Research On Interference Mitigation In Cognitive Radio Networks

With the rapid development of wireless communications technology, radio spectrum resource is increasingly scarce. Cognitive radio (CR) is a popular technology which can dynamically access to the vacant radio spectrum resource, effectively solve the problem of spectrum resources shortage, and increase the frequency spectrum efficiency, but at the same time, it brings new challenge to the interference mitigation mechanism.Based on the knowledge of the cognitive radio network, the interference mitigation between the unlicensed system and the licensed system in CR networks is focused. First, on the basis of the study of the interference between the two systems, where the adjacent channel interference and the cochannel interference are included, the restriction on the interference introduced to the primary user is straightforwardly converted to that on the CR user's transmission power. Then, the interference mitigation technology by insertion of cancellation carriers at the borders of?the licensed band to reduce the out-of-band radiation of the?unlicensed signal is investigated, and combined to the windowing technology. Simulation results show that with only two cancellation carriers at each side of the licensed band, the out-of-band radiation?can be reduced by more than 10 dB, and after windowing, the suppression result can rise to 30dB, which is caused by the raised-cosine window.Finally, according to the different purposes of optimization, several subcarrier and power allocation algorithms are proposed to mitigate the interference in CR networks, which can optimize the performance of the CR system, while keeping the total interference introduced to the PU band below a certain threshold and the total power allocated to the CR users under a constraint. Simulation results show that, the Fair-SAA can almost achieve fairness among all the CR users and it can obtain the tradeoff performance between the transmission rate and the interference. Furthermore, when the CR uses are close to the PU, the interference-based step power allocation algorithm can achieve the best performance, otherwise, the distance-based step power allocation algorithm A is the best.