Optimal Physical Carrier Sense for Maximizing Network Capacity in Multi-hop Wireless Networks

We investigate the problem of maximizing network capacity sustained by IEEE 802.11 DCF in multi-hop wireless networks. By explicitly incorporating two key system parameters – carrier sense threshold and transmit power – into our analysis, we derive an analytical relation between network capacity and the level of spatial reuse characterized by physical carrier sense. In homogeneous networks where each system parameter is set to the same value for all the nodes, network capacity depends only on the ratio of the transmit power to the carrier sense threshold. In this case, we find an approximate optimal carrier sense range which maximizes network capacity at a given node density. The obtained optimal carrier sense range is smaller than that for covering the entire interference range of the receiver, which is in sharp contrast to what has been considered to be optimal in previous studies. Only when the node density goes to infinity, the optimal carrier sense range converges to that for exactly covering the entire interference range, thereby eliminating all the hidden nodes. For heterogeneous networks where each system parameter is independently set by each node, we show that the problem of maximizing the network capacity corresponds to a noncooperative game, which is completely different from that in a homogeneous network. Any distributed algorithm in which a node only tunes its own parameters without coordinating with other nodes will fail to maximize the network capacity. In order to properly design a distributed algorithm for tuning system parameters, each node not only considers its own throughput as profit, but also needs to introduce a penalty as price.