Research On MAC-layer Spectrum Management Of Cognitive Radio Networks

Cognitive radio is an intelligent wireless communication technique that is aware of its surrounding environment,and learn from the environment by using the methodology of understanding-by-building and make corresponding changes in certain operating parameters,according to the incoming radio signal changes.There are two primary objectives for the application of cognitive radio networks: one is providing highly reliable communications whenever and wherever needed;the other is utilizing the radio spectrum efficiently.As traditional wireless MAC technique is designed for fixed spectrum allocation based wireless networks,it is not fit for cognitive radio networks which are based on dynamic spectrum allocation.Taking the basic functions of spectrum management of cognitive radio MAC: spectrum sharing,spectrum access and spectrum allocation as the research starting point,combined with the technical characteristics of cognitive radio MAC layer,we design and optimize related algorithms and protocols.The main research contents and contributions are as follows:1.In order to solve the reporting collision problem during the cooperative spectrum sensing process,we propose a contention-free scheme based MAC protocol.To realize the contention-free reporting,different from the traditional MAC protocols,two new phases have been added in the proposed MAC protocol.The newly added phases are reporting access phase and slot reassignment phase.To further improve the performance of the proposed MAC protocol,two admission control schemes are designed for throughput optimization and energy efficiency optimization.Simulation results show that the proposed MAC protocol outperforms existing protocols on throughput and energy efficiency.2.A dynamic backoff algorithm is proposed to solve the multi-user spectrum access problem in distributed cognitive radio networks.Furthermore,in order to implement the algorithm in cognitive radio network,a distributed multi-channel cognitive MAC protocol is proposed.In order to improve the network throughput,and reduce the channel access delay,the proposed dynamic backoff algorithm takes the number of competing cognitive users and the number of the sensed idle channels into consideration,and automatically selects the backoff window to maximize the expected network throughput in the initial backoff window selection process and subsequent backoff window selection process.The proposed distributed multi-channel cognitive MAC protocol applies dynamic backoff algorithm in its contention phase,so as to achieve dynamic adjustment of the duration of the contention phase and reduce the conflict of multi-user access.The simulation results show that the proposed cognitive MAC protocol has higher throughput and lower channel access delay compared with the existing protocols.3.A fair multi-channel allocation algorithm is proposed to solve the fairness problem of spectrum assignemnt in carrier aggregation technology based cognitive radio multi-channel networks.Considering the practical application of the proposed algorithm,a new MAC protocol is designed to solve the problem of spectrum sense and spectrum access.First,based on the Jain 's fairness index,a fair multi-channel assignment optimization problem is established considering the idle channel utilization efficiency maximization constraint,and the problem is transformed to a quadratic integer programming(QIP)problem.Then,according to the definition of Jain 's fairness index,a heuristic algorithm is designed to find the channel assignment method that maximizes the fairness index.Then,the channel assignment phase of the proposed MAC protocol uses the channel assignment solution obtained by the channel assignment algorithm to allocate the spectrum.After that,we further analyze the performance of the proposed algorithm and MAC protocol in terms of throughput,fairness,channel successfully grabbing probability,and blocking probability.The simulation results show that compared with the existing MAC protocol,the proposed algorithm and MAC protocol achieve a good tradeoff between the throughput and fairness.4.In order to handle the cross-tier interference problem of cognitive LTE-A heterogeneous networks,we propose a downlink partial spectrum sharing algorithm.The proposed algorithm first divides the radio resources into three parts: macro-dedicated portion,shared portion and femto-dedicated portion,so that the cross-tier interference problem is transferred to the downlink interference problem of the shared portion.Then,in view of the downlink interference problem of the shared portion,we combine two cognitive radio spectrum sharing mode: interweave mode and underlay model to design a hybrid downlink spectrum sharing algorithm.Using the algorithm,the femtocell can select the corresponding spectrum sharing mode according to the interference in the received downlink signal from the Macrocell,thus avoid the downlink cross-tier interference and improve the utilization efficiency of the sharing portion.Besides,considering the practical application of heterogeneous network,under the condition of given cross-tier fairness constraints,aiming at maximizing throughput,we build the optimization problem about the proportion of femto-dedicated portion,and get the optimal proportion of the femto-dedicated portion with the extensive search algorithm.The simulation results show that the proposed algorithm improves the total throughput of the heterogeneous network compared with the existing algorithms.