OFDM based Distributed Space Time Coding for Asynchronous Relay Networks

TL;DR

This paper extends OFDM-based distributed space-time coding to achieve full cooperative diversity in asynchronous relay networks, introducing new codes and differential encoding methods that operate without channel or timing error knowledge.

Contribution

It introduces a generalized transmission scheme using DSTBCs that attain full diversity, including differential encoding for asynchronous relay networks without channel information.

Findings

Achieves full cooperative diversity with any number of relays.

Proposes four group decodable distributed differential space-time codes.

Extends existing schemes to asynchronous relay networks without channel state information.

Abstract

Recently Li and Xia have proposed a transmission scheme for wireless relay networks based on the Alamouti space time code and orthogonal frequency division multiplexing to combat the effect of timing errors at the relay nodes. This transmission scheme is amazingly simple and achieves a diversity order of two for any number of relays. Motivated by its simplicity, this scheme is extended to a more general transmission scheme that can achieve full cooperative diversity for any number of relays. The conditions on the distributed space time block code (DSTBC) structure that admit its application in the proposed transmission scheme are identified and it is pointed out that the recently proposed full diversity four group decodable DSTBCs from precoded co-ordinate interleaved orthogonal designs and extended Clifford algebras satisfy these conditions. It is then shown how differential encoding at the source can be combined with the proposed transmission scheme to arrive at a new transmission scheme that can achieve full cooperative diversity in asynchronous wireless relay networks with no channel information and also no timing error knowledge at the destination node. Finally, four group decodable distributed differential space time block codes applicable in this new transmission scheme for power of two number of relays are also provided.