High rate OFDM-modem with quasi-coherent DAPSK

An OFDM system with 64-DAPSK (differential amplitude and phase shift keying) modulation is considered. The performance with quasi-coherent demodulation is analysed in AWGN and frequency-selective Rayleigh fading channels with and without channel coding (convolutional coding) and compared to incoherent (64-DAPSK) and coherent (64-QAM) demodulation. It is shown that in contrast to coherent demodulation, no pilot symbols are required for quasi-coherent demodulation. Using this redundancy for additional channel coding, both coherent and quasi-coherent demodulation show approximately the same performance at the same net bit rate, but due to the relatively complex channel estimation the hardware complexity is considerably higher with coherent demodulation.