Cooperative relay in the next generation wireless networks

Abstract

Cooperative relay becomes a promising solution for the next generation wireless communication systems and has been extensively studied during the past few years. Among the cooperative systems, there are many challenges towards the practical implementation of the relay networks. In this thesis, we shall try to develop useful relay protocols and tackle some of the practical issues of the relay networks. Specifically, we focus on the following discovery of the cooperative wireless networks. Cooperative spatial multiplexing for relay-assisted wireless systems. Most of the relay selection schemes considered in the existing literature deals with selecting one relay only. However, when we consider the wireless system with multi-antenna destination, we may have opportunities to transmit extra data through distributed cooperative spatial multiplexing by selecting multiple relays to participate during the cooperative phase. Therefore, we shall propose a low complexity multi-relay selection algorithm for the distributed cooperative spatial multiplexing using decode-and-forward protocol. We have also obtain asymptotic performance for the proposed system and discuss the diversity-multiplexing tradeoff as well as the throughput-reliability tradeoff at high SNR. Resource allocation for OFDMA systems with orthogonal relay. In the second piece of work, we consider the resource allocation problem in the wireless OFDMA system with a relay node. Since the use of relay node may enhance or degrade the achievable transmission rate depending on the instantaneous channel states between the source and the relay, the relay and the destination as well as the source and the destination. Hence, it is very important to dynamically adjust the resources allocated to the relay node so that the relay is used only at the right time according to the instantaneous channel states. We propose a resource allocation algorithm on the OFDMA system with orthogonal relay by employing rateless code. The resource allocation algorithm has low complexity and provable convergence property. Asymptotic achievable rate of the proposed algorithm is also derived. We show that the system achieves significant improvement compared with other baseline systems. Precoder design for correlated multi-antenna cooperative systems. Traditional approaches related to the precoder design of the multi-antenna cooperative systems focus on the relay node with amplify-and-forward and decode-and-forward schemes. Taking into consideration of the practical MMSE-SIC receiver at the relay and the destination node, partial decode-and-forward provides a better tradeoff solutions for the conventional amplify-and-forward as well as decode-and-forward relay protocols and achieves a better diversity-multiplexing tradeoff relations in the information theoretic sense. However, there are several important issues to be addressed regarding the application of partial decode-and-forward protocol in the practical cooperative wireless systems. Hence, we address the practical issues by proposing a joint MIMO precoder design for the multi-antenna cooperative system with correlated MIMO fading and partial decode-and-forward relay protocol. In addition, the MIMO precoders at both the source and the relay are matched to the MMSE-SIC receivers at the destination. We find that under similar system settings, joint MIMO precoder design with partial decode-and-forward relay protocol and MMSE-SIC receivers achieves substantial performance enhancement and has important practical significance. A low-overhead cooperative sensing protocol for cognitive radio systems. Conventional distributed sensing and centralized decision framework in the cognitive radio systems involving multiple sensor nodes is considered to enhance the sensing performance in the current literature. However, it is difficult to apply the conventional schemes in reality since theoverhead in sensing measurement and sensing reporting as well as in sensing report combining limit the number of sensor nodes that can participate in distributive sensing. In this part, we propose a novel, low overhead and low complexity energy detection based cooperative sensing framework for the cognitive radio systems. The energy detection based cooperative sensing scheme greatly reduces the quiet period overhead as well as sensing reporting overhead of the secondary systems and the power scheduling algorithm dynamically allocate the transmission power of the cooperative sensor nodes based on the channel statistics of the links to the BS as well as the quality of the sensing measurement. We show that the false alarm and mis-detection performance of the proposed cooperative sensing framework improve as we increase the number of cooperative sensor nodes.