A optimal CF-poll piggyback scheme in IEEE 802.11e HCCA

The HCCA, which is defined in IEEE 802.11e for delay sensitive service traffics, provides the parameterized QoS using the polling access method and the negotiation of TSPEC. It uses many different types of QoS data frames and their associated usage rules to increase the channel efficiency. A CF-poll is used to grant the channel to a QSTA and can be piggybacked in QoS data frame to increase the channel efficiency. However, the CF-poll piggyback scheme may decrease the channel efficiency when any QSTA associated in QBSS use the low physical transmission rate. We define this phenomenon as the CF-poll piggyback problem. To verify the CF-poll piggyback problem, we perform the simulation for the HCCA according to the minimum physical transmission rate and the normalized traffic load. Using the simulation results, we observed that the delay of QoS data frame including the CF-poll increased about 4.75 msec in the worst case. We also find that the cross point of the efficiency of the CF-poll piggyback with respect to the delay is between 24 and 36 Mbps and we propose the optimal CF-poll piggyback algorithm based on the simulation results