Researches On Error Protection And Code-Rate Allocation For Image Transmission

Recent years, image coding technique based on wavelet transform has made great progress. While the higher compressed rate is acquired than ever before, advanced wavelet based image coder produces scalable bitstreams and makes the progressive transmission and adaptability to dynamic bandwidth enable. However, this bitstreams are very sensitive to packets loss and bit errors in transmission channels. Even if a single bit error occurs, it is highly probable that all remaining bits will not be interpreted correctly. On the other hand, the Internet and wireless networks nowadays are lossy and cannot provide reliable data transmission in real time. As a result, one challenging problem is how to transmit scalable bitstreams reliably and efficiently over noisy channels.The error control strategy based on forward error correction is one of the important methods to cope with the problem of reliable transmission of image and video in real time. In this dissertation, special emphasis is put on the error protection and high efficiency code-rate allocation algorithms for scalable bitstreams over packet erasure channel and wireless channel. The main contributions and innovation points are as fellows:â… . For the unequal loss protection (ULP) system based on interleaver structure, a bidirectional local search algorithm with adaptive neighborhood is proposed to allocate the bit budget between the source and channel coders. By rationally selecting the initial point for the search and alternately using forward and backward search with adaptive neighborhoods, new algorithm reduces the computing complexity under the comparative protection performance.â…¡. For the problem of code-rate allocation for the ULP system with given transmission rate, an algorithm based on estimation to select the optimal interleaver parameters is proposed. Instead of computation of each ULP distortion-optimal solution for each possible choice of interleaver parameters, it estimates the expected distortion of each ULP distortion- optimal solution from its upper and lower bounds, which results in the speedup of the search process for the optimal interleaver parameters. The simulation shows that the algorithm has low computing complexity and is more robust.â…¢. A new objective function named the effective expected quality is proposed, which is defined as the expected quality excluding the contribution from failure transmission. Combining equal and unequal loss protection strategy, two algorithms are proposed as following: 1. a code-rate allocation algorithm is presented to maximize the effective expected quality. 2. A code-rate allocation algorithm is proposed to maximize the effective expected quality under the constraint condition that the probability of failure transmission is below a given threshold. For these two algorithms, relevant fast bidirectional local search methods are developed. The new objective function can overcome the disadvantage existing in the old objective function based on expected quality where the minimum image quality requirement is not considered. Numerical experiments show that the above two algorithms can provide higher effective expected quality and lower probability of failure transmission with significantly lower computational complexity compared to the previous algorithms, and the latter can provide QoS provision for a image communication system.â…£. A new code-rate allocation algorithm based on rearranging the source symbols within the runs of the same channel code rate is proposed for the ULP system. The relevant probabilistic formulas are developed to describe the expected peak signal-to-noise ratio (PSNR) at the receiver based on the rearrangement. The experiment results show that the new algorithm can provide significantly higher expected PSNR especially in the cases of small number of packets and large packet length compared to the previous algorithm.â…¤. Two code-rate allocation algorithms based on prediction for the system of product code error protection over wirwless fading channel are presented. By introducing the new objective function based on the effective expected quality, the two algorithms overcome the problem of potential high probability of failure transmission occurring to the existing system. The simulations show that the new algorithms can provide high prediction precision, and their running speeds are faster than the previous algorithms.