Research On Key Techniques In Wireless Digital Image Communication Systems

With the arrival of 21 century, which is also known as information society century, knowledge and information generate explosively. People have not been satisfied with obtaining information of text, speech, etc, via the media of magazine and telephone, and hope to get real-time field video information anywhere and anytime through digital image communication. Therefore, the research on digital video processing and transmission systems with high-efficiency, high-definition, and high-reliable is significantly important. So, the research works of the thesis mainly focus on high-data-rate wireless transmission and enhancement processing in wireless digital image communication systems.Wireless Transmission of Digital Video Image:In order to overcome the effects of multi-path fading over wireless channels, a wireless high-data-rate digital image communication system based on orthogonal frequency division multiplexing modulation technique is proposed, and a multi-path channel estimation algorithm based on power-spectrum-density (PSD) estimation is presented. Simulation results show that the mean-square-error between the estimated channel by PSD and the known channel is less than that of the least square estimation and the minimum-mean-square-error (MMSE) estimation, and the performance of the OFDM system approaches to that of the system with ideal channel information.Enhancement processing of Digital Image:First, a digital video enhancement algorithm based on morphological filter is proposed, which combines the neural network structure and morphological filtering theory. An optimization method is derived to implement the gray morphological filter, which resolve the problem that the structure of morphological filter is hard to track adaptively the complicated variation of video model. This method improves the performance of morphological filter, and is easy to implement.Then, an improved combinatorial criterion of advanced D-S theory of evidence based on information fusion is proposed, and a decision-level fusion filtering algorithm for digital image is presented, which resolves the problems of high-risk, low reliability and low-error tolerance in the decision based on the boundary data of single-source. It improves the precision of the decision based on the boundary data by changing the decision rules for the boundary data from single criterion to multi-criterions and using intelligent multi-source data fusion technique, which has high error-tolerance and improves the decision precision. The results show that the worse of the original image, and the better the improvement of the filtering performance. Especially when the boundary region is blurred or the quality of the image is bad, the performance improvement is more obvious.Finally, combined with the Cooley-Tukey iterative and cut algorithm of discrete Fourier transform, an improved parallel FFT iterative algorithm for image processing in frequency domain is presented. The complexity of the algorithm, average delay and the induced delay jitter are evaluated and an approximate evaluation formula is also derived. Compared with traditional FFT fast algorithms and the Cooley-Tukey iterative algorithm, this algorithm has low complexity, fast running time, and low complexity to implement.