Research On Dynamic Cooperative Relay Selection Schemes For Mobile Users In Cognitive Radio Networks

With the growing popularity of wireless communication terminals today, spectrum resources have become a valuable scarce resource. However, most of the spectrums are currently assigned to fixed users, which lead to a serious waste of spectrum resources and lower utilization, due to the temporal and special diversity. Cognitive radio network technology attracts lots of attention because it can access to the idle spectrum band and dynamically adjust the communication parameters to use the spectrum, which is considered to be an effective way to improve the spectrum utilization. However, in the cognitive radio networks, both sides of the communication will also be influenced by the shadow fading and other factors, and may not meet the communication quality. Cooperation relay technology with spatial diversity gain can be an effective way to against the fading and improve communication quality. Relay selection algorithm is the key issue of the cooperation relay. It is mainly to help users select the appropriate relay nodes efficiently. Considering the fact that most of the users in wireless network are in a constant state of movement, thus the combination of the theoretical research with mobile model is very necessary. Thus, the combination of the theoretical research with mobile model is very necessary. So this paper is to study cooperative relay selection algorithm for mobile users in the cognitive networks.This paper has two main innovations:Firstly, we make the cooperative relay selection algorithm based on the network scene where users are on the move, which is closer to the reality, and it is overlooked by previous studies and necessary to the implementation of the algorithm. The second is to apply the optimal stopping theory in the dynamic relay selection algorithm, making the selection process avoid to scanning all the candidate relay nodes, thus greatly reducing the time and the cost of relay selection, which increases the efficiency of relay selection. The paper are organized as follow, firstly introduces the research status of cooperative relay selection algorithm, and emphasis on the background, significance and necessity of this paper content. Then we introduce the basic principles of cognitive radio, common models of mobile social networks, cooperative relay technique as the basic principles of the algorithm. To address network mobility problem for users, we introduce Constrained Markov Decision process model, and we set the position and the buffer status of the primary users as the two states and the packets loss rate and the relay transmission cost as the constraint conditions. We solved the problem using linear programming. Our relay selection algorithm reaches a dynamic equilibrium between the QoS and the cost in the communication system. However, the algorithm we proposed above have two limits, first it doesn’t consider the mobility of the secondary users, what’s more, it is based on scanning all the candidate relay node, which decrease the efficiency of the relay selection. In order to move the model closer to reality, and to solve the problem of low efficiency caused by scanning all the candidate relay nodes during the relay selection, we build further complicated system model, where the secondary users have mobility as the primary users do. We transform the mobility problem into the probability of usability of secondary users, and we transform relay selection into a model based on the theory of dynamic optimal stopping theory that is widely used in the economic field, thus ensuring communication quality while improving the efficiency of relay selection. Finally, we verify the relay selection algorithm through simulations, and the two relay selection algorithms we proposed achieve the desired results and have a good performance in the network environment for mobile users.