Research On Modulation Techniques For Fusion Of Radar And Communications

The fusion of Radar and communications refers to a system that provides Radar and communication functions using the same band modulated waveforms on a single hardware platform.Considering the limited availability of spectrum resources has now been a tough problem for the development of communications of 5G and 6G,by using the joint waveforms for Radar and communication applications,the pressures from the limited availability of spectrum resources can be alleviated,which is from the communication perspective.While from the Radar perspective,using the joint waveforms for Radar and communication,the reduced Radar device size,suppressed electromagnetic interference and improved circuit integration can be achieved,which are key points that need to be overcome in the next generation Radar designs.Moreover,spectrum competitions between Radar and communication applications also can be addressed.In this dissertation,considering some potential applications,by combining with the modulation techniques and antenna array techniques,we propose different joint waveforms synthesis approaches for Radarcommunication fusion systems.The contributions of this dissertation can be summarized as follows:This dissertation investigates a Radar and wireless communication fusion system,using orthogonal frequency division multiplexing(OFDM)waveforms.Then this dissertation proposes a novel Radar-communication fusion system using the orthogonal frequency division multiplexing index modulation(OFDM-IM)waveforms,aiming at reducing the high peak-to-average ratios(PAPRs)associated with the OFDM signals.From the communication perspective,information is conveyed not only through modulated OFDM subcarriers but also by the active subcarrier indices that are dynamically updated at the transmitted symbol rates.When compared with conventional OFDM communication systems,only a subset of subcarriers is activated in the proposed OFDM-IM system,which reduces the PAPRs,leading to enhanced power amplifier efficiency.From the Radar sensing perspective,the Radar range-velocity profile obtained using compressed sensing approach combined with modulation symbol-based algorithm is simulated and presented.It is shown that the OFDM-IM Radarcommunication fusion system can enhance the transmission data rates when low-order modulation schemes are adopted,e.g.binary phase shift keying(BPSK),and maintain similar Radar performance compared with the OFDM counterpart when the system is carefully designed.This dissertation investigates the principle of directional modulation(DM)technology which can be used to achieve Radar tracking/location.Considering the existed trade-off between the enhanced DM secrecy performance and power efficiency,i.e.,the enhanced DM secrecy performance is achieved at the cost of low power efficiency,in traditional TMA OFDM DM scheme,this dissertation proposes using the three-state timemodulated array to construct the DM transmitters for OFDM wireless data transfer,which allow more flexible manipulation of the injected orthogonal artificial noise and hence improve security.In particular,this dissertation presents for the first time both static and dynamic three-state time-modulated OFDM DM systems.Simulated bit error rate(BER)spatial distributions are shown that the secrecy performance enhancement that can be achieved without consuming additional power efficiency by the proposed transmitter arrangement.This dissertation presents a new approach of synthesizing multi-carrier DM symbols using TMA,aiming at solving the high peak-to-average ratio(PAPR)associated with OFDM DM signals.In particular,the modulated waveform synthesis is achieved in RF feeding network,instead of in digital baseband,thus,resulting in a PAPR of 0 d B.The efficacy of the proposed DM approach is validated via simulations of two representative examples.Considering the single-direction DM beam is not able to track multiple targets,this dissertation presents a multi-direction DM beams synthesis approach using TMA.In the proposed approach,the DM symbols are synthesized at different harmonic frequencies by the careful design of the switching time sequences.Compared with other previous DM synthesis works,some promising features are exhibited,such as i)generates multiple beams simultaneously along different spatial directions,ii)enables the multiple access in frequency domain,iii)enjoys the PAPR of 0 d B,iv)enables beam steering without requiring phase shifters.Thus,the synthesized multi-direction DM beams can deliver multi-directional targets Radar tracking and wireless communication simultaneously.The efficacy of the proposed scheme is demonstrated by the simulation results.This dissertation investigates the principle of frequency diverse array(FDA),then the characteristics of the array pattern of FDA is introduced.In order to achieve FDA Radarcommunication fusion systems and address the issue of target range information cannot be obtained directly from the FDA beampattern peaks due to the range-angle coupling,this dissertation presents for the first time antenna element index modulation FDA concept which introduces the index modulation techniques to FDA Radar.In the proposed antenna element index modulation FDA scheme,information is transmitted by a dynamically selected subset of antenna element indices applying pre-defined carrier frequency offsets through closing the relevant radio frequency(RF)switches,which generate different radiation patterns.It is shown that this enables the capability for simultaneous wireless communication and FDA Radar that has the range-angle coupling issue resolved.The efficacy of the proposed antenna element index modulation FDA scheme is demonstrated by the simulation results.This dissertation investigates the effects of random frequency offset for logarithmically increasing frequency offset FDA(log-FDA)transmit beampattern.Then this dissertation presents the frequency offset index modulation FDA concept which combines the frequency offsets of FDA with the index modulation techniques.In the frequency offset index modulation FDA scheme,at the transmitter side,the incoming data bits are systematically mapped to the selected frequency offset indices randomly adopted by each element through closing the relevant RF switches.The proposed architecture here offers thumbtack-like beampatterns which can decouple the range and angle dependence.Meanwhile,information can be delivered through the selected frequency offset indices,thus enabling the communications capability.