Research On Directional Modulation For The Physical Layer Security Communication And The Integration System With Communication And Direction-finding

With the development of wireless communication technique, two issues have aroused people’sattention, one is the information security of wireless communication, the other is the integrationsystem with wireless communication and direction-finding, especially in military and homelandsecurity application. The directional modulation technique is researched in this doctoral dissertation,which is divided into two directions,(a) directional modulation signal using a phased array,multi-beam directional modulation signal and directional modulation spread-spectrum signal for thephysical layer security communication;(b) multi-beam directional modulation signal andDoppler-frequency directional modulation signal for the integration system with communication anddirection-finding.The main work of this doctoral dissertation is summarized as follows:1) A directional modulation signal using a phased array based on multi-objective genetic algorithmis proposed. According to the relationship between Euclidean space of constellation points and biterror rate performance, the values of the phase shifter are generated by means of optimizingmulti-objective genetic algorithm to synthesize a directional modulation signal. This signaltransmit different signal constellation at different directions. At the desired direction, the transmitsignal’s constellation is the same as the traditional baseband modulation signal while the transmitsignal constellation is scrambled at other directions. Compared with the traditional directionalmodulation signal, the directional modulation signal proposed in this doctoral dissertation hasmore narrow information beam-width. Simulation results show that the proposed technique offera more physical layer secure transmission signal for wireless communication.2) A dual-beam directional modulation signal using a corner reflector antenna is proposed. Theconstellation points of the receive signal maintain their positions as traditional basebandmodulation signal at the desired direction, but scramble in the phase at the undesired directions.This dual-beam directional modulation technique is compatible with the spread-spectrumtechnique because the transmit signal is modulated by the spreading sequence at the baseband andmodulated by two beams’ radiation pattern at the antenna level. In this way, the transmit signal ismodulation by the spreading sequence and the directional information of the receiver to offer asecure transmission method for wireless communication.3) A physical layer secure communication system aided by artificial noise using a sum-difference multi-beam Cassegrain antenna is designed. The main idea is that the sum beam transmitcommunication signal, simultaneously, two difference beams transmit artificial noise to guaranteesecure transmission of the sum beam. The eavesdropper’s channel is degraded by artificial noisebut the desired receiver’s channel does not affect because of the spatially orthogonal between thesum beam and two difference beams. In this way, the desired receiver can demodulate thecommunication signal while the eavesdroppers learn almost nothing about the information fromits observations.4) A directional modulation spread-spectrum signal is proposed using a switched antenna array. Themain idea is that a switching scheme of the switched antenna array is designed according to aspreading sequence. The harmonic components generated by the antenna switching spread thespectrum of the transmit signal. The transmit signal is associated with the spreading sequence andthe directional of the desired receiver. In this way, the desired receiver with a single antennademodulates the receive signal as the traditional spread-spectrum signal, while eavesdroppers cannot extract any useful information from the receive signal even if eavesdroppers know thespreading sequence of the directional modulation spread-spectrum signal. This transmit signalcombines the advantage of directional modulation signal and spread-spectrum signal with thecharacteristic of low-probability-of-interception, low-probability-of-detection and anti-jamming.5) A multi-beam directional modulation signal using an antenna array with eight elements isproposed for integration system with communication and direction-finding. The multi-beamdirectional modulation technique combines with the OFDM technique by which differentradiation patterns are modulated into different constellation of subcarriers. Therefore, the receiverwith a single antenna demodulates the communication information and the directionalinformation from the receive signal constellation, simultaneously. To increase the minimum spaceof element, a multi-beam without same phase directional modulation OFDM signal using a sparseantenna array with nine elements is proposed. The phase difference and the Chinese remaindertheorem are used to estimate the directional information of the receiver coarsely. Then, theradiation patterns generated by two-element sub-arrays with greater half wavelength space areused to estimate the directional information of the receiver accurately.6) A single beam Doppler frequency directional modulation signal using a switched antenna array isproposed for the integration system with communication and direction-finding. The virtualmotion transmit antenna is simulated by a linear switched antenna array which are controlled bythe high-speed RF switches. Therefore, the Doppler frequency shift information generated by the virtual motion of the transmit antenna is modulated into the transmit signal constellation. In thisway, the receiver can demodulate the directional information and communication informationform the receive signal constellation, simultaneously by a differential correlation demodulationalgorithm. However, the direction-finding performance is affected by the Doppler frequency shiftinformation generated by the receive motion. To solve this problem, a dual-beam Dopplerfrequency directional modulation signal using a uniform switched circular array is proposed forthe integration system with communication and direction-finding. The Doppler frequencydirectional modulation signal is transmitted by the uniform switched circular array simultaneouslythe reference signal is transmitted by a center antenna of the uniform switched circular array. Todistinguish the Doppler frequency directional modulation signal from the reference signal for thereceiver, a sum-difference coding scheme is designed as the traditional space-time coding.