Secure Wireless Communication Based On The Directional Modulation

Wireless communication technology plays an increasingly important role in people's lives.However,it also faces a great challenge in security because of its broadcast nature.These directly exposed digitally modulated information signals are easily intercepted by eavesdroppers.The information security in the transmission is especially important when the wireless communication technology is applied to the field of national defense and national security.In order to secure the data transmission,the key-based cryptographic algorithms are widely used at the protocol layer.However,these classical encryption algorithms are not absolutely safe due to the increasing computing capability nowadays.In recent years,wireless physical layer security technology has been paid more and more attention.The directional modulation(DM)is one of the promising wireless physical layer security technologies,which is able to send digitally modulated information signals into the desired spatial directions(or at the desired locations)in free space while simultaneously distorting the constellation formats of the same signals in all other directions(or at all other locations).Based on the frontier technical requirements of communication security problems faced by the national space telemetry,tracking and command(TT& C)and satellite communication systems,we mainly investigate direction-dependent and direction-range-dependent DM schemes.Firstly,several traditional direction-dependent DM schemes implemented on the radio frequency(RF)frontend are introduced.Then we point out the advantages of DM scheme based on the digital phased array structure.In the meanwhile,three common performance evaluation criteria of DM and their characteristics are also presented.Secondly,an artificial-noise-aided zeroforcing synthesis approach is proposed for direction-dependent DM based on the digital phased array structure.The calculation process of the baseband-weighted vector is simplified using the zeroforcing method,which is closely related to the concept of pseudoinverse.Compared with previous orthogonal vector and maximizing signal-to-leakage-noise ratio(Max-SLNR)-based synthesis approaches,the proposed approach is more efficient and easier to implement in practical systems with tolerable performance loss.Thirdly,since these DM schemes are only direction-dependent,eavesdroppers in the same directions as cooperative users but at different ranges can intercept the useful signals.Therefore,we propose a virtual DM scheme based on the orthogonal frequency diverse array(FDA)whose subcarriers are mutually orthogonal.The proposed scheme is direction-range-dependent,where standard signal constellation formats can be formed only in the virtual DM receiver at the desired location.The proposed virtual DM scheme expands the scope of direction modulation.Finally,a spread spectrum assisted virtual DM scheme is proposed.Combined with virtual DM and multi-carrier spread spectrum technology,it can further improve the security performance of DM system in practical applications.A general system architecture of the spread spectrum assisted virtual DM is presented,which can be applied to point-to-multipoint secure communication scenarios.At the same time,another simplified transmitter structure is proposed.Its computational complexity is proportional to the square of the number of antenna elements,which greatly reduces the complexity.However,it is only suitable for point-to-point secure communication scenario with fixed distance.Compared with the previous virtual DM scheme,it is much more difficult to be intercepted and cracked.