Design And Implementation Of OFDM Radar Communication Fusion System

Radar systems and communication systems have very broad application prospects in both the civilian and the military fields.With the rapid development of information technology,in order to alleviate the lack of spectrum resources and reduce the redundancy of multi-functional platform equipment,the design of radar communication fusion systems will surely become a research hotspot.The radar communication fusion system integrates radar and communication on the same hardware platform and combines with software defined radio technology to implement the functions of radar detection and wireless communication at the same time.Designing a fusion system can save platform space,manufacturing cost,and power consumption,reduce interference between devices,improve spectrum utilization and the platform's cooperative ability.Orthogonal Frequency Division Multiplexing(OFDM)signal,as one of the potential shared signals for the fusion system,has the advantages of high spectrum utilization,low function sidelobes,and resistance to multipath clutter interference,widely used in both communication and radar systems.Therefore,this dissertation carries out research work on the design of OFDM-based radar communication fusion system,which includes the OFDM shared signal design,the hardware experimental platform implementation,the radar and communication signal processing schemes,and the performance validation of the radar detection and wireless communication of the fusion system via the hardware platform.Firstly,the framework of the fusion system design is introduced.The overall framework mainly includes three parts:OFDM shared signal design,hardware platform implementation,radar and communication signal processing.Among them,the OFDM shared signal is designed based on the FDD-LTE(Frequency Division Duplexing Long Term Evolution)physical layer frame structure,which can improve the reliability of communication transmission and the concealment of radar detection.The hardware platform implementation includes a schematic diagram of the hardware link and a block diagram of the control program design,and the analysis of the workflow.In terms of radar signal processing,the ambiguity function of OFDM signal is first investigated,including its range and Doppler resolutions,and the influence of the FDD-LTE frame structure on the ambiguity function.Then,the ambiguity functions ranging and speed estimation method are investigated in the symbol domain,but it is limited by the inherent resolution,which is not conducive to the detection of close targets.In order to improve the resolution,based on the OFDM symbol domain,a radar ranging and speed estimation algorithm with spatial smoothed multiple signal classification(MUSIC)is proposed,which achieves super-resolution estimation of target's range and speed.On the basis of simulation verification,the performance of radar one-dimensional super-resolution estimation is validated via practical measurements on the hardware platform USRP RIO-2943R.The practical experimental results show that the one-dimensional super-resolution algorithm based on spatial smoothing can resolve and correctly estimate the distance information of two targets whose distance is less than the inherent resolution.In terms of communication signal processing,the communication performance of the fusion system is first investigated,including transmission rate and bit error rate.Then,the time synchronization,carrier frequency synchronization,channel estimation and equalization are analyzed.Among them,based on the cyclic prefix and pilot signal,the maximum likelihood estimation is employed for the implementation of carrier frequency synchronization,and the estimation accuracy can reach 10^-9.Based on the pilot signal,the least squares is employed for the implementation of channel estimation.Then,the wireless communication of fusion system is implemented on the hardware platform.The practical experimental results show that the designed synchronization,channel estimation and equalization processing algorithms for the communication are reliable and effective.Moreover,the increase in the transmission distance of the shared signal and the increase in the modulation order will also lead to an increase of bit error rate.Finally,the works presented in this dissertation are summarized,and the future work is presented.