Carrier frequency offset (CFO) is a factor that corrupts subchannel orthogonality resulting to performance degradation in multiple‐input multiple‐output orthogonal frequency division multiplexing systems. We investigate the effect of CFO on the channel estimation and the effect of both CFO and channel estimation on the system capacity. The main result of the paper is a lower bound on the capacity for a given CFO and channel estimation error covariance. The lower bound is based on the Gaussian bound of the multiplicative noise because of channel estimation errors. Copyright © 2012 John Wiley & Sons, Ltd.

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In this paper, novel cooperative automatic repeat request (ARQ) methods with network coding are proposed for two way relaying network where two communicating nodes are assisted by a relay node at the cooperative retransmission phase upon a failed transmission of a packet. The proposed approach integrates network coding into cooperative ARQ, aiming to improve the network throughput by reducing the number of retransmissions. For successive retransmission, three different methods for choosing the retransmitting node are considered. The throughput of the methods are analyzed and compared. The analysis is based on binary Markov channel which takes the correlation of the channel coefficients in time into account. Analytical results show that the proposed use of network coding enhance throughput performance up to 15% compared to cooperative ARQ without network coding and 40% compared to traditional ARQ when the relay channel conditions are better than the direct channel between two communicating nodes. It is also observed that correlation can have significant effect on the performance of the proposed cooperative network coded ARQ approach. In particular the proposed approach is advantageous for moderately fast to slow fading channels where channel correlation coefficient varies from 0.5 to 1.

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