hspa fundamentals

7/28/2019 HSPA Fundamentals

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HSPA Fundamentals

10/11/2011


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Definitions

HSDPA = High Speed Downlink Packet Access

HSUPA = High Speed Uplink Packet Access

HSPA = HSDPA + HSUPA

HSDPA and HSUPA are improvements on the basic R99 WCDMA system thatapply to packet data users only

HSDPA: higher bitrates and spectral efficiency for downlink

HSUPA: higher bitrates and spectral efficiency for uplink

HSPA in the standards

HSDPA is first introduced in 3GPP Rel 5- Refs: 25.308 (HSDPA overview), 25.321 (MAC),25.977 (HSDPA Iub/Iur)

HSUPA is an enhancement in 3GPP Rel 6 - Refs: 25.309 (EDCH overview), 25.808 (EDCHPHY), 25.214 (PHY layer procedures)

INTRODUCTION


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ARCHITECTURE

RNC

MAC-es

SGSNRNC

NodeB

MGW

GGSN

Iur

Iub

Iu-cs

Iu-ps Gn

L1

MAC

RLC

MAC-d

RLC

UuL1L1

MAC-hs

DL UL

MAC-e

Radio protocol stack in NodeB

Radio protocol stack in RNC

= Impact to Network elements due to HSPA

NodeB PHY layer modified

Part of MAC layer moved from RNC to NodeB

Contains Packet scheduling for HSPA

Specific CE for HSPA BB processing

RNC

Part of MAC layer moved to NodeB

3G SGSN

3G SGSN to realize higher bitrates


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High Speeds with HSDPA


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HSDPA Basic Principles

1. Shared Channel Transmission

2. Higher-order Modulation

3. Short Transmission Time Interval (2 ms)

4. Fast Hybrid ARQ with Soft Combining

5. Fast Link Adaptation

6. Fast Radio Channel Dependent Scheduling


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1.Shared Channel Transmission

Channelization codes allocated

for HS-DSCH transmission

8 codes (example)

SF=16

SF=8

SF=4

SF=2

SF=1

User #1 User #2 User #3 User #4

TTI

Shared

channelizationcodes

Resources are dynamically shared in Time and Code

domain Efficient Radio Resource Utilization


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2.Higher-order Modulation

Higher-order Modulation

HSDPA uses 16QAM, in addition to QPSK

16QAM allows twice the data rates compared to

QPSK

Higher Throughputs in good Radio Conditions


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3.Short Transmission Time Interval

Short Transmission Time Interval

Shorter frames (up to 2ms)

Reduced air-interface delay

Improved end-user performance and spectral efficiencyRequired by TCP at high data rates

Necessary to benefit from other features like

Fast Link Adaptation

Fast hybrid ARQ with soft combining

Fast Channel-dependent Scheduling


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ARQ = Automatic Repeat reQuest (method used for packet

retransmission)

HARQ is a very efficient ARQ that reduces error rates in retransmissions

Perform packet combining operations from retransmissions in the physicallayer

Two different ways of operating HARQSoft combining(or chase combining)

Incremental redundancy(IR)

P1,1

P1,1

P1,2

P1,2

P2,1

P2,1

P2,2

P2,2

P3,1

P1,1 P2,1 P3,1

+ +

Transmitter

Receiver

4.Fast Hybrid ARQ with Soft Combining


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1st Decoding in UE 2nd Decoding in UE Final Picture

During Retransmission, UE performs soft combining to

get the final product


contd.,


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Two different ways of operating HARQ

Soft combining(or chase combining): all the transmission attempts of a

packet are identical. If the retransmitted packet is again erroneous, then

the previous and current packet are combined to recover from errors

Incremental redundancy(IR): similar to Soft combining, but instead of

being identical to the first transmission attempt, the retransmissioncontains additional redundant bits, which are combined with the previous

transmission to resolve the errors

IR typically outperforms Soft combining at the expense of higher

complexity

Chase Combining was used in WCDMA RAN during Initial launch


contd.,


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5.Fast Link Adaptation

Adjust transmission parameters to match instantaneous channelconditions

Path loss and shadowing

Interference variations

Fast multi-path fading

HS-DSCH: Rate control (constant power)

Adapt on 2 ms TTI basis 500 times per sec

Encoding rate, number of Channelization codes

and modulation type adapted based on available Power

16 QAM: twice the data rate of QPSK

More sensitive to interference (use with good C/I)

Higher Speeds Close to cell site

High data rate

Low data rate

16QAM

4 bits

2 bits

QPSK


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Physical Channel Structure

A-DCHDPDCH-Dedicated Physical Data channel(UL)

DPCCH-Dedicated Physical control Channel(UL)

DPCH-Dedicated Physical Channel(DL)

Associated Dedicated

Channels(A-DCH)

HS-Control Channels1.HS-SCCH:Shared Control Channel(DL)

2.HS-DPCCH-Dedicated Physical Control Channel(UL)

AB

HSDPA Channels

3GPP Release 5 extends the specification of WCDMA

with a new downlink transport channel for packet data -High Speed Downlink Shared Channel (HS-DSCH)


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HSDPA Channels contd.,

HS-DSCH (High Speed Downlink Shared Channel) :

Common Downlink channel used for data

Supports link adaptation, hybrid ARQ and scheduling

Does not support soft handover or power control

Always associated with a DPCH

Fixed spreading factor (SF16)

Mapped to one or several HS-PSDCH, depending on number of codes (up to 15)

Timeslots & codes shared between users

HS-SCCH (High Speed Shared Control Channel)

Control Downlink signaling to the mobile(s) scheduled in a 2 ms interval

1 HS-SCCH can handle only 1 user in one timeslot, multiple HS-SCCH required

for code multiplexing( Max 4 can be enabled)

SF 128

HS-DPCCH (High Speed Dedicated Physical Control Channel)

Uplink Channel containing ACK/NACK information for fast ARQ

DL Channel Quality indicator (CQI), estimated transport block size, modulation &

codes that can be received in the DL with reasonable BER

HS-DPCCH: CQI,ACK/NACK

HS-DSCH: Data Transfer

HS-SCCH:DL Control Information


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HS-DSCH Overview

CN RNC RBS UE

-

DPCCH

DP DCH

HS DPCCH

HS-SCCH

HS-PDSCHHS -DSCH

DCCH

DCCH

DTCHInteractive PS RAB

DTCHInteractive PS RAB

DTCH

Interactive PS RAB

DCCHNAS

DCCHNAS

RRC

User 1

User 2

User n

For eachuser

Radio Access Bearers:- Intera ctive- Background

Logical Channels:

-Dedicated Control Channel, DCCH

-Dedicated Traffic Channel, DTCH

Transport Channels:

-Dedicated Channel, DCH

-High-Speed Downlink Shared Channel, HS-DSCH

Physical Channels:

-Dedicated Physical Channel, DPCH

-DPCCH, Dedicated Physical Control Channel

-DPDCH, Dedicated Physical Data Channel

-HS-DPCCH, HS-DSCH Dedicated Physical Control Channel

-HS-DSCH Shared Control Channel, HS-SCCH

-High Speed Physical Downlink Shared Channel, HS-PDSCH

DPCHDCH

DCH

Iu Iub Uu


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HSDPA Power

t

Dedicated channels (power controlled)

Common channels

HS-DSCH

Totalcellpower

HSDPA power is used based on remaining

power not used by Voice and R99


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HSDPA Code Tree

SF2 SF4 SF8 SF16 SF32 SF64 SF128 SF256

5 codes reserved for HSDPA

(40 potential codes not used for voice)

Every single SF16 code can

potentially carry 8 typical

voice calls (SF128)

10 codes reserved for HSDPA wouldleave room for 36 voice users in the cell

With 15 HSDPA codes there is room

for only 4 voice calls in the cell


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HS-DSCH UE Categories


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HS-DSCH Bit-Rate

Maximum achievable bit-rate on HS-DSCH will depend

upon

Radio condition

16QAM (or 64QAM) availability

Available HS-DSCH power

Available number of HS-PDSCH codes and

UE category


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1. Resource estimation:

estimates the amount of power and codes available for HSDPA traffic

2. Queue validation:

checks if it is possible to transmit data to a priority queue e.g. radio quality

sufficient, UE capable to receive data, presence of data in the buffers,)3. Queue selection:

selects which user the system shall transmit to in the next TTI based on resource

estimation & Queue validation checks.

4. Remaining resource check function for Code Multiplexing:

Is to check if more users can be selected if power & codes are available.

The Flexible Scheduler function consists of four main procedures,

performed in the following order every TTI:

MAC-hs Scheduler contd.,


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Call Process Overview

Interactive RAB is mapped on

Radio Bearer to be transmitted

over HS-DSCH.This Bearer is then Processed

by RLC & MAC-d Protocol Layer

in RNC

Resulting MAC-d PDUs are

transmitted over Iub to RBS using

HS-DSCH Frame Protocol.

Flow Control protocol in RBS &

RNC enables efficient control of

the PDUs over Iub.

MAC-d PDUs are buffered in Priority

queues to be transmitted over Uu to UE.

The Flexible Scheduler selects the userto be served in Next TTI & assigned HS-

DSCH.

The user data to transmit on the HS-

DSCH is put into one of several HARQ

processes in the MAC-hs HARQ protocol.

The amount of data to be transmitted is

determined by the TFRC selection

algorithms.

CQI adjustment algorithm

which adjusts the channel

quality reports from the UEbefore the channel quality

estimates are used by the

Flexible Scheduler and TFRC

selection algorithms
http://edw//alex?ac=image&fn=93_1553-HSD10102_4Uen.A-cpi-hsdpa-user-plane-figure-protocols.pdf


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Iub Flow Control
http://edw//alex?ac=image&fn=93_1553-HSD10102_4Uen.A-cpi-hsdpa-user-plane-figure-flowctrl.pdf


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New channel, time & code multiplexed - Dynamic

utilization of parallel codes (up to 15)

2 ms TTI: faster dynamics, reduced delays

Fast scheduler adapting to radio conditions (2ms)

Codes with fixed spreading factor (SF 16)

No power control: link quality controlled by adaptive

modulation and coding formats

No soft handover on the shared channel

Hybrid ARQ: fast retransmission with combining

16QAM modulation in addition to QPSK

2 ms

HSDPA Fundamentals - Summary


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HSUPA


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HSUPA Basics

Enhancement of existing DCH (E-DCH) to support up to 5.76Mbps

Soft handover and fast power control occursVariable spreading factor

Use of QPSK only

No time multiplexing

Main changesUse of HARQ

Multiple parallel codes

Faster dynamics: reduced TTI (10 and 2 ms options)

Special RRM

Fast uplink scheduler in NodeB (proportional fair is the optimum)

Faster outer loop power control (that adapts to the new shorter TTI)


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HSUPA Protocol Stack

Similar change to HSDPA

MAC layer split into MAC-d, MAC-es and MAC-e

MAC-d (dedicated)

Located in RNC

Same functionality as HSDPA MAC-d

MAC-es (enhanced, serving RNC)located in SRNC (Serving RNC)

Reordering + SHO combining functionality

MAC-e (enhanced)

located in the NodeB

HARQ, scheduling and PDU demultiplexing

Phy.

MAC-es/

MAC-e

UE

IP

Phy.

MAC-es

PDCP

RLC

IP relay

RNC

UTRAN

PDCP

Node B

Phy.

FP

Phy.

MAC-e FP

MAC-d

RLC

MAC-d


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HSUPA Terminal categories

Category Nr of codes TTI

Spreading

factor

Max

Throughput

1 1 10ms 4 700 kbps

2 2 10 and 2ms 4 1.44 Mbps

3 2 10ms 4 1.44 Mbps

4 2 10 and 2ms 2 2.88 Mbps

5 2 10ms 2 1.92 Mbps

6 4 10 and 2ms 2 5.76 Mbps

SF2: Higher speeds, but

lower processing gain

(requires better channel

conditions)


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EUL Overview

hspa fundamentals

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