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  • 1

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 1

    Lecture 9 - 10Link Adaptive Packet Scheduling

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 2

    Part I: Channel adaptive scheduling

  • 2

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 3

    Contents Brief introduction to HDR and HSDPA System model Slow scheduling

    Benefits of one-by-one scheduling Comparison of a class of slow schedulers

    Fast scheduling Gain of using fast scheduling Intercell interference Limited bandwidth Quantization of rates Measurement delay and errors Quality of service Limits of fast scheduling

    Conclusions

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 4

    High speed data in downlink Performance of the downlink shared channels could be

    improved by using Higher order modulation such as 8PSK and 16QAM Adaptive modulation and coding Shorter frame size Hybrid ARQ Fast cell site selection (FCS), no soft handover Fast scheduling Advanced receiver structures (e.g. IC) MIMO techniques

    Requirement: Scheduling, transport format (coding etc.) selection and

    retransmissions should be handled by base stations instead of radio network controllers in order to decrease the signalling delay.

  • 3

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 5

    HDR / 1xEV-DO Qualcomm's HDR was accepted as phase I of 1xEV Separate IS-95 (cdma2000-1x) forward link (downlink) RF

    carrier for data and voice. Transmissions are time multiplexed and transmitted with

    full power Channel SIR is estimated and data rate request (DRC) is

    fed back once 1.67 ms. QPSK, 8PSK, and 16QAM modulation at 1.2288 MHz symbol

    rate. 16 orthogonal codes are allocated to the active user. => RF signal have the same characteristics as an IS-95 signal allowing reuse of all analog RF designs developed for IS-95 base stations

    Fast ARQ based on negative acknowledgements or HARQ Peak data rate 2457.6 kbit/s

    [BEN00, JOU00]

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 6

    HDR / 1xEV-DO

    Link adaptation in CDMA2000 1xEV-DO

    A Data Rate Control (DRC) message is generated by the user, based on which scheduling decision is made and modulation and coding schemes are selected.

    Depending on the used coding scheme the number of slots per packet can vary between 1 to 16.

    DRC

    Forward link (downlink)

    Reverse link (uplink)User 1User 2

    Measurement delay 2*1.67 = 3,34 ms (due averaging)

    DRC

    User with best channel state can be selected

    Pilot & Reverse link (uplink)Power control bits

  • 4

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 7

    High Speed Downlink Packet Access WCDMA HSDPA (High Speed Downlink Packet Access)

    Max. data rate ~10 Mbit/s for best effort data transmission Advanced signal processing:

    MIMO antennas Interference cancellation

    Fast link adaptation: Modulation and coding schemes are changed based on the channel

    measurement: 1/2, 3/4 code rates (Convolution and Turbo coding) High order modulation: QPSK, 16 QAM No fast power control

    Fast cell selection: Rapidly select the base station with best pilot SIR. (Selection

    diversity) Hybrid ARQ: Rather than discarding the erroneous packets,

    they can be combined with subsequent transmissions to reduce the packet error rate.

    Modified frame structure: Shorter TTIs, minimum TTI = 3 slots Fast scheduling: Channel state is taken into account in packet

    scheduling Downlink shared channels: Many users share the same

    spreading code

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 8

    High Speed Downlink Packet Access

    Intelligence is shifted from RNC to NodeBs NodeB: MAC-HSDPA protocol

    Fast link adaptation Fast scheduling Hybrid ARQ

    RNC: RRM and RLC protocols Ciphering In-order delivery of data Fast intra-Node B selection (select the best possible

    base station out of the NodeBs controlled by the RNC.

    It could be difficult to support fast selection on cells if they are controlled by different RNCs

  • 5

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 9

    High Speed Downlink Packet Access

    Channel structure New transport channel: HS-DSCH (High Speed

    Downlink Shared Channel) HS-DSCH is preferably allocated one user at the

    time Optionally code multiplexing could be used to share

    the DSCH among several users at the time (Requires more control signaling)

    Short time slots for HS-DSCH (TTI 2 ms = three TPC time slots) in order to achieve high granularity in packet scheduling

    UE must have DCCH to transmit link measurements for the MAC-HSDPA

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 10

    High Speed Downlink Packet Access

    Orthogonal variable spreading factor (OVSF)

    One HS-DSCH can use up to 12 codes If a user scheduled for transmission has a small

    packet, then the excess capacity (codes) can be allocated to other users using code division.

    SF=1SF=2SF=4SF=8SF=16

    1 10

    1 1

    , 1k kkk k

    H HH H

    H H

    = =

    12 code channels reserved for HS-DSCHCode channels reserved for control channels and voice

  • 6

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 11

    High Speed Downlink Packet Access

    HSDPA Channel Structure

    http://www.nokia.com/link?cid=PLAIN_TEXT_2655

    CQI Channel Quality IndicatorDPCH Dedicated Physical Control CHannelHS-SCCH High Speed Shared Control CHannelHS-PDSCH High Speed Physical Downlink Shared CHannelHS-DPCCH Uplink High Speed-Dedicated Physical Control CHannel

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 12

    High Speed Downlink Packet Access

    Higher order modulation methods require higher SIR to for the same FER

    Constant transmission power: SIR increases when mobile moves towards base station

    Use the best possible modulation scheme that gives tolerable FER

    QPSK, 1/2QPSK, 3/416QAM, 1/216QAM, 3/4

  • 7

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 13

    1xEV-DV Competitor to Qualcomm's HDR (1xTreme by Nokia and

    Motorola) Backwards compatible with IS-95, both data and voice

    users Adaptive modulation QPSK, 8PSK, and 16QAM C/I feedback rate 800 Hz Scheduling time granularity 1.25 ms Variable packet duration 1,2,4,8 slots At most two Forward Packet Data Channels (F-PDCH) both

    of which can be scheduled for the same user Peak data rate 3.09 Mbit/s Incremental redundancy (IR) or chase combining (CH)

    HARQ

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 14

    High speed data in downlink

    OVSH SF=16Walsh code length 32

    Walsh code length 32

    Spreading

    10 Mbit/s3.09 Mbit/s2.4 Mbit/sPeak data rate

    CH or IRAsynch. IRHybrid ARQ

    QPSK16QAM

    QPSK, 8PSK,16QAM

    QPSK, 8PSK,16QAM

    Modulation

    500 Hz or 1500 Hz

    800 Hz600 HzChannel feedback rate

    Fixed2ms TTI(3 slots)

    Variable frame size1.25,2.5,5,10 ms

    Variable frame size1.67 ms up to 26.7 ms

    Frame size

    HSDPA1xEV-DV1xEV-DO

  • 8

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 15

    1xEV-DV and HSPDA 1xEV-DV and HSPDA have many similarities Harmonization process

    Ultimate objective: 1xEV-DV and HSDPA differ only in bandwidth

    2007?

    Real time servicePacket data

    Dedicated channels withfast power control

    Shared channels withfast link adaptation andscheduling

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 16

    Packet scheduling Slow scheduling

    Mean value of the channel state (received CIR) known to the scheduler

    Resources are divided among the user based on their average channel quality

    Snapshot analysis (constant channel gains) applicable

    Fast scheduling Instant value of the channel state , possibly

    with delay , is known to the scheduler. Channel variations are exploited: resources are

    allocated to the user when its channel is in good state.

    i

    ( )i t

  • 9

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 17

    System modelDownlink of a single in a cell DS-CDMA system Consider cell k users, -target of user is set to No power control, transmission power is set to Instantaneous channel state (CIR) is given by

    ( )( ) ik kii i

    g t PtI

    =+

    N 0bE I ii

    kP

    ( )ikg t time variant link gain betweenbase station k and user i

    intercell interference + receiver noiseat receiver i

    i iI +k

    i

    ikg

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 18

    Channel model We assume that can be accurately measured

    and that it is wide sense stationary, ergodic, and mutually independent

    We assume that the channel fading follows the noncentral distribution (Rayleigh K=0 or Ricianfading)

    ( )i t

    { }( )i iE t t =

    ( ) ( )1

    0

    4 11 , 0ii

    KK

    i i

    K KKf e I

    + ++

    =

    2

    0 ( )KI x

    Rice factor (linear scale)zeroth-order modified Bessel function

    { }( )

    22

    2 1var ( )1

    i iKt t

    K +=

    +

  • 10

    S-72.3260 Radio Resource Management Methods 3 op TKK Comnet 19

    Rate - channel state relation Rate - channel state relation

    Logarithmic relation: Information theoretic bound (variable coding &

    modulation)

    Linear relation: Fixed modulation, variable coding

    Wideband channel

    ( )2log 1i ir W = +

    ,i i i ii

    W Wr r Wr

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