A selection combining scheme for RAKE receivers

A selection combining scheme for a RAKE receiver operating over a multipath fading channel is introduced, by which the m largest channel outputs are selected instead of only the largest one, as in the conventional selection combining receiver. Expressions for the error probability of this scheme for an exponential multipath intensity profile (MIP) with arbitrary decay constant are found by first deriving the joint density function of the m ordered channel outputs, then averaging the conditional error probability over the joint density function. The performance is compared with that of maximal ratio combining in both an interference-limited and a noise-limited environment. The interference-limited environment chosen is a multicell CDMA system. Numerical results show that the performance of the selection combining scheme is superior to that of conventional selection combining, and can be very close to that of maximal ratio combining, depending upon the value of m and the rate of decay of the MIP