Forced Transmissions for Coping with the Effect of Blocked Stations in 802.11 Wireless Networks

In this paper, we consider the problem of blocked stations that appears in some spatial configurations of multi-hop wireless networks based on the 802.11 DCF (distributed coordination function). The problem leads to starvation of at least one station caused by the presence of neighbor stations within its carrier sensing range that do not hear each other. We propose Forced Transmissions, a simple and efficient solution to this problem. It consists of detecting that a station is blocked by others stations and forcing a transmission. This results in a collision that increases the contention windows of blocking stations and leaves some channel time to the blocked station for transmitting. The blocked station forces transmission only with some probability adjusted in function of the time spent waiting for the channel. Our simulations show that the proposed method increases the minimal throughput of the blocked stations at the expense of a slight degradation of the total throughput, which is unavoidable in any DCF based solution.