hsdpa_lt.ppt
TRANSCRIPT
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HSDPA Principles
Prepared by: Legend staff
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WCDMA services
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HSDPA
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HSDPA features
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• 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
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Shared channel transmissiom
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Fast link Adaptation
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Fast link dependent scheduling
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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
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Fast hybrid ARQ
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Fat hybrid ARQ schemes
• Chase combining : each retransmission is an identical copy of the original transmission.
• Incremental Redundancy : each retransmission may add new redundancy
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HSDPA channel structure
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HSDPA channel structure
Prepared by: Legend staff
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HSDPA – summary
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HSDPA channel structure
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HSDPA channel structure
• 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
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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
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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]
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timing relation between HS-SCCH andHS-PDSCH
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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
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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
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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
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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
update2. RBS initiates update of ACK/NAK and CQI feedback cycles based on CQI detection performance
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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
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Overall Timing Relation.
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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)
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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
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Dedicated Physical Control and Data Channel (Uplink)
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Dedicated Physical Control and Data ChannelDPCCH/DPDCH (Downlink).
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Transport Channels and Physical Channels.
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Transport Channels and Physical Channels.
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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
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RAB/RB combinations: Interactive PS RB on HS-DSCH
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Product Phasing in HSDPA.
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Protocol Stacks.
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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
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Data flow (When HS-DSCH is employed)
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MAC-d PDU.
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MAC-hs (Network side)
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MAC-hs (UE side).
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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
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HSDPA POWER USAGE
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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
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Admission control – HSDPA DL Power.
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Admission control – HSDPA DL ASE.
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Admission control – HSDPA DL Channelization Codes.
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HSDPA Mobility Tasks.
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Serving HS-DSCH Cell Selection.
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“Best cell” Serving HS-DSCH Cell Selection
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HSDPA – summary