A Minimum Dispersion Combiner for High Capacity Digital Microwave Radio

A new minimum-dispersion (MID) combiner, which reduces multipath degradation in a high capacity digital microwave radio, is proposed. A high capacity digital microwave radio is inherently very sensitive to waveform distortion caused by multipath in-band delay dispersion and in-band amplitude dispersion. To minimize the in-band dispersion, the combined-signal spectrum shape from the two antennas is monitored before and after a small change takes place in the combining phase. The phase shifter rotates in the direction of the flatter of the spectrum shapes, either the one before or the one after monitoring. Performance evaluations through simulation calculation and theoretical estimation using in-band amplitude dispersion probability density are given. More improvement can be obtained when the MID combiner is used instead of the maximum power (MAP) combiner currently in use. Laboratory and field experiments, using a 200 Mbit/ s 16-QAM signal, verify these analyses and show an additional outage reduction factor of more than 5.