1. Eun-Chan Park and Hwangnam Kim Dept. of Information and Communication, Dongguk University ( 南韓東國大學 ) Dept. of Electrical Engineering, Korea University ( 南韓韓國大學 ) IEEE Transactions on Communications, Vol. 57, No. 3, March, 2009 A Dual Feedback Approach of Request-based Bandwidth Allocation for Real-time Service in Broadband Wireless Access Networks

2. Agenda Introduction Optimal bandwidth-request algorithm for ertPS Analysis of the proposed algorithm Conclusion

3. Introduction Five types of bandwidth allocation mechanism Unsolicited Grant Service (UGS) Real-time polling service (rtPS) Non-real-time polling service (nrtPS) Best effort (BE) Extened real-time polling service (ertPS) Bandwidth request allocation mechanism No specific mechanism has been standardized Impacts the bandwidth utilization and delay constraints

4. Optimal bandwidth-request algorithm for ertPS Assumptions Uplink traffic consideration BS employs a priority-based scheduler to serve real-time services If the real-time services are admitted, the services are served with the guaranteed bandwidth Bandwidth-allocation interval T a is equal to packetization interval No queuing delay at BS

5. Optimal bandwidth-request algorithm for ertPS Dual feedback approach of bandwidth request mechanism Computes total additional bandwidth-request Δ B(t) Takes the following two metrics into considerations Queue size difference e q (t) Rate mismatch e r (t)

6. Optimal bandwidth-request algorithm for ertPS Target delay (sec.), T ref Tolerable MAC-to-MAC delay for real-time applications Delay incurred in application layer is not included Target transmission queue length in SS (bytes), Q ref Average packet size Additional delay ( processing delay at MAC, transmission delay over wireless link) Bandwidth allocation interval

7. Optimal bandwidth-request algorithm for ertPS Demonstration of ideal case: Q ref =q(t) Time BS Time SS T ref b bb P1P1 P2P2 P1P1 P2P2 P3P3 P3P3 TaTa TaTa ToTo P1P1 Data packet b BW request packet q(t)=3 ToTo ToTo

8. Optimal bandwidth-request algorithm for ertPS Demonstration of ideal case: Q ref >q(t) Time BS Time SS T ref b bb P1P1 P2P2 P1P1 P2P2 P3P3 P3P3 ToTo P1P1 Data packet b BW request packet q(t)=3 ToTo ToTo b TaTa TaTa TaTa P3P3 P2P2 P1P1 Excessive bandwidth allocation

9. Optimal bandwidth-request algorithm for ertPS Demonstration of ideal case: Q ref <q(t) Time BS Time SS T ref b b P1P1 P2P2 P1P1 P2P2 P3P3 ToTo P1P1 Data packet b BW request packet q(t)=3 ToTo TaTa P2P2 P1P1 Packet Delay

10. If, the bandwidth-allocation interval should be decreased to satisfy the delay requirement If, the bandwidth-allocation interval should be increased to reduce the excessive bandwidth allocation Optimal bandwidth-request algorithm for ertPS

11. Packet arrival rate a(t) Service rate of transmission queue s(t) e r (t)=a(t)-s(t)>0  Queue length grows e r (t)=a(t)-s(t)<0  Bandwidth wastage

12. Optimal bandwidth-request algorithm for ertPS Dual feedback approach of bandwidth request mechanism A feedback for the queue size difference A feedback for the rate mistach Queue differential for Previous t

13. Optimal bandwidth-request algorithm for ertPS Implementation issues First-order Eular approximation

14. Optimal bandwidth-request algorithm for ertPS Δ B(t) only considers the current and previous values of the queue length error Since Δ B(t) is the increment or decrement of bandwidth- request at the t-th allocation interval, the total bandwidth- request during this interval, B(t), becomes

15. Numerical analysis Evaluate the effect of target delay in the dual feedback architecture The difference between instantaneous queue length and the target value The response of service rate to time-varying arrival rate The cumulative distribution of MAC-to-MAC delay

16. Numerical analysis Parameters VBR traffic: rate = 500/20=25 (bits/ms) Bandwidth allocation interval T a =20ms Average packet size = 500 bytes Target delay T ref =200 ms

17. Results

20. Conclusions Optimal request-based bandwidth allocation algorithm for VBR in a centralized scheduling framework Concept of target delay Dual feedback architecture