Joint Source And Channel Coding Based On UEP With Turbo Codes

The requirements of digital image communication system for information storage, transmission and processing are very high. On the one hand, the image data have numerous information; on the other hand, a large amount of bit errors could occur in the poor wireless channel environment. In condition of insuring better reconstructed image quality, image data compression and error control technology are two key solutions in the digital image communication. Compressed image data are very sensitive to channel transmission errors because their most redundant information are removed. Sometimes a few errors may destroy the entire image bit streams and thus affect the quality of reconstructed image. Considering the characteristics of both source bit streams and channel state information, it is necessary that jointing source and channel coding (JSCC) to improve the overall performance of communication systems, and JSCC technique has attracted more and more attention. Unequal error protection technology (UEP) is an effective way for JSCC. According to the different levels of the image data streams and channel characteristic, many domestic and foreign scholars have studied unequal error protection methods.In term of the different sensitivity of image data streams to channel interference, this thesis presents a JSCC scheme based on UEP with Turbo codes, which can reduce the influence of channel transmission errors on reconstructed image quality, improve the reliability of image communication system, and reduce system transmission delay.The main contents are as follows:(1) Considering the drawbacks of both block and random interleavers which can not eliminate the more information correlation or not permute the low weight codeword sequence effectively, this paper presents a novel interleaver named unequal row-column cyclic cross interleaver. The experimental results show that the proposed interleaver used in Turbo codes can obtain better performance than the above-mentioned others, and it could improve the error correction performance of Turbo code effectively.(2) Focusing on the image pixels bits having different influence on the reconstructed image quality, we present a new UEP scheme based on Turbo codes. The proposed scheme employs multiple hierarchical transmissions in which the different coding strategies, the different interleaver of Turbo codes, the different decoding algorithms and the different iterative numbers are adopted. The simulation results show that the proposed scheme can obtain better reconstructed image quality than the equal error protection (EEP) scheme.(3) Aiming at the characteristic that the image data streams compressed by SPIHT algorithms have different sensitivity to channel bit errors, this paper presents a JSCC scheme based on UEP with Turbo codes. The scheme adopts the different Turbo coding and decoding adaptively, and can dynamically adjust the code rate to the estimated channel conditions. The experiments show that the proposed scheme can obtain better reconstructed image quality and improve the performance of the system but with no additional bandwidth.