Alamouti coded OFDM scheme for frequency asynchronous AF relay networks

In this paper, we propose an Alamouti coded orthogonal frequency-division multiplexing (OFDM) scheme for amplify-and-forward (AF) relay networks that contain multiple distributed relay nodes. The frequency asynchronous nature of the distributed system is considered in our design. By implementing simple operations, e.g., time reversal, conjugation and amplification, the proposed scheme eliminates the needs of knowledge of both channel states and the frequency offsets at the relay nodes. We prove that when the frequency offsets among the relay nodes are smaller than a certain threshold, full spatial diversity can be achieved at the destination node even with the linear receivers, e.g., zero-forcing (ZF) receiver. Numerical results are provided to corroborate the proposed studies.