Synchronizing codewords (SCs) have been previously studied as a means to stop error propagation in variable-length codes. However, SCs retain one disadvantage: the symbols after the SC may be put in the wrong positions since the number of decoded symbols before the SC can be different from the original number due to channel errors. Thus we propose the idea of extended synchronizing codewords (ESCs) which can overcome the drawback of SCs. After the decoder receives an ESC, the decoder correctly knows it is in synchronization, regardless of the preceding slippage. We derive some of the essential properties of ESCs and provide several upper bounds on the amount of overhead needed in designing a code with an ESC.

We present an algorithm to conceal bit errors in still images and image sequences that are coded using the discrete cosine transform (DCT) and variable length codes (VLCs). No modification is necessary to an existing encoder, and no additional bit rate is required. The concealment algorithm is kept simple so that real-time decoding and concealment is possible. A single bit error in these images can cause a block to split into several blocks or several blocks to merge into one. This causes the DCT coefficients of all subsequent blocks to be correctly decoded but stored in the wrong location in the image. Furthermore, the DC coefficient of all subsequent blocks may be incorrect. The error concealment algorithm uses transform domain information to identify the location of the affected blocks and to correct errors. The image quality after error concealment is shown to be significantly improved.

The authors consider parameter estimation in decentralized systems with distributed processors. They restrict the local processors to be quantizers and consider the optimal design of the systems to minimize the estimation error. They present necessary conditions for the optimal system based on the Bayes distortion functions and Fisher's information. The numerical results compare the resulting quantizers obtained by different distortion criteria.>

Variable-length codes are vulnerable to loss of synchronization if they are transmitted through a noisy channel. In order to achieve synchronization regardless of the preceding synchronization slippage, the concept of extended synchronizing codewords is introduced. An iterative algorithm is proposed to design extended synchronizing codewords efficiently. The extended synchronizing codewords are placed in fixed positions of an image to control error propagation due to synchronization slippage. However, the image can still be partially corrupted by channel noises. An error concealment method to further improve the image quality is discussed.>

The authors consider signal estimation using a communication system which consists of a quantizer, a noisy channel, and a decision device. By assuming that the lengths of the quantization intervals become arbitrarily small, they derive the asymptotic signal estimation error for the communication system. The asymptotic error consists of an interaction term which depends on both the quantization error and the channel error. The most significant property of the interaction term is that it can be negative. Next, the authors use the companding approach to find the optimal uniform quantizer. They then suggest using a suboptimal piecewise uniform quantizer to approximate the optimal nonuniform quantizer. Finally, they present several analytic and numerical results to justify the validity of the obtained asymptotic expression.>