Integrated Sensing And Communications Waveform Design Based On OFDM Subcarrier Allocation

With the continuous development of information technology,spectrum resources are becoming more and more scarce,and the demand of the system for radar and communication is gradually increasing.At the same time,radar system and communication system show isomorphism in signal generation and transmission,and the operating frequency bands of radar system and communication system have gradually become partially overlapping,all of which indicate good development trend of the Integrated Sensing and Communications(ISAC).The ISAC technology achieves target detection and communication transmission by sharing one set of equipment.ISAC enables integration and miniaturization,as well as efficient spectrum utilization,compared to traditional single radar or communication devices.This thesis investigates the ISAC under multiplexing scheme,and proposes the ISAC scheme based on Orthogonal Frequency Division Multiplexing(OFDM)subcarrier allocation.The integration scheme exploits the flexibility of OFDM in time domain allocation,time-frequency resource scheduling and bearer waveform,and overcomes the problems of low resource utilization rate and resource competition in traditional reuse design.This thesis analyzes the OFDM regime and proposes the ISAC design scheme based on the OFDM subcarrier allocation under the characteristics of flexible modulation of OFDM subcarriers.The radar data and communication data under this scheme are modulated on the corresponding subcarriers separately to produce integrated waveform.In this thesis,three subcarrier allocation schemes are designed,i.e.,subcarrier continuous allocation,subcarrier cross allocation and subcarrier random allocation.For this integrated design,the echo model of the integrated system is derived and the block diagram of the integrated system structure is analyzed,including: the processes of integrated signal generation,transmission and signal processing.The simulation results show that the integrated signal under three subcarrier allocation schemes can complete the radar detection and can realize the communication transmission.Secondly,due to the high Peak to Average Power Ratio(PAPR)problem of OFDM signals,this can lead to nonlinear distortion of the amplifier.To address the PAPR problem,this thesis proposes the Tone Reservation(TR)algorithm based on the weighted least squares method.The algorithm first divides subcarriers into the data subcarriers and the reserved blank subcarriers.The reserved blank subcarriers carry the blank data before the iterations and the data subcarriers carry the initial integrated data.Then the weighted least squares method is used to obtain the optimal clipping coefficients and clipping data,and the final clipping data are modulated on the blank subcarriers.The simulation results show that the algorithm can achieve a good PAPR suppression effect with a suppression value of about 1.5 d B in 1-3 iterations,and the convergence speed is greatly improved and the suppression effect is better compared with traditional schemes.Finally,this thesis designs the system simulation software for ISAC.The ISAC system simulation software can reduce the cost of integrated simulation testing and can reduce the environmental constraints.The ISAC system simulation software is divided into the following three parts: integrated system modeling,integrated parameter setting and terminal display.The goal of integrated system modeling is to complete the program design of each module,including: coordinate system conversion module,echo simulation module and signal processing simulation module,etc.The integrated parameter setting allows the user to customize the integrated signal waveform parameters,parameters of the detection target and parameters in signal processing,etc.The terminal display mainly completes the waveform display,detection result display and the display of performance index of radar and communication during the simulation.