HSDPA_LT

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HSDPA Principles

Prepared by: Legend staff

Legend Technologies Co. 2

WCDMA services


HSDPA


HSDPA features


• New HS-DSCH requires a new radio interface layer 2 functionality

• New functionality is placed in the functional entity of the MAC layer, called MAC-hs.

• MAC-hs is placed in the RBS to achieve desired signaling speed for supporting HS-DSCH


Shared channel transmissiom


Fast link Adaptation


Fast link dependent scheduling


Fast link dependent scheduling methods

• Round Robin (RR)– Cyclically assign the channel to users without taking channel

conditions into account– Simple but poor performance

• Proportional Fair (PF)– Assign the channel to the user with the best relative channel

quality– High throughput, fair

• Max C/I Ratio– Assign the channel to the user with the best channel quality– High system throughput but not fair


Fast hybrid ARQ


Fat hybrid ARQ schemes

• Chase combining : each retransmission is an identical copy of the original transmission.

• Incremental Redundancy : each retransmission may add new redundancy


HSDPA channel structure

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Prepared by: Legend staff


HSDPA – summary





• HS-DSCH - High-Speed Downlink Shared Channel:– transport channel that carries the user data.

• HS-PDSCH - High-Speed Physical Downlink Shared Channel:– physical downlink channel that carries the user data and layer 2 overhead

bits over the air interface.• HS-SCCH - High-Speed Shared Control Channel (s):

– physical downlink channel that carries control information how to decode the information on HS-PDSCH and which UE that shall decode it.

• HS-DPCCH - High-Speed Dedicated Physical Control Channel:– physical uplink channel to send ACK/NAK reports and channel quality

reports

• A-DCH (DPDCH+DPCCH) - Associated Dedicated Channel


HS-DSCH

• One transport block of dynamic size per 2 ms TTI.• Supports link adaptation and hybrid ARQ with soft combining.• Always associated with a DPCH.• Never in soft handover.• Mapped to one or several HS-PDSCH (SF=16).• TFRC: Transport Format and Resource Combination

– modulation, transport block size, channelization code set


HS-SCCH

• TFRI – Transport Format Related Information– Modulation scheme [1 bit]– Channelization Code Set [7 bits]– Transport Block Size [6 bits]

• HARQ(Hybrid Automatic Repeat reQuest) related parameters– HARQ process number [3 bits]– Redundancy version [3 bits]– New Data Indicator [1 bit]

• UE identity [16 implicit bits]


timing relation between HS-SCCH andHS-PDSCH


uplink HS-DSCH

• The uplink HS-DSCH-related physical-layer signaling consists of:– Acknowledgements for hybrid ARQ– Channel Quality Indicator (CQI), i.e., information

reflecting the instantaneous downlink radio-channel conditions to assist the Node B in the transport-format selection (fast link adaptation) and the scheduling


information carried on HS-DPCCH

• HS-DPCCH carries ACK/NAK and CQI from UE to RBS– one HS-DPCCH for each user in the cell

• ACK/NAK– single bit, repetition coded to 10 bits (1 slot)

• CQI (Channel Quality Indicator)– 5 bits coded to 20 bits (2 slots)– channel quality measurements based on CPICH– reporting rate is configurable through RRC/NBAP signaling

• ACK/NAK and CQI can be repeated in multiple subframes– controlled by RRC/NBAP signaling– useful in soft handover scenarios


Channel Quality Indicator.

• Channel quality knowledge at UE needed in the RBS– Link adaptation– Scheduling– Power control of HS-SCCH

• CQI– UE measures and reports a recommended transport format to

the RBS– Accounts for channel conditions and UE receiver

performance


HS-DPCCH power control.

• Important to secure good success rate of ACK/NAK and CQI transmission while keeping UL interference under control

• ACK, NAK, CQI power offsets with relation to DPCCH set by RRC signaling

• Two independent mechanisms:1. Two sets of power offsets (ACK, NAK and CQI) are configured per cell in RNC

• RNC reconfigures UE depending on number of RBS involved• Configuration changed at cell change and possibly after active set

update

2. RBS initiates update of ACK/NAK and CQI feedback cycles based on CQI detection performance


Channel structure

• Code multiplexed with DPDCH and DPCCH

– timing relative to downlink HS-PDSCH, not uplink DPCCH/DPDCH

– unused slots are DTX:ed

– transmission of ACK/NAK and CQI transmission independent of each other


Overall Timing Relation.


Hybrid ARQ Processes.

• One HARQ entity per user• Each HARQ entity consist of up to 8 HARQ processes

– multiple HARQ processes allows continuous transmission to a single user– separate reordering function needed to support in-order delivery

• (P2 correctly received before P1 in figure below)


A-DCH, ASSOCIATED DEDICATED CHANNEL

• One A-DCH per HSDPA enabled terminal in the cell• A-DCH is mapped on physical channels DPDCH and

DPCCH• A-DCH DL

– 3.4 kbps SRB (control signalling: RRC & NAS)

• A-DCH UL– 384 kbps (or 64 kbps) DCH– 3.4 kbps SRB (control signalling: RRC & NAS)– UL data transmission


Dedicated Physical Control and Data Channel (Uplink)


Dedicated Physical Control and Data Channel

DPCCH/DPDCH (Downlink).


Transport Channels and Physical Channels.


Transport Channels and Physical Channels.


Services and RABs in P4

• New RABs– PS Interactive 64/HS– PS Interactive 384/HS

• Throughput– 1.6 Mbps in DL with QPSK and HS-DSCH category 12– 2.08 Mbps in DL with QPSK and HS-DSCH category 5 – 10– 3.36 Mbps in DL with 16QAM and HS-DSCH category 5 - 6– 4.32 Mbps in DL with 16QAM and HS-DSCH category 7 – 10– 64 or 384 kbps in UL

• 16QAM is an optional add-on• 1–5 HS-PDSCH codes (configurable)• All HS capable UEs use HSDPA regardless of CN requested bit-

rate


RAB/RB combinations: Interactive PS RB on HS-DSCH


Product Phasing in HSDPA.


Protocol Stacks.


MAC-hs main responsibilities

• New L2 functionality located in RBS• RBS MAC-hs responsible for

– scheduling– TFRC selection (link adaptation)– HARQ protocol (selects redundancy versions, controls L1

soft combining)

• UE MAC-hs responsible for– In-sequence delivery– HARQ protocol


Data flow (When HS-DSCH is employed)


MAC-d PDU.


MAC-hs (Network side)


MAC-hs (UE side).


HSDPA Code Control.

• Enable for operator to set the number of HS-PDSCH codes for a cell.– Maximum 5 codes for HS-PDSCH (SF=16)– The number of HS-SCCH (SF=128) codes hard coded to one

• Parameter: numOfHspdschCodes– Increasing: Lock cell, release traffic– Decrease: No effect on ongoing traffic


HSDPA POWER USAGE


Admission Control

• Control the load so not too many radio links are set up and overload isachieved in the cell.– Radio Link Setup– Radio Link Addition– Radio Link Reconfiguration– Compressed Mode Command

• A-DCH – normal dedicated radio link that need to request admission

• Possible to limit the number of HSDPA users per cell


Admission control – HSDPA DL Power.


Admission control – HSDPA DL ASE.


Admission control – HSDPA DL Channelization

Codes.


HSDPA Mobility Tasks.


Serving HS-DSCH Cell Selection.


“Best cell” Serving HS-DSCH Cell Selection


HSDPA – summary

Documents

HSDPA_LT