Capacity enhancement using adaptive arrays in an AMPS system

Adaptive arrays for an advanced mobile phone service (AMPS) system can significantly increase cell capacity, improve signal quality, and reduce transmitter power requirements. In this paper, we investigate the capacity improvement that can potentially be achieved using adaptive arrays at the base station of an AMPS system. For the analysis, we use two types of spatial filters at the base station: an ideal and flat-top beamformer. An ideal beamformer has a flat main lobe and no side lobes, while a flat-top beamformer has flat main and side lobes. Analysis includes calculation of outage probability when a beamformer is used at the base station, and then we calculate the capacity increase that can be offered by practical antenna arrays. In this paper, we show that spatial-division multiple access (SDMA), i.e., all the users in a cell occupying the same frequency, is impossible to achieve in an AMPS system. A cell-reuse factor of four can be easily achieved with a five-element uniform linear array (ULA) with λ/2 spacings, but to achieve a reuse factor of three, a ULA with eight elements is required