Research On Resource Allocation In Cognitive Femtocell Networks

With the implementation of the LTE/LTE-A system, the proportion of indoor high-speed data services in the communications business is growing, which puts forward even higher standards for the indoor coverage and system capacity of mobile communication system. The frequency band of LTE/LTE-A system deployment is mainly distributed in the high frequency band and the attenuation of high frequency signal through the walls of buildings is worse than that of low frequency signal, which leads to the increase of indoor weak coverage and blind coverage.Deploying a number of femtocells base station in the traditional macro celluar network can effectively improve the indoor coverage quality of traditional macro cellular network. Due to the shortage of spectrum resources, the femtocells base station and the macro base station deploy in the same frequency, this deployment will bring serious interference to the macro cellular network and reduce the performance of the two-tier network. Therefore, it is necessary to study the interference management of the two-tier network. Cognitive radio technology can improve the low spectrum utilization of femtocell base station effectively. In this paper, we combine femtocell and cognitive radio technology together effectively and study the problem of interference suppression based on resource allocation in the coexistence of the cognitive femtocell base station and the macro cellular network. Two cognitive femtocell base station resource allocation methods are proposed.1) The existing algorithms based on spectrum sensing of resource allocation in cognitive femtocell base station are substantially negligible the factor of imperfect spectrum sensing, but the perfect spectrum sensing is difficult to achieve in practice. In this paper, we propose a novel network resource allocation scheme for cognitive femtocell network based on imperfect spectrum sensing method. The target of this proposed resource allocation algorithm is to maximize the sum of the throughput of all femtocell users under the QoS constraints of both femtocell users and macro communication combining the channel and power allocation method. Simulation proved that the all femtocells capacity of cognitive femtocell networks is more about 7.6% than that of the traditional femtocell networks; Meanwhile, the performance of the cross layer interference suppression and the spectrum utilization of the proposed algorithm is superior to that of the algorithm based on perfect spectrum sensing method, and the average cross layer interference of users of macro will not be higher than the cross layer interference limit.2) In view of the dense deployment of cognitive femtocell base stations in the cognitive femtocell base station system, simple overlay spectrum access mode can not fufill that all cognitive femtocell users can get free spectrum for data transmission, we present a mixed spectrum access scheme for resource allocation in cognitive femtocell network. The method is proposed to present a strategy to divide inside femtocell base station and outside femtocell base station for downlink of cognitive femtocell system. We prove that inside femtocell base station select the overlay spectrum access scheme and outside femtocell base station select the underlay spectrum access scheme can make cognitive femtocell system to obtain a higher system capacity. Simulation results show that hybrid spectrum access mode can obtain better system capacity than overlay spectrum access mode or underlay spectrum access mode. The system capacity of hybrid spectrum access scheme in this paper can be obtained more about 3% than the underlay model, and the total capacity of cognitive users get of overlay spectrum access mode is basically unchanged.