Timing and frequency synchronization for OFDM based cooperative systems

In this paper, we investigate the timing and carrier frequency offset (CFO) synchronization problem in decode and forward cooperative systems operating over frequency selective channels. A training sequence which consists of one OFDM block having a tile structure in the frequency domain is proposed to perform synchronization. Timing offsets are estimated using correlation-type algorithms. And since some subcarriers are nulled in the proposed tile structure, CFOs are readily estimated using subspace-based methods. By judiciously designing the size of the tile, these algorithms are shown to have better performance, in terms of synchronization errors and bit error rate, than the computationally demanding SAGE algorithm.