Researches On Joint Source Channel Coding Based Arithmetic Codes

With the development of wireless multimedia communication technologies, arithmetic codes as a type of entropy codes with high compression ability have been adopted by many image and video compression standards. However, arithmetic codes are very vulnerable to channel errors because of the disastrous error propagation property, which prevents arithmetic codes from wide implementation. Using joint source channel coding technologies can efficiently and effectively improve the error correcting ability of arithmetic codes and the quality of wireless multimedia communication. The core of joint source channel coding based on arithmetic codes is error correcting arithmetic codes, which are formed by adding some redundancy to arithmetic codes during encoding. The redundancy can be explored not only by error checking but also by error correcting.Firstly, the statistical characteristic of the error detection delay of finite precision binary error correcting arithmetic codes based on following bits is discussed, after discussing the error detection delay of error correction arithmetic codes based on bit stuffing. It is observed that, apart from the probability of the forbidden symbol inserted into the list of the source symbols, the probability of the source sequence and the operation precision as well as the position of the forbidden symbol in the coding interval can affect the statistical characteristic of the error detection delay. Experiments demonstrate that the actual distribution is quite different from the geometric distribution of infinite precision arithmetic codes. This phenomenon is researched deeply, and a new statistical model (gamma distribution) of the actual distribution of the error detection delay is proposed, which can make a more precise prediction of the error detection delay. The relation expressions between the parameters of gamma distribution and the related factors affecting the distribution are given.Secondly, a new arithmetic coding system combining source channel coding and maximum a posteriori decoding was proposed, after disscused the decoding methods of error correction arithmetic codes in the literature. It combines source coding and error correction tasks into one unified process by introducing an adaptive forbidden symbol. The proposed system achieves fixed length code words by adaptively adjusting the probability of the forbidden symbol and adding tail digits of variable length. The corresponding improved MAP decoding metric is derived, which can make use of the property of the codeword of arithmetic codes based on following bits. Simulations are performed on AWGN channels with various noise levels by using both hard and soft decision with BPSK modulation. Results show that the proposed system outperforms corresponding systems in the reference.Finally, based on the idea of pruning the states of maximum likely sequence detection and estimation receivers for fading channels, a new soft-in soft-out decoding algorithm for error correcting arithmetic codes with bit redundancy, AT-BCJR algorithm, is proposed. This algorithm can adaptively adjust the threshold of the forward metric based on the channel conditions. Simulation results show that its decoding performance as well as its decoding complexity can outperform M-BCJR algorithm. Then, an iterative joint source channel decoding system is proposed, which is constructed by soft-in soft-out error correcting arithmetic codes concatenated recursive convolutional codes for AWGN channel and BPSK modulation. Simulation results show that even without redundancy, this iterative joint source channel decoding system gains obviously than conventional separated system at the same overall coding rate. When the proposed system adds bit redundancy, its gain is more outstanding. With JPEG2000 encoded image as the source of the proposed system, the quality of image is improved apparently.