Uplink Scheduler and Admission Control for the IEEE 802.16 standard

1. Uplink Scheduler and Admission Control for the IEEE 802.16 standard Juliana Freitag Borin and Nelson L. S. da Fonseca Institute of Computing, University of Campinas IEEE GLOBECOM 2009 proceedings 報告者：李宗穎

2. Outline • Introduction and Related Work • Admission Control Algorithm • Scheduling Mechanism • Simulation and Numerical Result • Conclusion

3. Introduction • In 802.16 wireless network QoS guarantee, the major challenges are scheduling in the uplink direction at the BS • downlink direction and at the SSs are less complex since information about the queues status is locally available

4. Standard-compliant uplink scheduler • admission control mechanism should work jointly with the uplink scheduler • BS should distribute the uplink bandwidth such that QoS requirements of each connection are satisfied • the BS should allocate bandwidth not only for data transmission but also for bandwidth requests transmission • the uplink scheduler should support all QoS parameters defined by the standard

5. QoS Parameter • the admission of new connections • minimum reserved traffic rate • the scheduler allocates grants with size • maximum traffic burst • real time connections • maximum latency • UGS and ertPS • unsolicited grant interval • tolerated jitter • rtPS and nrtPS • unsolicited polling interval

6. Related Work (1/3) • Many solutions proposed for the IEEE 802.16 uplink scheduler combine classic scheduling policies developed for wired networks, such as Strict Priority, Weighted Fair Queuing (WFQ), and Earliest Deadline First (EDF) [5] D. Tarchi, R. Fantacci, and M. Bardazzi, Quality or Service management in IEEE 802.16 wireless metropolitan area networks. In Proceedings of the IEEE International Conference on Communications, pg. 1789-1794. [8] J. Chen, W. Jiao, and H. Wang, A Service Flow Management Strategy for IEEE 802.16 Broadband Wireless Access Systems in TDD Mode. In Proceedings of the IEEE ICC, pp. 3422-3426, 2005. [12] K. Wongthavarawat and A. Ganz, IEEE 802.16 based last mile broadband wireless military networks with Quality of Service support. In Proceedings of the IEEE MILCOM’03, pp. 779-784, 2003.

7. Related Work (2/3) • The admission control scheme proposed in this paper as well as other solutions available in the literature [7], [8] use only the minimum rate requirement in the decision process [7] H. Wang, B. He, and D. P. Agrawal, Above packet layer level admission control and bandwidth allocation for IEEE 802.16 wireless MAN. Simulation Modeling Practice and Theory, vol. 15, no. 14, pg. 266-382. [8] J. Chen, W. Jiao, and H. Wang, A Service Flow Management Strategy for IEEE 802.16 Broadband Wireless Access Systems in TDD Mode. In Proceedings of the IEEE ICC, pp. 3422-3426, 2005.

8. Related Work (3/3) • Chandra and Sahoo [16] considered the overhead of different type of services, however, the ertPS service is not included in the mechanism. • Additionally, the authors do not detail the algorithm used by the search routine, which is an important part of the proposed mechanism [16] S. Chandra, and A. Sahoo, An efficient call admission control for IEEE 802.16 networks. In Proceedings of the 15th IEEE Workshop on Local & Metropolitan Area Networks, pg. 188-193.

9. Admission Control Algorithm • TRiservice : the traffic rate that should be guaranteed to the new connection i of service type service (includes an estimate of the overhead) • Creserved: the capacity reserved to the connections already admitted in the system • C : the capacity available for the uplink scheduler

10. UGS and ertPS connections • The grant size is fixed, based on the maximum sustained traffic rate (minimum reserved traffic rate) of the service tolerated jitter unsolicited grant interval

11. rtPS and nrtPS connections • Besides the minimum reserved traffic rate, rtPS and nrtPS connections also need periodic grants to request bandwidth upSlots : the number of slots used by the unicast polling Upii: the value provided by the unsolicited polling interval parameter

12. Scheduling Mechanism (1/2) • The proposed uplink scheduler uses three queues : • Low priority queues • BE bandwidth requests • Intermediate priority queues • bandwidth requests sent by both rtPS and nrtPS connections • These requests can migrate to the high priority queue • High priority queues • periodic grants and unicast request opportunities

13. Scheduling Mechanism (2/2) • for UGS and ertPS, the scheduler generates periodic grants and inserts them into the high priority queue • for rtPS and nrtPS, the BS assigns a deadline for each bandwidth request in the intermediate queue • move to high priority queue • deadlines expiring two frames (rtPS) • not received the minimum reserved traffic rate in a window with duration T (nrtPS, rtPS)

14. Dual leaky bucket • the bandwidth allocated to a single connection is less than or equal to the maximum traffic burstrequirement • the scheduler does not allocate bandwidth for a connection if it results in violation of the maximum sustained traffic rate

15. Scheduling Algorithm

16. Check Deadline procedure • the scheduler tries to migrate the rtPS requests from the intermediate queue to the high priority queue • there is available bandwidth • the deadline of a rtPS request expires during the frame following the next one • the corresponding connection has not received the minimum reserved traffic rate

17. MigrateBWRequestprocedure • checks whether or not the amount of bandwidth solicited by the migrating request (BR[i]) is available in the uplink subframe • Avoid violation of the maximum traffic burst value, a new request j is created with BR[j] equals to BR[i] − grantSize and it is inserted at the end of the intermediate queue traffic maximum traffic burst BR[j] intermediate queue high priority queue

18. CheckMinimumBandwidthprocedure • Calculates and sort a priority value for each request in the intermediate queue • the scheduler tries to migrate requests to the high priority queue using the MigrateBWRequest procedure

19. DistributeFreeResourcesprocedure • distributes the available bandwidth among the BE requests by migrating some of them from the low priority queue to the high priority queue

20. Simulation Experiments (1/2) • The simulated network consists of a BS, with the SSs uniformly distributed around it (using ns2 with WiMAX module)

21. Simulation Experiments (2/2) Lifetimes : exponentially distributed mean 600s (rtPS), 300s (UGS, ertPS, and nrtPS) Arrival rates : exponential distribution mean varying 2s to 60s for each type BE connections : equal to 20 in all the simulated situations maximum latency requirement : 100ms (rtPS) minimum reserved traffic rate : 200Kbps (nrtPS), X-Kbps (each rtPS) maximum sustained traffic rate requirement : 300Knps (nrtPS), Y-Kbps (each rtPS) unsolicited grant interval : 20ms (UGS, ertPS) unsolicited polling interval : 20ms (rtPS) , 1s (nrtPS)

22. Blocking probability UGS : 26 Kbps ertPS : 80Kbps nrtPS : 200Kbps rtPS : 200 ~ 900Kbps

23. Average latency of UGS, ertPS and rtPS services rtPS ertPS UGS

24. average throughput of rtPS connections with minimum rate requirement 500 Kbps

25. Average throughput of nrtPS connections MAC header overhead

26. Conclusion • The proposed scheduler provides maximum latency and minimum rate guarantees without violating the maximum sustained traffic rate and the maximum traffic burst values