Zero-forcing equalisation for space diversity combining in microwave digital radio

One of the primary causes of performance degradation in microwave digital radio is frequency-selective fading caused by multipath propagation. For an M-QAM radio system, dual space diversity and adaptive zero-forcing equalisation countermeasures can be employed in two configurations. In an optimal-selection diversity structure, after equalisation of the two diversity channels, the better one is selected, while in a postcombining equalisation structure the channels are combined prior to equalisation. By analytic techniques and Monte Carlo simulation it is determined that for the same transmit power the improvement attained is greater with the postcombining equalisation structure. Also, it is shown that the seven-tap postcombining equalisation structure can outperform the conventional optimal selection-diversity structure even when infinite taps are used