Impacts of Packet Collisions on Link Throughput in CSMA Wireless Networks

摘要

It is known that packet collisions in wireless networks will deteriorate system performance, hence substantial efforts have been made to avoid collision in multi-user access designs. Also, there have been many studies on throughput analysis of CSMA wire-less networks. However, for a typical CSMA network in which not all nodes can sense each other, it is still not well investigated how link throughputs are affected by collisions. We note that in practical 802.11-like networks, the time is divided into mini-timeslots and pack-et collisions are in fact unavoidable. Thus, it is desirable to move forward to explore how collisions in such a network will affect sys-tem performance. Based on the collision-free ideal CSMA network (ICN) model, this paper attempts to analyze link throughputs when taking the backoff collisions into account and examine the effect of collisions on link throughputs. Specifically, we propose an Ex-tended Ideal CSMA Network (EICN) model to characterize the collision effects as well as the interactions and dependency among links in the network. Based on EICN, we could directly compute link throughputs and collision probabilities. Simulations show that the EICN model is of high accuracy. Under various network topologies and protocol pa-rameter settings, the computation error of link throughputs using EICN is kept to 4% or be-low. Interestingly, we find that unlike expect-ed, the effect of collisions on link throughputs in a modest CSMA wireless network is not significant, which enriches our understanding on practical CSMA wireless networks such as Wi-Fi.