1 2 hsdpa course intro updated

8/13/2019 1 2 HSDPA Course Intro Updated

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1 NOKIA 2004 HSDPA, June 2004. COMPANY CONFIDENTIAL

HSDPA Course

1. Introduction / Motivation, Channel

Structure, and Code Resources

by Klaus I. Pedersen


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HSDPA usage

The High Speed Downlink Packet Access (HSDPA) concept is a

natural extension of the Downlink Shared Channel (DSCH).

HSDPA is mainly intended for non-realtime traffic, but canalso be used for traffic with tighter delay requirements.

Not included in RAN06


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HSDPA - Taking WCDMA to the next stage!

T A R G E T S & M O T I V A T I O N

Peak data rates higher than 2Mbit/s (up to 10 Mbit/s)

Reduced (re)transmission delays

Improved QoS control (Node-B based packet scheduling)

Spectral and code efficient solution for fully loaded sites 50-100% packet data throughput increase over 3GPP release 4

HSDPA offers a lower cost per bit and potentially opens for newapplication areas with higher data rates and lower delay

variance.HSDPA is the natural evolution ofDSCH and also builds on the resourcesharing concept


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5/215 NOKIA 2004 HSDPA, June 2004. COMPANY CONFIDENTIAL

HSDPA data rates (examples)

Shown code rates are examples since real values are given by transport blocksize as well as transmission and rate matching parameters.

16QAM with 15 multi-codes supports >10Mbit/s throughput. QPSK alone cansupport up to 5.3 Mbit/s (up to 7.2 Mbit/s by disabling coding).

Theoretically up to 14.4 Mbit/s can be sustained but 3GPP hardwarespecifications do not support it (+ interference problems from e.g.synchronization channel).

QPSK

1/4

ModulationEffectiveCode rate

2/4

3/4

16

SF

16

16

16QAM2/4

3/4

16

16

1.2 Mbit/s

Data rate(10 codes)

2.4 Mbit/s

3.6 Mbit/s

4.8 Mbit/s

7.2 Mbit/s

1.8 Mbit/s

Data rate(15 codes)

3.6 Mbit/s

5.3 Mbit/s

7.2 Mbit/s

10.7 Mbit/s

600 kbit/s

Data rate(5 codes)

1.2 Mbit/s

1.8 Mbit/s

2.4 Mbit/s

3.6 Mbit/s

4/416 4.8 Mbit/s 7.2 Mbit/s2.4 Mbit/s



Architecture Change

RNC

MAC-d MAC-sh

Node-B

MAC-hs

Iub

CQI,Ack/Nack,TPC

CQI,Ack/Nack,TPCCQI,Ack/Nack,TPC

Packet scheduling forHSDPA is moved to the

Node-B



HSDPA - general principle

Fast scheduling is done directly in Node-B based onfeedback information from UE and knowledge of currenttraffic state.

UE2

Channel quality(CQI, Ack/Nack, TPC)

Channel quality(CQI, Ack/Nack, TPC)

Data

Data

Users may be time and/or code multiplexed

New base station functionsHARQ retransmissions

Modulation/coding selection

Packet data scheduling (short TTI)

UE1

0 20 40 60 80 100 120 140 160

-2

024

68

10121416

Time [number of TTIs]

QPSK1/4

QPSK2/4

QPSK3/4

16QAM2/4

16QAM3/4

InstantaneousEsNo[dB]



Main motivation for location ofthe MAC-hs in the Node-B

Enables fast layer one retransmissions using H-ARQ Layer one retransmissions are subject to significantly shorter delays than

RLC retransmissions, i.e., results in less delay jitter and is very attractivefor data services such as TCP, etc.

The use of H-ARQ (using either chase combining or incrementalredundancy) adds increased robustness to the system and a spectral

efficiency gain.

Enables utilization of fast air interface measurements

Scheduling of users can be conducted as a function of their radiochannel conditions.

Thus, we may chose to only schedule users which are experiencingconstructive fading (possible due to the shorter frame size).

This is also known as fast selection multi-user diversity transmission.Multi-user diversity provides a cell capacity gain of 40-100%, comparedto blind scheduling where no a priori knowledge of the radio channel isexploited.



Competing Technologies

Concepts similar to HSDPA are also being introduced in other wirelessstandards.

1xEV-DO (1x Evolution Data Only)

Also known as high data rate (HDR).

Adaptive modulation and coding + H-ARQ.

Offers peak data rates up to 2.4 Mbps. Dominated by Qualcomm.

1xEV-DV (1x Evolution Data and Voice)

Offers simultaneous high speed data and voice services.

Adaptive modulation and coding + H-ARQ.

Peak data rates up to 3.1 Mbps.

Concept is similar to WCDMA/HSDPA but uses narrower bandwidth.


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2. HSDPA Channel Structure


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Channel Structure (Downlink)

Downlink channels received by a HSDPA UE:

HS-PDSCH (High Speed Physical Downlink Shared CHannel) Modulation: QPSK or 16QAM, Fixed spreading factor: 16.

Contain data and 24 bit CRC.

Does not support SHO.

STTD and closed loop mode-1 Tx diversity is supported (mode-2 is still open).

HS-SCCH (High Speed Shared Control CHannel) Modulation: QPSK, Spreading factor: 128.

Contain UE id, modulation and coding setting, HARQ information, etc.

One UE can maximum listen to 4 HS-SCCHs.

Does not support SHO.

STTD supported. Closed loop schemes are not supported.

Associated DPCH (Dedicated Physical CHannel)

Modulation: QPSK, Spreading factor: 4-512.

Support SHO.

Overhead

Ti i Di f T i i t


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Timing Diagram for Transmision to oneUE

Time 1 slot 1 slot 1 slot 1 slot 1 slot

1 TTI

1 TTI

HS-SCCH

HS-DSCH

----------------->

Timer in

Node-B

HARQ InfoInfo about:-multicode-modulation

-UE Id

Data packet

Ack/Nack received

ackNackSignalDelay: 7.5 slots

packetTransTimeExpire

If no Ack/Nack received then initiate retransmission due to time-out.

- UE Id- Modulation- #codes

- TBS- HARQ info


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Channel Structure (Uplink)Uplink channels transmitted by a HSDPA

UE:

HS-DPCCH (High Speed Dedicated Physical ControlCHannel)

Primary modulation: BPSK, Spreading Factor: 256 (channel bitrate equals 15 kbps).

Contain Ack/Nack (repetition encoded) and Channel Quality

Indicator (protected by a (20,5) encoder). The HS-DPCCH transmit power equals the DPCH transmit

power plus an offset.

The HS-DPCCH may be received at two sectors on the sameNode-B in order to improve the detection probability, but ingeneral SHO is not supported for this channel.

3GPP status: Still ongoing discussions in WG4.

DPCH

Primary modulation: BPSK, Spreading Factor: 4-256.

Soft and softer handover supported.

Overhead


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Uplink HS-DPCCH Power Control (1/2)

The HS-DPCCH is power controlled relative to the uplink DPCCH every

slot period.

The power offset parameters [DACK; DNACK; DCQI] are controlled by the

RNC and reported to the UE using higher layer signalling. The poweroffset can be up to 6 dB within 9 possible quantization steps, see the

tables in 25.213.

Typically, DACK


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Uplink HS-DPCCH Power Control (2/2) Potential problem:

Notice that the standardized uplink HS-DPCCH power control scheme is sub-

optimum for UEs in soft handover (SHO) mode, i.e. UEs with an active set size largerthan one.

Basically because the uplink DPCH will be in SHO mode (and power controlledaccording to that), while the HS-DPCCH will be in non-SHO mode.

Solution:

This implies that a larger power offset (DACK; DNACK; DCQI) typically is required for UEs

in SHO mode, compared to UEs in non-SHO mode. In most cases a repetition factor of two is also required to ensure suffiently good

uplink reception of the HS-DPCCH. Thus, the same information is transmitted duringtwo TTIs on the HS-DPCCH.

Special case:

If the UE is in softer handover (i.e., in SHO between cells on the same Node-B) then

the Node-B may allocate Rake fingers for reception of the HS-DPCCH in the samecells as for uplink reception of the DPCH from the UE.

Thus, both the DPCH and HS-DPCCH will be received using maximal ratiocombining of the signals from the cells in the UEs active set => Improved uplink HS-DPCCH coverage and no power control problems.

Comments on Ack/Nack Detection


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Comments on Ack/Nack DetectionErrors

Error types and consequences:

Ack being interpretated as NackThe same transport block will be

transmitted on the HS-DSCH even though it was correctly received by theUE during the first transmission, i.e., this results in wasted DL bandwidth.

Nack being interpretated as AckThe MAC-hs errorneously believethat the transmission was successful so no physical layer retransmissionwill be executed. This triggers an RLC retransmission, which typically havemuch longer delays compared to the fast physical layer HARQretransmissions.

DTX being interpretated as AckMay happen if the UE fails tocorrectly decode the HS-SCCH and therefore also the HS-DSCH. Thissituation will trigger an RLC retransmission.

Means to reduce the UL HS-DPCCH error detection probability:

Use a larger Ack/Nack power offset or use repetition of Ack/Nacks so thesame information is transmitted more than once.

However, notice that the use of Ack/Nack repetition prevents the UE fromreceiving data in every TTI, i.e. potentially lower maximum DL bit rate onthe HS-DSCH.


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CQI Report Definitions (1/2)

The Channel Quality Indicator (CQI) expresses the data rate that the UE

can support, i.e., the recommended modulation scheme, number of HS-

PDSCH codes, and transport block size. The CQI definition yields [25.214]:

In deriving the CQI estimate, the UE assume that it receives the following

HS-PDSCH power level:

PHS-PDSCH=PCPICH+G+D[dB]

where PCPICHis the received pilot power, Gis a parameter reported to the

UE using higher layer signalling, and Dis a power offset which is included

in the CQI message.

Basedon an unrestricted observation interval, the UE shall reportthe highest tabulated CQI value that could be received in a 3-slotreference period ending 1 slot before the start of the first slot inwhich the CQI value is transmitted and for which the transport blockerror probability does not exceed 0.1 for a single transmission with a

TFRC corresponding to the reported, or a lower, CQI value.


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CQI Report Definitions (2/2)

The CQI report is represented by a 5-bit word.

Signalling of the CQI report from the UE is

periodically, every K-thTTI, whereK[0,2,10,20,40,80,160] ms (K=0 No CQIreporting).

The K-parameter is controlled by the RNC. TheNode-B can aske the RNC to use a specific Kvalue in the radio link parameter update

indication message. General assumption; a small Kvalue is used for

UEs in SHO mode, while other UEs are using alarger value. (this assumption may be subject tochanges)

A CQI repetition factor of [1,2,3,4] can be set to

improve the likelihood of correct decoding at theNode-B, i.e., improved uplink coverage.

The Gparameter can take values in the range of6 dB to +13 dB, in steps of 0.5 dB.

Alternatives to periodically CQI reporting are

CQIvalue

TransportBlock Size

Number ofHS-PDSCH

ModulationReference power

adjustment

0 N/A out of range

1 137 1 QPSK 0

2 173 1 QPSK0

3 233 1 QPSK 0

4 317 1 QPSK 0

5 377 1 QPSK 0

6 461 1 QPSK 0

7 650 2 QPSK 0

8 792 2 QPSK 0

9 931 2 QPSK 0

10 1262 3 QPSK 0

11 1483 3 QPSK 0

12 1742 3 QPSK 0

13 2279 4 QPSK 0

14 2583 4 QPSK 0

15 3319 5 QPSK 0

16 3565 5 16-QAM 0

17 4189 5 16-QAM 0

18 4664 5 16-QAM 0

19 5287 5 16-QAM 0

20 5887 5 16-QAM 0

21 6554 5 16-QAM 0

22 7168 5 16-QAM 0

23 7168 5 16-QAM -1

24 7168 5 16-QAM -2

25 7168 5 16-QAM -3

26 7168 5 16-QAM -4

27 7168 5 16-QAM -5

28 7168 5 16-QAM -6

29 7168 5 16-QAM -7

30 7168 5 16-QAM -8

CQI mapping table for UE categories 1-6.


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Timing diagram for DL & UL

HS-SCCH Transmission from Node-B

A/N

18 Time slots

TUE,Proc = 7.5 TS

2TS

Tprop

Tprop

4.5TS - 2Tprop

3 TS

1 TS

Tdelay approx 1.5+1+4.5 +2= 9TS

Tdelay approx 1 .5+1+4.5 +2+3 = 12 TS

CQI referencemeasurement(3 time slots)

CQI referencemeasurement(3 time slots)

A/N A/N A/N A/N

A/N A/N A/N A/N A/NCQI CQI CQI CQI CQI

CQI CQI CQI CQI CQI

HS-PDSCH Transmission from Node-B

HS-PDSCH recept ion at UE

CQI measurements performed at UE

1 2 3 4 5 6 7 8

2.5 TS 2Tprop

Tprop =Propagation delay

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8


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Code Resource Management (1/2)

Channel Spreading factor Offset (allocation, sf=16 level)

P-CPICH 256 1 (1/16)

P-CCPCH 256 1 (1/16)

S-CCPCH (FACH, PCH) 256 Not fixed (1/16)

PICH 256 Not fixed (1/16)

AICH 256 Not fixed (1/16)

HS-SCCH 128 Not fixed (2/16). We assume thatwe want to support codemultiplexing for ceil(M/5) in orderto fully utilize environments withUE that support up to 5 multi-codes.

The maximum number of UEs on HSDPA does in theory depend on the number ofavailable channelization codes for the associated DPCHs. For the sake of simplicity,we will considera scenario where all traffic is carried by HSDPA and the following amount of codes

areused for common channels:


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Code Resource Management (2/2)

HSDPA codeallocation (sf=16level)

Maximum number of HSDPA users.Number in paranthesis indicateSF=256 case for associate channelsNo code multiplexing assumed.

Maximum number of HSDPA users.Number in paranthesis indicate SF=256case for associate channels (weassume full support of M=5 UEs).

8 (5.7Mbps) 240 (120) 236 (118)

9 (6.4Mbps) 208 (104) 204 (102)

10 (7.2Mbps) 176 (88) 172 (86)

11 (7.8Mbps) 144 (72) 136 (68)

12 (8.6Mbps) 112 (56) 104 (52)

13 (9.3Mbps) 80 (40) 72 (36)

14 (10.0Mbps) 48 (24) 40 (20)

15 (10.7Mbps) 16 (8) 8 (4)

ource: T.E. Kolding, J. Wigard, HSDPA Code resources, December 2002, Version 0.1.0, NSR teamroom.

1 2 hsdpa course intro updated

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