Research On Resource Allocation Alagorithms For OFDM System Restricted In Physical-Layer Security

As the universal application of Orthogonal Frequency Division Multiplexing (OFDM)technology, the OFDM wireless communication system’s physical layer security has been widelyattracted. Physical layer security took advantage of the wireless channel difference andreciprocity to secure transmission. The unique allocation of powe, subcarrier and other resourcein OFDM system can influence the characteristics of communication channel, so as to influencesecurity of the system. Although the number of resource allocation algorithm consider security issmall, they all have some limitations:1) existing algorithm need to know the real timeinformation of wire-tap channel, but it is difficult to get;2）existing algorithm cannot protectsecure transmission of all users in the multi-user system, system’s whole security is hard topromote;3）existing algorithm do not take it into consideration that there might be severaleavesdroppers, when the eavesdropper sits in a situation where the condition of the channel isbetter, the system’s secure transmission cannot to be protected. So, relying on National NaturalScience Foundation, this paper performs specialized researches focusie on the problem of OFDMresource allocation restricted in physical layer security,.This paper establishes wire-tap model of ODFM system’ from single-user and multi-userperspectively. It proposes a power allocation algorithm according to get real time information ofwire-tap channel is difficult under secure transmission of single-user OFDM system; And aimingat the existing schemes which cannot guarantee the security of all user in multi-user OFDM, itproposes a resource allocation scheme restricted in physical layer security for multi-user OFDM.Then it proposes a resource allocation scheme restricted in physical layer security for OFDMAsystem under non-ideal environment for the problem that the assumptions of the existing securitymodel are too ideal. The specific research contents include:1. The paper proposes an optimal power allocation algorithm under security transmission ofsingle user OFDM system. On the basis of establishing the OFDM wire-tap model, the algorithmusing the secrecy capacity of when the SNR value of legitimate users and the eavesdropper aredifferent from each other to measure the security of the system, building the optimizationproblems model of maximization the secrecy capacity and minimization transmit powerseparately, and solving the optimal allocation result by finding the feasible KKT point under theKKT condition of the supposed optimization problems. The simulation results show thatcompared the average allocation the secrecy capacity of that algorithm can be improve3.109bit/s/Hz when the number of sub-carriers is128.2. This paper proposes a resource allocation scheme for multi-user OFDM system restrictedin physical layer security. On the basis of establishing the multi-user OFDM wire-tap channelmodel, the scheme sets required secrecy capacity values for every legitimate users, measuringthe overall security by defining total secrecy capacity of the system, building t he optimizationproblems model of maximization the total secrecy capacity and minimization the total transmit power separately, and completed the joint subcarrier and power optimization process by usingdual decomposition method. The simulation results show that, comparing to the referencescheme the total secrecy capacity of that scheme can be improved2.071bit/s/Hz at most, and atthe same time the scheme can meet the secrecy capacity value of0.5bit/s/Hz for legitimate allusers.3. This paper proposes a resource allocation scheme for OFDMA system in non-idealenvironment restricted in physical layer security. On the basis of establishing the OFDMAnetwork model in non-ideal environment, the scheme using multiple antennas at the sender,utilize artificial noise worsen the transmission channel of eavesdropper, so that can be ensuredthe secure transmission of information when there are more eavesdroppers. Using the secrecyoutage capacity to measure the security of system when unknown the real time channelinformation of eavesdropper’s channel, and completed the subcarrier and power optimization ofmaximization the secrecy outage capacity by using dual decomposition method. The simulationresults show that, the secrecy outage capacity of the system can achie ve5.91bit/s/Hz, when thetotal power of transmit is44dBm.