Research On Physical-layer-security Method In Multi-antenna OFDM System

Multi-antenna OFDM technology has been widely applied to various fields of wirelesscommunication, whereas communication security of the multi-antenna OFDM system has alsosuffered an increasing number of threats. Physical layer security technology enhances the safetyof communication with the difference, short-time reciprocity of radio channels, which is an idealand feasible security transmission scheme. However, physical layer security research in themulti-antenna OFDM system still faces the following problems:1) in the reciprocity channelscenario, when the sender does not have the multi-antenna advantage, the existing spatialscrambling methods can’t guarantee the safety of communication;2) in the non-reciprocitychannel scenario, the existing multi-user multi-antenna OFDM system security methods needfeedback plenty data result in the decease of securing throughput. Aimed at the above problems,the paper launch a special study on the physical layer security method of the multi-antennaOFDM system, which is supported by the National Natural Science Foundation of China.Firstly, on the reciprocal channel condition, a time-domain reference based physical layersecurity method and a joint scrambling of spatial and frequency based physical layer securitymethod are proposed. Secondly, on the non-reciprocal channel condition, a random beamformingbased MSIO-OFDMA physical layer security method is proposed. The content of this paperincludes:1. A time-domain reference based SIMO-OFDM physical layer security method isproposed. The receiver randomly adjusts the multi-antenna weights to control the sender’sreceived signal in each subcarrier called as time-domain reference variable when the reversetraining sequence is transmitted. The sender scrambles the transmitted symbols of this momentwith the time-domain reference variable. The receiver combines the received signals for correctdemodulation, the eavesdropper can’t get the time-domain reference variable to intercept thesecret information because of the difference of the radio channels. Security analysis andsimulation results show that the proposed method can effectively suppress the eavesdroppingwhile the legitimate users communicate properly.2. A joint scrambling of spatial and frequency based MISO-OFDM physical layer securitymethod is proposed. Firstly the sender randomly adjusts the spatial multi-antenna weights ofeach subcarrier, so that the multi-antenna weighted channel state of each subcarrier is same. Thusthe frequency-domain reference breaks the constant modulus constraint of the spatial scramblingmethods. Secondly, the receiver can correctly demodulate the remaining subcarriers with theestimation of the reference subcarrier. Because of the difference of the radio channels, thereference relationship doesn’t exist in the eavesdropper’s subcarrier channels. Security analysis and simulation results show that the eavesdropper can’t use the blind equalization, MUSIC-liketo intercept private information.3. A random beamforming based MISO-OFDMA physical layer security method isproposed. The method is divided into user selection phase and securing transmission phase, inthe user selection phase, the sender transmits randomly generated orthogonal beams by thepromised sequence, each user feedbacks the index of beams with the maximum SINR in everysubcarrier, which reduces the feedback overhead, then the subcarrier is assigned to the user withthe maximum SINR in the corresponding subcarrier. In the securing transmission phase, theuseful signal is transmitted on the beam with the maximum SINR, and the artificial noise istransmitted on the remaining beams. Performance analysis and simulation results show thatcompared with artificial noise method, the proposed method can effectively improve the securingthroughput.