wb1 1 data fundamentals ran

GPRS/EDGE FUNDAMENTALS

Prepared by Naveen Bhartiya 1

BSC

GGSN

IP/MPLS/IPoATM -

Applicatio

n Servers

(co -

located

2G

SGSN BTS

HLR/ AC/ EIR

TCSM

TC

MSC/VLR

Abis Gb BSC BSC

GGSN GGSN

- backbone

Application Servers

2G

SGSN

2G

SGSN BTS

HLR/ AC/ EIR

HLR/ AC/ EIR

TCSM

TC

MSC/VLR

Gn Gi

Gs

RF interface

• Coverage

•C/I

• Capacity

• Traffic volume

• Mobility

MS/Client parameters

• GPRS/EDGE capability and release

•Multislot support

Abis interface

• EDAP size / dimensioning

• # of E1/T1s

• GPRS/EDGE traffic

Gb interface

• Bearer size

• IP v.s. FR

• Dimensioning

BTS

• GPRS territory

• BTS HW considerations (TRX & BB-card)

• BTS SW (EPCR)

BSS

• PCU variant & dimensioning

• PCU strategy in mixed configuration

• BSS SW and features

SGSN

• Unit capacity (PAPU etc.)

• BSS Gb Flow control

RF

Server

• load

• settings (Linux/Win)

HLR

• QoS profile

• GPRS settings

(E)GPRS Optimization – Network Element and Configuration Assessment

2 Prepared by Naveen Bhartiya

General Packet Radio Service (GPRS) & Enhanced data rate for GPRS evolution(EDGE)

• GPRS uses a packet-mode technique to transfer high-speed and low-speed data and signaling in an efficient manner.

• GPRS optimizes the use of network and radio resources

• GPRS is designed to support from intermittent and bursty data transfers through to occasional transmission of large volumes of data.

• GPRS uses GMSK Modulation Scheme.


• Enhanced Data rates for GSM Evolution (EDGE) (also known as Enhanced GPRS (EGPRS) is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM.

• EDGE is the radio technology that allows operators to increase both data speeds and throughout capacity 3 times over GPRS.

• EDGE uses both GMSK and 8-PSK Modulation Scheme.

• EDGE produces a 3-bit word for every change in carrier phase. This effectively triples the gross data rate offered by GSM. EDGE. like GPRS uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel. and thus the bit rate and robustness of data transmission.


DEVICES

Class –A - Operates GPRS and other GSM services simultaneously. Class – B - Monitors control channels for GPRS and other GSM services simultaneously. but operates one set of services at a time. Class – C - Are connected to either GPRS service or GSM service. Must be switched manually between one or the other service.

GPRS Mobile Station(MS) modes of operation


http://www.nokia.fi/puhelimet/puhelinmallit/6230i/

http://www.nokia.fi/puhelimet/puhelinmallit/n92/

Multislot Class Downlink TS Uplink TS Active TS

1 1 1 2

2 2 1 3

3 2 2 3

4 3 1 4

5 2 2 4

6 3 2 4

7 3 3 4

8 4 1 5

9 3 2 5

10 4 2 5

11 4 3 5

12 4 4 5

30 5 1 6

31 5 2 6

32 5 3 6

33 5 4 6

34 5 5 6

Multislot Classes for GPRS/EGPRS

• The multislot class determines the speed of data transfer available in the Uplink and Downlink directions. • A multislot allocation is represented as. for example. 5+2. The first number is the number of downlink timeslots and the second is the number of uplink timeslots allocated for use by the mobile station. • A commonly used value is class 10 for many GPRS/EGPRS mobiles which uses a maximum of 4 timeslots in downlink direction and 2 timeslots in uplink direction. However simultaneously a maximum number of 5 simultaneous timeslots can be used in both uplink and downlink. The network will automatically configure the for either 3+2 or 4+1 operation depending on the nature of data transfer.

Under the best reception conditions. i.e. when the best EDGE modulation and coding scheme can be used. 5

timeslots can carry a bandwidth of 5*59.2 Kbit/s = 296 Kbit/s. In uplink direction. 3 timeslots can carry a bandwidth of 3*59.2 Kbit/s = 177.6 Kbit/s.


http://en.wikipedia.org/wiki/Uplink

http://en.wikipedia.org/wiki/Downlink

http://en.wikipedia.org/wiki/Modulation_and_coding_scheme


RF

Modulation schemes in GPRS/EDGE

• GPRS system is using GMSK (Gaussian Minimum Shift Keying). a constant-envelope modulation scheme. The advantage of the constant envelope modulation is that it allows the transmitter power amplifiers to be operated in a non-linear (saturated) mode. offering high power efficiency. The saturation means that even if the input signal level is increased. no increment will be seen in the output power. as shown.

• 8-PSK. in the form used in EDGE. has a varying envelope. see the lower part. It means that the amplifier must be operated in the linear region in case of 8-PSK since distortion is to be avoided.(There is an additional 22.5 deg rotation to avoid zero crossing.)


Modulation schemes in GPRS/EDGE

• In GMSK each bit is represented by one symbol. • In 8-PSK transmitted symbols are one of the eight sinusoids which have same amplitude and phase but differ in phase. The digital data are combined in group of 3 Bits. Thus there are 8 possible combinations starting from (0.0.0) to (1.1.1). • Each of the 3-bit patterns is then matched to one of 8-PSK Symbols. The Mapping is done in such way that there is a single bit difference between adjacent symbols. It ensures that if a symbol is received in error as an adjacent symbol only one of the bits will be in error.

(0,0,1)

(1,0,1)

(d(3k),d(3k+1),d(3k+2))=

(0,0,0) (0,1,0)

(0,1,1)

(1,1,1)

(1,1,0)

(1,0,0)

• 8-PSK (Phase Shift Keying) has been selected as the new modulation added in EGPRS

• 3 bits per symbol

• 22.5° offset to avoid origin crossing (called 3/8-8-PSK)

• Symbol rate and burst length identical to those of GMSK

• Non-constant envelope high requirements for linearity of the power amplifier


Coding schemes in GPRS

• GPRS provides four coding schemes: CS-1. CS-2 .CS-3. CS-4.

CS - 1 CS - 2 CS - 3 CS - 4

Increasing data throughput rates

Increasing protection against errors

Coding Scheme

Payload (bits) per RLC block

Data Rate (kbit/s)

CS1 181 9.05

CS2 268 13.4

CS3 312 15.6

CS4 428 21.4

Nokia GPRS PCU

Nokia GPRS PCU2

Dat

a

Erro

r C

orr

ecti

on

More Data =

Less Error Correction

• CS1 & CS2 – Implemented in all Nokia BTS without HW change

• CS1 & CS4 – S11.5 (with PCU2) and UltraSite BTS SW CX4.1 CD1 (Talk does not support CS3 and CS4)


CS-1 CS-2 CS-3

57 57 57 57 57 57 57 57

456 bits

MAC

USF BCS +4

puncturing

rate a/b convolutional coding

CS-1 CS-2 CS-3 RLC/MAC Block Size: 181 268 312 Block Check Sequence: 40 16 16 Precoded USF: 3 6 6 1/2 ~2/3 ~3/4 length: 456 588 676 0 132 220 Data rate (kbit/s): 9.05 13.4 15.6

interleaving

MAC

USF BCS

RLC/MAC Block Size: 428 BCS Size: 16 Precoded USF: 12 Data rate (Kbit/s): 21.4

CS-4

20 ms

Coding schemes in GPRS


Coding schemes in EDGE

DOCUMENTTYPE 1 (1)

TypeUnitOrDepartmentHere TypeYourNameHere TypeDateHere

Scheme Code rate Header Code rate

Modulation RLC blocks per Radio

Block (20ms)

Raw Data within one Radio Block

Family BCS Tail payloa

d

HCS Data rate kbit/s

MCS-9 1.0 0.36

8PSK

2 2x592 A 2x12 2x6

8

59.2

MCS-8 0.92 0.36 8PSK 2 2x544 A 54.4

MCS-7 0.76 0.36 2 2x448 B 44.8

MCS-6 0.49 1/3 1 592 A

12

6

29.6

MCS-5 0.37 1/3 1 448 B 22.4

MCS-4 1.0 0.53

GMSK

1 352 C 17.6

MCS-3 0.80 0.53 1 296

A 14.8

MCS-2 0.66 0.53 1 224 B 11.2

MCS-1 0.53 0.53 1 176 C 8.8

• EDGE provides nine coding schemes: MCS-1 till MCS-9.


Coding scheme

CS-1

CS-2

CS-3

CS-4

MCS-1

MCS-2

MCS-3

MCS-4

MCS-5

MCS-6

MCS-7

MCS-8

MCS-9

Bit rate (Kbps)

9.05

13.4

15.6

21.4

8.8

11.2

14.8

17.6

22.4

29.6

44.8

54.4

59.2

Abis PCM allocation (fixed + pool/slave)

GPRS and EDGE

EDGE

• Higher data rates don’t fit in 16 Kbit/s channels

• GPRS CS-2 requires 1 slave when EDGE activated (TRX/BTS)

• 32. 48. 64 or 80 Kbit/s Abis links per RTSL needed

Retrans.

EDGE and GPRS – Master / Slave Channel Usage


The LA algorithm measures the signal quality for each TBF in terms of the received signal quality (RXQUAL). RXQUAL is measured for each received RLC block. which makes it a more accurate estimate than BLER. The PCU determines the average BLER value separately for each BTS by continuously collecting statistics from all the connections in the territory in question. Based on the estimates. the LA algorithm determines which coding scheme will give the best performance. The new LA algorithm can be used in both RLC acknowledged and un-acknowledged modes in both uplink and downlink direction. Link Adaptation algorithm for PCU1 The GPRS Link Adaptation (LA) algorithm selects the optimum channel coding scheme (CS-1 or CS-2) for a particular RLC connection and is based on detecting the occurred RLC block errors and calculating the block error rate (BLER). Link Adaptation algorithm for PCU2 A new Link Adaptation algorithm is introduced with PCU2. which replaces the previous GPRS LA algorithm and covers the following coding schemes: • CS-1 and CS-2 if CS-3 and CS-4 support is disabled in the territory in question • CS-1. CS-2. CS-3. and CS-4 if CS-3 and CS-4 support is enabled in the territory .

GPRS Link Adaptation


The task of the LA algorithm is to select the optimal MCS for each radio condition to maximize RLC/MAC data rate. so the LA algorithm is used to adapt to situations where signal strength and or C/I level is low and changing slowly with time. Ideal LA would follow the envelope of the throughput of different MCSs. The PCU selects the data block and additionally selects the MCS depending on radio link quality and amount of available dynamic Abis channels. LA is done independently for each UL and DL TBF on RLC/MAC block level. but the LA algorithm is same for uplink and downlink . The MCS selection is not the same in case of initial transmission and retransmission. LA algorithm works differently for RLC acknowledged mode and unacknowledged mode. -In Acknowledged mode. the algorithm is designed to optimize channel throughput in different radio conditions. -In Unacknowledged mode. the algorithm tries to keep below a specified Block Error Rate (BLER) limit.

EGPRS Link Adaptation



Logical Channels


Logical Channels

Common Control channel(CCH) are bidirectional , point-to multipoint ,signaling channels that are used to establish dedicated channels. Packet Broadcast control channel (PBCCH): is a downlink-only channel for broadcasting packet data (GPRS) specific system information messages to all GPRS enabled MS in cell. Packet paging channel(PPCH) : is a downlink only paging channel used to page the MS prior to downlink packet transfer. Packet access grant channel(PAGCH) : is a downlink only channel used for resource assignment during the packet transfer establishment phase. Packet random access channel(PRACH) : is an uplink only channel , which MS uses for uplink traffic channel request and for obtaining the Timing advance. Packet data traffic channel(PDTCH) is reserved for GPRS packet data transfer. Packet associated control channel(PACCH) : is a bi-directional signaling channel dedicated for a certain MS . Packet timing advance control channel(PTCCH) : is used in uplink direction for the transmission of random access bursts to estimate the timing advance for one mobile

Temporary Block Flow (TBF): • Physical connection where multiple mobile stations can share one or more traffic channels – each

MS has own TFI • The traffic channel is dedicated to one mobile station at a time (one mobile station is transmitting

or receiving at a time) • Is a one-way session for packet data transfer between MS and BSC (PCU) • Uses either uplink or downlink but not both (except for associated signaling) • Can use one or more TSLs Comparison with circuit-switched: • normally one connection uses both the uplink and the downlink timeslot(s) for traffic In two-way data transfer: • uplink and downlink data are sent in separate TBFs - as below

BSC

Uplink TBF (+ PACCH for downlink TBF)

Downlink TBF (+ PACCH for uplink TBF)

PACCH (Packet Associated Control Channel): Similar to GSM CSW SACCH

Temporary Block Flow

Prepared by Naveen Bhartiya


Timeslot sharing by TBF

• Territory method is used to divide the CS and PS resources

– Timeslots within a cell are dynamically divided into the CS and (E)GPRS territories.

– Number of consecutive traffic timeslots in (E)GPRS territory are reserved (or initially available) for (E)GPRS traffic. the remaining timeslots are available for GSM voice .

– The dynamic variation of the territory boundary are controlled by territory parameters.

– The system is able to adapt to different load levels and traffic proportions. offering an optimized performance under a variety of load conditions.

– The PS territory can contain dedicated. default and additional capacity

• Dedicated capacity: number of timeslots are allocated to (E)GPRS on a permanent basis i.e. are always configured for (E)GPRS and cannot be used by the circuit switched traffic. This ensures that the (E)GPRS capacity is always available in a cell

• Default capacity: the (E)GPRS territory is an area that always is included in the instantaneous (E)GPRS territory. provided that the current CS traffic levels permit this

• Additional capacity= Additional (E)GPRS capacity means the extra time slots beyond the default capacity which are assigned due to a load demand.

(E)GPRS Resource Allocation


TRX 1

TRX 2

BCCH SD TS TS TS TS TS TS

TS TS TS TS TS TS TS TS

Circuit Switched Territory

Packet Switched Territory

Territory border moves based on Circuit Switched and GPRS traffic load

Default GPRS Capacity

CDEF Dedicated GPRS Capacity

CDED

TS TS

Additional GPRS territory

TS TS

Max GPRS

CapacityCMAX

Territory Method in (E)GPRS


TRX 1

TRX 2

= (E)GPRS Territory = CSW Territory

Case 1:

- Many (E)GPRS users

- Low CS traffic

TRX 1

TRX 2

Case 2:

- High CS traffic

- (E)GPRS user have

to take the ‘rest’

TRX 1

TRX 2

Case 3:

- No (E)GPRS user

- Zero CS traffic Default capacity

Dedicated capacity

Territory Method Load Examples


One 64 kbit/s (8 bits) channel in PCM frame is called timeslot (TSL)

One 16 kbit/s (2bits) channel timeslot is Sub-TSL PCM frame has 32 (E1) or 26 (E1) TSLs

One Radio timeslot corresponds one 16 kbit/s Sub-TSL (BCCH. TCH/F etc.) and one TRX takes two TSLs from Abis

0 MCB LCB

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18 TCH 0 TCH 1 TCH 2 TCH 3

19 TCH 4 TCH 5 TCH 6 TCH 7

20

21

22

23

24

25 TRXsig

26

27 BCFsig

28

29

30

31 Q1-management

One TRX has dedicated TRXsig of 16. 32 or 64 kbit/s

One BCF has dedicated BCFsig (16 or 64 kbit/s) for O&M

TRX1

Q1-management needed if TRS management under BSC

MCB/LCB required if loop topology is used

Abis

BTS BSC

Abis Basic Concepts – PCM frame (E1)


• The resources for signaling and voice are fixed.

• Dynamic Abis pool (DAP) for data

– Predefined size 1-12 PCM TSL per DAP (24 with Flexi EDGE BTS possible). Typically used range from 4 to 8 TSL.

– DAP can be shared by several TRXs in the same BCF (and same E1/T1)

– DAP + TRXsig + TCHs have to be in same PCM

– UL and DL EDAP is used independently

– DAP schedule rounds for each active Radio Block (20 ms)

– Different users/RTSLs can use same EDAP Sub-TSL

TRX1

TRX2

TRX3

EGPRS

pool

0 1 2 3 4 TCH 0 TCH 1 TCH 2 TCH 3 5 TCH 4 TCH 5 TCH 6 TCH 7 6 TCH 0 TCH 1 TCH 2 TCH 3 7 TCH 4 TCH 5 TCH 6 TCH 7 8 TCH 0 TCH 1 TCH 2 TCH 3 9 TCH 4 TCH 5 TCH 6 TCH 7

10 11 12 13 14 15 EDAP EDAP EDAP EDAP 16 EDAP EDAP EDAP EDAP 17 EDAP EDAP EDAP EDAP 18 EDAP EDAP EDAP EDAP 19 EDAP EDAP EDAP EDAP 20 EDAP EDAP EDAP EDAP 21 EDAP EDAP EDAP EDAP 22 EDAP EDAP EDAP EDAP 23 24 25 TRXsig1 TRXsig2

26 TRXsig3

27 BCFsig

28 29 30

31

(E)GPRS Dynamic Abis Pool – EDAP Introduction



Packet Abis means introduction of a new transport concept:

• Abis frames conveying traffic and signaling information between BTS and BSC are subject to packetization process prior to sending them to the transmission path as a result of packetization the incoming TRAU/PCU/LAPD frames are converted to new (Packet Abis specific) formats which are encapsulated and form IP packets eventually transmitted over Abis . • Bandwidth is pooled for all types of traffic (no dedicated allocation anymore) e.g. PS data traffic can utilize all bandwidth available.

Benefits of Packet Abis : • Bandwidth Savings in terms of E1 saving. • Reduction in congestion due to EDAP as bandwidth is pooled for all types of traffic. • Reduction in PCU Utilization as resource allocation are dynamic and not hardcoded. • Improvement in Latency.

Packet Abis Solution


BSS

• The PCU is the BSC plug-in unit that controls the (E)GPRS radio resources, receives and transmits PCU frames to the BTSs and Frame Relay (or IP packets) to the SGSN

• It handles both the Gb interface and RLC/MAC protocols in the BSS and acts as the key unit in the following procedures:

– (E)GPRS radio resource allocation and management

– (E)GPRS radio connection establishment and management

– Data transfer

– (Modulation and) Coding scheme selection

– PCU statistics

• The first generation PCUs (PCU or PCU1) are optimized to meet (E)GPRS requirements, i.e. non real time solutions (QoS classes "Background" and "Interactive“). EGPRS, NCCR, NACC are supported by both PCUs.

• The second generation PCU (PCU2) is a high capacity embedded plug-in unit that provides additional (E)GPRS processing power and extended functionality from BSS11.5 onwards. Second Generation PCUs have a new architecture.

• There are 3 PCU2 plug-in unit variants for the different NSN GSM/EDGE BSC variants:

• PCU2-U: BSCi and BSC2i

• PCU2-D: BSC3i 660, BSC3i 1000 and BSC3i 2000

• PCU2-E for BSC3i versions including the Flexi BSC

Packet Control Unit – PCU (Introduction)


• PCU types and capacity limits

• The relations between PCU and BSC types as well as the connectivity limits of BTSs, TRXs, TSLs, Abis and Gb TSLs are shown in the table:

PCU type PCU PCU-S PCU-T PCU-B PCU2-U PCU2-D PCU2-E**

BSCi type BSCi, BSC2i BSCi, BSC2i BSCi, BSC2i BSC3i BSC2i BSC3i BSC3i

#logical PCU per PIU 1 1 1 2 1 2 1

#Abis/BTS/TRX/RTSL/Gb per logical PCU 256 / 064 / 128 / 128 / 32* 256 / 064 / 128 / 128 / 32* 256 / 064 / 128 / 256 / 32* 256 / 064 / 128 / 256 / 32* 256 / 128 / 256 / 256 / 32* 256 / 128 / 256 / 256 / 32* 1024 / 384 / 1024 / 1024 / 128*

CPU/memory 166MHz / 128MB 200MHz / 128MB 300MHz / 256MB 300MHz / 256MB 450MHz / 256MB 450MHz / 256MB 1.33GHz / 1GB

* Maximum capacity of one FR link is 31 PCM TSL (31 x 64 kbps) in case of Gb over IP value gives the maximum processing capacity of one logical PCU (example 32 means 32 x 64kbps = 2048 kbps) * Each BCSU (Base Control Signaling Unit) can be equipped with

1-2 PCU for BSCi, BSC2i and BSC3i 660* 1-5 PCU for BSC3i 1000/2000* and Flexi BSC

Packet Control Unit (PCU) - Variants and Connectivity Limits



Packet Control Unit (PCU) Dimensioning

Consider site with 3+3+3 configuration : Dedicated TSLS(CDED) – 2+2+2 = 6 TSL Default TSLS(CDEF) – 2+2+2 = 6 TSL EDAP – 3 64 Kbps TSLS = 12 TSL 16 Kbps CMAX – 100% Considering additional 30% TSLS (((9*8)-6)*0.3) – 20 TSLS based on CMAX With 85% PCU loading and PCU2D we can have 217 TSLS Thus we can map 5 sites (44*5= 220 TSLS) in 1 NSEI or logical PCU

• With PCU2 Pooling feature the operator can easily take a new PCU PIU into use in live BSC

• PCU2 Pooling feature introduces the Packet Service Entity (PSE) concept. PSE is a logical concept, which covers several PCU PIUs in BSC. All PCUs in PSE are serving the same NSE

• When the operator adds a new PCU into PSE, the system automatically configures Gb interface to new PCU and then allocates DAPs and Segments to new PCU based on each Segment’s (E)GPRS load. The operator does not need to do any changes to the logical network configuration in BSC and either in SGSN

PCU2 Pooling – Introduction

Benefits for the customer:

• Easy way to increase (E)GPRS capacity in the network, in BSC. All PCUs are effectively in use • Savings in configuration costs (no modification to logical network configuration in the BSC and

neither in the SGSN)

• Abis and Gb resources are shared more efficiently and dynamically between PCUs in NSE

• (E)GPRS load is shared dynamically between PCUs within the PSE when the operator adds a new PCU into the PSE or reallocates PSE configuration

• Instead of configuring multiple NSEI we configured single NSEI and mapped all PCU IP’s to that NSEI

• Post PCU Pooling Gb traffic doesn't come NS-VCI wise but is generated based on PCU IP.

• The Gb interface is the interface between the BSS and the Serving GPRS Support Node (SGSN)

• It allows the exchange of signaling information and user data between one

– Packet Control Unit (PCU) or PSE (Packet Service Entity) at the BSS side and one

– Packet Processing Unit (PAPU) at the SGSN side

• Each PCU/PSE has its own separate Gb interface to the SGSN. Many users share the same physical resource. Resources are given to a user upon activity (sending/receiving)

• Signaling and user data are sent in the same transmission plane and no dedicated physical resources are required to be allocated for signaling purposes .

• Access rates per user may vary without restriction from zero data to the maximum possible line rate.

• One Gb interface can be implemented using the Frame Relay or IP.

Gb Interface - Introduction


Paging

UL TBF for MS location

Packet Control Ack (for TA)

Packet Polling

Packet Downlink Assignment

Data / Signalling

Ack / Nack

Packet Channel Request

Packet Paging Response (LLC Frame)

BTS

RACH

AGCH

PDTCH

PACCH

PACCH

PACCH

PCH

Immediate Assignment for UL TBF

Immediate Assignment for DL TBF AGCH

PDTCH

PACCH

PACCH

Establishing a DL TBF and Sending Data


TFI2

TFI5

TFI3

TFI2 BTS

The TFI included in the Downlink RLC Block header indicates which Mobile will open the RLC Block associated with its TBF

RLC Data Block

Multiple Mobiles and Downlink Transmission


Packet Channel Request

Immediate Assignment for UL TBF

UL Data

Signaling + Ack/Nack

Final UL Data

Final Ack/Nack

Packet control Ack

RACH

AGCH

PDTCH

PACCH

PDTCH

PACCH

PACCH

BTS

Establishing an UL TBF and Sending Data


• Several mobiles can share one timeslot

• Maximum of 7 Mobiles are queued in the Uplink

• Mobile transmissions controlled by USF (Uplink State Flag) sent on DL (dynamic allocation)

TS 1

TS 2

TS 3

Uplink State Flag

• Mobile with correct USF will transmit in following Uplink block

• Timeslot selected to give maximum throughput

New MS

Multiple Mobiles and Uplink Transmission


USF = 1

USF = 2

USF = 3

USF = 3

BTS

RLC Data Block

The USF included in the Downlink RLC Block header identifies which Mobile will transmit in the following Uplink RLC Block

Multiple Mobiles and Uplink Transmission



Packet Data Protocol stack

3G RAN Data Fundamentals

Sections:

WCDMA Overview

Architecture and Call Flow

RAN Dimensioning

Concept of LA, RA and URA

WCDMA Overview

• Multiple Access Technology for 3G is wideband CDMA (WCDMA) – All Cells Use Same Carrier Frequency

– Spreading Codes are used to separate Cells and Users

– Signal Bandwidth is 3.84 MHz

• Multiple carriers can be used to increase capacity

• Inter-System Functionality to support mobility between GSM and WCDMA

• Initial version of 3G is known as Release 99

• HSDPA in Downlink and HSUPA in Uplink are newer versions supporting higher data rates with the help of Fast Link Adaptation, Effective Power Control and Higher order Modulation and Coding Schemes.

WCDMA Benefits

Wideband CDMA is the Access Technology of UMTS. It offers some

key benefits against GSM systems.

• Soft Handover

– Make before Break Connection, unlike GSM. Provides greater reliability.

• Processing Gain

– Basic CDMA benefit => the wider the transmitted bandwidth compared to the

user data rate the less power is needed for the transmission

• Advanced Radio Resource Management (RRM)

– RRM will control call admission and packet scheduling and all RRM building

blocks are closely related to each other

• Multipath Signal Processing

– Combines power for increased signal integrity => RAKE receiver

Soft Handover Soft Handover provides greater reliability to the links. It works as follows:

• UE is simultaneously connected to 2 to 3 cells during soft handover

• Soft Handover is performed based on UE Cell Pilot Power measurements and

Handover thresholds set by radio network planning parameters.

• Soft Handover consumes both base station and transmission resources.

Concept of Spreading – The Processing Gain

CDMA uses a concept of “spreading” the actual Information signal, which can be of different

bandwidth, over a final bandwidth of 3.84 Mchips /sec. This makes it more robust and less

prone to external noise, which generally is narrow band and can affect only a portion of the

spread signal. This gain in robustness is termed as Processing Gain.

So, more the extent of spreading, less would be the actual data rate and more would be the

processing gain. Mathematically, processing gain is represented as:

Processing Gain (dB) = 10* log (W/R). where W= Final Bandwidth, which is 3.84 Mcps and

R = The actual Information Rate.

Extent of spreading depends upon the multiplication factor used to increase the bandwidth.

This is known as the spreading Factor and is explained further in the next slide

Bits, Chips and The Spreading Factor

• Spreading is done by multiplying the Baseband signal with a specific spreading

sequence. In the example about, each bit is multiplied by 8 chips to generate a

spread signal.

• So, the spreading factor of the spreading code is 8.

• At the receiver’s side, the spread signal, when multiplied with the same spreading

code results in the original signal. This is known as “De-spreading”.

Concept of Code Tree

C0(0)

=[1]

C2(1)=[1-

1]

C2(0)=[11

]

C4(0)=[11

11]

C4(1)=[11-

1-1]

C4(2)=[1-

11-1]

C4(3)=[1-1-

11]

C8(0)=[11111

111]

C8(1)=[1111-1-1-

1-1]

C8(2)=[11-1-111-

1-1]

C8(3)=[11-1-1-1-111]

C8(0)=[1-11-11-

11-1]

C8(5)=[1-11-1-11-

11]

C8(6)=[1-1-111-1-

11]

C8(7)=[1-1-11-

111-1]

C16(0)=[....

........] C16(1)=[....

........]

C16(15)=[..

.........]

C16(14)=[..

.........]

C16(13=[...

........]

C16(12)=[..

.........]

C16(11)=[.....

......]

C16(10)=[....

.......]

C16(9)=[....

........]

C16(8)=[....

........]

C16(7)=[....

........]

C16(6)=[....

........]

C16(5)=[....

........]

C16(4)=[....

........]

C16(3)=[....

........]

C16(2)=[....

........]

• Channelization Codes used to spread

information signal.

• These codes are orthogonal to each

other.

• Spreading provides gain in the form of

robustness and is known as Processing

gain

• More the spreading, less the data rate.

• Lower SF codes are used to generate

higher SF codes, which result into a

code tree.

• If a lower SF code is being used, the

codes in the branches below it are

blocked.

• Channelization codes are used to

distinguish between users. SF=1 SF=4 SF=2 SF=8…

Modulation & Coding Schemes Used

WCDMA offers 3 Modulation schemes viz. QPSK, 16 QAM and 64 QAM. It supports

adaptive modulation, meaning the modulation to be used is selected based on the

capability of the User Equipment, as well as the RF conditions that it is in. Each

Modulation has its own benefits and limitations.

QPSK:

• Known as Quadrature Phase Shift Keying

• 2 Bits per Symbol

• Can support double the data rate of BPSK with

same bandwidth

• Is more robust in nature as compared to 16 QAM

and 64 QAM Constellation

Diagram of

QPSK

Modulation & Coding Schemes Used contd..

16 QAM:

• Known as Quadrature Amplitude Modulation

• Combines Phase Shifting with Amplitude Modulation to

support more data rates.

• For example symbols 0011 and 0001 have same phase but

different amplitude. Similarly symbols 0000 and 1000 have

different phase but same amplitude.

• Provides 4 bits per Symbol

• Is not as robust as QPSK. Needs better RF conditions, i.e. a

better SNR.

64 QAM:

• Higher order Modulation using combination of PSK and

Amplitude Modulation like 16 QAM

• Provides 6 bits per symbol and hence can support quite

higher data rates.

• Needs very good RF conditions as it is more prone to errors

than 16QAM or QPSK

•Next slide provides details of theoretical Data rates in 3G

using these Modulation Schemes with different coding

rates.

Constellation

Diagram of

16QAM

3G Data Rates

Bandwidth Spreading Factor Channel Symbol Rate (Ksps) Channel Bit Rate with QPSK(kbps)

3840000 512 7.5 15

3840000 256 15 30

3840000 128 30 60

3840000 64 60 120

3840000 32 120 240

3840000 16 240 480

3840000 8 480 960

3840000 4 960 1920

Release 99:

HSDPA

Bandwidth Spreading Factor Channel Symbol Rate

(Ksps) Modulation Coding Rate Channel Bit Rate (kbps) Rate with 5 Codes(kbps)

Rate with 10 Codes(kbps)

Rate with 15 Codes(kbps)

3840000 16 240 QPSK 1/4 120 600 1200 1800

3840000 16 240 QPSK 2/4 240 1200 2400 3600

3840000 16 240 QPSK 3/4 360 1800 3600 5400

3840000 16 240 16QAM 2/4 480 2400 4800 7200

3840000 16 240 16QAM 3/4 720 3600 7200 10800

3840000 16 240 16QAM 4/4 960 4800 9600 14400

3840000 16 240 64QAM - 1440 7200 14400 21600 HSDPA +

Bandwidth Coding Rate 1xSF4 (kbps) 2xSF4(kbps) 2xSF2(kbps) 2xSF2 + 2xSF4(Mbps)

3840000 1/2 960 1920 3840 2.88

3840000 3/4 960 1920 3840 4.32

3840000 4/4 960 1920 3840 5.76

HSUPA

HSDPA UE Categories

3GPP

ReleaseCategory

Max No. of HS-

DSCH codesModulation Coding Rate

Max Data

Rate (Mbps)

Release 5 1 5 16-QAM 0.76 1.2

Release 5 2 5 16-QAM 0.76 1.2

Release 5 3 5 16-QAM 0.76 1.8

Release 5 4 5 16-QAM 0.76 1.8

Release 5 5 5 16-QAM 0.76 3.6

Release 5 6 5 16-QAM 0.76 3.6

Release 5 7 10 16-QAM 0.75 7.2

Release 5 8 10 16-QAM 0.76 7.2

Release 5 9 15 16-QAM 0.7 10.1

Release 5 10 15 16-QAM 0.97 14

Release 5 11 5 QPSK 0.76 0.9

Release 5 12 5 QPSK 0.76 1.8

Release 7 13 15 64-QAM 0.82 17.6

Release 7 14 15 64-QAM 0.98 21.1

Sections:

WCDMA Overview


RAN Dimensioning


3G Network Architecture

GSM /GPRS BSS

BTS

BSC

PCU

SS

7

SCP

SMS

SCE

PSTN/other PLMN

Internet,

Intranet

MSC/VLR GMSC

HLR/AUC

SGSN

CG BG

GGSN

PS backbone

Other PLMN

CS domain

PS domain

NodeB

RNC

UTRAN

Iu-CS

Iu-PS

A

Gb

3G System introduces some new Network Elements viz Radio Network

Controller (RNC) and Node-B. Combined together it is known as UMTS

Terrestrial Radio Access Network.

3G Call Setup Phases

Setup

Complete

Access

Complete

Active

Complete

Setup Access Active

Att

em

pts

Setup failures (blocking)

Access failures

Acce

ss

Active

Release

Active

Failures

RRC Drop

Success

Phase:

RRC and RAB phases Call Setup divided into 3 phases:

1. Setup Phase: Resource is reserved by the

“System”

2. Access Phase: UE confirms the Setup back to

the “System”

3. Active Phase: Ready for communication

These 3 phases are applicable to both RRC and

RAB stage

RRC is about radio connection, the owner of

which is RAN

RAB is about the actual Bearer, which is owned

by the Core Network.

RRC Connection Setup and Access and Active Phase

BTS UE RNC CN

RRC: RRC connection Request

RRC: RRC connection Setup

RRC SETUP phase

(Resource Reservation in RNC, BTS, Transport)

RRC ACCESS phase

(RNC waits for Reply from UE)

RRC: RRC connection Setup Complete

RR

C S

etu

p tim

e

RRC: Initial Direct Transfer

RANAP: Initial UE Message

RANAP: Iu Release Command

UE-CN Signalling

(E.g. RAB Establishment and Release)

RRC: RRC connection Release

RRC: RRC connection Release Complete

Release RRC resources in RNC, BTS,

Transport

RRC ACTIVE phase

RAB Setup & Access and Active Phases

RAB Reconfiguration Actions

(Reconfigure RAB resources in RNC, BTS, Transport)

BTS UE RNC CN

RRC: Radio Bearer Setup

RAB SETUP phase

(Resource Reservation in RNC, BTS,

Transport)

RAB ACCESS phase

(RNC waits for Reply from UE)

RRC: RB Setup Complete

RA

B S

etu

p tim

e

RRC: RB Reconfiguration

RANAP: RAB Assignment Response


Release RAB resources in RNC, BTS,

Transmission

RRC Connection Active Phase, UE-CN Signalling

RANAP: RAB Assignment Request


RAB ACTIVE phase

(User Plane Data Transfer)

RANAP: RAB Assignment Request with IE: RAB reconfiguration

RRC: Radio Bearer Release

RRC: RB Reconfiguration Complete

RANAP: RAB Assignment Request with IE: RAB Release

RRC: Radio Bearer Release Complete

RA

B H

old

ing

Tim

e

UMTS QoS Classes When RAB is being setup, the core network (CN) provides to RNC bearer attributes like:

Traffic QoS class, Maximum bit rate, Guaranteed bit rate, Residual BER, Transfer delay

and so on.

There are four different QoS classes defined for UMTS

• Conversational Class

Conversational RT

Preserve Time variation between information entities of the stream

Conversation pattern (stringent and low delay)

Voice falls under Conversational Class

• Streaming Class

Streaming RT

Preserve Time variation between information entities of the stream

Streaming Video falls under Streaming Class

UMTS QoS Classes contd..

• Interactive Class

Interactive Best Effort

Request Response Pattern

Preserve Payload Content

Web Browsing falls under Interactive Class

• Background Class

Background Best Effort

Destination is not expecting the data within a certain time

Preserve Payload

Background Download of emails falls under Background Class

Key Interfaces

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B Node B

Iu Iu

Iur

Iub Iub Iub Iub

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

the Iu.

A RNS consists of a Radio Network Controller and one or more Node Bs. A Node B is connected to

the RNC through the IuB interface.

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.

Key Interfaces contd..

IuB Interface:

• Logical Interface between NodeB and RNC

• Manages Transport Resources

• Handles Logical O&M of the NodeB

• Manages traffic of Common & Dedicated Channels

IuR Interface:

• Logical Interface between two RNCs

• Manages Transport Network

• Manages traffic of Dedicated Channels and reporting Measurements

Iu Interface: Logical Interface between RAN and Core Network. Responsible for establishing ,

maintaining and releasing RABs. Also responsible for performing handovers and serving RNC

relocations. Paging is also handled by Iu interface. It has two instances:

• Iu-CS Interface:

Between RAN and Circuit Switched domain in the Core Network

Carries communication between RAN & MSC and also UE & MSC

• Iu-PS Interface:

Between RAN and Circuit Switched domain in the Core Network

Carries communication between RAN & SGSN and also UE & SGSN

Sections:

WCDMA Overview


RAN Dimensioning


Radio Dimensioning Data Flow

Radio Dimensioning follows the process as shown in the flow chart below, which is

based on both Coverage and Capacity Requirements.

Capacity Dimensioning of Node-B ,RNC and the interface between them, i.e. IuB

is covered in subsequent slides

Node-B Overview

Specifications: •Up to 3 RF Modules per system Module

• Up to 2 System Modules

• 1 Tx sub module per System Module

• Up to 2 AC/DC Power Modules

• Optional Outdoor Cabinet

Main functions of RF Module:

• Antenna Filtering

• Power Amplification (Transmitter)

• Low Noise Amplification (Receiver)

• Combiner (Carriers)

Node-B Dimensioning

System Module

No. of RF Modules

HW Support for No. of Cells CCH

Max HW CE Capacity

Max SW Capacity (traffic)

Total Max SW Capacity with 2 SM

FSMB 3 6 240 240 480

FSMC 3 6 250 180 360

FSMD 3 12 500 396 792

Channel Elements of a Node-B reside inside the System Module. So, Capacity

Dimensioning from a HW point of view is done considering the CE capacity of a

System Module, which has three variants

Number of Channel Elements Required during a call depend upon the RAB type.

Following slide provides the details.

RAB wise CE Requirements RAB Traffic

Class CS/PS Max

rates for each RAB

SF UL SF DL CEs UL CEs DL

AMR Speech Conversational CS 12.2 64 128 1 1







Packet INT / BG PS 16 64 128 1 1






UDI Conversational CS 64 16 32 4 4

Streaming Streaming CS 57.6 16 32 4 4

Streaming Streaming CS 14.4 64 128 1 1

RNC: Overview

Radio Network Controller performs the following Key Functions:

• Radio Resource Management

• Telecom

• Transmission and Transport

• O&M

• WCDMA Radio Resource Management can be broken down into following functions:

Resource Manager

Admission Control

Load Control

Power Control

Handover Control

Packet Scheduler

• Telecom Functions can be broken into:

Security Functions: Integrity Checking, Ciphering

User Plane Processing towards CS and PS (e.g. Management of RABs)

Radio Network Layer Control Processing

Service Area Broadcast

Location Services

RNC Dimensioning RNC Capacity is licensed as:

• IuB PS Data Throughput

• AMR Capacity

• Number of carriers, BTS or cells

Generally RNC Dimensioning is done considering the factors as given in the below

flowchart.

RNC Model NodeB Equipped

Capacity IuB Throughput Capacity (Mbps)

AMR erlangs Capacity (Erl)

MODEL3 900 900 11700

MODEL3 900 900 11700

MODEL2 600 600 7800

IuB Dimensioning - ATM

• Each Tellabs 8660 caters 50% of the total NodeBs

• MSP 1+1 between STM cards in RNC, Tellabs and ALU MUXs

• All STM cards have optical STM1 interfaces

• Each NodeB connected to 4 E1s (17960 cps) to Tellabs 8660.

• 15 NodeBs (60 E1s) on one ch. STM-1 link to Tellabs.

• Tellabs – RNC interface are overbooked with 19 - 25 NodeBs on 1 VC4 link to RNC.

• In RU10/RU20, Overbooking is supported only for UBR+ VPs carrying NRT traffic.

IuB Dimensioning – Dual IuB Ethernet

• Each Tellabs 8660 caters 50% of the total NodeBs • 2N redundancy for NPGE cards • Each GE Module has 8 x 1000 opt. interfaces • ELP redundancy for GE modules b/w RNC and Tellabs.

• Each Dual IuB NodeB is planned with 17Mbps Ethernet bandwidth for HSPA and R99 traffic.

• All RT traffics along with Signaling & DCN are kept on ATM.

• All Dual IuB sites have HSPA fallback feature enabled

Sections:

WCDMA Overview


RAN Dimensioning


Location Area & Routing Area

• Location Area (LA) and Routing Area (RA) are used by the Core Network to track UEs

• LA are used by CS Domain whereas RA are used by PS Domain

• The main CS Service States are CS-Detached, CS Idle and CS-Connected

• The main PS Service States are PS-Detached, PS-Idle and PS-Connected

Location Areas:

• A UE in CS Idle Mode does not have to update the CS Core of its location when

moving within an LA.

• LA consists of one or more RNCs connected to the same CN, i.e. MSC / VLR.

• The mapping between a LA and its associated RNCs is handled by the

MSC/VLR

• The mapping between LA and its Cells is handled by the RNC.

• A LA is identified using a Location Area Identity

Routing Areas:

• A UE in PS Idle Mode does not have to update the PS Core of its location when moving

within an RA.

• RA consists of one or more RNCs connected to the same CN, i.e. SGSN.

• A RA is always contained within a single LA.

• The mapping between a RA and its associated RNCs is handled by the SGSN

• The mapping between a RA and its cells is handled by the RNC

• A RA is identified using a Routing Area Identity

UTRAN Registration Area

• RU 10 onwards, RNC supports URA_PCH State

• The purpose of this state is to decrease the cell update signaling due to cell reselection

, which saves RNC and UE resources

• When the UE is in Cell_FACH or Cell_PCH state, its location is known at the cell level.

Cell updates are sent by the UE when Cell reselection occurs.

• If too many cell updates are received in a pre-defined window, the UE is ordered to

transfer to URA_PCH state in order to reduce cell update signaling between the UE and

the RNC.

• In URA_PCH state, UE sends the URA update to RNC after reselection to new URA.

• Planning of URA involves a balance between paging load and signaling load. Large

URA would increase the signaling load whereas small URA will lead to frequent URA

updates which increases signaling load as well as UE power consumption.

THANKS


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