Offered load control in IEEE 802.11 multi-hop ad-hoc networks

In a multi-hop ad-hoc network, stations may pump more traffic into it than can be supported, resulting in high packet-loss rate, rerouting instability and unfairness problems. The paper shows that controlling the offered load at the sources can eliminate these problems. In addition, we provide an analysis to estimate the optimal offered load that maximizes the throughput of a multi-hop traffic flow. We use this result to devise schemes that can achieve fairness when there are multiple flows from different sources to different destinations. We believe this is the first paper in the literature to provide a quantitative analysis (as opposed to simulation) for the impact of hidden nodes, exposed nodes, and signal capture on sustainable throughput. The analysis is based on the observation that a large-scale 802.11 network with hidden nodes is a network in which the carrier-sensing capability breaks down partially. Its performance is therefore somewhere between a carrier-sensing network and an ALOHA network. Indeed, our analytical closed-form solution has the appearance of the throughput equation of the ALOHA network. Our approach allows one to identify whether the performance of an 802.11 network is hidden-node limited or spatial-reuse limited.