OFDM Based Distributed Space Time Coding for Asynchronous Relay Networks

Abstract

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.

A Simple Orthogonal Space-Time Coding Scheme for Asynchronous Cooperative Systems for Frequency Selective Fading Channels

“…Second, it is only valid for flat fading channels. In [3], it is extended to the case of any number of relay nodes but is still limited to flat fading channels. Moreover, the complexity of the four group decodable codes used in [3] is higher than the symbolwise decoding of OSTBCs.…”

“…In [3], it is extended to the case of any number of relay nodes but is still limited to flat fading channels. Moreover, the complexity of the four group decodable codes used in [3] is higher than the symbolwise decoding of OSTBCs. Recently, there is a similar scheme in [4] to achieve cooperative diversity in asynchronous twoway relay networks.…”

Asynchronous cooperative communication systems: A survey on signal designs

“…In time-domain approaches, various DSTCs without the requirement of time synchronization have been proposed [30][31][32][33][34][35][36][37][38][39][40][41]. In frequency-domain approaches, the basic idea is to treat the paths from cooperative nodes to the destination node as multipaths and then use OFDM technology [32,[42][43][44][45][46][47] to deal with the multipaths (or ISI). Using OFDM, cyclic prefix (CP) can be exploited to combat the time asynchronism, and the channels are now ISI-free and DSFCs are designed on the subcarriers of OFDM to collect spatial/cooperative diversity.…”

“…Figure 5 shows the performances of the scheme. In [43], the idea of four group decodable code is exploited so that it is extended to the case of any number of cooperative nodes. In [44], a DSFC based on a layered structure similar to universal space-time codes in [56] has been proposed, which is using the tool of algebraic number theory.…”

“…In [44], a DSFC based on a layered structure similar to universal space-time codes in [56] has been proposed, which is using the tool of algebraic number theory. The schemes proposed in [42][43][44] are for flat fading channels. Under frequency-selective fading scenarios, [46] generalizes the idea in [42] and proposes a simple orthogonal STBC (OSTBC) coded system where the cooperative nodes work in the same way as (or similarly) [42].…”