GSM语音加密技术研究

发布时间：2018-11-04 17:17

【摘要】：针对GSM网络的安全缺陷及当前端到端语音保密通信方式存在的问题，本文研究了基于话音业务通道的语音保密通信方案。为实现方案中的加密语音抗声码器压缩传输，本文通过分析现有的方法，总结了类语音调制解调的功能特性，重点从两个方面研究了类语音调制解调技术。首先，本文通过对声码器进行建模分析，测定了由GSM声码器组成的“黑匣子”信道系统的幅频响应，研究了基于OFDM的类语音调制解调算法。该算法采用OFDM技术将加密后的数据承载到调制信号上，通过选择合适的子载波频率使得该信号的频率被限制在“黑匣子”系统的近似带通范围内，因此能以较小的失真通过声码器信道，被相应的解调器准确解调，同时加入信道编码并且通过序列加密来降低误码率和防止错误扩散，从而实现数据抗声码器压缩传输。仿真结果显示，该算法同时具有低误码率和高调制速率，因此能更好的保证通话的实时性。另外，根据声码器对语音信号的处理特性，将声码器的失真分为帧内失真和帧间失真，，为同时抵抗这两类失真本文提出了双码书语音调制解调加密方案，相邻语音帧使用不同码书调制来生成类语音信号。为减小帧内失真，将码书搜索范围定义在TIMIT语音数据库中，并根据‘最大错误概率符号’的概念进行码书筛选，生成对声码器有良好适应性的一组语音符号；同时为减小帧间失真，通过逐步合并汉明距离最大语音符号来将码书分割为两部分，从而使得信道容量最大。仿真结果显示，双码书调制后的语音具有动态频谱包络，可避免语音激活检测，在满足传输语音所需的误码率条件下比同类方法具有更高的调制速率。
[Abstract]:Aiming at the security defects of GSM network and the existing problems of end-to-end voice secure communication, this paper studies the voice secure communication scheme based on voice service channel. In order to realize the compression and transmission of the encrypted speech anti-vocoder, this paper summarizes the functional characteristics of the speech like modulation and demodulation by analyzing the existing methods, and focuses on the study of the similar speech modulation and demodulation technology from two aspects. Firstly, by modeling and analyzing the vocoder, the amplitude and frequency response of the "black box" channel system composed of GSM vocoder is measured, and the similar speech modulation and demodulation algorithm based on OFDM is studied. The algorithm uses OFDM technology to carry the encrypted data onto the modulated signal. By selecting the appropriate subcarrier frequency, the frequency of the signal is limited to the approximate bandpass range of the "black box" system. Therefore it can be demodulated accurately by the corresponding demodulator with less distortion through the vocoder channel. Meanwhile the channel coding and the sequence encryption are added to reduce the error rate and prevent the error diffusion so that the data can resist the compression and transmission of the vocoder. The simulation results show that the algorithm has both low bit error rate and high modulation rate. In addition, according to the speech signal processing characteristics of vocoder, the distortion of vocoder is divided into intra-frame distortion and inter-frame distortion. In order to resist these two kinds of distortion, this paper proposes a dual-codebook speech modulation and demodulation encryption scheme. Adjacent speech frames use different codebook modulation to generate speech-like signals. In order to reduce the intra-frame distortion, the codebook search range is defined in the TIMIT speech database, and the codebook is filtered according to the concept of 'maximum error probability symbol' to generate a set of speech symbols with good adaptability to the vocoder. In order to reduce the inter-frame distortion, the codebook is divided into two parts by merging the hamming distance maximum speech symbol step by step, so that the channel capacity is maximized. The simulation results show that the dual-codebook modulated speech has dynamic spectrum envelope, which can avoid speech activation detection, and has higher modulation rate than the similar method under the condition of satisfying the BER of speech transmission.
【学位授予单位】：中南民族大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN929.532

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