Time and frequency synchronisation scheme for orthogonal frequency division multiplexing-based cooperative systems

In the cooperative relay system, different frames from different relays are not aligned in the time domain, and have different carrier frequency offsets (CFOs). Estimation of these timing offsets and CFOs is a crucial and challenging task. In this study, a new training structure is proposed, and a novel time and frequency synchronisation scheme is presented for orthogonal frequency division multiplexing-based (OFDM-based) cooperative systems. The coarse time synchronisation is accomplished by using the symmetric conjugate of the training symbol and the fine time synchronisation is accomplished by segment-moving correlation. The fractional frequency offset is estimated by using the phase difference of the received signal and the integral frequency offset is estimated by utilising the good autocorrelation of the training symbol in frequency domain. The analysis and the simulation results show that, compared with the traditional scheme, the proposed scheme has better timing and frequency offset estimation performance and lower complexity for OFDM-based cooperative systems.