High-Speed Downlink Packet Access (HSDPA) Downlink Packet Access (HSDPA) ... UMTS Networks Andreas Mitschele-Thiel, ... Advanced transmission to increase data throughput

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  • High-Speed Downlink Packet Access (HSDPA)

    HSDPA Background & BasicsPrinciples: Adaptive Modulation, Coding, HARQChannels/ UTRAN ArchitecturePrinciples: Fast scheduling, MobilityPerformance Results

  • UMTS Networks 2Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Motivation (as of 2000)

    As the UMTS networks are rolled out, the demand for high bandwidth services is expected to grow rapidly. By 2010, 66% of the revenues will come from data services (source: UMTS forum).Release 99/4 systems alone will not be capable to meet these demands. (Realistic outdoor data rates will be limited to 384kbps).A more spectral efficient way of using DL resources is required.Competition with CDMA 2000 1x EV-DO/DV


    UMTS Rel. 99

    Voice, low speed packet data No Multimedia, Limited QOS

    Medium rate Packet data Theoretical 2 Mbps but ~384 kbps subjected to practical constraints

  • UMTS Networks 3Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    HSDPA Background

    Initial goalsEstablish a more spectral efficient way of using DL resources providing data rates beyond 2 Mbit/s, (up to a maximum theoretical limit of 14.4 Mbps)Optimize interactive & background packet data traffic, support streaming serviceDesign for low mobility environment, but not restrictedTechniques compatible with advanced multi-antenna and receivers

    Standardization started in June 2000Broad forum of companiesMajor feature of Release 5

    Enhancements in R7 HSPA+Advanced transmission to increase data throughputSignaling enhancements to save resources

  • UMTS Networks 4Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    HSDPA Basics

    Evolution from R99/ R45MHz BWSame spreading by OVSF and scrambling codesTurbo coding

    New concepts in R5Adaptive modulation (QPSK vs. 16QAM), coding and multicodes (fixed SF = 16)Fast scheduling in NodeB (TTI = 2ms)Hybrid ARQ

    Enhancements in R7 HSPA+Signaling enhancements64QAMMIMO techniques, increase of the bandwidth

  • UMTS Networks 5Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Higher Order Modulation

    Standard modulation scheme in UMTS networksQPSK 2 bit per symbol

    With HSDPA, modulation can be switched between two schemesQPSK 2 bit per symbol16-QAM 4 bit per symbol

    Low bitrate robust High bitrate Sensitive to disturbances

  • UMTS Networks 6Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Key Principles

    Adaptive Modulation and Coding(Mother Turbo code rate = 1/3)

    For wireless data, link adaptation through Rate Control is more effective then Power Control.Users in favorable channel conditions (based on Channel Quality indication) are assigned higher code rates and higher order modulation (16QAM).This means higher data rates = Reduced latency

    But what about when channel is changing at high rate;Can AMC guarantee reliability?

  • UMTS Networks 7Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Hybrid ARQ

    H-ARQ automatically adapts to instantaneous channel conditions by:fast retransmissions at physical layeradding redundancy only when needed

    The retransmitted packets are combined with original packet to improve the decoding probability.Simple form of Hybrid ARQ shows significant gains over link adaptation alone. Different schemes can be used for retransmission of original data packet.

    Chase combiningIncremental Redundancy

    No. In fast fading conditions, AMC alone is not enough.

  • UMTS Networks 8Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Fast Scheduling

    Channels are uncorrelated Multi-user diversityAssign the resources to the best user(s) in time to maximise throughputGains increase with number of users

    Max C/IProportional fair Round Robin


    With HSDPA Scheduling function is moved from RNC to Node-B.

    Fading is good in multi-user environment!!

  • UMTS Networks 9Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    HS-DSCH Principle I

    Channelization codes at a fixed spreading factor of SF = 16Up to 15 codes in parallel

    OVSF channelization code tree allocated by CRNCHSDPA codes autonomously managed by NodeB MAC-hs scheduler

    Example: 12 consecutive codes reserved for HS-DSCH, starting at C16,4Additionally, HS-SCCH codes with SF = 128 (number equal to simult. UE)





    Physical channels (codes) to which HS-DSCH is mapped CPICH, etc.


  • UMTS Networks 10Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    HS-DSCH Principle II

    Resource sharing in code as well as time domain:Multi-code transmission, UE is assigned to multiple codes in the same TTIMultiple UEs may be assigned channelization codes in the same TTI

    Example: 5 codes are reserved for HSDPA, 1 or 2 UEs are active within one TTI

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

    Time (per TTI)


    not used

  • UMTS Networks 11Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    UMTS Channels with HSDPA

    Cell 1


    Cell 2

    R99 DCH (in SHO)UL/DL signalling (DCCH)UL PS serviceUL/DL CS voice/ data

    Rel-5 HS-DSCHDL PS service(Rel-6: DL DCCH)

    = Serving HS-DSCH cell

  • UMTS Networks 12Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    HSDPA Channels

    HS-PDSCHCarries the data trafficFixed SF = 16; up to 15 parallel channelsQPSK: 480 kbps/code, 16QAM: 960 kbps/code

    HS-SCCHSignals the configuration to be used next: HS-PDSCH codes, modulation format, TB informationFixed SF = 128Sent two slots (~1.3msec) in advance of HS-PDSCH

    HS-DPCCHFeedbacks ACK/NACK and channel quality information (CQI)Fixed SF = 256, code multiplexed to UL DPCCHFeedback sent ~5msec after received data

  • UMTS Networks 13Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Timing Relations (DL)

    NodeB Tx viewFixed time offset between the HS-SCCH information and the start of the corresponding HS-DSCH TTI: HS-DSCH-control (2 Tslot= 1.33msec)HS-DSCH and associated DL DPCH not time-aligned

    TB size & HARQ Info

    Downlink DPCH



    3 Tslot (2 msec)

    HS-DSCH TTI = 3 Tslot (2 msec)

    HS-DSCH-control = 2 Tslot

    Tslot (2560 chips)

    ch. code & mod

  • UMTS Networks 14Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Timing Relations (UL)

    UE Rx viewAlignment to m 256 to preserve orthogonality to UL DPCCHHS-PDSCH and associated UL DPCH not time-aligned (but quasi synch)


    Uplink DPCCH



    3 Tslot (2ms)

    m 256 chips

    UEP = 7.5 Tslot (5ms) 0-255 chips

    Tslot (0.67 ms)


  • UMTS Networks 15Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    HSDPA Architecture





    Logical Channels

    Transport Channels








    Upper phy


    Evolution from R99/R4

    HSDPA functionality is intended for transport of dedicated logical channels

    Takes into account the impact on R.99 networks



    HSDPA in R5

    Additions in RRC to handle HSDPA

    RLC nearly unchanged(UM & AM)

    Modified MAC-d with link to MAC-hs entity

    New MAC-hs entity located in the Node B





  • UMTS Networks 16Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    MAC-hs in NodeB


    MAC Control


    Priority Queue distribution

    MAC-d flows


    Priority Queue

    Priority Queue

    Priority Queue

    UE #1 UE #2

    UE #N

    MAC-hs FunctionsPriority handlingFlow Control

    To RNCTo UE

    SchedulingSelect which user/queue to transmitAssign TFRC & Tx powerHARQ handling

    Service measurementse.g. HSDPA provided bitrate

    TFRC: Transport Format and Resource Combination

  • UMTS Networks 17Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    MAC-hs in UE


    MAC Control

    Associated Uplink Signalling HS-DPCCH

    To MAC-d

    Associated Downlink Signalling HS-SCCH



    Reordering Reordering

    Re-ordering queue distribution

    Disassembly Disassembly

    MAC-hs Functions

    HARQ handling

    ACK/ NACK generation

    Reordering buffer handling

    Associated to priority queues

    Flow control per reordering buffer

    Memory can be shared with AM RLC

    Disassembly unit

  • UMTS Networks 18Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Data Flow through Layer 2

    Higher Layer


    Higher Layer PDU


    MAC-d SDU

    MAC-d PDU



    MAC-d SDU

    MAC-d PDU



    MAC-dheader L2 MAC-d


    L2 RLC(non-transparent)Segmentation



    Higher Layer PDU


    MAC-hs SDU MAC-hs SDUMAC-hsheader L2 MAC-hs(non-transparent)

    Transport Block (MAC-hs PDU)

  • UMTS Networks 19Andreas Mitschele-Thiel, Jens Mckenheim Nov. 2011

    Hybrid Automatic Repeat Request

    HARQ is a stop-and-wait ARQUp to 8 HARQ processes per UE

    Retransmissions are done at MAC-hs layer, i.e. in the Node BTriggered by NACKs sent on the HS-DPCCH

    The mother code is a R = 1/3 Turbo codeCode rate adaptation done via rate matching, i.e. by puncturing and repeating bits of the encoded dataTwo types of retransmission

    Incremental RedundancyAdditional parity bits are sent when decoding erro

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