Integrated Radar-communications Waveform Design Based On Phase Modulation

With the development of technology,a large number of electronic devices are emerging in endlessly.The exponentially increasing electronic devices have caused serious congestion in spectral resources.As two important applications of radio frequency spectrum,engineers of radar and wireless communications are encouraged to develop the spectrum sharing technique.Combining radar and communication systems to design an integrated radarcommunications system,which is called Dual-Function Radar-Communications(DFRC)system,has been regarded as an efficient way to realize the spectrum sharing between radar and communications.As the core of the DRFC systems,integrated radar-communications signal is difficult to design to meet the requirement of radar and communications system at the same time.As a basic modulation method,phase modulation has been widely used in communication modulation.Applying phase modulation technology to design integrated radar-communications signals can not only solve the problem of how to modulate the communication information to the radar signal,but also control the influence of randomly modulated communication information on the radar performance.High rate/ high quality communication transmission can be realized without sacrificing the radar performance.In this dissertation,we focus on designing integrated radar-communications signals based on phase modulation scheme.The main contributions and innovative research results of this dissertation can be summarized as follows:1.Aiming at the problem that it is difficult to suppress the influence of randomly modulated communication information on the radar by using the traditional constant envelope OFDM signal,a new integrated radar-communications signal design method based on phase modulation technology is proposed.The phase modulation term is attached to the phase of the constant envelope signal and it is designed to be the sum of the mutually orthogonal radar modulation phase term and the communication modulation phase term,both in the form of an OFDM signal.The orthogonality can be used to separate the communication modulation phase term and demodulate the communication information at the communication receiver.A weighted coefficient is added to the communication modulation phase term to suppress the influence of random communication symbols on radar.Taking the modulated coefficient of the radar modulation phase term as a set of random sequences as an example,the ambiguity function of the designed signal,the upper limit of the communication modulation phase term and the demodulation scheme are analyzed.Theoretical analysis and simulation results show that: high range-velocity resolution detection can be achieved by using the designed signal;the influence of randomly modulated communication information on the radar can be suppressed by reducing the weighting coefficient of the communication modulation phase term;high-rate/high-quality communication information transmission can be realized without sacrificing the radar performance.2.Aiming at the problem that it is difficult to solve the contradiction between beam scanning and beam coverage by using the integrated radar-communications signal used in the phased array system or to design multiple orthogonal signals,an integrated radar-communications signal design method based on circulating code array is proposed.Circulating code array is used to avoid designing multiple orthogonal signals.The chirp signal is used as the basic signal transmitted by the circulating code array and phase modulation terms are added to each chirp signal transmitted from different antennas.There is no need to design new signal.The communication information-carrying signal can be received by communication receivers located in any directions.The spectrum and the multi-dimensional ambiguity functions of the synthesized signal are analyzed,the form of the transmitted beampattern is deduced,the demodulation procedure based on multiple matched filtering and phase extraction is designed.Theoretical analysis and simulation results show that: a beampattern with omnidirectional coverage is synthesized by using the designed signal,and the gain of the beampattern is almost the same in all directions;the communication function can be realized in any directions and the communication performance will not be affected by the communication direction.3.To avoid designing multiple orthogonal signals,reduce computational complexity,suppress the influence of randomly modulated communication information on radar,a phase modulated integrated radar-communications signal design method based on circulating code array is proposed.The relationship between the spectrum band of the transmitted signal and the space angle is used to choose communication modulation spectrum band.In the chosen spectrum band,the communication symbols are embedded into the continuous phase modulation term and then attached to the LFM signal.Only one signal needs to be designed,multiple orthogonal signals designing has been avoided.The multi-dimensional ambiguity functions of the synthesized signal and the demodulation procedure are analyzed.Theoretical analysis and simulation results show that: an omnidirectional coverage beampattern can be synthesized by using the designed signal,and the gain of the beampattern is almost the same in all directions;by adjusting the modulation coefficient of the continuous phase modulation signal,the influence of randomly modulated communication information on radar can be suppressed effectively;for non-cooperative receivers from directions other than the communication directions,communication information is secure.4.Aiming at the problem that it is inevitable to solve complex optimization problem and hard to synthesize wide and narrow beam simultaneously for the existing integrated radarcommunications signal design method,a new integrated radar-communications signal design method based on circulating code array is proposed.The relationship between the spectrum band of the transmitted signal and the space angle is used to implement spectrum planning.By choosing spectrum band of the transmitted signal,flexible beampattern synthesis can be realized.Phase modulation term is attached to the phase of the designed transmitted signal in the corresponding spectrum band,and it is used to carry communication information.Only the spectrum planning of the designed signal is required to synthesize the desired beampattern,which avoids solving optimization problems.Theoretical analysis and simulation results show that: it is easy to synthesize wide beampattern and narrow beampattern simultaneously by using the designed signal;the isolation between the radar and the communication functions can be realized benefit from the use of multiple beampattern,thus,there is no interplay between the radar and the communication functions;all the energy of the transmitted signal is used to synthesize the desired beampattern,energy waste has been avoided;for non-cooperative receivers from directions other than the communication directions,communication information is secure.