Effect of Payload Length Variation and Retransmissions on Multimedia in WLANs

Multimedia transmission over wireless local area networks (WLANs) is a challenging task due to the varying nature of the wireless channel as well as the inherent difference between multimedia traffic and data traffic. In the MAC layer, a single bit error in the packet can lead to the entire packet being discarded. This results in a higher packet error rate for higher payload sizes. Retransmission due to packet errors causes the contention window to double, and this leads to a decrease in throughput if the wireless channel does not improve for the retransmitted packets. Hence, throughput is a function of packet payload length as well as the maximum number of allowable retransmissions. In this paper, we investigate the effect of payload length adaptation and retransmissions on the throughput and capacity of multimedia users. Numerical results and simulations reveal that careful payload adaptation significantly improves the throughput performance at low signal to noise ratios (SNRs). It is also observed that excessive retransmissions can reduce the effective throughput, thereby reducing the capacity of multimedia users in the presence of data users. Since multimedia traffic is more latency constrained and less error constrained, this suggests that by carefully selecting the payload length and maximum number of allowable retransmissions based on the channel conditions, a higher number of multimedia users can be supported.