BER performance of DQPSK in Nakagami fading with selection diversity and maximal-ratio combining

A new expression for the average bit-error rate (BER) of differential quadr ature phase-shift keying in slow frequency-nonselective Nakagami fading is derived for a space-diversity receiver having a cascade arrangement of L gr oups of M-branch selection combiners and an L-branch maximal-ratio combiner (MRC). This allows the use of a large number of antennas, for performance improvement, and a small number of inputs to the combiners, for Low complex ity. The average BER performance of the cascade receiver is investigated fo r different fading severity conditions characterized by the Nakagami m fact or, and compared with the conventional MRC receiver. As the fading gets les s severe (m increases), performance improvement over the conventional MRC s cheme is only noticeable for the larger range of average signal-to-noise ra tio.