DSCH, due to the possibility of transmitting turbo-codewords comprised predominantly of systematic bits. The estimated performance loss due to the non-uniform distribution in such very unlikely cases is between

Code Block Segmentation – It is done if the number of bits output from the bit scrambler is more than the maximum input code block size of the FEC encoder. The maximum encoder code block size in case of HS-DSCH is 5114 bits. If segmentation is performed, all the resulting segments are of equal size and may require adding some filler bits to the beginning of 1st code block. The filler bits are all 0s and are transmitted along with data.


HS-DSCH Channel CodingChannel Coding

Rate 1/3 Turbo coder used for Channel coding

Effective code rate changes after HARQ

HS-DSCH Channel Coding (continued)

FEC Coding – Rate 1/3 turbo coder is used for encoding HS-DSCH bits. FEC coding is done on one or more code blocks, where code blocks are formed by segmenting bit scrambled HS-DSCH data (if more than 5114 bits). The output from turbo coder consists of Systematic bits (original input data bits) and Parity bits. For each input bit, there is 1 Systematic bit and 2 Parity bits.

Twelve tail bits are added per block after encoding for the trellis termination. The encoded blocks, when more than one, are serially concatenated and fed to the HARQ block. The code rate after turbo encoding is 1/3 but the effective coder rate after HARQ rate matching may be different. An effective code rate of close to 1 is required to achieve peak throughput of 14.4 kbps.

Systematicbits

Parity 1bits

Parity2bits

RM_P1_1

RM_P2_1

RM_P1_2

RM_P2_2

RM_S

First Rate Matching Second Rate MatchingVirtual IR Buffer

Nsys

Np1

Np2

Nt,sys

Nt,p1

Nt,p2

bitseparation

NTTIbit

collection

NdataC W


HS-DSCH Channel CodingHybrid ARQ (HARQ)

Combines ARQ with adaptive channel

coding

NodeB sends new set of parity bits if

previous transmission failed (NACK)

UE buffers the failed decodes for soft

combining with future retransmission

Soft Combining is done before each

channel decoding attempt

HS-DSCH Channel Coding (continued)

Hybrid ARQ (HARQ) – HARQ is a technique combining FEC and ARQ methods that save information from previous failed decode attempts to be used in the future decoding. There are two different HARQ schemes, Chase Combine and IR, depending on which bits are chosen to be sent over the air to UE. The redundancy version (RV) parameters, r and s, indicate to the UE the HARQ scheme used for the current transmission.

Both HARQ combining schemes soft combine bits from the previous failed decodes with the currently received retransmission. Soft combining helps minimize the number of retransmissions. For a retransmission, HARQ uses the same transport block size and consequently the same number of HS-DSCH bits that were used in the initial transmission.


HS-DSCH Channel Coding – Physical Layer HARQ Functionality

Physical Layer HARQ consists of two rate matching stages and a

virtual buffer

1st stage: matches number of input bits to the virtual IR buffer size

IR buffer size is determined by UE’s soft memory capability

Puncturing is done if inputs bits exceed the virtual IR buffer size

2nd stage: matches numbers of bits to the number of HS-PDSCH bits

in the given TTI

Redundancy Version (RV) parameters control the output from 2nd stage

Repetition or puncturing is done to perform 2nd stage rate matching

First Transmission

Always self-decodable, RV parameters s = 1

Chase Combining

Each retransmission is self decodable, RV parameter s = 1, Systematic bits are prioritized

Same coded data packet may be sent in each retransmission, Using the same RV parameter r in each retransmission

Retransmission with a different r value implies different set of punctured bits

Receiver attempts to decode by soft combining multiple copies

Incremental Redundancy (IR)

Retransmissions are not self decodable, RV parameter s = 0, Parity bits are prioritized

Redundant information is incrementally transmitted if initial decoding fails

Each retransmission provides additional redundant bits to the receiver

RV parameter r is different for different set of redundancy bits

Receiver attempts to decode based on accumulated bits

Systematicbits

Parity 1bits

Parity2bits

RM_P1_1

RM_P2_1

RM_P1_2

RM_P2_2

RM_S

First Rate Matching Second Rate MatchingVirtual IR Buffer

Nsys

Np1

Np2

Nt,sys

Nt,p1

Nt,p2

bitseparation

NTTIbit

collection

NdataC W

HS-DSCH Channel Coding – HARQ Combining Schemes

HARQ combining refers to the combining of the HS-DSCH soft bits in the receiver (UE). If an HS-DSCH sub-frame transmission is not correctly decoded (CRC failure) by the UE’s Physical Layer the soft bits from this failed decode are buffered in the IR buffer to be combined with the future retransmissions. This type of combining changes the effective received code rate with each retransmission and helps in minimizing the number of retransmissions. There are different types of HARQ combining schemes:

� Chase combining requires each retransmission to be self-decodable. The transmitter may retransmit the same coded data packet in which case the decoder at the receiver combines multiple copies of the same transmitted packet weighted by the received SNR. Time diversity gain is thus obtained. Using a different redundancy version parameter r, a different set of puncture bits can be used in each retransmission.

� Incremental Redundancy (IR) is another implementation of the HARQ technique where retransmissions are not self decodable, i.e., they may have a very low proportion (or none) of the systematic bits. Additional redundant information, prioritizing the parity bits, is incrementally transmitted if the decoding fails on the prior attempt. Retransmitted sub-frames are soft combined with the buffered soft bits to achieve additional coding gain, which helps the UE to successfully decode the sub-frame.

The RV parameter signaled to the UE indicates the HARQ scheme used, allowing the UE to use the same scheme for HARQ combining.

RV parameters mapping list (3GPP TS25.212)


HS-DSCH Channel Coding –Segmentation and interleaving

Physical Channel SegmentationSegments data equally into P segments

P is number of HS-PDSCHs allocated to UEUp to 15

Total HS-PDSCH bits per TTI:

P * ( Number of bits per HS-PDSCH channel )

HS-DSCH interleavingBlock interleaving using 32*30 matrix

Write in rows, read out columns

Done separately on each HS-PDSCH


HS-DSCH Channel Coding-16QAM Constellation Re-arrangement

Bit Reliability

change with bit position within a symbol

is different for 0 and 1 in case of i2 and q2

HS-DSCH Channel Coding – 16-QAM Constellation Rearrangement

An optional 16-QAM modulation scheme has been introduced for HS-PDSCH to achieve high data rates. Constellation rearrangement is required in the case of 16-QAM modulation because two of the four bits in a 16-QAM symbol have a higher probability of error than the other two bits. The rearrangement occurs during retransmission and disperses the error probability equally among all the bits when averaged over retransmissions.

The reliabilities of the bits mapped to the 16-QAM symbols vary from the most significant bits (i1, q1) to the least significant bits (i2, q2). These variations reduce the performance of the turbo decoder with respect to having equal bit reliabilities. By rearranging the signal constellation during retransmissions, the same bit gets placed at different positions within a symbol across different retransmissions and the bit reliabilities are averaged out over the retransmissions. For both Chase combining and IR, the decoder performance increases with the constellation rearrangement due to a more homogeneous input of log-likelihood values to the turbo decoder.

The bits output from the HS-DSCH interleaver are taken in groups of four consecutive bits (i1q1i2q2) and then rearranged based on the value of constellation version parameter b. NodeB signals this parameter to the UE on HS-SCCH channel so that the UE can undo this bit rearrangement. In case of QPSK modulation, the constellation rearrangement block is transparent.

Constellation re-arrangement for 16QAM [TS25.212]

Swapping MSBs with LSBs and inversion of logical values of LSBs3

Inversion of the logical values of LSBs2

Swapping MSBs with LSBs1

None 0

OperationOutput bit sequence constellation

version parameter b

3,2,1,, +++ kpkpkpkp vvvv

1,,3,2, +++ kpkpkpkp vvvv

3,2,1,, +++ kpkpkpkp vvvv

1,,3,2, +++ kpkpkpkp vvvv


HS-DSCH Physical Channel Mapping

Bits are mapped to one or more HS-PDSCH

Same number of bits/sub-frame on each HS-PDSCH

HS-DSCH Physical Channel Mapping

After constellation rearrangement (only for 16-QAM) or HS-DSCH interleaving (for QPSK), the HS-DSCH bits are finally mapped to one or more HS-PDSCH channels. This is called Physical Channel Mapping. A UE may be assigned one or more HS-PDSCH codes depending on the UE capability, QoS requirement, and the NodeB’s radio resource availability. In case of more than one HS-PDSCH channel assigned to a UE, the number of bits in the given sub-frame on each

assigned HS-PDSCH channel is the same.


Physical Layer Process Case for HS-DSCH


Downlink HS-SCCHHigh Speed Shared Control Channel (HS-SCCH)

Fixed rate 60kbps (SF 128) channel with one slot format

UE may need to simultaneously monitor up to four HS-SCCHs

More than four HS-SCCHs possible under one cell

QPSK only

DL HS-SCCH – High Speed Shared Control Channel

The NodeB transmits control information required for detecting and decoding HS-PDSCH sub-frames to UEs on HS-SCCH channel. UEs are signaled to monitor a set of HS-SCCH channels containing up to a maximum of four HS-SCCHs. At any time, only one of the four HS-SCCHs contains information for a given UE. There may be more than four active HS-SCCHs under a cell. Multiple users are assigned to the same HS-SCCH (or set of HS-SCCHs) and thus a

UE can successfully decode the information on this channel only when the information is intended for that UE. The HS-SCCH information is scrambled with the UE ID, which enables the desired UE to successfully decode HS-SCCH. The reason for having multiple HS-SCCHs is to enable NodeB to address multiple UEs in the same sub-frame.


Downlink HS-SCCHHS-SCCH Processing chain

HS-SCCH Channel Coding

Convolutional coding and CRC coding are used as the main channel coding schemes by NodeBforthe HS-SCCH channel. Part 1 and Part 2 of an HS-SCCH sub-frame are individually coded and mapped to the allocated slots in a sub-frame. Both Part 1 and Part 2 are scrambled with the UE ID. The UE ID used for scrambling HS-SCCH is a 16-bit HS-DSCH Radio Network Temporary Identity (H-RNTI).

Part 1 consists of the following information:

Channelization Code Set – Contains the number of in-sequence HS-PDSCH codes assigned to a UE and the offset of the first code.

Modulation Scheme – HS-PDSCH modulation scheme where 0 = QPSK and 1 = 16-QAM.

Part 2 consists of the following information:

Transport Block Size – The transport block size used for the corresponding HS-PDSCH sub-frame is signaled as a 6-bit Transport Format Resource Indicator (TFRI). The actual transport block size in bits is derived from TFRI and depends on the modulation scheme and the number of HS-PDSCH channelization codes signaled on HS-SCCH.

HARQ Process ID – Contains the HARQ process ID for the corresponding HS-PDSCH sub-frame. There may be one to eight simultaneous HARQ processes running in a UE.

Redundancy & Constellation Version – Contains RV parameters r and s that are used by the Physical Layer HARQ functionality. If 16-QAM modulation is used, this field also contains the constellation version parameter b that indicates the rearranged version of 16-QAM constellation used for the corresponding HS-PDSCH sub-frame transmission.

New Data Indicator – Contains 1-bit indicator that toggles every time the NodeB sends new HS-DSCH data. The indicator is not toggled in case of retransmissions.


HS-PDSCH and HS-SCCH Spreading and Modulation

HS-PDSCH is spread with SF 16, scrambled with Primary Scramble Code

HS-SCCH is spread with SF 128, scrambled with same code as HS-PDSCH

The Downlink physical channels (except SCH) are spread to the chip rate with individual channelization codes and then scrambled with the same scrambling code. All such channels use QPSK modulation except HS-PDSCH, which can use either QPSK or 16-QAM.

The Downlink physical channels HS-SCCH and HS-PDSCH consist of a sequence of binary symbols. In the case of QPSK modulation, each pair of two consecutive symbols is first serial-to-parallel converted and then mapped to the I and Q branches. The QPSK modulation mapper maps the even and odd numbered symbols to the I and Q branch respectively. In the case of 16-QAM modulation, a set of four consecutive binary symbols nk, nk+1, nk+2, nk+3 (with k mod 4 = 0) is serial-to-parallel converted to two consecutive binary symbols (i1= nk, i2= nk+2) on the I branch and two consecutive binary symbols (q1= nk+1, q2= nk+3) on the Q branch and then mapped to 16-QAM constellation by the modulation mapper. The modulation mapper converts the binary symbols into the real-valued symbols.


Uplink HS-DPCCHHigh Speed Dedicated Physical Control Channel (HS-DPCCH)

3 slots format, SF 256, OVSF code – Cch,256,64

Fixed power offset ( ΔACK, ΔNACK, ΔCQI ) relative to Uplink associated DPCCH

CQI measurement reference period is 3 slots, ending 1 slots before CQI is sent

UL HS-DPCCH – High Speed Dedicated Physical Control Channel

Each UE operating in the HSDPA mode has an active Uplink HS-DPCCH along with the dedicated UL DPCCH. The UE uses UL DPCCH as reference for adjusting the HS-DPCCH channel power. UE transmits HS-DPCCH at a fixed power offset relative to UL DPCCH but the offset is different for ACK, NACK, and CQI fields. These power offsets are signaled to UE by UTRAN and are used by UE’s Physical Layer to calculate the HS-DPCCH gain factor (βhs). As the HS-DPCCH power is adjusted relative to UL DPCCH, the Uplink power control is indirectly

adjusting the HS-DPCCH power.

Each subframe (2 ms) of HS-DPCCH has one slot for HARQ ACK/NACK and two slots for Channel Quality Indicator (CQI) field. UTRAN may configure the UE to repeat each ACK/NACK and/or CQI report up to three more times in the consecutive subframes. If there is nothing to acknowledge, i.e., no data received on HS-PDSCH or CRC error on HS-SCCH, then DTX bits are sent in the ACK/NACK field.

UTRAN configures CQI reporting by signaling CQI feedback cycle parameter to UE. Based on the feedback cycle parameter, UE may be asked to not send CQI at all or send CQI at periodic intervals ranging from 2 ms to 160 ms. For example, if the CQI feedback cycle is 4 ms, the UE reports CQI in every other subframe. Those subframes not scheduled to report CQI have DTX bits in place of CQI.

CQI value reflect wireless environment quality of previous sub-frame (i.e reference period in above figure)


HS-DPCCH Channel Coding1 bit ACK/NACK is coded as 10 bits

5 bits CQI is coded as 20 bits

Sub-frame repetition of ACK/NACK and CQI add more reliability

HS-DPCCH Channel Coding

Channel coding is done by UE’s Physical Layer to add redundant bits to the HS-DPCCH information. In general, there are different methods of doing channel coding such as repetition, convolutional coding, turbo coding, Reed-Muller (RM) coding, etc., but the basic strategy is to add some redundant bits to the original bit(s). This redundancy helps the receiver correctly decode the original bits which may have been impaired due to bad RF channel conditions. The

1-bit ACK/NACK information is coded into 10 bits by repeating the original bit. The 5-bit CQI information is coded into 20 bits by using RM coding.


HS-DPCCH Spreading and Modulation

Unique OVSF code Cch,256,64

Gain factor βhs is derived from power offsets (ΔACK , ΔNACK , ΔCQI)

Multiplexed on Q branch

Same scrambling code as on UL DPCH

QPSK modulation

HS-DPCCH Spreading and Modulation

The HS-DPCCH channel is I/Q code multiplexed with UL DPCH. Depending on whether the number of active UL DPDCHs is even or odd, HS-DPCCH is mapped on to I or Q branch, respectively. The SF used for HS-DPCCH is 256 with OVSF code number Cch, 256, 64 when there is only one active UL DPDCH. The power offsets ΔACK , ΔNACK , and ΔCQI are signaled to UE by UTRAN through higher layer signaling.


UMTS Protocol Stack

UMTS Protocol Stack

The UMTS signaling protocol stack is divided into Access Stratum (AS) and Non-Access Stratum (NAS). The Non-Access Stratum architecture evolved from the GSM/GPRS upper layers and is divided into Circuit Switched (CS) and Packet Switched (PS) protocols.

The Access Stratum consists of three layers:

1. Layer 3 – The Radio Resource Control (RRC) layer handles establishment, release, and configuration of radio resources.

2. Layer 2 – Consists of two sub-layers. The Radio Link Control (RLC) sub-layer provides segmentation, re-assembly and other traditional Layer 2 functions. The Medium Access Control (MAC) sub-layer multiplexes data and signaling onto the appropriate channels and controls access to the Physical Layer.

3. Layer 1 – The Physical Layer transfers data over the radio link.

UTRAN protocol structure to be found in 25.301

L3

cont

rol

cont

rol

cont

rol

cont

rol

LogicalChannels

TransportChannels

C-plane signalling U-plane information

PHY

L2/MAC

L1

RLC

DCNtGC

L2/RLC

MAC

RLCRLC

RLCRLC

RLCRLC

RLC


UuS boundary

BMC L2/BMC

control

PDCPPDCP L2/PDCP

DCNtGC

RadioBearers

RRC


HSDPA Protocol Stack

1. HSDPA Protocol Stack

1. In a Release 99 PS network, the NAS layer protocols are terminated at the SGSN. RRC, RLC,and MAC protocols are terminated at the RNC. The Physical Layer protocol is terminated at the Node B.

2. The Release 5 specifications define a new sublayer of MAC called MAC-hs, which implements the MAC protocols and procedures for HSDPA. This sublayer operates at the NodeBand the UE.

3. UTRAN MAC-hs is responsible for fast scheduling of the HS-PDSCHs. The scheduler determines:

1. To which UEs the channels are assigned.

2. How much data to send.

3. Which modulation scheme to use.

4. Whether to send new data or retransmitted data.

5. Which redundancy version to send.

4. UE MAC-hs is responsible for:

1. Sending ACK or NACK after decoding a block.

2. Re-ordering data blocks before submitting to upper layers, if retransmissions caused data to be received out of order.


UTRAN Mac Architecture

1. UTRAN MAC Architecture

1. The UTRAN MAC protocol consists of three entities:

2. MAC-hs – Responsible for the high speed HSDPA channels and the only entity of MAC that resides in the Node B. When a UE operates in HSDPA mode, MAC-hs maps user data and signaling from DCCH and DTCH onto the sharedHS-DSCH transport channels.

3. MAC-c/sh – Responsible for common and shared logical (PCCH, BCCH, CCCH, and CTCH) and transport (PCH, BCH, RACH, FACH) channels. MAC-c/shresides in the RNC, and there is one MAC-c/sh entity per RNC. When a UE operates in Cell_FACH state, MAC-c/sh maps user data and signaling from its DCCH and DTCH onto the common FACH and RACH transport channels.

4. MAC-d – Responsible for mapping data from dedicated logical channels (DCCH and DTCH) onto dedicated transport channels (DCH). MAC-d resides in the RNC, and there is one MAC-d entity for each UE to which dedicated logical channels have been assigned.


UTRAN MAC-hs Architecture

1. UTRAN MAC-hs Architecture

2. Data enters the UTRAN MAC-hs from a set of MAC-d flows. The data is routed to a set of priority queues with the following properties:

1. Up to 8 priority queues and 8 MAC-d flows are allowed per UE.

2. The queue distribution entity maps each MAC-d flow onto one or more priority queues.The mapping is configured when the HSDPA operation begins.

3. Each priority queue is mapped to only one MAC-d flow.

3. When data is removed from a priority queue for transmission, it is assigned to a HARQ process.

4. There are a minimum of 6 and a maximum of 8 HARQ processes per UE. The HARQ process tracks the ACK/NACK signaling for the data block and determines when retransmission is necessary.

5. In response to CQI and ACK/NACK signaling on HS-DPCCH, the scheduler decides:

1. To which UEs the HSDPA channels will be assigned.

2. For each scheduled UE, whether to send new data from a priority queue or a retransmission from a HARQ process.

6. Signaling on HS-SCCH indicates the scheduling decision to the UEs operating in HSDPA mode.


Mac-hs functionsFlow Control

The flow control entity controls the HSDPA data flow between

RNC and NodeB

Purpose: to reduce the transmission time of HSDPA data on

the UTRAN side and to reduce the data discarded and

retransmitted when the Iub interface or Uu interface is

congested

The transmission capabilities of the Uu interface and Iub

interface are taken into account in a dynamic manner in the

flow control


Mac-hs functionsScheduling

The scheduling entity handles the priority of the queues and

schedules the priority queues or NACK HARQ processes of the

HS-DSCH UEs in a cell to be transmitted on the HS-DSCH

related physical channels in each TTI

Purpose: to achieve considerable cell throughput capability and

to satisfy user experience


Mac-hs functionsHARQ

The HARQ entity handles the HARQ protocol for each HS-

DSCH UE

Each HS-DSCH UE has one HARQ entity on the MAC-hs of

the UTRAN side to handle the HARQ functionality

One HARQ entity can support multiple instances (i.e.HARQ

processes) of stop and wait HARQ protocols

Based on the status reports from HS-DPCCH, a new

transmission or retransmission is determined

The round trip time at the physical layer is 12 ms. Therefore, it is necessary for one UE to have multiple parallel instances (HARQ processes) of the stop and wait HARQ protocol to increase the Uu interface throughput

One problem in the receiver caused by multiple HARQ processes is that, in a specific time window, the TBs may arrive out of sequence. Therefore, it is necessary to have reordering functionality on the receiver side


Mac-hs functionsTFRC selection

The TFRC selection entity selects an appropriate transport

format and resource for the data to be transmitted on HS-

DSCH

The transport format includes the transport block size and

modulation scheme. The resource includes the power resource

and code resource of HS-PDSCH

Transport Format and Resource Combination (TFRC) for each

UE is channel quality based, where AMC is the key technique


UE MAC-hs Architecture

1. UE MAC-hs Architecture

1. When the UE Physical Layer decodes a data block addressed to it, the associated HARQ process determines whether to ACK or NACK the block. If an ACK is sent, the data block is passed to the assigned re-ordering queue.

2. Re-ordering of MAC-hs PDUs is necessary because up to 8 HARQ processes can be operating on sequentially transmitted data. MAC-hs PDUs can be received out of order when a HARQ process sends a NACK.

3. The re-ordering queue passes the block up to the disassembly entity when it receives consecutive data blocks. The disassembly entity takes apart the MAC-hs PDU into its constituent MAC-d PDUs and passes them up to the appropriate MAC-d flow for processing by the MAC-d layer.


Data Flow ExampleData Flow

Transmitter (NodeB)

RNC RLC PDU to NodeB priority queue

NodeB Mac-hs PDU assembly

NodeB HARQ Process

Receiver (UE)

UE HARQ process

UE re-ordering queue

UE Mac-hs PDU disassembly


Data Flow Example RNC Mac-d PDU to NodeB Priority Queue

Data Flow Example – RNC MAC-d PDU to NodeBPriority Queue

In this example, two logical channels, DTCH 1 and DTCH 2, are mapped to one MAC-d flow.

The MAC-d entity in the RNC constructs MAC-d PDUs by prepending a header to each RLC PDU. The MAC-d header contains a C/T field that identifies the DTCH from which the data came. The priority DTCH 1 is higher than DTCH 2, so MAC-d selects all the PDUs from DTCH1, and then all the PDUs from DTCH 2.

The MAC-d flow is mapped to a MAC-hs priority queue. The RNC transfers the data across the Iub interface to the Node B, where the MAC-hs entity stores the MAC-d PDUs in the priority queue, preserving the order of the PDUs as sent across the Iubinterface.


Data Flow Example NodeB Mac-hs PDU Assembly

Mac-hs PDU structure

Data Flow Example – NodeBMAC-hs PDU Assembly

When the scheduler in the NodeB MAC-hs decides to send data from a given priority queue, it constructs a MAC-hs PDU. The scheduler determines the size of the MAC-hsPDU as a function of the UE’s CQI report, number of HS-PDSCHs, available transmit power, and other proprietary parameters.

MAC-d PDUs are packed into the MAC-hs PDU sequentially. The MAC-hs PDU is then sent to the Physical Layer as the HS-DSCH transport block. The MAC-hs PDU header consists of the

following fields:

Version Flag (VF) – Always set to 0 for this release.

Queue Identifier (QID) – Identifies the priority queue in the NodeB from which the data came, and the re-ordering queue in the UE to which the data is being sent.

Transmission Sequence Number (TSN) – Used by the re-ordering protocol to ensure inorder delivery of MAC-d PDUs when retransmissions occur.

Size Index Identifier (SID) – When HSDPA operations begin, the RNC sends a signaling message to the UE that maps valid MAC-d PDU sizes to a set of up to 7 SIDs.

Number (N) – Indicates the number of consecutive MAC-d PDUs of the size given by the previous SID. The maximum number of MAC-d PDUs in a MAC-hs PDU is 70.

Flag (F) – One-bit flag field to indicate the end of the MAC-hs header.

Padding – MAC-hs adds padding as needed to fill the MAC-hs PDU size (transport block size) chosen by the scheduler.


Data Flow Example NodeB HARQ Process

Data Flow Example – NodeB HARQ Process

The scheduler chooses a HARQ process from which to send the PDU. The NodeB supports up to 8 HARQ processes for each UE.

The NodeB transmits the HARQ process ID in the second part of the HS-SCCH. A one-bit indicator, the New Data Indicator (NDI), in the second part of HS-SCCH is toggled whenever a new PDU is transmitted.

The Physical Layer uses the UE’s H-RNTI to scramble the HS-SCCH. When the UE monitors the HS-SCCH, it looks for subframes scrambled with its H-RNTI, ignoring those that don’t match and processing those that do.

The NodeB sends the MAC-hs PDU to the Physical Layer on the HS-DSCH transport channel. The Physical Layer processes the data and maps it onto one or more HS-PDSCHs.

The HARQ protocol supports the following features:

� Soft combining – If the UE NACKs a data block, the NodeB may retransmit the data. The Physical Layer performs soft combining of the retransmitted symbols with those previously received.

� Stop and Wait (SAW) – Each HARQ process, up to a maximum of 8, operates independently on one data block until that block is correctly decoded or transmission is aborted by the NodeB.

� Synchronous ACK/NACK – The UE transmits an ACK or NACK for a given block at a fixed time following reception of the data.

� Asynchronous retransmission – The NodeB sends a retransmission any time after an NACK is received. The earliest this can occur is 10 ms after the previous transmission. A more typical value is expected to be 12 ms, due to internal delays in the Node B scheduling algorithm. A retransmission could occur later than 12 ms depending on channel quality reported by the UE and other internal scheduling decisions.

HARQ Protocol signaling on HS-SCCH

HARQ Protocol HS-SCCH Information

The Node B sends control Information for the HARQ protocol on the HS-SCCH. The first slot of the HS-SCCH is scrambled with the UE’s H-RNTI, which identifies the UE to which this HSDPA assignment belongs. A 16-bit CRC masked with the UE’s H-RNTI is computed over both parts.

The information on HS-SCCH includes:

� Channelization Code Set – Which HS-PDSCH codes to use, and how many channels.

� Modulation Scheme – QPSK or 16-QAM

� HARQ Process ID – Which HARQ process should decode the next HSDPA assignment.

� Transport Format Resource Indicator (TFRI) – A 6-bit value that maps to the Transport Block size of the data.

� Redundancy and Constellation Version – The redundancy version indicates to the Turbo decoder which combination of systematic and parity bits will be sent. For 16-QAM, the constellation version indicates how the symbols were mapped to the constellation.

� New Data Indicator (NDI) – A 1-bit value that is toggled whenever new data is sent to a given HARQ process, to allow it to distinguish a retransmission from a new transmission.


Data Flow Example UE HARQ Process

Data Flow Example – UE HARQ Process

Each UE HARQ process performs operations within the Physical Layer and within the MAC-hs layer.

Physical Layer HARQ Process Operations

When the UE decodes its H-RNTI on the HS-SCCH, it prepares to decode the next HS-DSCH TTI. The HS-SCCH includes a HARQ process ID. In the Physical Layer, the HARQ process decodes the associated HS-PDSCHs. If the data is decoded correctly, the data is routed to the MAC-hs part of the HARQ process.

MAC-hs Layer HARQ Process Operations

The MAC-hs HARQ process generates either an ACK or a NACK to be sent in the subframe numbered 5 in the diagram above. If the UE sends an ACK and the NodeB decodes the ACK correctly, the earliest that HARQ process 1 can be used for a new data block is the subframe numbered 8 above. If other data blocks are sent to the UE during the intervening subframes, they must be assigned to other HARQ processes.

UE HARQ Process flowchart

UE HARQ Process Flowchart

The control flow for a HARQ process in the UE is as follows:

1. When a data block is received, compare the New Data Indicator (NDI) bit with the value

received in the previous block.

If NDI is different, flush data in the buffer and store new data

If NDI is the same and the buffer is empty, this data has already been decoded correctly, so discard it and send an ACK. This can happen if the Node B interprets an ACK as a NACK, and retransmits the data block.

If NDI is the same and the buffer is not empty, soft combine the new data with data already in the buffer.

2. Attempt to decode the data in the buffer.

If correctly decoded, deliver the data to the re-ordering queue, flush the buffer, and send an ACK.

If incorrectly decoded, keep the data in the buffer and send a NACK.

HARQ Protocol Errors

Errors can occur in the HARQ protocol if the Node B misinterprets the UE’sACK/NACK.

If the Node B receives nothing in the HS-DPCCH slot in which it expects an ACK or NACK, it treats it as a NACK

If the Node B interprets an ACK as a NACK, a packet may be retransmitted when it was not necessary to do

The UE HARQ process detects this condition by the fact that the New Data Indicator bit is the same value as the previous transmission, so it discards the data and sends another ACK

Another type of protocol error occurs if the Node B misinterprets a NACK as an ACK. In this case, the Node B assumes the UE correctly decoded the data, so it sends a new data block to the same HARQ process

The HARQ process in UE side must discard the previous transmission and attempt to decode the new block, sending the ACK or NACK accordingly.

This is a worse error than mistaking an ACK, because data is lost and must be recovered by higher layer protocols (i.e., RLC)


Data Flow ExampleUE re-ordering Queue

Data Flow Example – UE Re-ordering Queue

When the UE’s HARQ process ACKs the data block, it routes the MAC-hs PDU to a re-ordering queue, according to the QID given in the MAC-hs header. The re-ordering queue uses the TSN in the MAC-hs header to put the PDUs in the correct order. The re-ordering queue routes consecutively received PDUs to the disassembly entity.

If a HARQ process sends a NACK, this can create a hole in the re-ordering queue. The re-ordering queue buffers subsequent PDUs until either the missing PDU is successfully received, or the reordering protocol stops waiting for that PDU. Two mechanisms, timer-based and window-based, are used for stall avoidance. These are examined in detail in later slides.

This example illustrates a simple case in which consecutive assignments originate from the same NodeB priority queue and thus are all routed to the same re-ordering queue. In a more complicated example, data from multiple priority queues can be interleaved according to the NodeB MAC-hs scheduling decisions.


Data Flow ExampleUE Mac-hs PDU Disassembly

Data Flow Example – UE MAC-hs PDU Disassembly

The UE MAC-hs entity disassembles the MAC-hs PDU, using the information in the MAC-hs header to separate the PDUs. It passes the MAC-d PDUs to the MAC-d entity, which then delivers the PDUs to the DTCH logical channels, using the C/T field to differentiate channels.


Re-ordering ProtocolFeatures of the MAC-hs Re-ordering Protocol

Each reordering queue operates independently

Control information in MAC-hs headerQueue ID (QID), 3 bits

Transmission Sequence Number (TSN), 6 bits

In-sequence delivery of MAC-d PDUs to RLCHARQ protocol may deliver data out of sequence

RLC requires in-sequence delivery

Re-ordering Protocol – MAC-hs Header

The MAC-hs PDU header consists of the following fields:

� Version Flag (VF) – Always set to 0 for this release.

� Queue Identifier (QID) – Identifies the priority queue in the Node B from which the data came, and the re-ordering queue in the UE to which the data is being sent.

� Transmission Sequence Number (TSN) – Used by the re-ordering protocol to ensure in-order delivery of MAC-d PDUs when retransmissions occur.

� Size Index Identifier (SID) – When HSDPA operations begin, the RNC sends a signaling message to the UE that maps valid MAC-d PDU sizes to a set of up to 7 SIDs.

� Number (N) – Indicates the number of consecutive MAC-d PDUs of the size given by the previous SID. The maximum number of MAC-d PDUs in a MAC-hs PDU is 70.

� Flag (F) – One-bit flag field to indicate the end of the MAC-hs header.

� Padding – Padding as needed to fill the scheduled MAC-hs size.


Re-ordering ProtocolIn-sequence Delivery of Mac-hs PDUs

Re-ordering Protocol – In-sequence Delivery of MAC-hs PDUs

When a HARQ process sends a NACK, a hole is created in the re-ordering queue for which that PDU was intended. As subsequent PDUs are received, the re-ordering queue buffers those PDUs to prevent them from being delivered out of order to the RLC layer above MAC-hs.

When the missing PDU is received correctly, the re-ordering queue inserts it into the correct position in the buffer and delivers it and all subsequent consecutive PDUs that are awaiting delivery.

wcdma ran planning and optimization (book1 wrnpo basics)

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