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Eun -Chan Park and Hwangnam Kim

A Dual Feedback Approach of Request-based Bandwidth Allocation for Real-time Service in Broadband Wireless Access Networks. 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 )

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Eun -Chan Park and Hwangnam Kim

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  1. A Dual Feedback Approach of Request-based Bandwidth Allocation for Real-time Service in Broadband Wireless Access Networks 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

  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 Ta 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 ΔB(t) • Takes the following two metrics into considerations • Queue size difference eq(t) • Rate mismatch er(t)

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

  7. Optimal bandwidth-request algorithm for ertPS • Demonstration of ideal case: Qref=q(t) P1 P1 P2 P3 BS Time P3 b b b SS Time P2 P1 Ta Ta q(t)=3 To To To Tref Data packet BW request packet b

  8. Optimal bandwidth-request algorithm for ertPS Excessive bandwidth allocation • Demonstration of ideal case: Qref>q(t) P1 P1 P2 P3 BS Time P3 P3 b b P1 P2 b b SS Time P2 P1 Ta Ta Ta q(t)=3 To To To Tref Data packet BW request packet b

  9. Optimal bandwidth-request algorithm for ertPS • Demonstration of ideal case: Qref<q(t) P1 Packet Delay P1 P2 BS Time P3 b P1 P2 b SS Time P2 P1 Ta q(t)=3 To To Tref Data packet BW request packet b

  10. Optimal bandwidth-request algorithm for ertPS • 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

  11. Optimal bandwidth-request algorithm for ertPS • Packet arrival rate a(t) • Service rate of transmission queue s(t) • er(t)=a(t)-s(t)>0  Queue length grows • er(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 • ΔB(t) only considers the current and previous values of the queue length error • Since ΔB(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 Ta=20ms • Average packet size = 500 bytes • Target delay Tref=200 ms

  17. Results

  18. Results

  19. Results

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

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