  This paper proposes and analyses selection combining (SC) at the destination
for differential amplify-andforward (D-AF) relaying over slow Rayleigh-fading
channels. The selection combiner chooses the link with the maximum magnitude of
the decision variable to be used for non-coherent detection of the transmitted
symbols. Therefore, in contrast to the maximum ratio combining (MRC), no
channel information is needed at the destination. The exact average
bit-error-rate (BER) of the proposed SC is derived and verified with simulation
results. It is also shown that the performance of the SC method is very close
to that of the MRC method, albeit with lower complexity
