Synchronization in Cooperative Networks: Estimation of Multiple Carrier Frequency Offsets

The distributed nature of cooperative networks may result in multiple carrier frequency offsets (CFOs), which make the channel time-varying and overshadow the performance gains promised by collaborative communications. However, much of the analysis in the area of cooperative communications assumes perfect synchronization. This paper seeks to address frequency synchronization in cooperative communication systems, where CFO estimation using a training sequence is analyzed. The Cramer-Rao lower bound (CRLB) for various cooperative protocols is derived. In the next step, we propose two computationally efficient iterative estimators based on the MUltiple SIgnal Characterization (MUSIC) algorithm, that can estimate the CFOs from all the relays simultaneously. Unlike existing multiple CFO estimation algorithms, the proposed estimators are effective and accurate in the presence of both large and small CFO values and numerical and simulation results show that both methods outperform the existing algorithms and reach the CRLB at mid-to-high signal to noise ratio.