Optimal association of wireless devices to cellular and Wi-Fi base stations

Communication devices such as cellular phones are now capable of using different communication technologies, such as 3G/4G and WiFi. The high data rate requirements of current user applications have lead to the important engineering problem of optimally associating a communication device with different networks using different communication technologies so as to maximize data rates. In this paper, we study the problem of optimally associating a group of users to a single base station and a single WiFi access point so that the sum throughput of all the users is maximized. Compared to prior work, we find that under realistic models for throughputs which are achievable on WiFi, the above association problem is a fractional programming problem, namely a “maximising sum of ratios” problem. Although the general sum of ratios problem is hard to solve, for the above association problem, we suggest heuristic algorithms that are shown to have a sum throughput close to the maximum. We also suggest a novel upper bound to the maximum sum throughput which has applications in performance evaluation.