Novel association control strategies for multicasting in relay-enabled WLANs

Multicast is a fundamental communication service in Wireless Local Area Networks (WLANs). Unfortunately, multicast packets are transmitted at the base rate needlessly, which prevents rich multimedia contents from being delivered to users. To this end, a number of prior studies have proposed to increase multicast capacity whereby an Access Point (AP) transmits at the highest data rate that can be decoded by all subscribers. Another approach is by controlling subscriber-AP associations such that a given objective, e.g., AP load, is met. Moreover, they have also proposed using relays to help boost stations with weak channel condition. In this paper, we propose an approach that exploits association control, high number of APs and relays simultaneously to improve the performance of multicast in WLANs. We show that the problem is NP-hard by reducing it from the Maximum Coverage with Group Budget (MCG) problem. We then propose a number of heuristics that consider two types of relays: non-subscribers and subscribers. The former are stations that are not part of any multicast groups whereas the latter comprise of stations that are actively receiving multicast packets. Our extensive simulation studies with varying APs, station numbers, and multicast transmission rates show the efficacy of our heuristics in reducing the average and maximum AP load, and are able to support a higher number of users at high multicast rates. Specifically, they result in up to 83% reduction in AP load, and support up to 17% and 53% more users in low and high rate multicast scenarios respectively.