Mobile radio performance for a 2-branch equal-gain combining receiver with correlated signals at the land site

It has generally been accepted that in a two-branch diversity receiver a near maximum diversity advantage is realized when the cross-correlation between the two branches is less than 0.7. Based on this figure, space diversity reception at the mobile presents little problem since the antenna separation distances that achieve this amount of decorrelation in the mobile environment are very small (≤20 centimeter at 850 MHz). However, the space diversity antenna separation requirement at the land site necessary to achieve the same amount of signal decorrelation is in the range of 10 wave-lengths or more at antenna elevations of 150 feet or greater. Therefore, a comprehensive characterization of the effect of changing the cross-correlation between the two received signals at the land site is important to effective system design. This paper describes the performance of the two-branch equal-gain diversity system as a function of the cross-correlation between the two received signals from the diversity antennas. The cumulative probability distributions, level crossing rates and duration of fades from a two-branch equal-gain combined diversity signal with variable correlation between the two branches are described.