Research On Physical Layer Security Strategies In Cooperative Transmissions In Cognitive Radio Networks

In cognitive radio networks(CRN),due to the broadcast feature of wireless media,the transmitted signal is easily eavesdropped and attacked by eavesdroppers.Cooperative transmission is performed via relay forwarding to assist the transmission of source signals,in order to increase transmission reliability and defeat channel fading during signal transmission.In addition,cooperative diversity that induced in the process of relay cooperation improves secure channel capacity,which effectively defeats eavesdropping attack and enhance system security.Currently,green wireless communication technology that featured by energy-efficiency as its objective is attracted by many researchers.Green communication is set as one of the development perspectives in future CRN.This thesis constructs secure and reliable green CRN scenario,and investigates physical layer security(PLS)strategies in cooperative transmission in CRN.PLS strategies and security-reliability tradeoff(SRT)perfonnance analysis are studied in both single and multiple eavesdropper scenarios in CRN.Meanwhile,security guaranteed energy-efficiency optimization scheme is also studied in single eavesdropper scenario.Simulation and performance analysis of the tradeoff between energy-efficiency and security as well as secutiy and reliability are conducted in CRN cooperative transmission respectively,in order to realize energy-efficiency guaranteed secure and reliable transmission in CRN.Specific research works are provided as below.1)PLS strategy in cooperative transmission in cognitive decode-and-forward relay networks with single eavesdropper and SRT performance are investigated.In Nakagami-m fading channels,relay forwards information to destination via cooperation while eavesdropper attempts to intercept the relay forwarding information via eavesdropping channel.A best relay selection(BRS)scheme against eavesdropping attack is proposed,in order to guarantee the maximum secure main link channel capacity.In addition,SRT performance is presented.The reliability performance is measured by outage Probability(OP)while the security performance is quantified by intercept probability(IP).Numerical results show that the proposed SRT scheme strictly outperforms traditional direct transmissions in terms of SRT performance.SRT performance can be enhanced obviously with the increasing of relays and Nakagami channel fading factor m for a given numbers of relays.2)PLS strategy in cooperative transmission in CRN with multiple eavesdroppers and SRT performance are studied.In Nakagami-m fading channels,consider multiple independent identical distribution(i.i.d)eavesdropping channel and channel capacity,BRS is performed via the maximization of secure channel capacity.Meanwhile,closed-form expressions of OP and IP are derived respectively and the corresponding SRT performance is analyzed.Numerical results indicate that,the multiple eavesdroppers over Nakagami-m fading channel scenario expands the SRT performance of direct transmission and single relay BRS scheme in single eavesdropper scenario.In addition,SRT performance is also enhanced obviously with the increasing of relay mimbers and Nakagami channel fading factor m.3)Security guaranteed energy-efficiency optimization scheme in CRN cooperative transmission is studied and the relationship between security and energy-efficiency is investigated.For single eavesdropper scenario,BRS is conducted with the objective of secure channel capacity maximization,and the closed-form expressions of IP and energy-efficiency are given respectively.Numerical results show that,the proposed scheme can implement the effective tradeoff between CRN energy-efficiency and security,which realizes secure and reliable transmission in high energy-efficient CRN.The thesis initially designs and studies physical layer security strategies in cooperative transmissions in CRN.Research results are of great value for farther works.