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Packet Scheduling for Fairness and Performance Improvement in OFDMA Wireless Networks Nararat RUANGCHAIJATUPON and Yusheng JI The Graduate University for Advanced Studies National Institute of Informatics (NII), Japan The 26 th Asia-Pacific Advanced Network Meeting August 4 – 8, 2008, Queenstown, New Zealand

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August 4-8, 200826th APAN Meeting2 Presentation Outline OFDMA Scheduler and Resources Utility Matrix & Proportional Fairness Modified Simple Moving Average Utility Matrix-based Scheduling Simulation & Results Conclusion

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August 4-8, 200826th APAN Meeting3 OFDMA Orthogonal Frequency Division Multiple Access Reliability against fading channel Subchannelization (IEEE 802.16) Distributed subcarrier permutation Adjacent subcarrier permutation Adaptive Modulation Coding (AMC) Connectivity

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August 4-8, 200826th APAN Meeting4 System Model - Centralized scheduler on BS - Uniform power allocation to each subchannel

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August 4-8, 200826th APAN Meeting5 Resources

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August 4-8, 200826th APAN Meeting6 Utility Matrix & Proportional Fairness R m,n (t) – Achievable data rate of user n via subchannel m T n – Average data rate

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August 4-8, 200826th APAN Meeting7 Modified Simple Moving Average T n – Average data rate in PF utility function U n (t) – keep sum of total instantaneous rates obtained by user n during the non- empty-queue period Ω n (t) – the set of subchannels in which user n is scheduled at frame t V n (t) – records the number of frame while user n has data in the queue W n (t) – to retain the average data rate when user n s queue is empty

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August 4-8, 200826th APAN Meeting8 Utility Matrix-based Scheduling Find the maximum PF element Allocate required time slots Update average rate (and PF element) Delete (column/row) from the utility matrix

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August 4-8, 200826th APAN Meeting9 Example A system of 3 MSs and 3 subchannels MS1: Queue size 60 bits, average data rate 5 bps MS2: Queue size 100 bits, average data rate 6 bps MS3: Queue size 100 bits, average data rate 3 bps Each subchannel has 8 time slots Each time slot is 1 second A packet has 1 bit

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August 4-8, 200826th APAN Meeting10 Example (cont.) A utility matrix Subchannel 1 Subchannel 2 Subchannel 3 MS 1 MS 2MS 3

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August 4-8, 200826th APAN Meeting11 Example (cont.) MS3 MS1 MS2 60 bits 100 bits Avg rate: 5 bps 6 bps 3 bps6.5 bps 20 bits 0 bits 7.5 bps

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August 4-8, 200826th APAN Meeting12 Example (cont.) MS3 MS1 MS2 60 bits 100 bits Avg rate: 5 bps 6 bps 3 bps6.5 bps 20 bits 0 bits 7.5 bps 28 bits 7.5 bps

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August 4-8, 200826th APAN Meeting13 Simulation Cell diameter1 km Number of MSs48 Number of subcarriers/subchannel48 Number of subchannels4 Number of DL slots/subchannel80 Frame duration0.005 sec User initial locationUniformly distributed User speedUniformly distributed [3,100] km/hr Simulation time20,000 frames

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August 4-8, 200826th APAN Meeting14 System Throughput

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August 4-8, 200826th APAN Meeting15 System Queue Size

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August 4-8, 200826th APAN Meeting16 Maximum Difference Maximum difference of throughput per user Maximum difference of queue size per user

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August 4-8, 200826th APAN Meeting17 Throughput Fairness Index

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August 4-8, 200826th APAN Meeting18 Computational Complexity Scheduling schemeComplexity MaxC/IO(M 2 N) OFPF-MSMAO(M 2 N 2 ) OFPFO(M 2 N 2 ) PFO(M 2 N 3 ) Max-minO(M 2 N 2 )

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August 4-8, 200826th APAN Meeting19 Conclusion Centralized scheduler for OFDMA-TDD system To maximize system throughput and to provide fairness with a consideration of queue status Utility function bases on proportional fairness with modified simple moving averaging Utility matrix-based scheduling exploits multi- user multi-channel diversity with a consideration of computational complexity Simulation results show improvement in system throughput, queue length (queuing delay), and fairness (throughput difference, queue length difference

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Thank you very much Questions and Answers

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