| Cognitive radio networks(CRNs)integrate the cognitive radio(CR)into the traditional wireless networks and enable the unlicensed secondary users(SUs)to opportunistically access the licensed spectrum allocated to the primary users(PUs)after sensing it,which has efficiently improved the spectrum efficiency and alleviated the contradiction between the dramatically increasing demand for spectrum resources and the underutilization of existing spectrum resources.From the perspective of networking,CRNs can be classified into the centralized,which can be managed easily and runs with high efficiency,and the distributed,which is more flexible.The existing literatures mostly focus on CRNs with single architecture,but researches about taking full advantages of multiple architectures to adapt to complex environment are limited.At the same time,the unbalance of spectrum resources in CRNs is much more severe than that in traditional wireless networks.Due to the dispersed geographic locations and the sensing nature of the SUs,along with the dynamic traffic of PUs,the available channels for SUs may be different,and the spectrum heterogeneity occurs.In order to solve the problem of weak connectivity caused by the spectrum heterogeneity and the problem of bad flexibility and survivability of CRNs with single and fixed architectures,we study the dynamic cooperative access with multiple channels and the network architecture self-adaption technology.The main works and significances are as follows:First of all,to solve the problem of direct link failing to satisfy the communication demand,which caused by the spectrum heterogeneity in distributed CRNs,a mass-sensing-blindly avoidance multichannel cooperative media access control protocol(MSBA_MAC)based on channel status list is proposed.With the proposed MAC protocol,SUs maintain simple available channel lists and avoid sensing the data channel with known status.Besides,as for the problem of whether to cooperate and the relay selection,we consider the extra time overhead in control phase and the transmission rate in data phase jointly.Simulation and experiment results show that the proposed MAC protocol can reduce the time overhead in control phase of the communication,and the optimal relay selection algorithm can achieve a maximum transmission rate.Then,considering the advantages and disadvantages of three typical architectures of CRNs,i.e.the centralized,single-hop ad hoc and the cooperative relay,in order to improve the connectivity and survivability of CRNs in complex environment,an anti-jamming network architecture self-adaption technology(NAST)based on cooperation and cognition is proposed.Through AP breakdown/recovery judging and direct link availability detecting,the technology enables the CRN to switch among centralized,single-hop ad hoc and cooperative relay architecture in an autonomous and flexible way.This self-adaptive switching can deal with physical breakdown and invalid communication link due to great distance or spectrum heterogeneity,and enhance the network robustness thereby.Finally,a testbed consisting of GNU Radio and Universal Software Radio Peripherals(USRPs)is set up to validate the architecture switching scheme of the technology aformentioned,which provides support for the promotion of NAST.Especially,we provide the detailed process of the implementation of NAST protocol from the perspective of access point,source node,destination node and the neighbor node respectively,and we also test the feasibility of NAST and the switching time among the three architectures using reasonable methods.Experimental results validate that NAST enables CRNs to switch among centralized,single-hop ad hoc and cooperative relay architecture in an autonomous and flexible way,which significantly improves the connectivity and Quality of Service(QoS). |
