Study On Integrated Radar And Communications Design Method Based On OFDM

Radar and communications devices are widely used in both military and civil applications,and both radar and communications functions are required to be performed in several applications.To perform radar and communications functions,the traditional way is to stack the separate radar and communications devices together,while the subsystems of radar and communications,such as transmitter,receiver,signal processor,and so on,are shared in the integrated radar and communications system,which can significantly reduce system redundancy,size,weight,cost,operation complexity,and so on,and has important research significance and practical value.Moreover,with the development of millimeter-wave radar and the fifth generation(5G)or even the sixth generation(6G)wireless communications in future,both radar and communications need larger bandwidth,and they may occupy the same frequency band,which leads spectrum resource to become more insufficient.To solve this problem,an important approach is sharing the radar and communications waveforms,that is the integrated radar and communications waveforms.The performance metrics of radar are usually the resolution and estimation accuracy of the parameters of targets,maximum detection range,maximum unambiguity range and velocity,detection and classification performance,and so on.In contrast,the performance metrics of communications are usually the data rate,bit error rate,Doppler tolerance,and so on.The requirements of the performance metrics of both radar and communications for different system parameters are either consistent or inconsistent.Due to this,it is difficult to design the system parameters and the integrated radar and communications waveform.Moreover,the communications information may deteriorate the performance of the ambiguity function of the integrated radar and communications waveform,degrade the performance of coherent accumulation of the echoes reflected by the target,and increase the difficulty of estimating target parameters.This dissertation focuses on solving the aforementioned problems of parameters design,waveform design,and target parameters estimation in integrated radar and communications system.To satisfy the requirements of both radar and communications,an optimization method is proposed to design the parameters of multiple input multiple output orthogonal frequency division multiplexing(MIMO-OFDM)system.To ensure the property of the ambiguity function of transmitted waveform and the performance of the coherent accumulation of the echoes reflected by the target,a method is proposed to design the communications codes.In order to improve the detection probability,estimation accuracy,and classification performance of radar as well as the channel capacity of communications,several optimization methods are proposed to devise the integrated radar and communications waveform by exploiting the frequency diversity of OFDM.According to the properties of the echoes of the integrated radar and communications waveform,several methods are proposed to estimate the parameters of radar target.A brief summary is given as follows: 1.To solve the problem that the ambiguity function of integrated radar and communications waveform is sensitive to the communications information,a method by premodulation of communications information is proposed.First,the model of OFDM integrated radar and communications waveform is developed,and its ambiguity function is derived.Then,the influence of the communications information on the ambiguity function is analyzed.The method of premodulation of communications information is proposed to make sure that communications codes modulated over different OFDM symbols in different transmit pulses have excellent autocorrelation and cross-correlation property,so that the effect of modulated communication information on the ambiguity function of the OFDM integrated radar and communications waveform can be reduced and the ambiguity function of the OFDM integrated radar and communications waveform has thumbtack shape.Moreover,the method of premodulation of communications information is employed to ensure that the communications phase codes modulated to the OFDM integrated radar and communications waveform have uniform distribution,and the performance of coherent accumulation of multiple pulses is improved in the mainlobe after pulse compression.2.To detect an extended target and simultaneously convey communications information in the frequency selective fading channel,it is of low efficiency to use the OFDM integrated radar and communications waveform with equal power allocated over each subcarrier.To improve the efficiency,an adaptive OFDM integrated radar and communications waveform design method is proposed.According to the frequency diversity of OFDM,the detection probability and communications channel capacity are respectively derived based on the integrated radar and communications waveform.Under the constraint of limited transmit power,the objective function that maximizes the detection probability and communications channel capacity is developed.By using Karush-Kuhn-Tucker(KKT)condition,the optimal solution is derived.Then,an adaptive OFDM integrated radar and communications waveform is designed,which can adaptively adjust with the change of environment.Moreover,the condition under which the radar and communications can simultaneously achieve the optimal performance is derived.Simulation results show that the designed waveform is better than the waveform with equal power allocated over each subcarrier.3.The parameter estimation accuracy of an extended target is poor and communications data rate is low by using the OFDM integrated radar and communications waveform with equal power allocated over each subcarrier.To solve this problem,a multiobjective optimization method is proposed to design the OFDM integrated radar and communications waveform.Based on the received OFDM integrated radar and communications signal,the Cramér Rao bounds(CRBs)of the estimates of the target scattering coefficients,range,and velocity are derived,and they are employed as the performance metrics of radar for parameter estimation accuracy.Moreover,the channel capacity is used as the performance metric of communications.Under constrains of total transmit power and minimum allocation power over each subcarrier,the multiobjective optimization model is developed,which minimizes the estimates of radar target parameters and maximizes the communications channel capacity.The weighted-optimal and Pareto-optimal OFDM integrated radar and communications waveform design methods are proposed.The proposed methods can improve the estimation accuracy of radar target parameters and communications channel capacity.4.For radar target classification and communications information transmission,the OFDM integrated radar and communications waveform with equal power allocated over each subcarrier has poor performance.To improve the performance,the OFDM integrated radar and communications waveform design method based on mutual information is proposed.The mutual information between the random target impulse response and the OFDM integrated radar and communications waveform is derived,which is used as the performance metric of radar.Under the constraint of total transmit power,the optimization problem that maximizes mutual information and communications channel capacity is established.Using KKT condition,the optimal solution is obtained,and the optimal OFDM integrated radar and communications waveform is devised.The devised waveform can improve the classification performance and communications channel capacity.However,the errors of frequency responses of a random target and communications channel will deteriorate the performance of the designed waveform.To solve this problem,a robust OFDM integrated radar and communications waveform design method is proposed.Following the philosophy of minimax robust waveform design,the robust OFDM integrated radar and communications waveform optimization problem is developed.The robust OFDM integrated radar and communications waveform is devised by solving the optimization problem.Under the worst possible case,the designed robust waveform has the optimal performance.5.To obtain the super-resolution estimation of radar target parameters based on OFDM integrated radar and communications waveform,a joint range and velocity super-resolution estimation method is proposed based on the compensation of communications information.First,the model of the received OFDM integrated radar and communications waveform is developed,and the samples of the received waveform is vectorized.Then,the communications information is compensated and the received signal model that is similar to the received signal model of a uniform linear array is established.Following the philosophy of spatial smoothing,the spectrum smoothing method is proposed to eliminate the coherence of different targets.Finally,subspace projection method is used to obtain the joint super-resolution estimation of range and velocity,and the range ambiguity is resolved by pulse compression.Compared with the traditional method,the proposed method can obtain unambiguity estimates of range and velocity with higher resolution by using the property of the received OFDM integrated radar and communications waveform.6.The data rate and angle resolution of the single input single output integrated radar and communications system are low.To solve this problem,the MIMO integrated radar and communications system is proposed.Under the constraints of the requirements of both radar and communications,the parameters of the MIMO-OFDM integrated radar and communications system are optimized.Furthermore,to exploit the bandwidth and aperture of the designed system sufficiently,the joint time and space processing method is proposed.First,according to the devised system,the received MIMO-OFDM integrated radar and communications waveform is formulated.Then,the differences among the transmit power of different transmitted waveforms are eliminated by mismatched filtering in time domain.Finally,the matched filtering in space domain is performed to extend the virtual aperture,and the high-resolution range and angle estimates of targets are obtained.To evaluate the estimation performance of the proposed method,the CRBs of the range and angle estimation based on MIMO-OFDM integrated radar and communications waveform is derived.Simulation results show that the proposed method has higher range and angle estimation accuracy than the traditional method.