| In recent years, with the rapid development of wireless communicationtechnology, the available spectrum resource is going into short supply day by day,and the traditional fixed spectrum assignment policies lead to an underutilization ofthe allocated spectrum. The cognitive radio network， an intelligentcommunication systems which could utilize spectrum holes to boost spectrumefficiency is one of the possible options to solve the problem of the shortage ofspectrum resources. What’s more, with the development of signal processing andhardware technology, the smart antenna could greatly improve the spectrum efficiencyin space domain by space division multiplexing. In this paper, we argue that thecognitive radio equipped with smart antenna could share the spectrum with primaryusers in the same area, thus further improve spectrum efficiency by exploring spatialspectrum holes and break the bottleneck of the cognitive radio network capacity.The paper analyzes the background of cognitive radio networks and smartantenna technology and then focus on spectrum sharing technology in cognitive radionetwork with smart antenna. Firstly, in order to further improve the spectrumutilization efficiency, a spectrum access scheme which enables secondary users tocoexist with primary users and optimizes the allocation of spectrum and spaceresources was proposed for cognitive radio network with smart antenna. In addition,the successful communication probability of the secondary users when this scheme isapplied was investigated. The simulation results show that, compared to the Omniantenna, the cognitive radio network with smart antenna can get more opportunitiesfor transmission, and throughput significantly improved.Secondly, a spectrum handoff scheme was proposed. The scheme enablessecondary users change the antenna pattern to avoid interference to primary users andmaintain its communication without carrying out spectrum switch immediately. Bymodeling two antenna adjustment strategies, we investigate the statistical probabilityof secondary users utilizing the licensed channel with primary users simultaneously.Our analysis indicates that using smart antennas can greatly reduce the probability ofspectrum switch and increase the spectrum efficiency in the spatial domain. Also, wecompare the performance of smart antennas with different adjustment strategies withOmni antenna. The simulation results show that the higher PU density, the morethroughput improvement can be achieved using the smart antenna compared to the Omni antenna.Finally, we investigate the performance of the cognitive radio network withsmart antenna in the USRP2software-defined radio based test bed. The results showthat the cognitive radio systems with smart antenna can significantly improve thespectrum access opportunities and reduce the negative impact of the spectrum handoff,and proved that the proposed spectrum sharing scheme is feasible and effective. |
