Research On Node Selection In Wireless Cooperative Networks

Cooperation technology has played an important role in the rapid evolution of wireless communication. The cooperation among nodes in wireless cooperative communication networks can improve the outage performance, and the cooperation in wireless cooperative spectrum sensing networks can improve the cognitive performance. The node selection is a basic research topic in wireless cooperative networks, and has attracted more and more attention.First, this thesis introduces the basic model and schemes of wireless cooeprative communication networks. Then it reviews the study of node selection in networks. The work showed that it improved the outage performance through optimal node selection. Moreover, this thesis introduces the basic scheme and node selection in cooperative spectrum sensing networks.Currently, most of the research on node selection in the cooperative communication networks is based on the instantaneous Channel State Information (CSI). It needs accurate channel estimation and feedback of CSI which is not easy to achieve. In resource-constraint systems, it is more appropriate to get the instantaneous CSI of one hop rather than two hops. Considering both the instantaneous CSI of one hop and the statistic CSI of another hop, we propose two novel relay selection schemes and analyze the outage performance of the two schemes. In order to futher reduce dependence on channel estimation and feedback, this thesis studies how to select the optimal node set to cooperation in Amplify-and-Forward cooperative networks with the knowledge of statistic CSI. An optimal relay selection scheme is proposed with the descend order of equivalent channel gain which is a parameter based on the statistic channel information. The scheme implies that different relay nodes should be selected into cooperation under different SNR range.Network coding in cooperative communication has attracted more and more attention recently. The thesis brings network coding in the coded cooperation, and proposes a novel network-coding-based coded cooperation scheme. The outage probability of the proposed scheme is analyzed, and the result shows that a full diversity order can be achieved. Numerical evaluations reveal that the proposed scheme outperforms the classical scheme when the inter-user channel is poor, yet is worse when the inter-user channel is strong. To combine the advantages of the proposed scheme and the classical scheme under different inter-user channel conditions, we propose an adaptive solution. This adaptive scheme enhances the system performance considerably in all channel conditions regardless of the inter-user channel quality, at the expense of only one ACK/NACK bit. Then this thesis proposes two node selection schemes in network-coding-based coded cooperative networks with the knowledge of all statistical CSI. Numerical evaluations show that the proposed schemes can obtain the similar outage performance as the exhaust search scheme while reducing the complexity greatly.Cognitive radio (CR) is an important technology for efficient utilization of precious radio spectrum. Spectrum sensing plays the most important role in CR. This thesis firstly proposes a weighted fusion rule when the SNR of the secondary nodes are not identical. The weighted rule utilizes the differences of SNR. Then it derives the sensing performance of the weighted fusion rule. Numerical results show that the sensing performance of the weighted fusion rule is better than that of conventioanl rule. Considering the minor contribution of the secondary nodes with small weighted factor, a selective cooperative spectrum sensing scheme is proposed where the secondary nodes with SNR less than threshold are not selected into cooperation. The number of the nodes in cooperation is less while the performance doesn't degrade. Considering the resource consuming in the spectrum sensing, this thesis defines the utility fuction which is a tradeoff between the sensing performance and consuming resource. Then it proposes a selection scheme to maxmize the utility which is more practical.This thesis studies the node selection in wireless cooperative networks. It proposes the node selection alogrithms based on the partial CSI and statistic CSI in AF cooperative networks. The proposed algorithms are pratical. Then a novel network-coding-based coded cooperation scheme is proposed to improve the outage performance. The scheme can be used in the future cooperative communications. We propose two low-complexity node selection algorithms whose performances are similar to the exhaust search algorithm in the network-coding-based coded cooperation networks. The weighted fusion rule in cooperative spectrum sensing networks improves the sensing performance. Moreover, this thesis proposes a node selection scheme based on the utility which is a tradeoff between the sensing performance and resource cost. In all words, the studies on node selection improve the performance and they are more practical.