Packet Scheduling for Fairness and Performance Improvement in OFDMA Wireless Networks

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

2. Presentation Outline • OFDMA • Scheduler and Resources • Utility Matrix & Proportional Fairness • Modified Simple Moving Average • Utility Matrix-based Scheduling • Simulation & Results • Conclusion 26th APAN Meeting

3. 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 26th APAN Meeting

4. System Model - Centralized scheduler on BS - Uniform power allocation to each subchannel 26th APAN Meeting

5. Resources 26th APAN Meeting

6. Utility Matrix & Proportional Fairness Rm,n(t)– Achievable data rate of user n via subchannel m Tn– Average data rate 26th APAN Meeting

7. Modified Simple Moving Average Tn– Average data rate in PF utility function Un(t)– keep sum of total instantaneous rates obtained by user n during the non-empty-queue period Ωn(t)– the set of subchannels in which user n is scheduled at frame t Vn(t)– records the number of frame while user n has data in the queue Wn(t)– to retain the average data rate when user n’s queue is empty 26th APAN Meeting

8. 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 26th APAN Meeting

9. 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 26th APAN Meeting

10. Example (cont.) • A utility matrix MS2 MS3 MS1 Subchannel 1 Subchannel 2 Subchannel 3 26th APAN Meeting

11. Example (cont.) MS1 0 bits 60 bits Avg rate: 5 bps 7.5 bps MS2 100 bits Avg rate: 6 bps MS3 100 bits 20 bits Avg rate: 3 bps 6.5 bps 26th APAN Meeting

12. Example (cont.) MS1 0 bits 60 bits Avg rate: 5 bps 7.5 bps MS2 28 bits 100 bits 7.5 bps Avg rate: 6 bps MS3 100 bits 20 bits Avg rate: 3 bps 6.5 bps 26th APAN Meeting

13. Simulation 26th APAN Meeting

14. System Throughput 26th APAN Meeting

15. System Queue Size 26th APAN Meeting

16. Maximum Difference • Maximum difference ofthroughput per user • Maximum difference ofqueue size per user 26th APAN Meeting

17. Throughput Fairness Index 26th APAN Meeting

18. Computational Complexity 26th APAN Meeting

19. 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 26th APAN Meeting

20. Thank you very much Questions and Answers