Research On Confidential Communications Algorithm Of Physical Layer In MIMO Systems Based On Jamming Strategy

The broadcast nature of wireless communication decides that the communication signal iseasily intercepted by illegitimate receiver. Therefore, how to prevent from disclosing thecommunication messages in order to implement confidential communication has been the factorthat must be considered in the design of wireless communication systems. Traditional securitystrategies and regime are based on the design above the physical layer and all think physicallayer link is error-free. Unlike these thinking, artificial interference or cooperative jammingbased on the physical laye are used to achieve the security and confidentiality of communicationmessages for MIMO systems in this paper. The main work is as follows:1. For the problem that the secrecy capacity equals to zero while the illegitimate channel isnot the degrade of legitimate channel, the secrecy capacity algorithm of MIMO systems based onGSVD precoder and three algorithms of power allocation is studied. Meanwhile, equal powerallocation between null space subchannels corresponded zero singular values of illegitimatechannel or the method that take a limiting process of the power expression are proposed. Thus,the power allocation methods based on maximize subchannel difference and KKT condition arecompletely produced which achieving the filter and discard of the subchannel reasonablely.Simulation result shows that the precoder based on GSVD combined with the two powerallocation methods mentioned above can effectively increase the secrecy data rate of MIMOsystems.2. For single-user MIMO system, two ideal algorithms of confidential communication arestudyed under the condition that the CSI regarding the illegitimate channel be given. Amongthem, while the algorithm of null space of illegitimate channel could make the illegitimatereceiver be ignorant of the message completely, the algorithm based on generalized eigendecomposition can maximize the difference of SINR of legitimate receiver and illegitimatereceiver. Othermore, an artificial interference algorithm in which the transmitter not onlytransmit message signal but also transmit artificial interference signal in order to make theillegitimate receiver’s SINR drop sharply that could not decode the signal but do not affect thelegitimate receiver is studyed under the assumption that no information regarding the illegitimatechannel available at transmitter.3. For multi-user MIMO systems, an artificial interference algorithm based on singlemessage symbol means of transmission is studied. Then, a power allocation method of dynamicadjustment is proposed. This method do not need numerical calculation for the power allocationbetween the artificial interfenrence signal and each legitimate receiver’s message signal, butneed an interactive process between transmitter and each legitimate receiver. Because thealgorithm mentioned above has the disadvantage of low communication efficiency, an artificialinterference algorithm based on precoder of messages block is proposed. In this algorithm,except for confidentiality, the effectivity and efficiency of confidential communications are alsotaken into consideration. The artificial interference selectively degraded the passive illegitimatereceiver’s signal while do not effect each legitimate receiver. The precoding technique combined the existed zero-forcing method that used to eliminate the multi-user interference with singularvalue decomposition (SVD)-based linear precoder so that enhances the efficiency of confidentialcommunications. Simulation result shows that this precoding method degrades the illegitimatereceiver’s signal to interference plus noise ratio (SINR) even more and enhances the capacity ofmulti-user MIMO systems compared with the precoding method based on single messagesymbol.4. For transmitter’s power is limiting and in order to make full use of space dimension ofillegitimate receiver to implement interference, the secrecy capacity algorithm of gaussianMIMO channel based on cooperative jamming is proposed that three times to optimize thetransmitted covariance matrix in the order of “transmitter-helper-transmitter” by refering existingalgorithm and making use of property of positive semi-definite matrix so as to enhance thesecrecy capacity of MIMO systems. Espetially, a new way of thinking that find preferentially thecovariance of helper satisfied the condition of positive semi-definite matrix then determine thepower of helper used to transmitting the cooperative jamming signal is proposed that can correctsome deficiencies in related paper. Othermore, secrecy data rate in the condition of existingmulti-helpers is studied. CCJ and UCJ methods are given. Then, the factors which effect thesecrecy data rate are analyzed by modeling the quantity of helper as stochastic process whichobeys poisson distribution. Simulation result shows that the indicators such as the distributiondensity, the quantity of helper and so on are interrelated directly with secrecy data rate in the twocooperative jamming methods.