DOQPSK-differential demodulation of filtered offset QPSK

Offset QPSK (OQPSK) and π/4-QPSK have been studied intensively over the last years for application in digital mobile radio systems. Though OQPSK shows a better performance over nonlinear channels than π/4-QPSK, the latter is preferred, since it allows for differential demodulation, which is an attractive combined channel estimation and demodulation technique on fast fading channels. In the present paper, we describe a receiver for the differential demodulation of differentially modulated OQPSK signals. The bit error rate of the new receiver is compared with π/4-DQPSK on AWGN and Rayleigh fading linear channels, with transmitter and receiver raised cosine pulse shaping being assumed in all cases. On these linear channels and a roll off factor r=0.5, a loss of less than 0.5 dB of DOQPSK with respect to π/4-DQPSK is found. Therefore, the advantage of OQPSK over π/4-DQPSK on non-linear channels will essentially be maintained with differential demodulation