On the Detection of Distributed STBC AF Cooperative OFDM Signal in the Presence of Multiple CFOs

This paper deals with the interference mitigation problem of the distributed space time block coded (STBC) amplify-and-forward (AF) cooperative orthogonal frequency division multiplexing (OFDM) signal in the presence of carrier frequency offsets (CFO). Multiple CFOs introduce phase drift, inter-carrier interference (ICI) and inter-block interference (IBI) to the received signal. A joint time domain (TD) and frequency domain (FD) method is presented to recover the phase distortion and mitigate the ICI and IBI with low complexity and high performance. The TD compensation proposed in this paper removes the IBI first and then the ICI is mitigated through FD equalization (FDE) methods. For the FDE, the minimum mean square error (MMSE) equalizer has been derived which has a different noise covariance matrix from the conventional MMSE. Sub-block processing is employed to reduce the computational complexity in FD equalization. Furthermore, a two-pilot-block assisted channel estimation method is proposed for AF cooperative OFDM in the presence of CFOs. The bit-error-rate (BER) performance evaluated via computer simulation demonstrates the effectiveness of the proposed method.