Balancing download throughput in densely deployed IEEE802.11 multi-cell WLANs

Multi-cell wireless LANs (WLANs) are often densely deployed in order to achieve full coverage of a given area, in particular in indoor environments. In such scenarios, it is widely believed that the co-existence of hidden and exposed APs simultaneously results in a dramatic download throughput degradation for the clients. Indeed, in such environment, intutively, each AP while competing for channel access with neighbouring exposed APs may suffer collisions from hidden APs each time it wins such competition. In this paper we study the problem of fairly allocating download bandwidth to clients in such dense multi-cell WLANs. To this end, we design algorithms that adapt client association, airtime sharing among clients and rate control to achieve optimal fairness in bandwidth access. We model this problem as a non-linear programming problem, and propose a distributed algorithm to solve such an NP-hard problem via transformation into a convex problem as well as approximations. Our numerical and simulation results show that, the proposed algorithm significantly improves the performance compared to existing solutions, and leads to the counter intuitive conclusion that intelligently adding exposed APs will lead to better system performance.¹