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Study On Waveform Design And Signal Processing For Integrated Radar And Communication System

Posted on:2020-02-22Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y B GuFull Text:PDF
GTID:1368330602950817Subject:Signal and Information Processing
Abstract/Summary:PDF Full Text Request
Lacking a unified structure,the independent developments of different electronic systems have caused a series of serious problems,such as hardware redundancy,power inefficiency and electromagnetic spectrum competition.An integrated radar and communication system is the present effective approach,in which the radar function and communication function can be performed simultaneously with a same signal.As the critical technology of the system,the sharing waveform design has been attracted more and more attentions.In the waveform design process,the following two issues need to be payed attention to that is how to embed information bearing communication sequences into the radar transmit and how to control or analyze the effect of embedded information bearing communication sequences on radar waveform performance.For different requirements,the corresponding design schemes are proposed in this dissertation.The contents are summarized as the following:A signal processing method based on correlation function is proposed for an integrated radar and communication system with orthogonal frequency division mulplexing(OFDM)signal in pulse-Doppler mode.Because of the movement of the target,the Doppler phase varies in different pulse repetition intervals(PRIs),which causes a coherence loss when the Doppler processing technique is applied over the compressed echo.The Doppler shift among PRIs is firstly compensated,then the cross ambiguity function is taken between the compensated signal and transmitted sequence,and finally,the square of modulus of the cross-ambiguity function is regarded as the cost function.The range and velocity can be estimated from the peaks of the cost function in Range-Doppler plane.The mathematical expression of the peak shape and sidelobe mean level is derived to analyze the effect of the embedded communication symbols on radar performance.Finally,the simulation experiments indicate the validity of the proposed method.The applicable range of the proposed algorithm is also given based on the analysis of the effect of the Doppler within the pulse on the output of the correlation function.Compared with the traditional OFDM signal,the subcarrier becomes into Chirp signal from sin subcarrier in fractional Fourier transform(FRFT)OFDM system.By applying the freedom of the transform order,it has the capacity to control the peak to average power ratio(PAPR)and inter-carrier interference.The signal processing problem with adding the cycle prefix(CP)at the front of the symbol is first analyzed.Because the CP is the duplicate of the end of the OFDM symbol,high level sidelobe arises at the both sides of mainlobe when the pulse compression technique is applied.When there are multiple scatters in the detection area,the echo from different scatters blend in together which makes the conventional communication compensation method no longer applicable.A multiple-scatter radar signal processing method is proposed based on maximum likelihood.The received signal is firstly modeled as the convolution of the transmitted sequence and the weighted radar cross section(RCS)coefficient after sampling the received signal with a certain delay,then the maximum likelihood method is applied to perform range reconstruction.Finally,FFT is applied along the pulses within a coherent processing interval.Theoretical analysis and simulation results indicate that the proposed method can improve bit error rate performance and obtain multiple-scatter range reconstruction and velocities estimation.An approach for embedding communication symbols into radar waveform is investigated,while holding constant envelope with spectral containment.A new frequency modulation(FM)scheme is proposed,where the proposed FM is the addition of communication frequency modulation term(CFMT)and the base radar FM.For communication information modulation,the CFMT is designed to be a linear combination of multiple sub-FM terms and the information-bearing communication symbols are carried out by the coefficients of different sub-FM terms.This technique is based on these sub-FM terms comprising of the CFMT mathematically orthogonal to each other in the inner product domain.In addition,in order to mitigate the interference caused by the radar FM on the demodulation procedure,the CFMT is designed mathematically orthogonal to the radar FM.Therefore,the resulting FM of emission is actually a group of orthogonal FM terms.The design criteria of CFMT is given when the radar FM term is LFM.And the “integration process” is applied here to quantitatively analyze the effect of embedded information bearing communication symbols on radar waveform performance and the upper bound of the CFMT is given.The adjustable weighted coefficient provides an opportunity to achieve a balance between the degrees of range sidelobe modulation(RSM)and the communication bit error rate(BER)performance.The performance of the designed radar-embedded communication waveform,including ambiguity function,spectral,weighted coefficient design and the demodulation procedure,is analyzed.Simulation results show that a satisfactory communication BER performance can be obtained without sacrificing the radar performance.For different mission and function,radar and communication have different beam pattern scan mode.The spatial resource is taken into consideration to obtain resource sharing in time,frequency and spatial domain.An integrated radar and communication system based on circulated code array is proposed.The particular relationship between the transmitted base signal and the synthesized signal in the spatial domain of a circulating code array provides an opportunity to demodulate the embedded communication symbols in the transmitted base waveform.The multiple orthogonal waveform design or multidimensional optimization problem in a conventional multiple input and multiple output(MIMO)system becomes into the transmitted base waveform design.The spatial-frequency modulation coefficient(SFMC)is firstly analyzed to ascertain the relationship between the frequency band used for modulation and the direction of the communication receiver.Perturbation phase modulation(PM)term is attached to a certain time duration of a linear frequency modulation(LFM)signal to embed communication symbols,in which the SFMC is not equal to zero.The effect of the perturbation modulation term on radar performance is analyzed and a design method for the upper bound of the perturbation PM term is also given.In our proposed method,the radar and communication function can perform simultaneously and the communication receiver can be in any position.Theoretic analysis and simulation results indicate that the effect of embedded communication symbols on radar performance can be effectively controlled with satisfactory BER performance.
Keywords/Search Tags:Integrated radar and communication system, Radar-communication sharing signal, Waveform modulation, OFDM, FRFT, Frequency modulation, Circulating code array
PDF Full Text Request
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