Unique word-based distributed space-time block codes for two-hop wireless relay networks

Distributed space-time block codes (DSTBCs) have been developed to exploit diversity gains in cooperative communications systems. In this paper, we propose a new DSTBC based on unique word (UW) extension, referred to as the D-UW-STBC. The D-UW-STBC is devised for wireless relay networks with the amplify-and-forward protocol and frequency selective fading channels. The data is transmitted from the source to the destination by a block-wise manner, resembling the block level of the Alamouti scheme. At the source, a UW is padded to the tail of each data block, which plays as a cyclic prefix, and thus allows for low-complexity implementation in the frequency domain. The additional purpose of using UW in this paper is to estimate the channels. However, the introduction of UWs makes it difficult to decouple the detection of data blocks. To achieve the orthogonality of the equivalent space-time channel, we carefully cancel the interference induced by the UWs. Also, a least square (LS) channel estimation approach is proposed, in which, the relay is transparent to the source and destination. The optimal UWs are designed to minimise the effect of additive noise. Bit-error-rate (BER) performance comparison of various receiver schemes is carried out by computer simulations.