Multiple association in ultra-dense networks

The cell association is of a paramount effect on the operation of cellular network. In Ultra-Dense Networks (UDN), different types of small cells are deployed with extremely large densities. This comes with a great advantage of dense reuse of spectrum. In this paper, we investigate the downlink association of a given user equipment (UE) to multiple small cells, which we termed multiple association. In multiple association, a user connects to M ≥ 1 small cells forming what we call MultiCell. Consequently, this overcomes the backhaul limitation of individual cells. Specifically, we derive the idle mode probability in the proposed setting, and based on that we derive an analytical expression for the average ergodic downlink rate of the link between the typical user and its jth nearest cell. Additionally, we exploit the aforementioned findings to study the area spectral efficiency in multiple association, and to investigate its relation to the main system parameters, namely: small cells density, users density, and MultiCell size M. We simulate the proposed model to assess the accuracy of the analytical results. Our results provide a mathematical framework, and pave the way to consider the association of a user to multiple small cells.