An evaluation of specific diversity combiners using signals received by vertically-spaced base-station antennas

A series of field trials has been conducted in which a 900 MHz CW signal was transmitted from a vehicle moving along a test route some 1·3 km from a base station. The recorded envelopes of the signals received on two vertically-separated antennas at the base station have been used in a computer simulation of two-branch predetection diversity reception. Several different systems have been simulated and the computed results show that the theoretical diversity advantages can still be obtained for an envelope cross-correlation (¿env) of less than 0·7 for all strategies except switching. For a 1·3 km radius cell, a ¿env less than 0·7 can be obtained using antennas with a vertical separation of about 12¿. It has been found that the cumulative distribution and level-crossing rates of the signal are substantially improved and the average fade duration is approximately halved.