On the Impact of Far Away Interference on Evaluations of Wireless Multihop Networks

It is common practice in wireless multihop network evaluations to ignore interfering signals below a certain signal strength threshold. This paper investigates the thesis that this produces highly inaccurate evaluations in many cases. We start by defining a bounded version of the physical interference model, in which interference generated by transmitters located beyond a certain distance s from a receiver is ignored. We then derive a lower bound on neglected interference and show that it is approximately two orders of magnitude greater than the noise floor for typical parameter values and a surprisingly small number of nodes. We next evaluate the effect of neglected interference through extensive simulations done with a widely-used packet-level simulator (GTNetS), considering 802.11 MAC with both CBR and TCP traffic in networks of varying size and topology. The results of these simulations show very large evaluation errors when neglecting far-away interference: errors in evaluating aggregate throughput when using the default interference model reached up to 210% with 100 nodes, and errors in individual flow throughputs were far greater.