Joint Clustered-SPIHT and Turbo-codes Via Equalizing Bit Error Sensitivities to Improve the Quality and Robustness of Transmitted Images over AWGN Channels

• Main Authors: Jiunn-Tsair Fang, 方俊才
• Other Authors: Kim-Joan Chen
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/67167050468444069305

博士 === 國立中正大學 === 電機工程研究所 === 92 === With the increasing population of mobile users and the innovation of technology, it will be natural for the wireless communications to support multimedia communications in the near future. The demanding of Quality of Service (QoS) in wireless communications will be more stringent due to the competing of new service and the variety of multimedia. Therefore, how to maintain QoS to users over bandwidth-limited and error-prone wireless channels will be a good topic to be explored. In this paper, we first cluster source output bits. Bits with similar Bit Error Sensitivity (BES) are clustered so that different bit-clusters can be protected differently. Then, we derive a formula to assign channel coding rates. The optimal assignment of channel coding rates to bit-cluster is to equalize the mean BES of bit-clusters. In other words, the error probability after channel decoding of bit clusters should be inverse proportional to the mean BES of bit-clusters. Finally, we propose a step of unequal error protection for source output bits so that the transmission quality can achieve the highest PSNR performance under a give transmission bandwidth. Set Partitioning In Hierarchical Trees (SPIHT) image coding is adopted as source coding for its low-bit-rate and progressive transmission. However, the embedded coding structure of SPIHT will cause the potential error propagations. We thus propose C-SPIHT to modify SPIHT coding algorithm. C-SPIHT first adopts Fixed-Length Coding (FLC) to improve the error resilience of output bits. Then, it clusters the output bits according to their BES. Based on our proposed scheme of Equalizing BES (EqBES), we adopt Rate Compatible Punctured Convolutional (RCPC) codes and assign different channel coding rates to C-SPIHT output bit-clusters. Since Turbo-codes is popular for its high ability of error correction, we joint design Turbo-codes and C-SPIHT. The different protections of C-SPIHT output bit-clusters is based on the proposed EqBES scheme. In order to detect the bit error rate of Turbo iterative decoding, Cyclic Redundancy Code(CRC) is concatenated. Then, for different importance of C-SPIHT bit-clusters, we assign different tolerant number of erroneous CRC-frames within Turbo iterative decoding. This assignment is based on the EqBES scheme. So, the optimal assignment of different protections to C-SPIHT bit-clusters can be achieved. Since the assignment of erroneous CRC-frames is independent to channel noise and the number of Turbo iterations is determined by the receiver, the output performance preserves stable, which is robust to channels. Simulations are taken under different Signal-to-Noise (SNR) over Additive White Gaussian Noise (AWGN) channels. It shows that the best PSNR performance can be achieved under a given transmission rate, and C-SPIHT outperforms SPIHT with higher PSNR and less PSNR variations. Besides, the application of EqBES scheme to Turbo-codes on C-SPIHT can achieve stable transmission quality under different channel SNR.