Research On Physical Layer Secure Transmission Schemes With Discriminatory Scrambling Based On Channel Diversity

Wireless physical layer secure transmission techniques aim at the maximization of secrecyrate. The essential of differentiating from the traditional security techniques lies in using theindividual characterizes of wireless channels to distinguish the legitimate user and eavesdropper.The premise of achieving secure transmission is the channel advantage owned by the legitimateuser compared with eavesdropper, but no longer the assumed constraints on the priorknowledge and computing capability of eavesdropper. Private information carried via thechannel advantage, physical layer secure transmission techniques can create secure “dedicatedlink” for the legitimate user in the wireless channel. Discriminatory scrambling can adequatelyexploit the secrecy gain provided by the channel advantage and improve the performance ofsecure link. The connotation of discriminatory scrambling is introducing additional randomizedchannel scrambling, which can deteriorate the received signals of eavesdropper more seriouslythan the legitimate user. Furthermore, the realization of discriminatory scrambling generallyneeds the redundancy of channel resource based on channel diversity.However, there are no explicit definition and systemic methods for the design ofdiscriminatory scrambling. The design of discriminatory scrambling with different systemassumptions, in particular for the scenario existing unknown eavesdropper, is the key forpractical application of physical layer secure transmission techniques. As for the problems andrequirements mentioned above, this dissertation takes the design of discriminatory scramblingas the principal line. After refining the designing framework of discriminatory scrambling, thisdissertation makes further research on the physical layer secure transmission schemes withdiscriminatory scrambling based on channel diversity for different channel models and networktopologies. The main research achievements are as follows:1In order to specify the definition and systemic methods of discriminatory scrambling, wepropose the linear randomization framework, which includes additive and multiplicativenoise discriminatory scrambling methods. The theoretic analysis shows that the additivenoise following complex Gaussian distribution would yield the maximum interference tothe eavesdropper. To verify and characterize the secrecy capability of multiplicative noise,we propose a random beamforming security scheme in MISO wiretap channel. The randombeamforming vector can be treated as equivalent multiplicative noise to the eavesdropper,which is transformed into additive one via a logarithmic operation. When the amplitude andphase follow lognormal and uniform distributions, respectively, the multiplicative noisewould yield the maximum interference to the eavesdropper. We derive the achievablesecrecy rate of the multiplicative noise and optimize the power allocation between desired signal and multiplicative noise for the improvement of secrecy rate.2For the MISO fading wiretap channel, we optimize the additive noise discriminatoryscrambling to improve the secrecy performance of artificial noise scheme. Two secrecymodels involving noise transmitted by source node and aided node, respectively, areconsidered. The closed-form of secrecy outage probability is derived based on the Jacobianprinciple, and then the power allocation with adaptive and fixed methods are optimized forminimizing the secrecy outage probability. Effects of fading correlation on the secrecyperformance are analyzed for the considered two secrecy models. The results show that thefading correlation would have impacts on both the transmitted signal and noise, and thenincrease the outage probability.3An information-guided randomization physical layer secure transmission scheme isproposed, through the design of multiplicative noise discriminatory scrambling, toguarantee the secure transmission in MIMO wiretap channel. The scheme is based onspatial modulation technique with receiving antenna index for carrying information.Combined with the similarity of using channel differential to distinguish informationsymbols and users, respectively, dual-randomization discriminatory scrambling of randomweights and random channel handoff is created by the designs of redundant preprocessingweights. The multiplicative noise guided by information source renders the signals ofeavesdropper to be random fast varying. Three methods for the designs of preprocessingweights are proposed for different system configurations. Analysis and numerical resultsshow that the proposed scheme can decrease the probability of interception.4Much more channel advantage can be created for the legitimate user with the assistance ofcooperative nodes. For the multi-carrier cooperative relay system, based on the channelredundancy provided by the various channel diversity, a random selection of relay nodesbased security scheme is proposed through the design of multiplicative noisediscriminatory scrambling, which can guarantee the security of two hops, simultaneously.The scheme uses sub-carrier block as forwarding unit, only one relay node is randomlyselected and activated via the preprocessing weights to execute DF forwarding. Then theselected node achieves the secure transmission by creating random sub-carrier referencingin the sub-carrier block, and the distribution of random weights for the sub-carrier isoptimized. The analysis and numerical results verify that random selection of relay nodewould restrain the interception of eavesdropper.