On large throughputs in high density wireless local area networks

Abstract

While the density of access points in enterprise settings has increased, the sharing of the spatial resource amongst links in 802:11 wireless local area networks remains ine cient. Conservative mechanisms based on a static carrier sense range (CSR) are used and are designed to avoid occurrence of interfering transmissions. Even when the CSR is adapted to allow interfering transmissions, it is with the goal of increasing spatial reuse, which may not translate to larger network throughput. We formulate the network throughput optimization problem, which is to decide which links in a network must share in space (transmit data simultaneously) such that the network throughput is maximized. Links share in space by piggybacking on data transmission opportunities seized by another link using RTS/CTS as speci ed in the distributed coordination function (DCF) of 802:11. Sharing in space increases interference and hence reduces the PHY rate at which a link can send data. It also increases the opportunities a link gets to transmit data, however. We show that the optimization problem is NP hard. A relaxation of the problem gives an upper bound on network throughput. Computationally feasible algorithms that achieve a signi cant percentage of the upper bound are proposed. We will restrict our network modeling and evaluation to 802:11 networks in which all nodes always have a packet to send and are within carrier sense range of each other. Networks with a high density of clients and AP(s) are shown, via simulation, to achieve large throughput gains (up to 400% for a network of 25 clients and AP(s)), over standard 802:11.