Toward realistic wireless cooperative communications networks

Recently, the space-time block codes (STBCs) were suggested to use in wireless relaying networks (WRNs), denoted as distributed-STBCs (D-STBCs). This is to exploit effectively the spatial diversity and hence improve the link reliability. In addition, this usage may increase the network’s spectrum efficiency as it allows concurrent transmission from the relaying nodes. However, these networks encounter numerous issues that limit their wide practical use. This thesis addresses three critical issues of WRNs, and proposes solutions for each part individually. In Part I, WRNs are considered under imperfect synchronization. In the literature, most research tends to assume perfect synchronization among the cooperative relays. Unfortunately, this level of synchronization is almost impossible to achieve in real communication networks, and this introduces a significant performance degradation if imperfect synchronization is present in the network. This part includes mathematical models that are derived for WRNs, either one-way or two-way, under imperfect synchronisation conditions. Unlike existing models, this model provides a simple method of evaluating the problem for variant network configurations. In addition, this model considers the WRNs with N relays, each is equipped with Ra antennas, where N, Ra ∈ N+. With respect to current literature, the contributions of this part are : (1) both the existing PIC and SIC based detectors, which were proposed for specific network configurations instances, are extended here to work with the general model. (2) an enhanced interference cancellation based detector (EIC) is proposed. These proposed detectors shows significant performance improvement compared to the conventional detector under imperfect synchronisation conditions. In addition, the proposed EIC detector provides better improvement due to the designed interference cancellation process. It reduces the reliance on low-performance symbols and it benefits from interference components of currently-detected symbols using a modified maximum likelihood (ML) scheme. Accordingly, an extra performance improvement is achieved, particularly in the first iteration. Part II considers the issue of designing D-STBCs for WRNs with an arbitrary number of relays. It has been shown that the reliability of WRNs increases by adding more relays as a result of more communication paths becoming available. Unlike most existing D-STBCs, this part proposes two high rate coding schemes to accommodate an arbitrary number of relays, while retaining low decoding complexity at the destination. The first scheme, full-rate distributed space-time block coded-joint transmit/receive antenna diversity (D-STBC-JTRD), is proposed for AF WRNs. Its code rate is independent of the number of relays and hence no code rate loss is incurred as the relays number increases. In addition, this scheme deploys the same encoding matrices at every relay; this eliminates the need for additional network overhead to coordinate the code generation by the relays. In other words, there is no need to interrupt the transmission if a relay has been up/down. The second scheme aims to find a flexible trade-off between reliability and code-rate that can be offered by DF networks. Towards this end, a method to construct a D-STBC that is combined with spatial modulation (SM), denoted as D-STBC-SM, is proposed. This method is not restricted to a specific number of relays and can be constructed as necessary. In addition, a novel adaptive transmission protocol that uses the constructed codes, is proposed to achieve higher space diversity gain, even with relays equipped with a single antenna. Unlike most existing schemes, this protocol offers a throughput that increases as the number of relays increases. Moreover, the offered throughput is achieved using the same total average transmit energy, as only N0 of the N available participating relays are active at any given time. In Part III, the multi-user interference of WRNs is considered. Two transmission protocols with an interference cancellation scheme are proposed: the concurrentS−R−D-PICR,D protocol for DF WRNs and the concurrentS−R−D-PICD protocol for AF WRNs. Unlike existing protocols, these protocols allow the concurrent transmission in both phases of the transmission. Thus, high spectral efficiency is offered while maintaining low decoding complexity. This low decoding complexity is maintained due to the adaptation of the partial interference cancellation group decoding (PICGD) approach for WRNs, which was initially proposed by Guo, et al., for point-to-point (P2P) communication link. For a WRN consisting of J users equipped each with Ja-antenna, a single half duplex (HD) Ra-antenna relay, and M-antenna destination, the concurrentS−R−D-PICR,D protocol achieves the interference-free diversity gain (i.e., Ra × min {Ja,M}) without imposing any conditions on a node’s antenna number. The interference-free is the diversity gain achieved, assuming that each user in the network is transmitting solely without experiencing any interference from other users, hence it is considered as the natural upper bound of the diversity gain in multi-user WRNs. Similar to most exiting protocols, this protocol requires the CSI of the users-relay links at the relay. In contrast, the concurrentS−R−D-PICR,D protocol achieves a diversity gain of Ja ×M, given that Ra > 8, while the CSI is required only at the destination. Although the diversity’s upper bound is not achieved, this protocol uses a simple relay as no CSI or encoding is required at the relay. In addition, and unlike the existing protocols, the achievable diversity gain is determined by both Ja and M and it is not sacrificed while J is increased. This part also establishes sufficient conditions for an STBC to achieve the prior mentioned diversity gains, when the PICGD approach is employed by multi-users WRNs