Distributed multiple antenna carrier- and sampling-frequency synchronization for OFDM

Multiple antenna systems have been shown to provide significant performance improvements for network nodes; however, the vast majority of nodes in military networks will be limited to single channel devices due to mobility (size and power) and ease of use considerations. In this paper we apply a new joint synchronization-pilot sequence (JSPS) optimization design technique to multiple transmitter OFDM systems. We consider the cases where the transmitters could be co-located or distributed (i.e. multiple single-channel transmitters) in space. Independent JSPSs are designed for each transmitter in a multiple antenna system and can be utilized to estimate the carrier frequency offset (CFO) and sampling frequency offset (SFO) of each antenna independently. We study the mean square error (MSE) for the estimation of CFO and SFO and compare the performance of our estimators to a closed form solution for AWGN channels. We show that the performance of our proposed iterative estimators for distributed CFO and SFO estimation is approximately equivalent to the estimation performance in the co-located CFO and SFO estimation case. The iterative estimator for the distributed case is also found to be of low complexity, with only a linear complexity increase over the co-located estimator. We have also measured, via simulation, the performance of the CFO estimator for distributed Rayleigh fading multipath channels.