Thesis "Inducing Chaos using Resonant Perturbations"

Abstract: A chaotic system is one whose long term behavior is unpredictable and is sensitive to the initial conditions. This thesis explores the idea of inducing chaos in systems as a means to render them inoperable. The idea is to use resonant external perturbations to drive nonlinear oscillators into progressively higher resonant states and eventually into chaos. The advantage of this approach over conventional schemes which use high amplitude signals to jam circuits is that relatively weaker signals can be used to induce chaos in systems that need to operate in a restricted parameter regime of order. Weak periodic signals with time varying frequency are used to induce chaos in circuits which are by themselves incapable of exhibiting any chaotic behavior in the region of operation. This thesis also presents an experimental verification of the idea of inducing chaos using resonant perturbations by using a Duffing oscillator along with a phase locked loop. It is seen that resonant perturbations can indeed drive the system into chaos from a periodic state while random perturbations cannot achieve the same effect. This setup makes it possible to design systems that are small and consume very little power.

Telecommunications "Simulation of Multipath Fading Channels"

Abstract: This project simulates multipath fading channels using the Jakes method and the Filtered Gaussian Noise (sum of sinusoids) method. The BER vs. SNR was estimated for the case where ideal CSI (channel state information) is available and the case where CSI is not available and the channel has to be estimated using pilot symbols. The effect of pilot duration over the BER was also investigated.
"Jamming mitigation in spread-spectrum communications"

Abstract: Spread spectrum (SS) communication systems such as the Global Positioning System (GPS) are jammed very easily due to the extremely low power of the received signal even though SS systems have an inherent immunity to jammers upto a certain dB level. As part of a funded project, this involved a review of existing jammer excision techniques to compare them using size, cost, power, flexibility and complexity as parameters. A mitigation technique that uses Bilinear Signal Representations (BSRs) was implemented. This involved representing the jammed signal in the time-frequency domain using the Extended Discrete Time Wigner Distribution (EDTWD), excising the jammer in the t-f domain using a threshold, and then reconstructing the jammer using Bilinear Signal Synthesis

Signal Processing "Design of a content-based image search engine"

Abstract: We live in an age where information is produced at the rate of 1 to 2 exabytes (1018 bytes) of which a large portion is in the form of visual content. With most data being available online, it is necessary and certainly desirable to be able to search for images by content. While it is currently being done by correlating images with the textual content around it, it would be desirable to be able to read in the image information and associate text with it on the basis of the image information, much like the human brain does. This would make it possible to index the vast quantities of image information available on the Web without the need for any manual effort. This project studies the work done in content based image search and introduces a new approach to the problem of image learning to enable search engines to learn about visual content over time and index new images using previously learned information.

Chaos /Non-linear dynamics "Experimental characterization of stochastic resonance in coupled-Chua circuits"

Abstract: Stochastic Resonance is a phenomenon observed in nonlinear systems whereby an input signal is optimized due to the beneficial effect of noise. This phenomenon has been observed in many real-world systems including lasers, chemical reactions and biological systems and has many potential applications. This report will focus on the phenomenon of phase synchronization in coupled chaotic systems and will present a metric which gives a better indication of the optimum level of phase synchronization in the presence of noise. This metric, known as the average phase synchronization time will result in a curve that is cusp shaped which gives a narrower range of optimum noise levels than the bell shaped curves obtained for other metrics such as signal-to-noise ratio. Finally experimental evidence for the theory will be presented using coupled Chua circuits along with a discussion of the phenomena observed therein.

publications Ying-Cheng Lai, Anil Kandangath, Satish Krishnamoorthy, John A. Gaudet, and Alessandro P. S. de Moura, "Inducing Chaos by Resonant Perturbations: Theory and Experiment," Phys. Rev. Lett. vol 94, 214101 (2005)

Open-Source I did most of these are projects as an undergrad and I am no longer updating any of these. Feel free to use the code if you find it useful.

• • Database-less hit counter
  • [download/details]
  • Uses a text file to log hits
• • Discussion Board
  • [download]
  • ASP/Access based discussion board with user authentication. Includes admin system and File Manger v3. Stores message threads in text files. Sadly, no templating system.
• • File Manager v1
  • [download/details]
  • A file browser for ASP enabled servers.
• • File Manager v2
  • [download/details]
  • Includes text editor and file download/upload etc.
• • File Manager v3
  • [download/details]
  • Better code organization.
• • Game of Life
  • [download]
  • The Game of Life written in C++.
• • Graph Generator
  • [download/details]
  • Generates a slick bar-graph using flash. Supports dynamic data.
• • Password quality checker
  • [download/details]
  • Does what it says.