Joint carrier frequency offset and channel estimation in OFDM based non-regenerative wireless relay networks

Cooperative relaying is an effective approach to combat wireless fading. However, the reliability enhancements depend strongly on the accuracy of the carrier frequency offset (CFO) compensation and channel estimation algorithms. In this paper, we show that CFO compensation at relay is necessary in non-regenerative OFDM based wireless relay networks with relays employing space-time coding. A simple training scheme available for estimating space-time channel is exploited to estimate the CFO at the relay. Maximum likelihood (ML) and least squares (LS) based joint CFO and channel estimators are constructed for estimating the CFO and the product channel (effective channel from source to destination) at destination. For non-regenerative OFDM based wireless relays, we prove that the LS based estimator is equivalent to the ML based estimator. Theoretical mean square error for the product channel estimator is also derived.