Closed Loop Control Scheduling in Multihop Cellular Networks

Transcription

1 Closed Loop Control Scheduling in Multihop Cellular Networks VDE/ITG Workshop Contribution Dr.-Ing. Rainer Schoenen ComNets, RWTH Aachen.0.009

2 Outline Packet vs. resource scheduling: Packet scheduling: QoS, Priorities etc. Resource scheduling Fading channel (frequency & time varying) Channel State Information (CSI,CQI) OFDMA scheduling under fading conditions Dynamic Subcarrier Assignment (DSA) Adaptive Modulation&Coding (AMC) Adaptive Power Control (APC) Closed Loop Control Resource Scheduling The schedulers in OpenWNS

3 Motivation Packet scheduling vs. resource scheduling: - Packet scheduling chooses packets/bits from queue, handles QoS - Resource scheduling allocates OFDMA subchannel, modulation and coding (PhyMode), transmit power packet scheduling 3

4 Packet Scheduling - Scheduler Classes 4

5 Scheduler Performance e-3 FCFS Delay: Pr { d>t } e-3 EDF e-4 ~ a ē bt t e-4 e-5 00 e-5 Round Robin ~ a ē b(t+x) 00 Weighted Round Robin t 0.0 e e-3 e-4 e-5 higher rate t e-4 e higher rate t 5

6 QoS with priorisation %0 Separation of QoS classes High channel utilisation due to unlimited best effort traffic and flow control 00 % typical load on a controlled channel: Throughput load Last ABR VBR CBR RBV RBA RBC 0 0 W50. W50. W RBV RBA RBC 0 0 W000. W000. W average packet delay [s] with CDMA time %00 %04 Total offered load %05 6

7 Advanced Wireless Scheduling Why is the scheduler so complicated? Components of the scheduler: CQI : Channel Quality Indication DSA : Dynamic Subcarrier Assignment AMC : Adaptive Modulation & Coding APC : Adaptive Power Control Multi-Antenna: MIMO/Beamforming Resource Partitioning QoS : Priorities and Substrategies Buffer/Queue management resource scheduling packet scheduling 7

8 FDD Multihop Frame Scheduling for LTE Advanced DL UL f Sync Sync RACH BCH Full duplex half duplex B S DL UL f Sync Sync RACH BCH time DL f Sync BCH Switch Rx + Tx 0ms RN UL Sync RACH DL UL f Sync Sync RACH BCH Full duplex half duplex 8

9 Half-Duplex FDD Frame Scheduling HalfDuplex Group frequency DL UL framenumber / time BS frequency DL UL Map framenumber / time RN Data frequency DL UL BS BS BS BS BS BS BS BS framenumber / time Remote HalfDuplex Group frequency DL UL framenumber / time

10 Multihop Resource Partitioning (between BS and RN) 4 3 R6 R7 5 BS hop RN hop R8 UL frequency DL TaskPhase BS BS RN 67% BS RN 67% BS BS... BS RN BS RN BS BS BS RN BS RN BS BS frame time 0

11 Half-duplex multihop (uplink) throughput Using simple stateless scheduler Using stateful scheduler: ProportionalFair Using proper Resource Partitioning Throughput per station [bit/s] (* 0 7 ) R6 R7 R8 Throughput per station [bit/s] (* 0 7 ) R7 R6 R8 Offered total traffic [Mbit/s] Offered total traffic [Mbit/s]

12 Fading: Variable in Frequency and Time

13 Dynamic Subcarrier Assignment DSA strategies: LinearFFirst, BestChannel, BestCapacity. CQI CQI LinearFFirst BestChannel 3

14 Adaptive Modulation & Coding AMC: PhyMode choice depends on: SINR 4

15 Control loop representation of scheduler Reference: Schoenen, R. et al, Resource Allocation and Scheduling in FDD Multihop Cellular Systems, Proceedings of the International Workshop on Multiple Access Communications (MACOM) at ICC 009 desired RxSINR (0dB) + - maxpower Adaptive Power Control RxSINR with nominal TxPower Adaptive Modulation and Coding PhyMode(f,t), TxPower(f,t) RxPower Physical channel (Path loss + fading) Interference + Noise + measurement noise SINR(f,t) + SINR Estimation with nominal txpower BS channel quality measurement Dynamic Subchannel Assignment special procedures to get downlink channel quality at BS Interpolation filtering L send filtered info back to BS I Prediction of path loss Prediction of interference (Kalman Filter) Raw PathLoss Interference normalization Averaging the filtered info z - 5

16 Performance of adaptive resource scheduling Dynamic Subcarrier Assignment DSA Strategies Evaluation: (768m) pathloss on downlink Resource usage: old method (LinearFFirst) on downlink Resource usage: new method (BestChannel) on downlink 6

17 Performance of adaptive resource scheduling Adaptive Modulation & Coding AMC Strategies Evaluation: (600m) QPSK-/3 QPSK-/ QPSK-/3 QAM6-/ QAM6-/3 QAM6-5/6 QAM64-/3 PhyMode usage: method (WithoutCQI) on downlink SINR: method (WithoutCQI) on downlink QPSK-/3 QPSK-/ QPSK-/3 QAM6-/ QAM6-/3 QAM6-5/6 QAM64-/3 QAM64-5/6 PhyMode usage: method (WithCQI) on downlink SINR: method (WithCQI) on downlink 7

18 Performance of adaptive resource scheduling Adaptive Power Control APC Strategies Evaluation: (768m) TxPower: method (UseNominalTxPower) on downlink SINR: method (UseNominalTxPower) on downlink TxPower: method (FCFSMaxPhyMode) on downlink SINR: method (FCFSMaxPhyMode) on downlink 8

19 Conclusions Packet and resource scheduling can and must be separated QoS distinction by priorities is sufficient in the early phase Sub-strategies are important for further QoS differentiation and fairness QoS aware scheduling and optimum utilization go hand in hand Resource Scheduling and Resource Partitioning happen on different timescales The wireless link is a loop (DL+UL). Delay=RTT (round trip time) DSA and AMC are straightforward (open loop), but APC requires a closed control loop system view CQI, DSA, AMC and APC optimally utilize the channel capacity All known algorithms are building blocks in the control block diagram 9

20 Thank you for your attention! Dr.-Ing. Rainer Schoenen Any questions? 0