The characteristics of the wireless physical layer can be exploited to complement and enhance traditional security. In this thesis, we study the channel-based physical layer authentication. The authentication problem is formulated as a sequence of hypothesis test problems. By exploiting the time-of-arrivals, received signal strengths, and cyclic-features of the channels, support vector machine (SVM) based authentication schemes, the linear Fisher discriminant analysis (LFDA) based authentication scheme, and the combining scheme are proposed to improve the detection probability and to reduce the false alarm probability. These schemes can reliably authenticate the sender by identifying channels from different users.In SVM based schemes, the linear and nonlinear SVMs are used to generate classifiers to solve the hypothesis test problems. Using the real channel data measured in a regular office from Utah University, simulation is performed. Simulation results demonstrate that SVM based schemes have lower misdetection probability and false alarm probability than some existing schemes at a cost of extra time complexity and space complexity due to the training stage.To reduce the space complexity and time complexity during the training stage, LFDA based authentication scheme is proposed. In LFDA based scheme, a linear combination of the channel features is used as the test statistic, which is compared with a threshold to perform authentication. LFDA is used to compute the weights based on some training data. Furthermore, an adaptive threshold scheme (ATS) is proposed to set and adjust the threshold. Simulation results demonstrate that the proposed LFDA based scheme performs better in terms of the sum of misdetection probability and false alarm probability, and the receiver operating characteristic curves, compared with several existing channel-based authentication schemes. Moreover, the analysis of time complexity and space complexity is provided, which shows that the LFDA based scheme is also better than SVM based schemes in terms of space complexity, time complexity, misdetection probability, and false alarm probability.The misdetection probability and false alarm probability can be reduced greatly by two-user cooperative authentication. The combining scheme is proposed to combine the data from another legitimate user when cooperation is available. The combining scheme is proven to have the capacity to improve the performance at cost of extra communication and computation overhead. The time complexity, space complexity, and communication overhead are analyzed.iii Acknowledgements I would like to thank all the people who made this thesis possible. They are my supervisor and my colleagues in the Broadband Communications Research (BBCR) group, and my families. Without their help and encouragement, I cannot finish my study.
Camera-equipped consumer electronics tend to become cheaper and cheaper currently. These cameras can provide high-speed communication links to combat the shortage of radio spectrum. This paper introduces SoftOC, a novel realtime projector-wall-camera communication system. We name our system software optical communication (SOC) system. In order to improve the reliability of these systems and to speed up the computing process, we propose some schemes. We verify the effectiveness of our proposed schemes on real-time communication prototype. I. INTRODUCTIONMore and more consumer electronics are camera-equipped today. In [1, 2], cameras and liquid crystal displays (LCDs) are proposed to act as secure high-speed communication links. In these links, data are modulated to the spatial frequency domain of a series of coded images, which are emitted by LCDs and then captured by cameras. This kind of modulation is called spatial discrete multiple tone (SDMT).However, line-of-sights are essential for these LCD-camera links. More and more consumer electronics will be projectorequipped in the near future. Projector-wall-camera links were proposed and studied as the extension of LCD-camera links to the non-line-of-light (NLOS) ones [3] in order to increase link robustness and ease of use.We present a real-time projector-wall-camera communication system, SoftOC, for the first time. To improve their reliability, we propose nonlinear quantization, iterated positioning scheme, and over-sampling based synchronization. To speed up the computing process, we propose parallel architecture of convolutional coding and decoding. We verify the effectiveness of our proposed schemes on real-time communication system demo. In addition, our proposed two-channel transmission scheme has higher information rate than existing SDMT schemes.The core part of our SoftOC system is a software package, which can run on general computers connected to projectors and cameras. We name this kind of systems software optical communication (SOC) systems. Software packages can be downloaded to consumer electronics with pico-projectors or cameras to provide communication services without aid of extra hardware, which can make our life more colorful.
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