Embracing asynchronism: Achieving cooperative diversity using zigzag interference cancellation

Synchronization between the received signals from several transmitters is a challenging problem for cooperative communications. In the literature it is often assumed that the signals are somehow perfectly synchronized, but the problem of communication with asynchronism is rarely addressed. Moreover, in the few works where the problem is addressed, the proposed techniques are designed for a maximum delay whose value determines the decoding complexity. Thus in practice, only small delays can be dealt with. In this paper, instead of trying to avoid asynchronism between the received signals from two different transmitters, we propose to exploit it to provide cooperative diversity by optimally combining the two signals resulting from forward and backward zigzag interference cancellation. In addition to being tolerant to any delay, our bit error rate derivations and simulations show that the proposed scheme provides similar performance as delay-tolerant space-time block codes, such as the delay-tolerant Alamouti code, with a much lower complexity compared to a maximum likelihood (ML) decoder.