【作者】 胡幸；

【导师】 杨霖；

【作者基本信息】 电子科技大学 ， 工程硕士（专业学位）， 2020， 硕士

【摘要】 如今,无线通信的数据传输量呈现出爆发式增长,频谱资源变得日益匮乏,而多载波技术的提出,提高了频谱利用率,因此被大量应用。与此同时,由于无线通信的传播媒介具有开放性与普遍性,使得无线通信的安全问题存在于每个人的身边。物理层安全技术与上层加密的方式不同,前者利用信道的特性,然后采用物理层面的技术手段保证安全通信,因此,物理层安全技术为通信系统增添了又一层安全防护。所以,基于多载波的物理层安全技术是保障无线通信安全的重要技术之一。正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)作为一种常用的多载波技术,具有高频谱效率和抗频率选择性衰落等优势。稀疏码多址(Sparse Code Multiple Access,SCMA)能为通信系统提供海量连接和高频谱利用率。本文将SCMA与OFDM两者相互结合,利用OFDM的正交子载波对SCMA的非正交信息进行传输,并将结合后的系统称之为SCMA-OFDM系统。本文针对SCMA-OFDM系统,对其物理层安全技术进行研究。论文的工作安排如下:首先,部分传输序列(Partial Transmit Sequence,PTS)算法通常用于抑制信号的峰均功率比(Peak-to-Average Power Ratio,PAPR),基于循环移位的改进部分传输序列(Modified Partial Transmit Sequence,MPTS)也可以达到相同的目标,并且,MPTS算法还具有一定的安全作用。本文采用MPTS算法增强SCMA-OFDM系统的安全性能,并改善系统中的PAPR问题。在提出的安全模型中,通过研究窃听者的破解复杂度和有无先验信息时的误码率,定量地分析了MPTS对系统起到的安全效果,研究结果表明,窃听者在无先验信息时,依然能译出系统中的少部分安全信息,因此MPTS在安全性上存在些许不足。接着,针对MPTS在安全性上存在的缺陷,本文提出联合使用SCMA子块交织器和MPTS算法的物理层安全技术,以提高SCMA-OFDM系统的安全性能。利用信道信息和混沌映射产生所需要的交织器,以及MPTS的相关参数。然后,根据所提的安全模型,分析了多种攻击模型的情况下,交织器与MPTS所起到的安全效果。最后仿真了窃听者有无先验信息时的误码曲线,结果表明,窃听者在系统同时采用交织器与MPTS时的误码率都高于仅使用MPTS时的情况,因此,两者共同提升了SCMA-OFDM系统的安全性能。更多还原

【Abstract】 With the explosive growth of transmission data in wireless communications,spectrum resources have become increasingly scarce.The introduction of multi-carrier technology has increased the spectrum utilization efficiency.Therefore,multi-carrier technology is widely adopted in wireless conmmunication.Meanwhile,due to the characteristics of openness and universality of wireless communication media,the security of wireless communication becomes a public concern.The basic idea of the physical layer security technology is to use the uniquencess of the wireless channel,then take physical layer techniques to ensure secure communication.Therefore,multi-carrier based physical layer security technology is one of the most important technologies to provide the security of wireless communication.Orthogonal frequency division multiplexing(OFDM),as a typical multi-carrier technology,has the advantages of high spectral efficiency and resistance to frequency selective fading.Sparse code multiple access(SCMA)provides massive connections and high spectrum utilization.We combine SCMA and OFDM,and uses OFDM to modulate SCMA signals to get SCMA-OFDM signals.The combined system is called SCMAOFDM system.We researche the physical layer security technology of SCMA-OFDM system.The work arrangement is as follows:First of all,partial transmit sequence(PTS)and modified partial transmit sequence based on cyclic shift(MPTS)can both suppress the peak-to-average power ratio(PAPR)of the modulate signal.Besides,MPTS can be used to achieve physical layer security.Therefore,this paper uses the MPTS algorithm to enhance the security of the SCMAOFDM system and to reduce PAPR.In the proposed security model,by studying the decrypted complexity of the eavesdropper and the error curve with or without prior information,the security effect provided by MPTS is investigated.The simulation results show that even if eavesdropper has no prior information,a very small part of the information of legal users can still be recovered.Thus,the security that MPTS provided for the SCMA-OFDM system is not good enough.To adderss these problems,we further develop a noval physical layer security technology that combines interleaver and MPTS algorithm to improve the security performance of SCMA-OFDM system.The channel information and chaotic mapping are used to generate the interleaver and some parameters of MPTS.Then,according to the proposed security model,the security performance of the interleaver and MPTS in the case of multiple attack models are analyzed.Finally,the error performance of the eavesdropper with or without prior information is simulated.The results indicate that the proposed technique where MPTS is combined with an interleaver can significantly increase the eavesdropper’s error rate,compared with the case when only MPTS is considered.更多还原