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In this paper, we investigate the effect of packet aggregation on the delay performance of the IEEE 802.11 Point Coordination Function (PCF) MAC. We intend to use packet aggregation to reduce polling overhead of 802.11 PCF and improve the delay performance. We consider two different polling schemes for assembling variable-length packets for transmission: poll once and multiple poll. An analytical model is developed for evaluating the queueing delay of packets at nodes using 802.11 PCF MAC for medium access. Based on this model, we derive several closed-form expressions for computing average delay and queue length. To verify the correctness of our analytical model, we also develop a simulator for the 802.11 PCF MAC. The simulation results well match the analytical results. Several quantitative examples are given for illustrating the reduced average delays under various load conditions and limits of aggregated frames. We find that the average delay decreases with the limit of aggregated frames. We also find that, between the two polling schemes, the multiple-poll scheme achieves a smaller average delay and queue length.
Date of Publication: April 2013