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- Type of Document: Ph.D. Dissertation
- Language: Farsi
- Document No: 48273 (05)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Behnia, Fereidoon
- Abstract:
- Nowadays, swift development of cellular network with the increased penetration rate, have made mobile voice channels widely available almost everywhere with higher priority comparing to the other conventional channels, e.g., GPRS, EDGE, HSDPA and etc. Leveraging on this fact two important utilization can be considered. The first one is related to urgent transmitting of vital data. As mentioned earlier, since this channel deems to be available everywhere and, recalling its priority, it is even accessible in congestion condition, it can be exploited as an efficient way to transmit small volume of emergence data urgently. Transforming the crash data on the road is an example of utilizing such technology which will be debuted soon in Europe under the name of ecall. The next example is providing an end to end secure communication through mobile voice channels which is extremely needed by security agencies. The next utilization is corresponded to the hiding information through the human voice speech while talking on their cellular phones. These information can be used as secret message, authenticating information and etc. This thesis has been prepared in two main parts. In the first part, we propose new methods for communicating over vocoder channels. In this regard, we statistically model the channel output by the aid of Weibull and Chi-square probability distribution function and consequently derive the optimal decoders based on Maximum Likelihood criterion. Moreover, to evaluate and investigate the performance of proposed decoders we compute the capacity of mentioned channel and compare it with the achieved results by the offered detection schemes. In the second part, we concentrate on modeling the mentioned channel subject to our goal, i.e., data hiding, and consequently propose several encoder/decoder schemes based on both additive and multiplicative spread spectrum methods. Next, we investigate the performance of proposed structures as well as their imperceptibility level according to objective and subjective benchmark. Finally, we express new idea based on transportation theory to avoid or at least decrease leaking the information which may be exploited by the eavesdropper
- Keywords:
- Data Hiding ; Spread Spectrum ; Channel Capacity ; Mobile Communication Vocoder ; Sphere Packing ; Weibull Detection Scheme ; Squared-Chi Detection Scheme
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