Multiple Carrier Frequency Offset and Channel Estimation for Distributed Relay Networks

Cooperative communication using decode and forward (DF)-based distributed relays is one important solution to achieve better connectivity and higher data rates in wireless fading channels. In distributed relay networks, each relay has an independent local oscillator which when unsynchronized results in the presence of multiple carrier frequency offsets (CFOs) at the destination. The maximum likelihood estimator (MLE) for estimating the multiple CFOs requires a two dimensional grid search involving matrix inversion for each search point. Thus, the multiple CFO and channel estimation is computationally prohibitive and challenging in distributed relay networks. In this paper, we propose a simple estimator for multiple CFO and channel estimation at the destination by exploiting the fact that the relays receive information from a common source. Computer simulations show that the mean square error (MSE) performance of the proposed estimator is close to the Cramer-Rao lower bound for small carrier frequency synchronization errors at the relays.