User assignment strategies for throughput maximisation in hierarchical wireless networks

Hierarchical wireless networks such as the 3G/WLAN integrated networks are considered as a promising solution to effectively support next-generation wireless applications. We investigate the problem of assigning mobiles to the different layers in such networks. In this paper, we focus on the real-time application users, while the case of non-real-time users is treated in a separate paper. By real-time applications, we mean the applications which can adapt their data transmission rate (i.e. throughput) depending on the current channel conditions. The connection time (i.e. the call holding time) of these elastic applications is typically independent of their throughput. Such applications would for example include multimedia applications that can adjust the quality of the audio/video signal in order to adapt to lower network capacities. We present a generic framework under which different assignment strategies can be formulated and evaluated. Specifically, three assignment schemes which utilise the estimated velocity and/or the requested data rate of the mobiles are studied. The relative merits of these schemes are compared and it is in particular shown that, under various circumstances, the joint velocity - rate decision scheme significantly outperforms the other two schemes (i.e. velocity- and rate-only decision schemes). Extensive numerical results are presented to quantify the respective performances and to study the influence of relevant system parameters. Our main contribution is to build a generic framework for optimal user assignments, into which various wireless technologies can be plugged.