A comparative study of higher-order differential phase shift keying schemes over AWGN and Rayleigh fading channels

Double differential phase shift keying (DDPSK) is known to be immune to Doppler shift, a property that is valuable in mobile communication systems. The present paper is about DDPSK and analyzes its two variations, the adjacent DDPSK and the nonadjacent DDPSK. The performance is evaluated for the case of slow Rayleigh fading with and without frequency offset using the three receiver structures: the IQ demodulator, the autocorrelation demodulator, and the multiphase autocorrelation demodulator. In additive white Gaussian noise channels (AWGN), the performance of both schemes is evaluated in the presence of a frequency offset with the above demodulators. The obtained analytical results are verified via Monte Carlo simulations. The obvious disadvantage of DDPSK is its power requirements when compared to the conventional DPSK. In order to overcome this shortcoming, a demodulator structure is proposed in this paper. The performance of this demodulator is found to yield a lower probability of error when compared to the other demodulators for DDPSK as well as for DPSK. Results obtained using computer simulation of the proposed demodulator was found to be in good agreement with the analytical results derived in this paper.