HSDPA_Overview.pdf

7/28/2019 HSDPA_Overview.pdf

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HSDPA OverviewThomas Winter, UMTS Network Engineering, Com MN PG NT NE 2


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Content

HSDPA Principle

Mechanisms for Capacity Improvements

New modulation schemes and Adaptation

Fast Scheduling and Multi-user Diversity

Hybrid ARQ

Peak Rates and Throughput per User


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HSDPA Principle


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HSDPA Principle (1)

User A

User B

User C

DCH

-A

DCH

-B

DCH

-C

NodeB w/ HSDPA

Scheduling

A,B,C

User C

User B

User A

NodeB w/o HSDPA

Dedicated pipe for every UE

Release `99Fat pipe is shared among UEs

Release 5


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HSDPA Principle (2)

HSDPA uses spare capacity on the air interface

Uu Iub

UE Cell Node B RNC

P

t

DCH + Rel. 99

HSDPARAB1

RAB2

RABn

Scheduler

Scheduler: Maximum Carrier-to-Interference Ratio (Max-CIR)

RLC1

RLC2

RLCn

Pthr


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HSDPA Limitations

HSDPA only for PS Interactive/Background Rel. 5 users

HSDPA users get resources if available on the air interface, i.e. CS

and PS Streaming users have priority Data rate for PS Interactive/Background Rel. 99 users can be

restricted

HSDPA not supported over Iur Core network is not aware of using HSDPA


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HSDPA Principle

RRM Functions in the Node B

ResourceAllocation

Scheduling

Power Control

Open Loop

Power Control

ResourceAllocation

Scheduling

Power Control

Open Loop

Power Control

Major HSDPA RRM functions in NodeB!


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HSDPA Principle

Radio Bearer Translation

UE UL and DL configuration with HSDPA

DL

DCCH

DPCH

HS-DSCHDCHDCH

DTCH

0 kbps

UL

DCCH

DPCH

DCHDCH

DTCH

DL Shared Channel

UL Dedicated Channel

Up to 15 HS-PDSCH (High Speed Physical Data Shared Channels)

can be configured per cell


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HSDPA principle

Time / Code Multiplex

SF=8

SF=16

SF=4

SF=2

SF=1

Physical channels ( codes) to which HS-DSCH is mapped

SFHSDPA = 16Number of codes to which HSDPA transmission is mapped: 12 ( example)

TTI = 2 ms

All codes to whichHSDPA transmission

is mapped

(5 in this example)

Data to UE #1 Data to UE #2 Data to UE #3 CodeCode

Time


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HSDPA Mechanisms for Capacity Improvement


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Siemens ICM N templ-example.ppt 11

Mechanism for Capacity Improvements

Higher Order Modulation and Coding

Higher order Modulation is used:

Release 5: 16-QAMRelease 99: QPSK

Channel bit rate of 960 kbit/s

(SF 16)

Channel bit rate of 480 kbit/s

(SF 16)

Different Coding rates possible: from 0.143 to 0.887


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Modulation and Coding Schemes

680588510420342250172throughput per HS-

PDSCH code[kbps]

0.70830.61250.531250.8750.71250.520830.3586Coding Rate

16QAM16QAM16QAMQPSKQPSKQPSKQPSKModulation

MCS7MCS6MCS5MCS4MCS3MCS2MCS1MCS


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Fast Scheduling and Multi-user Diversity

Constructive use of fading:

multi-user diversity!2 ms

P

t

Scheduler

Node B

t

RNC

t

Feedback of

recommended

code rate and

modulationSource:Dr. Alexander Seeger


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Scheduling Algorithm

Maximum Carrier-to-Interference Ratio (Max-CIR) scheduler assigns all

transmission resources (power, channelisation codes) to the UE with the

best channel quality.

This strategy maximizes throughput.

QoS depends just on channel quality / UE position; no fairness between

UEs.

Deviations from the MaxCIR strategy reduce capacity, like for

guaranteed bit rates (for streaming services),

priority classes,

QoS demands.

Proportional Fairgives better throughput values for all users.


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Hybrid ARQ

If transmission fails, request for repetition and transmit with higher code rates(weaker error correcting code).

Receiver combines all transmission attempts

Minimisation of redundancyChase Combining:

Each re-transmission is an identical copy of the first transmission; maximum-ratio-

combining is performed at the UE

Incremental redundancy:

Each re-transmission contains additional redundancy that has not been sent before.

This code-combining at the UE has better performance than Chase Combining butinclude higher complexity at the UE

both options defined for HSDPA by 3GPP


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Performance: Magic Numbers

Peak rate 10.8 Mbps

This figure dates back to spring 2001, when Motorola pushed for

standardization of HSDPA in 3GPP. It is based on a code rate of 3/4

and 16QAM.There is no justification for this figure in current 3GPP specifications

anymore.

Peak rate 14.4 Mbps Theoretical value, based on uncoded 16QAM transmission.

Peak rate 16.0 Mbps (TS 23.107, 24.008)

Maximum peak rate that can be requested from the UE.


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Realistic Peak Rates

Realistic estimations on peak rates should assume:

16 QAM

code rate

90% successful transmissions (10% retransmissions)

12 channelisation codes(otherwise no channelisation codes are left for the associated DCHs;

each UE on HS-DSCH needs one associated DCH)

This yields a peak rate of 7.8 Mbps

Throughput per user depends on radio condition, number of users andUE type.


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HSDPA Admission Control


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HSDPA Admission Control

Generic Formula used for Admission Control

Current load + New load old Load < Threshold

Uplink load

based on RTWP

No changes from UMR4.0 to UMR4.0 HS

Downlink load

Dedicated channels: in HSDPA cells

measurement of non-HSDPA power (in percentage of the

Maximum Configured Node B power)

Dedicated channels in non-HSDPA cells (or HSPDA disabled) Measurement of total Transmitted Carrier Power (TCP)


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Motivation (1)

HSDPA uses the remaining carrier power after DPCHs and CCHs have

been served on a very fast time basis.

Admission Control is based on non-HSDPA-Transmitted Carrier Power

BRA requests of PS Interactive/Background UE for higher rate are

evaluated by Admission Control based on non-HSDPA load.

Even if HSDPA is fully loaded, many UE on DCH may still receive 384kbps. This can cause degradation of HSDPA performance.

Rel.99 UE or UE rejected on HSDPA setup may experience much

better performance than UE on the HSDPA, this will also degradeoverall cell performance

Possibly bad QoS perception by the HSDPA user


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Motivation (2)

PMAX

t

PDL

HSDPA

DCH

CCH

Possible HSDPA traffic degradation due to high Rel99 PS traffic on DCH

HSDPA


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Parameters for Admission Control

Name Type Range Default Description

Minimum SFavailable for PSInt/BG on DCH inHSDPA cell

ENUM 8, 16, 32 8 The minimum SF available in thisHSDPA cell for PS Int/BG if thecondition of at least x UE onHSDPA is fulfilled.Default of 8 means disabled.

Note: A similar parameter alreadyexist under the name Minimum SF

available This parameter is stillneeded since AC will determinethe maximum of both (if HSDPAcondition applies!)

Threshold forActivating Raterestriction for PSINT/BG on DCHin HSDPA cell

Integer 0,..,256 0 If the current number of UE on theHSDPA exceeds this value in theHSDPA cell, rate restriction for PSInt/BG on DPCH will be applied inthis cell. 0= one HS-UE onHSDPA suffices to start RC-hs


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HSDPA Code Allocation


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Codes for HSDPA

HS-DSCH is mapped in DL on

1-15 HS-PDSCH (SF 16)

1-4 HS-SCCH (SF 128)

Constraints in DL:

all DL HS-DSCH codes have to be below primary SC

in case 15 HS-PDSCH are configured, only 3 HS-SCCH

are possible to be configured

UL: no channelisation Code constraints for HS-DPCCH (SF 256)

R/W1-4IntegerNumber-of-HS-

SCCH-codes

R/W1-15IntegerNumber-of-HS-

PDSCH-codes

R/WRangeTypeName


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Code usage after cell setup

16

32 32

64 64 64 64

128 128 128 128 128128128128

256

256

256

256 256

256

256

256

256

256

256

256

256

256

256

Agenda:

16 16

256

- allocated, used SF

- SF unavailable, because of other used SF

- available

+ 15xHS-PDSCH

SF of common channels:

CPICH 256, P-CCPCH 256, S-CCPCH 64, AICH 256, PICH 256, Sec. S-CCPCH for PCCH 128


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Parameters

Name Q3-Name LMT-Name

Type Range Unit R/W

Default

Description

Numberof HS-PDSCHcodes

no_pdsch

Integer 1,..., 15 - RW*)

- Number of HS-PDSCH codes per cellIf HS-PDSCH = 15 and PCH is mappedon standalone PCCH, then Nr of HS-SCCHs


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HSDPA Questions


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Questions about HSDPA

RRM for HSDPA

HSDPA power: Is the assignment of HSDPA power fixed or dynamical?

How does the resource assignment between Release 99 and HSDPAtraffic work?

When using HSDPA and UMTS in the same carrier, how codes are

shared? (same code tree?) How is the assignment of channelization codes for the HS-DPSCH

done?

How many users per code?

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