Robust Topology Building And Resources Assignment Optimizing In Cognitve Radio Networks

In cognitive radio networks, to avoid collision with primary users, cognitive users must vacant channels when they are being reoccupied because primary users have the absolute priority of using licensed channels. Thus, cognitive users’ data transmission will be disrupted. Interference will generate when the action is not taken in time and co-channel interference will happen when cognitive users which have the same interference zone are using the same channel. To prevent these conditions from happening, we must ensure the network connectivity and minimize the network interference. Besides, cognitive users need to detect channels before utilizing them. However, there exists the shadow effect, the shelter effect and the multi-path effect in the real network environments, those factors lead to the happening of the missed detection probability and the false alarm probability. Thus, imperfect channel detecting will occur.To reduce the effects of these factors on the network performance, we propose two solutions for the above two problems:(1) Assuming that there exists only one primary user share spectrum with multiple cognitive users, we prove there exist at least a robust channel assignment strategy when cognitive users have multiple radios in a cognitive radio network. To find out a robust channel assignment strategy which has the minimal network interference, CRTCA(Central Robust Topology Control Algorithm) gives the topology control algorithm and the channel assignment algorithm. Considering the interference to primary user which is caused by cognitive users, we propose ICAA(Improved Channel Assignment Algorithm) based on the algorithm. Simulation results indicate that ICAA can decrease the collision between cognitive users and primary user and increase the network throughput effectively.(2) Considering the false alarm probability and the missed detection probability which are caused by the shadow effect, shelter effect and the multipath effect in the actual network environment, we propose NICSA(Non-ideal Channel Selection Algorithm).By flexibly changing thresholds of the two indicators which are the channel access probability and the collision probability, the algorithm not only can dynamically adapt to different network environment but also can minimize the collision between primary user and cognitive users.