Research On Waveform Design And Optimization Technology For Integrated Communication And Detection Sonar System

With the increasing development of equipment manufacturing level and information technology,underwater combat equipment is marching towards the direction of integration,systematization and informationization.Detection sonar and communication sonar can realize the detection of underwater target and the exchange of underwater information respectively.Because of their different functions,the two systems are independent of each other,which brings many problems such as large space occupation and high resource consumption.However,the similarity in many aspects such as working principle and system structure makes it possible to integrate the two systems.The integration technology of communication and detection can integrate two systems so that the active sonar has both communication and detection functions simultaneously.The application of this technology can effectively solve the above problems and improve the system survivability and strain capacity.Aiming at the integration of communication and detection of active sonar system,the integrated waveform design and optimization are studied in this paper.Through the spatial gain and design freedom of sonar array,enhance the information embedding and environment adaptability of integrated signal,and the effective and reliable transmission of information is realized on the premise of satisfying the detection performance.The main research contents of this paper are as follows:Firstly,the paper analyzes the typical working scenes of the underwater communication and detection integrated system,and studies the integrated waveform design method under the split-beam system.Aiming at the problem of low communication rate of narrowband integrated waveform,the method of constructing integrated waveform based on OFDM signal is studied,which is more suitable for underwater environment.The cyclic prefix can effectively reduce the influence of multipath channel on downlink OFDM communication signal,but the detection pulse and communication signal are formed in the far field of the corresponding beam.Thus,it cannot be operated directly before the signal is transmitted.To solve this problem,via the optimization of constraints in the integrated waveform design method,cyclic prefixes are embedded in downlink communication signals to make the signal structure more complete and receive more stable performance.Moreover,the method does not change the detection signal structure in order to ensure the detection performance.Secondly,analyze the receiving signal model of downlink communication node,and the corresponding signal processing method is studied.During the working period of the integrated system,there are interference signals with different incoming directions.In this paper,alignment matrix transformation and beamforming algorithm are used to extract and enhance downlink communication signals and,on the contrary,suppress interference signals.Then,the paper studies the processes of doppler estimation,channel estimation and decoding in downlink communication signal processing,and verifies the effectiveness of the proposed method through simulation experiments and experimental data from the South China Sea.Finally,the paper studies target detection methods.Based on the multi-carrier characteristics of integrated waveform,a target detection method based on generalized likelihood ratio test is studied.In this method,the echo signal is represented by a growth curve model at first,and then the generalized likelihood ratio test is carried out to determine the existence of the target.In this process,the maximum likelihood estimation result of Doppler factor is also obtained.In addition,a method to optimize the waveform of the next working cycle based on the test results of the current echo signal is also given.This method redistributes the transmitting power of each subcarrier in the integrated waveform of the next period so that the energy is concentrated on the subcarrier being sensitive to channel and target.It enhances the environmental adaptability and improves the detection performance.The paper also analyzes the effect of target detection algorithm in single-path and multi-path channel respectively,and verifies its detection performance in the case of different carrier numbers,path numbers and before and after optimization respectively.