Distributed Space Time Block Transmission and QRD Based Diversity Detector in Asynchronous Cooperative Communications Systems

Based on the zero prefix (ZP) structure, we propose an efficient block transmission algorithm using distributed space-time codes in the asynchronous cooperative communication systems. To accomplish the new frame, ZP is inserted in front of the data block to combat the relative delay between the asynchronous relays, while zero suffix (ZS) is appended at the end of the block to remove the interblock interference caused by the time dispersing channel; so, we employ this ZP-ZS precoding form to make the coded frames synchronous. It should be noted that single carrier transmission and orthogonal frequency division multiplexing (OFDM) are both compatible with the frame. For single carrier transmission, conventional space-time equalizers can be investigated at the destination node to cancel the multipath interference. To further improve the performance, an improved QR decomposition-based recursive interference cancellation (QRD-RIC) detector is employed, where joint QRD is adopted on the combination of channel matrices from different relays, and then spatial-and-multipath diversity combinations are introduced and improved into the proposed system, where the spatial and multipath diversities are acquired. For OFDM, the fractionally spaced frequency-domain MMSE diversity receiver is employed, since the guard interval in our framing scheme implies oversampling in the frequency domain. Numerical simulations show that the proposed algorithms are effective for the asynchronous transmissions under frequency selective fading channels.