Minimizing contention through cooperation between densely deployed wireless LANs

Contention at shared medium access may seriously degrade the performance of a CSMA/CA-based wireless LAN. Where wireless LANs from different operators are densely deployed, controlling contention merely by intelligent selection of installation sites and assignment of operating channels becomes challenging at least. We show that cooperation between these networks may lead to a significant reduction in overall contention. To this end, we present a mathematical programming formulation of the minimal inter-domain contention problem and derive theoretical lower bounds for it. We show how to practically determine exact solutions for small problem instances and near-optimal solutions for larger scenarios. Most importantly, we introduce a distributed algorithm and protocol that allows access points to self-coordinate in order to minimize contention and relies solely on information about each access point’s immediate neighborhood. In experiments, we show that cooperation between domains may more than halve contention even in only moderately dense deployments. Furthermore, we demonstrate that our distributed algorithm may reduce contention by 19% compared to cooperation using standard WLAN mechanisms. Contrary to common belief, our findings suggest that in dense deployments switching off selected access points may be more effective in decreasing contention than using them for load balancing.