On optimizing base station antenna array topology for coverage extension in cellular radio networks

Use of higher frequencies (1.8 GHz) for the US upper tier PCS cellular service and the FCC regulations on the network build out have resulted in significant interest in improving coverage of cellular networks. Networks whose coverage is limited imply that thermal noise is the limiting factor. Also, since the forward link (base station to mobile) has higher power than the reverse link, cell coverage is usually limited by the reverse link. This coverage can be extended by improving the reverse link budget. Use of receive antenna arrays for boosting array gain on the reverse link is therefore of great interest. When receive antenna arrays are used at the base station, several conflicting choices affect system performance and cost. Some of these aspects are: the number of antenna elements (and channels) improves coverage but also increases system cost; the maximum span of the array increases diversity hut must be limited for convenient deployment on a tower; large inter-element spacing can increase diversity but cause grating lobes at the same time. These conflicting requirements mean that a careful design of the array topology can minimize the cost. In this paper, we study performance of linear and circular base station antenna arrays with different topologies, angle spread, and the number of elements. We compare alternate topologies using maximal ratio combining for narrowband systems such as AMPS and IS-54