Joint Frequency Assignment and Association Control to Maximize the Aggregate Throughput in IEEE 802.11 WLAN

The performance of an IEEE 802.11 wireless local area network is highly dependent on how the stations (STAs) are associated with the access points (APs). Frequency channels are assigned to the APs satisfying the interference constraints among them. As the number of non-overlapping frequency channels are limited, all APs in a given area may not be activated simultaneously because of mutual co-channel interference. The major concern of this paper is to select an appropriate subset of APs together with their frequency assignment as well as to find out an efficient association between the STAs and APs that maximizes the aggregate throughput of the network. We argue that, the two-step solution of the problem may become a suboptimal solution whereas ignoring the interference may cause a significant overestimation of the performance. Motivated by these, we propose an integrated model based on integer programming and an efficient greedy algorithm that address both aspects simultaneously. The performance of the proposed approach is analyzed for different utility functions and association policies. We have shown that the proposed approach outperforms some existing approaches and takes care of load balancing across the APs as well as fairness in throughput obtained by the STAs. Moreover the approach is robust enough to support user mobility and able to manage external interference.