Research On The Technique Of Physical Layer Security For Wireless Cooperative Relay System

As one of the key techniques of4G mobile communication, the technique of cooperativerelay system achieves huge advantages of quality and rate between users. But the openness ofwireless communication brings serious challenges on the security. Physical layer security bringsthe new way to resolve this problem. However, nowadays the techniques of physical layersecurity in cooperative relay system has some disadvantages:1) the method to grouping therelays based on physical layer security is not perfect, and the secrecy rate is low;2) the methodto resist the unreliable relays eavesdropping has the low profitability in power.3) the methodbased on artificial noise and randomly weighting will be of no effect if the wiretapping user hasmore antennas. To resolve the problems above, Supported by the National Natural ScienceFoundation of China, this paper spreads the research on the methods of physical layer security incooperative relay system.Firstly, a method that grouping and cooperation between decoded-and-forwarding strategyand noise forwarding strategy is proposed to improve the maximum secrecy rate; Secondly, topromote the efficiency of power when relays were untrusted, a scheme that joint randomizedweighting is proposed, In the last, to resolve the problem that cooperative jamming andrandomized weighting scheme failed if the eavesdropping user has more antennas, asecond-order spatial hopping transmission scheme is proposed. Concretely, the content isspreaded as follows:1. To promote the secrecy rate of system, this paper proposes a method that cooperationbetween decoded-and-forwarding strategy and noise forwarding strategy to improve themaximum secrecy rate. Firstly, in accordance with the gain in cascade channels ofsending-relaying-receiving, the relays were classified into collaboration jamming group andcollaboration relaying group. Then, the collaboration interference group and collaborationrelaying group through collaboration between groups, which collaboration jamming groupforwarded noise and beamforming by the group collaboration, towards the eavesdropping user;while collaboration relaying group decoded and forwarded signal, to form a beam towards thelegitimate users by collaboration within relays in the group; Finally, optimized the total powerallocation to achieve maximize secrecy rate. Simulation results show that: the maximum secrecyrate in the proposed method is more high than the referenced method, and keep upgrading withthe increase of the forwarded power; the proposed method can get up to0.6bps/Hz performanceboost than the referenced method.2. To resist the untrusted relays, this paper proposes a joint randomized weighting scheme.Firstly we add the channel between sender and legal user, to conceive the joint channel;Secondly the sender cooperated with relays, to design the randomized weighting coefficient, thejoint channel and the randomized weighting coefficient in sender and relays satisfied that thelegal user’s equivalent receiving channel was steady. Simulation results show that the BER ofuntrusted relay and the wiretapping user are nearly50%, however, the BER of legal user will be 103when the SNR is10dB.3. The method based on cooperative jamming or randomized weighting scheme failed ifthe eavesdropping user has more antennas than the sender. To solve this problem, this paperproposes a second-order spatial hopping transmission scheme. The sender, by the antennaswitching and the spatial hopping pattern, forms equivalent spatial channel of the first-order;Acting as a virtual multi-antenna receivers, relays use time-varying coefficient of beam-formingto weighted-and-forward, form equivalent spatial channel of the second-order. Simulation resultsshow that the scheme proposed achieves low probability of intercept (LPI) in eavesdropping userand the power consumption is lower than the method based on cooperative jamming.