Optimal resource sharing in multi-cell wireless LANs: Joint channel assignment, association control, airtime sharing and contention resolution

In this paper we study the problem of throughput maximization, with fairness guarantee, in multi-cell WLANs with hidden terminals. In such a scenario, the throughput gained by each flow is generally determined by the four major control mechanisms that make the basis of WLAN control protocols - viz., radio frequency channel assignment, association control, intra-AP airtime sharing between the associated clients, and the access rate control which is determined by the MAC layer contention window tuning. Instead of focusing on each of the four mechanisms apart, in this paper we optimize the network performance via a joint channel assignment, association control, airtime sharing, and contention window tuning; we formulate this joint problem as a non-linear programming problem. Because such a problem is in general NP hard due to the integral nature of both channel assignment and association control, we solve it by iteratively approximating it via a convex programming problem. Numerical and simulation results show that, the resulting solution significantly improves the network throughput and fairness, compared with methods that optimize separately the different mechanisms. Our solution also gives further insights into the importance of each one of these mechanisms when considered jointly.