On optimal hotspot selection and offloading

Devices like smart phones come with 3G/4G and WiFi radios, which creates possibilities of heterogeneous network access. We investigate scenarios where Internet access to a device is available only via the cellular network. However, not every user may connect directly to it. Users in the network may be split into hotspots and clients. Hotspots are the users that connect directly to the cellular network and may provide connectivity to the internet to other users by allowing them to connect to their WiFi interface. Clients connect to the cellular network only via hotspots. The optimization problem is to find the split of hotspots and clients, and the association between clients and hotspots, that maximizes the sum of the link rates of users. Importantly, the users must get at least the link rate they get when all are directly connected to the cellular network. In this paper, we formulate the optimization problem. We provide insights into the interplay of WiFi connectivity amongst users, their link rates to the cell tower, and the split that maximizes sum rate. We propose a novel heuristic approach to split the network. Median gains of 1.5× are observed over networks of up to 40 nodes.