Performance of antenna arrays in an urban multipath environment

The performance of an antenna array in a distributed fading environment depends on how the signal gets distributed in space. It is known that the scattering in an urban area mainly happens within a 100 wavelength radius around a mobile. Assuming that the base station antennas are above the rooftop in urban areas, and approximately 1-2 kilometers from the mobile, the angular spread of the signal impinging on the array is on the order of 5-10 degrees, for a 1.8 GHz system. This angular spread results in an array response where the fading of the array elements is correlated along the array. We study how correlation effects the ability of the array to separate cochannel signals, and propose estimation algorithms which exploit this correlation. We derive the approximate theoretic performance of the array as a function of both angular spread and input SNR. Performance results are presented that compare the performance of different estimators, as well as the proposed theoretic performance, as a function of the input SNR.