Waveform Design And Signal Processing For Fusion Of Communications And Radar

With the development of electronic and information technology,wireless communication and radar detection tend to be more and more similar in spectrum employment,hardware architecture,system architecture and signal processing.Considering spectrum efficiency,hardware cost-effectiveness and new business applications,the demand of the internet of vehicles(Io V)and the sixth generation(6G)for the fusion of communication and radar(Rad Com)technology will keep growing in the future.Since it can meet the requirements of high-speed communication and small range resolution and can eliminate the mutual interference between communication and radar waveforms,the orthogonal frequency division multiplexing(OFDM)Rad Com waveform within waveform sharing mode has become one of the best candidate Rad Com waveforms.Aiming at the problems of high peak to average power ratio(PAPR)faced by OFDM Rad Com waveform within waveform sharing mode,Rad Com waveform design under the condition of spectrum interference and Rad Com multi-user networking in timefrequency domain,this dissertation mainly studies OFDM Rad Com waveform design and signal processing within waveform sharing mode.The specific research contents and contributions are as follows:(1)Aiming at the inherent high PAPR problem of traditional OFDM Rad Com waveform,this dissertation considers reducing the waveform PAPR at the cost of part of spectrum resources.This dissertation first proposes a generic Rad Com waveform design structure based on flexible subcarrier allocation,i.e.,all subcarriers are used for radar detection,in which arbitrary subcarriers can be utilized for communication and the other subcarriers are remained for waveform design.Then,based on this generic waveform design structure,this dissertation proposes three low-PAPR waveform design algorithms by numerical optimization.The upper bound of PAPR of the time domain waveform is linearly related to the aperiodic integrated side-lobe level(AISL)of the frequency domain signal.Therefore,the PAPR optimization problem is transformed into the power spectrum optimization problem of frequency domain signal DFT results,and then the partiallyreserved Gerchberge-Saxton algorithm and the partially-reserved MaximizationMinimization algorithm are proposed.Meanwhile,the PAPR of time domain waveform optimization problem can also be expressed as the infinite-norm of time-domain energy spectrum optimization problem.Therefore,this dissertation transforms the PAPR optimization problem into the l-norm of time-domain energy spectrum optimization problem,and proposes the l-norm cycle algorithm.The simulation results show that the three waveform design algorithms can effectively reduce the PAPR of OFDM Rad Com waveform without affecting the performance of communication and radar.(2)Based on the constant envelope requirement of OFDM Rad Com systems,a constant envelope orthogonal frequency division multiplexing(CE-OFDM)Rad Com waveform design method based on phase modulation is proposed in this dissertation.At transmitter,the proposed method first loads half of the subcarriers with quadrature amplitude modulation(QAM)symbols and the other half with their conjugate symmetric,then acquires the real OFDM waveform through inverse discrete Fourier transformation(IDFT),and finally obtains the CE-OFDM Rad Com waveform through nonlinear phase modulation.The proposed method achieves 0 d B waveform PAPR through linear and nonlinear signal processing at the cost of half spectrum resources,which perfectly solves the problem of high PAPR of traditional OFDM Rad Com waveform.The simulation results certify that when the modulation index is properly selected,the CE-OFDM Rad Com system can achieve good communication performance and radar detection performance.(3)Aiming at the problem that traditional OFDM Rad Com system cannot complete both communication and radar functions when existing burst spectrum interference with unknown number and width in the environment,a non-contiguous orthogonal frequency division multiplexing(NC-OFDM)Rad Com waveform design method based on spectrum sensing is proposed in this dissertation.The proposed method firstly discriminates the spectrum by spectrum scanning and subcarrier-based power spectrum detection algorithm,and obtains the spectrum mask sequence with 1 as available and 0 as unavailable.At transmitter,the communication symbols are loaded on the available subcarriers according to the spectrum mask sequence,and then the NC-OFDM Rad Com waveform is acquired through IDFT.The proposed method enables the Rad Com system to avoid spectrum interference through signal processing methods such as real-time spectrum sensing,subcarrier-based power spectrum detection and unavailable subcarrier setting 0.The simulation results prove that the NC-OFDM Rad Com system can complete communication and radar functions in the environment with spectrum interference.And the less the number and proportion of spectrum interference,the better the communication performance and radar detection performance of this system.(4)Aiming at the problem of OFDM Rad Com multi-user networking,this dissertation proposes a time-frequency domain multi-user networking approach for OFDM Rad Com based on continuous-wave time division multiple address(TDMA).In this approach,each user transmits OFDM Rad Com waveform in its period,and transmits a fixed Zadoff-Chu(ZC)sequence in the other periods.Each user first demodulates the obtained communication signal by successive interference cancellation(SIC)on the known ZC sequences for completing communication,then reconstructs and eliminates the communication waveform,and finally performs radar processing on the echoes.The simulation results demonstrate that the continuous-wave TDMA OFDM Rad Com multiuser approach can effectively accomplish the both functions of communication and radar after interference elimination.In addition,the fewer the number of users and the bigger the signal to interference ratio(SIR),the better the communication performance and radar detection performance of this system.