Energy-efficient cooperative single-carrier frequency-division multiple-access

A variety of cooperative relaying schemes are designed for the single-carrier frequency-division multiple-access (SC-FDMA) uplink, when communicating over broadband wireless channels. Our goal is to reduce the battery power dissipated both by transmission and signal processing, so that the overall energy-efficiency may be increased. We assume that there are a number of inactive mobile terminals acting as potential relays, which have either fixed or time-variant positions in a cell. Our investigations are focused on the optimum exploitation of all the resources, when considering relay selection, power allocation and channel-quality-aided adaptive subband allocation. We exploit the benefits of combining the path-loss reduction and diversity gains arising from both fixed and opportunistic relaying, user cooperation and from all the propagation paths, as well as from multiple antennas. Novel frequency-domain equalisation and diversity combining approaches are also conceived. Specifically, we firstly conceive two single-relay assisted topologies for the sake of exploiting the achievable cooperative diversity, namely the single-dedicated-relaying (SDR), where each relay is dedicated to a single user, and the single-shared-relaying (SSR), when a single relay assists multiple users. In order to eliminate both the multi-user interference and for the sake of mitigating the noise-amplification imposed by amplify-and-forward (AF) relaying, we propose an efficient subband-based AF scheme, which is benchmarked against the conventional AF regime in the context of both the SDR and SSR topologies. Furthermore, by assuming that the channel state information (CSI) is available at the base station (BS)’s receiver, a joint frequency-domain equalisation and diversity-combining scheme is proposed for the sake of increasing the achievable cooperative diversity gain. In this case, when considering the different number of available relays that are geographically dispersed across a large-scale environment subject to both path-loss and shadowing, we propose three different dynamic relay selection schemes, namely single-user relay selection (SU-RS), multi-user relay selection (MU-RS), and multiple-access relay selection (MA-RS), combined with source/relay vi power allocation in the context of opportunistic cooperation (OC) for the sake of increasing the multi-user system’s throughput. By contrast, when the source-to-destination (S-D) direct links are of low quality and hence are deemed to be unavailable, we exploit the relays which are roaming within each other’s vicinity in geographically localised manner in a cluster. Therefore, by assuming that these cooperating relays are capable of exchanging their channel quality information (CQI), we propose two first-hop-quality-aware (FHQA) joint dynamic resource allocation (DRA) schemes for opportunistic relaying (OR) based SCFDMA uplink, which beneficially combines channel-quality-aware subband allocation with efficient relay selection. The FHQA joint DRA schemes optimise the multi-user multi-relay networks relying on whether it is the source-to-relay (S-R) or the relay-to-destination (R-D) link, which dominates the attainable performance, when the BS’s receiver employs either single or multiple antennas. Additionally, the benefits of OR are quantified in the context of interleaver-aided decode-and-forward (DF) relaying for transmission over correlated fading channels. Therefore, the length of the interleavers combined with channel coding may be shortened. As a result, we benefit from a reduced interleaving delay and/or from a total transmit power reduction. In comparison to the benchmark schemes considered in the literature, the reliability and energy-efficiency of our proposed systems are significantly improved.