Study On The Radar Performance Of OFDM Sharing Signal

To alleviate the congested spectrum resources problem and meet the requirement of some application scenarios,where multi-functions need to be achieved simultaneously on one platform,the development of multifunctional equipments,such as the radar and communication sharing system(Rad Com SS),will be one of the hot research topics.Rad Com SS is designed with many advantages such as saving space for platform and energy,improving frequency resource utilization,reducing interferences among devices,etc.Since the sharing signal(SS)based Rad Com SS has the highest integration level,the highest hardware sharing rate can be achieved.However,as one of the technical challenges,to design a suitable SS,which can simultaneously and excellently perform wireless communication and detection,is one of the most important steps in Rad Com SS.The orthogonal frequency division multiplexing(OFDM)signal is a kind of promising SS.As well known,the OFDM communication signal possesses some remarkable properties such as high data transmission rate,immunity to frequency selective fading and high spectral efficiency.Meanwhile,OFDM radar has the advantages of good range and Doppler resolution,low autocorrelation sidelobes,multipath clutter suppression capability,etc.Nonetheless,as SS,the communication structure of OFDM will influence its radar performance.Therefore,this dissertation mainly focuses on the research of the OFDM based SS design in Rad Com SS.Firstly,the ambiguity function property of OFDM signal is investigated.To eliminate the effect brought by the random communication data modulated onto OFDM to the ambiguity function analysis,the average ambiguity function is utilized for analysis.In addition,the relationship between Doppler resolution,range resolution and peak-to-sidelobe ratio and system parameters is derived,and the effects of system parameters on the Doppler and range dimensions are analyzed.Next,based on the commonly used OFDM signal under the standards of Digital Television Terrestrial Multimedia Broadcasting(DTMB)and the Fourth Generation(4G)mobile communication,the detection ability of OFDM radar is analyzed from the perspective of maximum detectable range.Explicitly,the effects of different reference signal selections on the radar detection performance under these two standards are analyzed,as well as the comparison with the radar detection performance achieved by the traditional pseudo noise(PN)signal.The results show that the OFDM structure in DTMB and 4G frequency division duplex(FDD)downlink signals,compared with traditional PN signal,will raise up the noise base level,which would degrade target detection performance,when using the same reference signal.What’s more,different reference signal selections will leave an impact on the detection performance.To continue,from the perspective of radar target localization,OFDM modulation symbol domain and multiple signal classification(MUSIC)algorithm based method to perform range and Doppler estimation is proposed,which can efficiently improve the resolution of range and Doppler estimation.The research illustrates that the performance of target localization will be improved with the increase of signal-to-noise ratio(SNR)and can be affected by the correlation of signal sources.What’s more,the performance of range and Doppler estimation for a single target is investigated.According to the analytical and numerical results,it is demonstrated that the corresponding estimation performance will be improved with the increasing of OFDM symbol or carrier number,as well as SNR.