Coverage Optimization Tradeoffs in Heterogeneous WCDMA Networks with Co-Channel Small Cells

This study examines the tradeoffs related to the problem of coverage auto-configuration of open access small cells (SC) that (i) are on-demand deployed in the macro-cells (MC) of a WCDMA network, and (ii) operate in the same frequency channel as the hosting/neighboring MCs. The purpose is to identify stable and practically detectable equilibrium states whose achievement can represent an optimality criterion for implementing automatic coverage adaptation of the SCs. In particular, it is shown that, on the downlink (DL), the offloading of the MC hotspot users by a nearby SC improves the DL signal-to-interference-and-noise ratio (SINR) and the DL effective throughput at the expense of the current SC users. On the uplink (UL), the maximum achievable UL SINR of the MC and SC users follows a similar trend. Moreover, in terms of the UL capacity and power usage, there exists a distinct equilibrium state of the MC-vs-SC tradeoff defined on the basis of the spectral radius of a network information matrix. Yet, unless the performance requirements of the MCs and SCs are identical, the DL and UL equilibria do not generally coincide which complicates an autonomous search for optimum partitioning of the SC power budget. Numerical simulations are based on a 3GPP-compliant system model.