On Bounds and Algorithms for Frequency Synchronization for Collaborative Communication Systems

Cooperative diversity systems are wireless communication systems designed to exploit cooperation among users to mitigate the effects of multipath fading. In fairly general conditions, it has been shown that these systems can achieve the diversity order of an equivalent multiple-input multiple-output (MIMO) channel and, if the node geometry permits, virtually the same outage probability can be achieved as that of the equivalent MIMO channel for a wide range of applicable signal-to-noise ratio (SNR). However, much of the prior analysis has been performed under the assumption of perfect timing and frequency offset synchronization. In this paper, we derive the estimation bounds and associated maximum a posteriori estimators for frequency offset estimation in a cooperative communication system. We show the benefit of adaptively tuning the frequency of the relay node in order to reduce estimation error at the destination. We also derive an efficient estimation algorithm, based on the correlation sequence of the data, which has mean squared error close to the Cramer-Rao Bound (CRB).