Channel Security Of Distributed Wireless Cooperative Communication Systems

As one of the key techniques to improve the capacity of wireless communicationsystems, the cooperative technique achieves huge advantages of quality and rateamong users. The openness nature of wireless channel makes the signal vulnerable toeavesdropping, which brings serious challenges on the security. The securityperformance of wireless relay systems in view of information theory is studied, andthe main research work is specified as follows:The security of single-relay two-way cooperative systems is investigated. In atwo-way communication system, artificial noise is introduced by relay node tointerfere the channel of eavesdropper, and the security capacity of this symmetricalcommunication system is deduced. Under the limited total power, the average powerallocation and the optimal power allocation schemes based on full CSI are discussedrespectively, and the corresponding closed-form solution of optimal power allocationfactor is calculated, which depends on the location of eavesdropper. As theeavesdropper’s location is difficult to obtain actually, a more practical sub-optimalpower allocation scheme is proposed. Simulation results show that the proposedsub-optimal power scheme can reduce the quality of eavesdropper channel effectively,maximize security communication region and secrecy rate.The multi-relay wiretap channel communication system is researched. Twojamming schemes that artificial noise broadcasted by the source or relay nodes areproposed. With the full CSI known, the optimal power allocation factors closed-formsolutions between useful signal and artificial noise of the two schemes are obtained. Itis found that the power allocation factors depend on whether the main channel isbetter than wiretap channel: when the main channel is better, the factors are largerthan0.5, otherwise, they are smaller than0.5, and more transmitting power shouldbe used to broadcast artificial noise to interfere the wiretap channel and assure thesystem security. As it is difficult to obtain the CSI of eavesdropper, a sub-optimalpower allocation scheme in high SNR is proposed. To maximize secrecy rate, the totalpower allocation between source and relay nodes is optimized with limited power, the optimal power allocation factor closed-form solutions are also derived. With thepartial CSI known, the secrecy outage probability of flat Rayleigh fading channel isdiscussed, and the optimal power allocation factor to minimize secrecy outageprobability of the two schemes are obtained and compared. Simulation results verifythe validity of the proposed schemes, as well as the superiority of optimal powerallocation schemes. Since the performances between sub-optimal and optimal powerallocation schemes are similar, the sub-optimal power allocation scheme is alternativein practical applications.