Waveform Design Of Radar Communication Integrated System Based On OFDM

With the rapid development of commercial wireless technology,the communication system and radar system are more closely connected in practical applications,however,it also exacerbates the problem of RF spectrum congestion.Driven by the need to improve spectrum utilization and reduce hardware costs,the joint radar and communication integrated system has attracted widespread attention.In order to reduce the complexity of the system architecture,the joint Rad&Com integrated system mostly uses a unified waveform for target detection.Due to the advantages of strong anti-interference ability,high spectrum utilization,and large time-bandwidth product,OFDM signal is regarded as the most potential integrated waveform.However,the signal processing process and the indicators of waveform performance are quite different between radar and communication systems,which means that OFDM communication signal cannot be directly used for target detection.In this regard,this thesis will study the waveform design and detection method of the integrated signal,and expect to achieve the goal that the system can take into account the performance of both communication and radar.This thesis firstly studies the design of OFDM integrated waveform.In order to keep the signal structure of the existing communication physical layer standard basically unchanged,the idea of using OFDM communication frames to construct radar pulses is proposed,and the ambiguity function of OFDM signal is briefly analyzed based on the transmitted model.For the deterioration of radar performance when the system transmits high-correlation communication data,the method of precoding the modulated data is used to improve the ambiguity performance of the transmitted signal.In order to improve the performance of precoding,a binary sequence design algorithm based on the coordinate descent method is then proposed,which enables the optimized sequence to obtain a performance trade-off between PSL（Peak Sidelobe Level）and ISL（Integrated Sidelobe Level）by setting a trade-off factor.In addition,the parameter optimization problem in the waveform design is also demonstrated,and the relationship between the performance of the transmitted signal,that is,the theoretical detection performance and communication performance,and the waveform parameters have been analyzed.On this basis,a waveform parameter optimization model is given,in which the communication channel capacity is regarded as the objective function,and then the sparrow search algorithm is used to solve the problem to obtain the ultimate optimized parameters.Then,the target detection method based on OFDM integrated waveform is also studied in this thesis.To address the problem of pulse compression sidelobes induced by the preamble in the IEEE 802.11 protocol communication frame,a mismatched filter design algorithm is proposed to suppress the sidelobes caused by the repeated part in the preamble,and a two-dimensional FGOS-CA（Fast Generalized Order Statistics-Cell Average）CFAR algorithm is also proposed to achieve fast and accurate detection of echo data.And lastly,a multi-target detection method based on the CLEAN algorithm is proposed.By introducing the CLEAN algorithm into the traditional pulse Doppler radar detection process,the strong target detection in each cycle will be eliminated from the original pulse compression output,thus avoiding the obscuring effect between adjacent targets.The simulation results show that the multi-target detection method can accurately detect the adjacent multi-targets with an interval of 0.1278m,and the distance and velocity estimation MSE（Mean Square Error,MSE）both reach to 10^-2under the condition of a signal-to-noise ratio of 16d B.