On the Impact of Far-Awy Interference on Evaluations of Wireless Multihop Networks

It is common practice in wireless multihop network evaluations to ignore interfering signals below a certain threshold, which typically come from far-away interferers. However, the amount of error introduced by this approximation has been mostly disregarded in the litera- ture. In this paper, we address this fundamental issue both theoretically and through extensive, packet-level simulations. We start by defining a bounded version of the well-known physical interference model, in which interference generated by transmitters located beyond a certain distance s from a receiver is ignored when computing the SINR value. We then formally prove that, under the assumption of constant transmitter density per unit area, the aggregate interference generated by far-away interferers converges to 0 if and only if s is an unbounded, increasing function of the number of nodes. This analysis also yields a lower bound on neglected interference that is approximately two orders of magnitude greater than the noise floor for typical parameter values and a surprisingly small number of nodes. These results suggest that the way interference is commonly dealt with in evaluation of wireless multihop networks could be highly inaccurate. We next validate this claim 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 density. The results of these simulations fully confirm the theoretical findings: 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. Unfortunately, our evaluations also show that considering all possible interferers has a significant detrimental effect on simulation running time, which can increase by as much as one to two orders of magnitude