Outage analysis and optimization for wireless multiuser relay networks

In this thesis, we propose a suite of schemes for wireless multiuser relay networks, where multiple source nodes (SNs) and relay nodes (RNs) share the spectral resources and hence we take into the account the co-channel interference (CCI). Our objective is to deal with both the channel fading and CCI in order to improve the attainable outage performance. Firstly, we consider the opportunistic relay selection (ORS) design in the scenario, where multiple RNs are available for assisting the transmission of a single SN, while CCI is imposed by other SNs in the network. We design the single-user-detection-aided (SUD-aided) and multi-user-detection based successive interference-cancellation-aided (MUD-SIC-aided) systems, where multiple-user detection (MUD) receivers using successive interference cancellation (SIC) at the destination node (DN) are adopted to combat co-channel interference. In SUD-aided system, we employ single-user detection (SUD) at the RNs and MUD SIC at the DN. In MUD-SIC-aided system, we employ MUD-SIC at both the RNs and DN. We present the outage analysis of both systems based on an outage-optimised ORS scheme, implying that the proposed ORS scheme provides the best outage performance. We show that the traditional ORS scheme proposed for SUD receivers based on the highest SNR criterion is not outage-optimal, when employing MUD-SIC in the presence of CCI. Hence, we propose a novel ORS scheme based on a best-effort detection (BED) criterion that outperforms the traditional ORS scheme. Furthermore, considering the effects of the outdated channel state information (CSI), an improved BED-ORS is proposed for enhancing the robustness towards CSI imperfections. Then, we study the scenario, where multiple SNs are coordinated to share a RN. In this case, network coding (NC) may be invoked at the RN, which treats the CCI from other SNs as useful messages and superimposes them to reduce the time slots required for relaying, therefore achieving higher spectral efficiency. However, NC systems may not always be beneficial in cooperative communications, where the detrimental interference of the undesired SNs, often referred to as network coding noise (NC noise), may outweigh the benefits of NC. In previous works, the outage performance was only evaluated numerically for several case studies. Against this background, we propose a systematically analytical framework for evaluating the outage performance for a multi-unicast NC-aided network, where each DN extracts the information of the desired SN from the NC signal forwarded by the RN. As our main contribution, we present the outage analysis of this system in the presence of NC noise and the closed-form analytical outage probability expressions are derived for an arbitrary number of SN-DN pairs. We show that if NC is employed, the quality of the worst SN-DN link may dominate the outage performance of every SNs. We then consider a two-hop network, where multiple SNs transmit to a DN with the aid of a RN and we assume the direct link between the SNs and the DN is weak. In this scenario, we show that the NC-aided relaying is not preferred and hence the buffer-aided relaying (BAR) is advocated for improving the uplink. The RN is equipped with a buffer, which is capable of storing multiple frames received from the SNs. During each time slot, the proposed protocol activates either the SNRN hop or the RN-DN hop, depending on the channel quality of each hop and the buffer state at the RN. In order to optimise the hop selection for the network, we design a hop quality metric (HQM) and propose a multi-user buffer-aided-relaying uplink (MU-BR-UL) protocol. The benefits of the proposed protocol is analysed in terms of the end-to-end outage probability and the end-to-end transmission delay. Then, the optimal power allocation is proposed for minimizing the end-to-end outage probability under the total power constraint. Furthermore, the impact of the buffer size, the number of users and the relay position on the achievable outage performance are characterized. The results indicate that the outage performance is significantly improved when theproposed power allocation is utilized in the MU-BR-UL protocol. Finally, we consider a new family of networks, in which the SNs and RNs have energy harvesting (EH) capability, which allows the nodes to harvest energy from the environments and convert it to electrical energy for wireless transmissions. The EH removes the constraints of relying on a battery for constant power supply, but also demands novel energy usage policy (EUP) design for effectively utilizing the random power supply gleaned from the EH system. We start with the point-to-point (P2P) network and by effectively exploiting the statistics of the energy arrival rates, we propose novel search algorithms for designing the EUP, which achieve a significantly better outage performance than the state-of-the-art designs reported in the literature. Based on the proposed methods in P2P network, we design novel EUPs for spacedivision- multiple-access (SDMA) and SDMA-based relay sharing networks. We show that the proposed EUPs significantly outperforms the state-of-the-art benchmarks in terms of outage performance.