CAC and Scheduling Schemes for Real-time Video Applications in IEEE 802.16 Networks

1. CAC and Scheduling Schemes for Real-time Video Applications in IEEE 802.16 Networks Ou Yang WCNG @ UR 10/11/2006

2. Outline • Overview of IEEE 802.16 Networks • Motivation • Proposed CAC Scheme • Proposed Scheduling Scheme • Simulation Results • Conclusion

3. Overview

4. Overview of IEEE 802.16 Networks

5. Brief Introduction to 802.16 • Fixed Wireless Broadband Access Networks - Line of sight • Connection Oriented - Block incoming calls when QoS fails • Medium Access Mechanism - TDMA • Differentiated Quality of Service - Support real-time video application

6. Motivation

7. Motivation • Real-time video applications demands high bandwidth efficiency and guaranteed QoS • IEEE 802.16 standard defines a frame of MAC but leaves CAC and scheduler open to discuss • Varying bit-rate and stringent delay bound make the design of CAC and scheduler difficult

8. State of the Art • CAC- Determines throughput- Influences delay performance • Scheduler- Determines fairness- Influences delay performance • No reference focuses on throughput, delay performance and fairness simultaneously.

9. State of the Art -CAC • Make decision as soon as incoming flows arrive • Conservative bandwidth reservation. Reserve bandwidth according to the maximum I frame • These cause low throughput

10. State of the Art - Scheduling • Earliest Deadline First (EDF)- Maximizing throughput under delay constraint- Unfair- Commonly used • FIFO + Weighted Fair Queuing (WFQ)- Unfair under delay constraint- Low throughput under delay constraint- Seldom used • None achieve good delay performance and fairness simultaneously

11. Solution – Utilize Traffic Traits • Periodicity: - I B P frames constitute a GOP - Control the bandwidth occupancy • Regularity: - I frame bigger than non-I frame - I frame less than non-I frame- Consider I and non-I frame separately in bandwidth reservation

12. Proposed CAC Scheme

13. Pending Period • Decision is made in the pending period • Less traffic burst causes delay violation

14. Consider I and non-I separately • Detect delay violation until find out a proper access time or the pending period expires • Step 1: Accessed I vs. Incoming I - Utilize periodicity to predict the arrival of I frames • Step 2: Accessed non-I vs. Incoming I- Estimate the average bit-rate of non-I frames- Reserves bandwidth based on estimation • Effect: Adjust estimation to balance delay performance and throughput

15. Proposed Scheduling Scheme

16. EDF - > Earliest LST First • LST (Latest Starting Time)- latest time to start transmission in order to catch up with deadline • Effect - Being scheduled = Meet delay constraint- The same deadline, larger frame will be scheduled first in result of earlier LST

17. Loose Constraint on ELSTF • Enlarge the Pool of Prospective Packets • Consider fairness

18. Effect • ELSTF improve the delay performance • Loose constraint improves fair service • L is adjustable, compromising delay and fairness

19. Simulation Results

20. Analysis • Throughput, delay performance and fairness are involved in two trade-offs, handled by Re and L • Re↑ Throughput↓ Delay performance↑ L ↑ Fairness ↑ Delay performance ↓

21. Conclusion

22. The proposed CAC introduces a pending period and utilizes traffic traits to compromise throughput and delay performance • The proposed scheduler applies loose constraint on ELSTF to balance fairness and delay performance • Simulation results show the proposed schemes significantly improve the throughput with acceptable delay performance and fairness.

23. Thank You