Digital and analog signal encryption and decryption in mid rf range using hybrid acousto-optic chaos

Date of Award


Degree Name

M.S. in Electrical Engineering


Department of Electrical and Computer Engineering


Advisor: Monish R. Chatterjee


Modern day communication techniques are often prone to hacking and disturbances in the communication system while in transit from one place to another. Signal encryption using chaotic waves may be a good solution to this problem. A modulation scheme uses a carrier frequency to be modulated by the signal waveform, and generally the message can be readily decoded. A chaotic signal is a non-deterministic signal and not a well defined sinusoid. Hence, a modulated chaos wave is secure and cannot be decoded without knowledge of the chaos parameters. A chaotic signal is generated by carefully choosing the right set of parameters such as feedback gain, bias input and time delay. Encrypting a wave using a chaotic wave as a carrier also depends critically on these parameters. A signal used to encrypt a chaotic carrier can only be recovered or decoded by knowing exactly three parameter set, viz., the bias input alpha, feedback gain beta and time delay Td. Thus, the transmitter parameters serve as a decoding key, and hence signal encryption using a chaotic carrier provides data-security and reliability. In this research, we examine signal encryption using an acousto-optic chaos signal. For this, we generate a chaos signal with average frequency as high as 10MHz that is suitable for practical communication applications. We then examine encryption for different signals using the chaos wave with a set of fixed parameters. Finally, we recover the original signal using the same parameter set at the receiver and check for its robustness for cases where the receiver keys are mismatched or detuned. We derive the spectral characteristics using the simulation results from MATLAB by displaying waveforms on oscilloscopes, spectrum analyzers and so forth to check for the reliability or accuracy of the software results. We also perform a digital encryption using a gray scale image transmitted over the 10 MHz chaos as carrier and successfully decrypt the image at the receiver using low pass filter and then fine tuning the image. This research concludes with a rigorous check for the robustness of the system for both analog and digital data under single or multi parameter mismatch or detuning.


Data encryption (Computer science) Research, Signal processing Digital techniques Data processing Research, Signal theory (Telecommunication) Research

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Copyright © 2012, author