Postdetection diversity reception of QDPSK signals under frequency selective Rayleigh fading

Bit error rate (BER) performance improvements achieved by the use of postdetection diversity with selection combining for Nyquist raised cosine filtered quadrature differential phase shift keying (QDPSK) signal transmissions in frequency-selective Rayleigh fading channels are investigated. Theoretical analysis shows that diversity reception can significantly increase the maximum bit rate. If an average BER of 10^-4 is required, a five-fold increase in the tolerable normalized rms delay spread (rms delay spread X symbol rate) is possible by using simple two-branch diversity reception. The effects the Nyquist filter roll-off factor have on average BER are also analyzed to show that average BER can be reduced at the cost of a slightly increased bandwidth. Laboratory and field experimental results that support these theoretical results are shown.