通信信号中的隐蔽信息传输机理研究

Information covert transmission technology is an energetic research topic, but most research focus on the multimedia digital signal, i.e. digital watermarking technology. The project is to solve the problems about the covert information transmission in communication signals, which is called as communication watermark in the project. The performance of the multimedia digital watermarking system is evaluated by fidelity, but the performance of the communication system is evaluated by bit error rate. Therefore, the imperceptible and robust performance of the communication watermarking should be redefined, which are shown that the bit error rates of the original information and the covert information are both less than the specific criterion. For the modulated signals in the common communication system, we establish the covert information transmission model to analyze the channel capacity. Then we design the watermark generation, embedding and extraction scheme, based on which the test system is established to verify the scheme. Finally, we investigate the quantitative assessment methods for the imperceptible and robust characteristics of the watermarking system, find the main parameters for determining the performance, and optimize the system parameters by the evaluation results. This project attempts to reveal the factors that determine the performance of the communication watermarking system, i.e. transmission bit rate, imperceptibility and robustness. Then we establish the transmission theory of the communication watermarking and provide the solution for the design of the covert information transmission scheme in the communication system.

信息隐蔽传输技术一直是一个研究的热门课题，但是大多数研究的载体是多媒体数字信号，即数字水印技术。本项目则将研究的对象转移到通信信号上，主要研究通信信号中的隐蔽信息传输技术，我们称之为通信水印。多媒体数字水印系统性能主要由信号保真度来评价，但是衡量通信系统性能的主要指标是误码率，因此通信水印的隐蔽性和可靠性体现在原有通信信息和附加隐蔽信息的误码率指标上。本项目针对通信体制中常见的调制方式，通过建立通信水印的传输模型，分析信道容量；并设计通信水印的生成、嵌入和提取方案，搭建试验验证系统；最后对通信水印系统的隐蔽性和可靠性给出定量的评估指标，找出影响性能的主要参数，并以此为基础对系统性能进行优化。本项目研究试图揭示影响通信信号中隐蔽信息传输性能（即传输速率、隐蔽性和可靠性）的主要因素，建立通信水印传输理论，为通信信号中的隐蔽信息传输系统设计提供解决方案。

项目组成员通过三年的研究工作，对于通信信号中的隐蔽信息传输理论进行了深入研究，在理论分析和实验测试方面都取得了一定的成果。在理论方面，通过引入数字水印中常用的Costa脏纸模型，开展了通信信号背景下的隐蔽信道容量研究，设计了水印编码方案，完成了通信系统中载体和水印信号误码率的理论分析与仿真。理论分析和仿真结果表明，通过适当的设计隐蔽信息嵌入形式，可以在几乎不影响载体误码率的情况下，实现水印信号的可靠传输，同时信道容量可以逼近香农信道容量。在实验测试方面，通过USRP设备搭建了信号水印传输系统，在实验室环境下实现了信号水印的可靠传输，验证了通信信号中隐蔽信息传输的可行性。虽然该系统目前仍然处于实验室原型研究阶段，要将该方案应用到实际通信环境中，还需要进行持续深入的工作，但是我们的研究工作已经证明了通信信号中传输隐蔽信息是完全可行的。