| With the rapid development and advance of the mobile Internet, the wireless communication network, which is the basic for mobile Internet, is also put forward higher requirements on network performance such as transmission rate and stability. In future, it is Cognitive Radio and cooperative relay that, of great significance, are two kinds of key technical means in wireless communications networks. Cognitive Radio is designed to intelligentize the network and enable the network to access and identify the environmental information for independent optimal variable, while cooperative relay is to ensure the quality of the transmission. In this paper, the transmission performance of the cognitive radio network using cooperative relay were studied and optimized.Cognitive and cooperative relay are both of high flexibility, whose application of system and standards are in exploratory stage. Related research ranges from the microscopic theory to the macroscopic system architecture on some typical scenarios. Based on of a typical cognitive cooperative relay scenario, two kinds of relaying technology are studied theoretically, and the closed-form optimal solution is obtained, which has being verified through a large number of simulation. This article mainly includes the following three aspects:The first part is the summary of existing research results, lists some typical study scenario and analyzes the research characteristics of each scenario. In this part, two kinds of collaborative transmission technology, Amplify-and-Forward (AF for short) and Decode-and-Forward (DF for short), would be mainly introduced. AF refers to the way that every relay node forwards what it has received directly, by which the noise might also be pushed at the same time. It is very liable and simple for the relay node to accomplish this progress, and information security is not affected. Then in DF, signal need be decoded in each relay node to achieve the content of information, and send the information again after re-coding. The process of decoding and re-coding could filter the influence of noise step by step, while the information may be altered or steal, and it is much more complicated for the relay node than that in AF. When it comes to the select one, different specific scenario should have different choice.In the second part of the thesis, Dual-hop and Multi-hop cooperative relay system in cognitive wireless network are the main target for us to research theoretically and implement the scheme design, focusing in relay selection and power allocation. In the study of dual-hop scenario, information will be sent to the destination node by direct transmission link from the source node and by the relay node through the relay path simultaneously. However, in multi-hop scenario, the direct transmission will fade away on account of the distance, so that only relay path is available. Closed-form solution of power allocation would be achieved by theoretical derivation in both of the two scenarios and relay nodes is selected by enumeration and dynamic optimization respectively. Our goal is to optimize energy consumption and system capacity consistently.The third part is based on the former part, to forward the relay hop count as a variable factor for research and modeling. Closed-form solution of the optimal transmit power is given through strict theoretical derivation under the condition of variable hop count relay. What’s more theoretical relation between energy consumption and the relay hop count is given under the hypothesis of ideal system. On the choice of relay nodes, two relay selection schemes is designed based on theorems which were proved beforehand.All the theoretical achievements and designed algorithms above have be verified and compared through a comprehensive simulation. Implementation mechanisms, designed by the theoretical achievements, could improve system performance with high execution efficiency. |
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