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An Adaptive Polling Algorithm for PCF Mode of 802.11 Wireless LANs

An Adaptive Polling Algorithm for PCF Mode of 802.11 Wireless LANs. Xuanming Dong Pravin Varaiya Anuj Puri. Speaker：Mark Yang. Outline. Abstract Introduction Adaptive Polling Algorithm Simulation Conclusion Reference. Abstract.

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An Adaptive Polling Algorithm for PCF Mode of 802.11 Wireless LANs

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  1. An Adaptive Polling Algorithm for PCF Mode of 802.11 Wireless LANs Xuanming Dong Pravin Varaiya Anuj Puri Speaker：Mark Yang 1

  2. Outline • Abstract • Introduction • Adaptive Polling Algorithm • Simulation • Conclusion • Reference 2

  3. Abstract • Proposes an adaptive polling algorithm to improve the wireless medium utilization. • The priority for each mobile station will be dynamically updated using the Additive Increase/Multiplicative Decrease algorithm. • The performance of wireless LANs are improved in terms of the successful poll rate and the aggregate throughput. 3

  4. Introduction – PCF mode • DCF (Distributed Coordination Function) – Contention Mode PCF (Point Coordination Function) – Contention Free Mode • PCF most suitable for time-bounded applications. • Polling frame • Stations are allowed to send data only when they receive the polling frames from the AP. • If the AP enables the PCF mode, the stations still can decide whether they want to be polled or not. • Round Robin polling algorithm • Traffic is not evenly distributed over all mobile stations → Inefficient scheduling. 4

  5. Introduction – Polling list • Only the stations in the polling list maintained by the point coordinator are eligible to receive polls. • Station can ask to be appended to the polling list by sending the Association Request frame. • If a station is in the polling list initially but it doesn’t want to be polled late, it can send Reassociation Request frame to the point coordinator. 5

  6. Introduction – Superframe 6

  7. Adaptive Polling Algorithm– Basic Notations • Definition: • Successful poll • Missed poll • Good polling algorithms: • Keep the medium busy for payload data instead of management and control frames • Keep the medium shared by all stations fairly. • Adaptive polling algorithm: • based on recent poll feedbacks from wireless stations to dynamically update priority • Improve the overall throughput and successful poll rate. 7

  8. Highest Priority Lowest Priority Adaptive Polling Algorithm– Dynamic priority Assignment (1) • A successful poll means more potential traffic from a station. • Priority of a station is related to the amount of traffic from it. • Additive Increase / Multiplicative Decrease (AIMD) 8

  9. Adaptive Polling Algorithm– Dynamic priority Assignment (2) Mac-802_11.cc 9

  10. Adaptive Polling Algorithm– Dynamic priority Assignment (3) • If a station has bursty traffic, it takes at most log2m consecutive polls for the station to reach the highest priority . Log28 = 3 10

  11. Adaptive Polling Algorithm– Poll scheduling Algorithm (1) • All stations with the same priority are placed in the same list. 11

  12. Adaptive Polling Algorithm– Poll scheduling Algorithm (2) • In round i , stations with priorities from i to 1will be polled. • Priority = 1 ….. i ….. m poll slot = m …. m-i+1 ….. 1 12

  13. 1 1 1 1 1 2 2 2 2 3 3 3 4 4 5 Adaptive Polling Algorithm– Poll scheduling Algorithm (3) 13

  14. Adaptive Polling Algorithm– Poll scheduling Algorithm (4) Mac-802_11.cc 14

  15. 1 1 1 1 1 1 1 2 2 2 2 3 3 3 4 4 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 5 Adaptive Polling Algorithm– Debug & Verify 15

  16. Simulation – Setup (1) • Software: • Linux 6.2 + NS 2.1b8a + PCF support patch • Geography : • AP connected to a wired node via a 10 mbps Ethernet link. • The wireless LAN consists of the AP and 10 wireless stations. • All stations and the AP are close enough to receive signals from each other. In addition, all stations don’t move around. • Traffic : • 10CBR flows from 10 different stations to the wired node through the AP. • These CBR flows send packets at rates of 200 packets per second with packet size 1000 bytes. • These flows are started one by one with a 2 second interval. They last 20 seconds and terminate. 16

  17. Simulation – Setup (2) TCL 17

  18. Simulation – Trace (1) namtrace newtrace 18

  19. Round robin Adaptive Node ID Time Traffic Simulation – Trace (2) 19

  20. Simulation – Performance (1) X. Dong & P. Varaiya & A. Puri Mark Yang 20

  21. Simulation – Performance (2) X. Dong & P. Varaiya & A. Puri Mark Yang 21

  22. Conclusion • This paper present an efficient polling algorithm based on dynamic priority assigned by the point coordinator. • The priority of each station is updated regularly based on the recent poll feedback from the station. • Proposed polling algorithm improves the performance of wireless LANs in terms of the successful poll rate and the aggregate throughput of AP. • Future work focuses on the theoretical analysis of the new polling algorithm. It will also be interesting to study how the DCF mode affects PCF performance. 22

  23. References 23

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