Reconfigurable intelligent surface(RIS)assisted dual-function radar communications(DFRC)system is a promising integrated sensing and communication(ISAC)technology for future 6G.In this paper,we propose a scheme of RIS...Reconfigurable intelligent surface(RIS)assisted dual-function radar communications(DFRC)system is a promising integrated sensing and communication(ISAC)technology for future 6G.In this paper,we propose a scheme of RIS-assisted DFRC system based on frequency shifted chirp spread spectrum index modulation(RDFI)for secure communications.The proposed RDFI achieves the sensing and transmission of target location information in its radar and communication modes,respectively.In both modes,the frequency-shifted chirp spread spectrum index modulation(FSCSS-IM)signal is used as the baseband signal for radar and communications,so that the signal sent by the radar also carries information.This scheme implements the RIS-assisted beamforming in the communication mode through the azimuth information of the target acquired in the radar mode,so that the signal received from the eavesdropper is distorted in amplitude and phase.In addition,this paper analyzes the radar measurement accuracy and communication security of the FSCSS-IM signal using ambiguity function and secrecy rate(SR)analysis,respectively.Simulation results show that RDFI achieves both excellent bit error rate(BER)performance and physical layer security of communications.展开更多
以探测功能为主的雷达通信一体化(Dual Function Radar and Communication, DFRC)系统发射一体化信号,能够在保证探测性能的条件下,尽可能高效地与合作目标通信,使其在设备集约化要求高的电磁对抗环境中占有一席之地。因此,探通一体化...以探测功能为主的雷达通信一体化(Dual Function Radar and Communication, DFRC)系统发射一体化信号,能够在保证探测性能的条件下,尽可能高效地与合作目标通信,使其在设备集约化要求高的电磁对抗环境中占有一席之地。因此,探通一体化信号设计是以探测功能为主DFRC系统研究的关键科学问题之一。但电磁对抗环境复杂多变,可能存在非均匀、多变和强独立散射的散射体与雷达探测信号相互作用,使DFRC系统接收的回波中含有在空间上呈现非均匀特性的杂波分量,从而给雷达目标检测带来挑战。针对杂波环境中DFRC系统探测性能下降的问题,本文采用认知系统架构,获取空间非均匀杂波先验知识,以信干噪比(Signal Interference to Noise Ratio, SINR)为准则,保障雷达的探测性能。引入发射方向图主瓣和旁瓣约束,使天线方向图具有低旁瓣特性同时集中探测能量在目标所在的方位,进一步保障探测性能。此外,考虑信号变模约束平衡雷达系统发射机功放的非线性失真和优化自由度。采用了一种空间合成信号频谱置零的方法实现信息传输,构建了通信调制约束。为求解上述多约束高维非凸优化问题,研究了一种联合序列块增强(Sequential Block Enhancement, SBE)、丁克尔巴赫(Dinkelbach’s Iterative Procedure, DIP)、凸序列逼近(Sequential Convex Approximation, SCA)和内点法(Interior Point Method, IPM)的迭代求解算法。理论分析了该算法的收敛性和计算复杂度。仿真结果表明,所设计的波形能够在信号相关旁瓣杂波下,同时实现探测和多用户通信。展开更多
The chemical structures of bagasse EMAL （enzymatic hydrolysis/mild acidolysis lignin） were revealed quantitatively with ^31p-NMR, DFRC （derivatization followed by reductive cleavage）. The thermochemical characteri...The chemical structures of bagasse EMAL （enzymatic hydrolysis/mild acidolysis lignin） were revealed quantitatively with ^31p-NMR, DFRC （derivatization followed by reductive cleavage）. The thermochemical characteristics of bagasse and bagasse EMAL were evaluated with thermogravimetry. The results show that bagasse EMAL is mainly formed by the phenolic hydroxyl group of guaiacyl and syringyl units. The DBDO content in bagasse EMAL was found to be 0.180 mmol.g^-1. The decomposition characteristics of bagasse EMAL under elevated temperature were much different from that of bagasse.展开更多
基金supported by the National Science Fund for Young Scholars(Grant No.62201539)the Project of Innovation and Entrepreneurship Training for National Undergraduates(Grant No.202210356005)the project of Zhejiang University Student Science and Technology Innovation Activity Plan(Grant No.2023R409055)。
文摘Reconfigurable intelligent surface(RIS)assisted dual-function radar communications(DFRC)system is a promising integrated sensing and communication(ISAC)technology for future 6G.In this paper,we propose a scheme of RIS-assisted DFRC system based on frequency shifted chirp spread spectrum index modulation(RDFI)for secure communications.The proposed RDFI achieves the sensing and transmission of target location information in its radar and communication modes,respectively.In both modes,the frequency-shifted chirp spread spectrum index modulation(FSCSS-IM)signal is used as the baseband signal for radar and communications,so that the signal sent by the radar also carries information.This scheme implements the RIS-assisted beamforming in the communication mode through the azimuth information of the target acquired in the radar mode,so that the signal received from the eavesdropper is distorted in amplitude and phase.In addition,this paper analyzes the radar measurement accuracy and communication security of the FSCSS-IM signal using ambiguity function and secrecy rate(SR)analysis,respectively.Simulation results show that RDFI achieves both excellent bit error rate(BER)performance and physical layer security of communications.
基金The authors are grateful for the financial support of this research from the National Natural Science Foundation of China(No.30371138 and 20576043)the Visiting Scholarship Grant from the Key Laboratory of Lignocellulosics Chemistry,Chinese Academy of Sciences(No.109).
文摘The chemical structures of bagasse EMAL （enzymatic hydrolysis/mild acidolysis lignin） were revealed quantitatively with ^31p-NMR, DFRC （derivatization followed by reductive cleavage）. The thermochemical characteristics of bagasse and bagasse EMAL were evaluated with thermogravimetry. The results show that bagasse EMAL is mainly formed by the phenolic hydroxyl group of guaiacyl and syringyl units. The DBDO content in bagasse EMAL was found to be 0.180 mmol.g^-1. The decomposition characteristics of bagasse EMAL under elevated temperature were much different from that of bagasse.
