Study On Cooperative Communication In Cognitive Radio Networks

With the development of communication technology and the higher quality of communication,the evolution of communication technology is seriously constrained by the low utilization of thespectrum. The appearance of cognitive radio solves the problem well. The user can senses thesurroundings and reconfigure its own parameters according to the results of sensing to access theideal spectrum. The cognitive user keeps sensing the idol spectrum to utilize the spectrumeffectively. Cooperation communication is a novel technology that uses other user’s idol antennain the network to transmit the message by some certain ways. Like the multi-input multi-outputsystem, the receiver can obtain the spatial diversity gain and improve the system capacity.Combining cognitive radio and cooperative communication, the system allows other users tohelp sense the spectrum and transmit message. The combination enhances the detection accuracy,the utilization of spectrum and increases the system capacity, makes the most use of wirelessresource. However, cooperative communication also brings the potential safety hazard. Theprimary user cannot know whether the cooperative is reliable. The primary user should protect itssignal to be safe.This paper will combine the cognitive radio and cooperative communication to solve theproblem that the primary user cannot transmit the message while he is occupied the spectrum.Network coding will be used at the cooperative node to improve the capacity of the whole network.Also the power allocation strategy is raised to optimize the utilization of the system resource.Considering the security of the transmission, whether the cooperative node is reliable will bediscussed.First, this paper introduces the cognitive radio and cooperative communication and describesthe necessity of the combination of the two technologies. It emphasizes some common models,dynamic access methods and some safety problems in cognitive radio, cooperative protocol incooperative communication and the methods about the combination.Then, considering the primary user cannot finish the transmission but occupy the spectrum,the primary should give up the occupation and select a cooperative that want to access thespectrum to send message to help transmit the signal effectively. The cooperative node uses theamplify-forward method and modulation coding to forward the mixed signal. According to theprimary’s request, the power allocation strategy is designed to maximum the system capacity. Also the strategy can help the primary use select an appropriate cooperator.At last, it introduces a cooperative communication model based on security in the cognitiveradio networks. Relay selection strategy is also used in the cooperative process. The primary usermakes the untrusted relay not decode the code words by adding the artificial noise in the message.It analyses the system secret capacity and according to this, the relay selection method is workedout. And the power allocation strategy about the artificial noise is considered. The results showthat the system secret capacity is improved obviously by cooperation.