Multi-User Performance of the Amplify-and-Forward Single-Relay Assisted SC-FDMA Uplink

This paper characterises two single-relay assisted single- carrier frequency-division multiple-access (SC-FDMA) amplify-and- forward (AF) based cooperative strategies employed for multiuser uplink transmissions over multipath fading channels. For the sake of exploiting the benefits of cooperative diversity, we investigate both single-dedicated- relaying (SDR) as well as single-shared-relaying (SSR), and propose a frequency-domain (FD) subband-based AF scheme combined with subband remapping, which is benchmarked against conventional time- domain (TD) AF in the context of both of the above-mentioned relaying topologies. Our simulation results show that cooperative diversity is beneficial for both SDR and SSR, both in the absence and in the presence of multipath diversity. More importantly, the proposed FD-AF scheme is capable of attaining a multiuser performance, which is better than that of the conventional single-user TD-AF protocol operating in a multipath environment, because of the subband-based AF and noise suppression capability of the relay. I. INTRODUCTION Wireless cooperative communications and relaying have attracted substantial research attention over the past decade as a benefit of their spatial diversity gain attained in a virtual multiple-input multiple-output (V-MIMO) scenario created by the distributed single- antenna terminals by sharing resources with their cooperative part- ners. This cooperation allows the system to mitigate the radio channel's fading by jointly exploiting the benefits of frequency- , time- and spatial-diversity. Furthermore, the cooperative strategy nal subcarrier mapping in order to support multiple users without con- tamination by MUI. Furthermore, our single-relay assisted SC-FDMA system allows user cooperation to achieve a diversity gain without imposing MUI by the cooperating sources and relays upon the UL- receiver at the basestation (BS). It is worth noting that SC-FDMA is capable of exploiting the benefits of multipath diversity for transmis- sion over broadband channels, while in orthogonal frequency-division multiplexing (OFDM) (12) each subcarrier experiences a single-path channel, hence no multipath diversity gain is achieved. It has been indicated in (13) that SC-FDMA attains a similar overall performance as orthogonal frequency division multiple access (OFDMA), but it is more suitable for uplink transmission due to its lower peak-to- average power ratio (PAPR), which is typically high in multicarrier systems (12). Additionally, the combination of based modulation with the discrete Fourier transform and inverse discrete Fourier transform (DFT/IDFT) SC-FDMA transmitter can be adaptively reconfigured in order to mitigate the effects of time-variant channels. The system is also available to cooperative communications. Hence, our novel contribution is that we achieve cooperative diversity by utilising a sophisticated SC-FDMA scheme, which exploits the benefits of AF based single-relay assisted user cooperation aided UL transmis- sions. Our simulation results show that cooperative diversity may be achieved for both the single-dedicated-relaying (SDR) and single- shared-relaying (SSR) strategies in both single-path and multipath scenarios. As a result, the proposed frequency-domain (FD) subband- based amplify-and-forward (AF) scheme is combined with subband remapping at the relay. By contrast, the system invokes minimum mean-square error (MMSE) assisted FDE for each of the cooperative branches at the BS, where a simple time-domain (TD) equal-gain combiner (EGC) (14) is adopted. The resultant system is capable of achieving a multiuser performance, which is better than that of the conventional single-user TD-AF protocol operating in a multipath environment.