ABSTRACT
The ill-effects of multipath fading in wireless systems can be reduced by employing spatial diversity, where a multielement antenna at the receiver is employed. When fading is present, a higher than otherwise average carrier power is needed to perform at a given bit-error rate. It is assumed that the spacing is chosen so that signals received are sufficiently decorrelated. The signal received at one antenna element constitutes one diversity branch. Because of multipath and movement of the mobile, the signal received at each element is not a constant, but fluctuates at the fading rate. In maximum ratio combining, the branch signals are weighted and combined so as to yield in the highest instantaneous carrier-to-noise ratios (CNRs) possible with any linear combining technique. The diversity gain must be distinguished from the antenna gain that is defined as the ratio of the output CNR of the array to the output CNR ratio of a single element for highly correlated input signals.
