Throughput Analysis of CSMA Wireless Networks with Finite Offered-load

摘要

This paper proposes an approximate method, equivalent access intensity (EAI),for the throughput analysis of CSMA wireless networks in which links havefinite offered-load and their MAC-layer transmit buffers may be empty from timeto time. Different from prior works that mainly considered the saturatednetwork, we take into account in our analysis the impacts of empty transmitbuffers on the interactions and dependencies among links in the network that ismore common in practice. It is known that the empty transmit buffer incursextra waiting time for a link to compete for the channel airtime usage, sincewhen it has no packet waiting for transmission, the link will not performchannel competition. The basic idea behind EAI is that this extra waiting timecan be mapped to an equivalent "longer" backoff countdown time for theunsaturated link, yielding a lower link access intensity that is defined as themean packet transmission time divided by the mean backoff countdown time. Thatis, we can compute the "equivalent access intensity" of an unsaturated link toincorporate the effects of the empty transmit buffer on its behavior of channelcompetition. Then, prior saturated ideal CSMA network (ICN) model can beadopted for link throughput computation. Specifically, we propose an iterativealgorithm, "Compute-and-Compare", to identify which links are unsaturated undercurrent offered-load and protocol settings, compute their "equivalent accessintensities" and calculate link throughputs. Simulation shows that ouralgorithm has high accuracy under various offered-load and protocol settings.We believe the ability to identify unsaturated links and compute linksthroughputs as established in this paper will serve an important first steptoward the design and optimization of general CSMA wireless networks withoffered-load control.