The Impact of MAC Buffer Size on the Throughput Performance of IEEE 802.11

The medium access control protocol of IEEE 802.11 networks has been extensively studied to explore its throughput performance. A popular regime of study is the saturation regime where users are assumed to be saturated with information bits. The throughput achieved in this regime, called the saturation throughput, is commonly interpreted as the maximum achievable throughput for any given system. In this paper, we formalize the conditions under which saturation throughput is indeed the maximum achievable throughput. We provide specific settings which may increase the maximum aggregate throughput of the system beyond the saturation throughput. Furthermore, we observe and prove that reducing the MAC buffer size significantly increases the maximum aggregate throughput, beyond the saturation throughput, a fact that seems counter-intuitive. We formally establish that under small buffer conditions and under UDP-type traffic, a reduction in effective collisions due to the buffer size choice has a positive effect on the throughput performance. This is despite the fact that some packets are dropped because of likely buffer overflow events. In other words, by identifying the notion of saturation throughput as an inherently pessimistic notion, this paper brings to the attention the significant impact of an optimized choice of MAC buffer size on the performance of 802.11 networks. Index Terms IEEE 802.11, medium access control, statistical multiplexing, saturation throughput.