Adaptive polling list arrangement scheme for voice transmission with PCF in wireless LANs

Potting based PCF is the optional channel access mode in the MAC sub-layer of IEEE 802.11 WLAN. The detail of the polling list arrangement is not defined in the standards, and the traditional round robin (RR) polling scheme is inefficient for packetized voice transmission. This paper proposes two adaptive polling list arrangement schemes in order to decrease the average delay of voice packets, by means of reducing the possibility of null polls. One scheme is called dynamic descending array (DDA), which resets the polling array after each beacon at the beginning of the contention free period, in a descending order according to the number of packets queued in the stations´ buffers. The other scheme combines RR and our DDA to further avoid waiting too long for some station, which is termed as hybrid DDA and RR (HDR). The improvement of DDA and HDR on delay performance of our schemes is testified in dissimilar simulation scenarios, which assumes different indoor wireless channel quality, network scale, traffic load and polling access policies etc. It is shown that the proposed DDA and HDR schemes outperform RR scheme from the delay viewpoint. What´s more, the HDR works extremely well with gated access policy when the signal-to-noise ratio of the wireless channel is low and the network traffic load is high.