Distributed Double Differential Space-Time Coding with Amplify-and-Forward Relaying

This paper provides the double differentially modulated distributed space-time coding for amplify-andforward (AF) relaying cooperative communications system under time-varying fading channels. In many wireless systems, the communication terminals are mobile. In such case, frequency offsets arise subjected to Doppler’s effect and frequency mismatch amongst the terminals’ local oscillators. The double differential coding is proposed to overcome the problem of frequency offsets that present in the channel due to the rapidly fast moving nodes. The advantage of the double differential is that the scheme requires neither channel nor frequency offset knowledge for decoding process at the desired destination. However, the conventional two-codeword approach fails to perform and leads to error floor, a region where the error probability performance curve flattens for high signal-to-noise ratio (SNR) regime in fast fading environment. Hence, a low complexity multiple-codeword double differential sphere decoding (MCDDSD) is proposed. The simulation results show that the proposed MCDDSD significantly improve the system performance in time-varying environment.