Evaluation of IF and Baseband Diversity Combining Receivers

Techniques of diversity reception have advanced rapidly with the advent of over-the-horizon communication. Because of the rapidly fluctuating signals encountered in tropospheric scatter propagation, strong-signal selection (switching diversity) has been largely supplanted by more sophisticated signal-combining techniques. Present tropospheric scatter systems commonly employ either postdetection ratio-squared combining, or more recently, a technique of predetection linear addition. A theoretical and experimental study comparing these two methods is the subject of this paper. Apart from obvious advantages of simplicity, the predetection technique exhibits lower distortion under multipath conditions, due to the linear combining process.