This paper provides an overview on the recent research on networked control with an emphasis on the tight relation between the two fields of control and communication. In particular, we present several results focusing on data rate constraints in networked control systems, which can be modeled as quantization of control-related signals. The motivation is to reduce the amount of data rate as much as possible in obtaining control objectives such as stabilization and control performance under certain measures. We also discuss some approaches towards control problems based on techniques from signal processing and information theory.

In this paper, we propose a combination-based novel technique of dithered subband coding with spectral subtraction for improving the perceptual quality of coded audio at low bit rates. It is well known that signal-correlated distortion is audible when the audio signal is quantized at bit rates lower than the lower bound of perceptual coding. We show that this problem can be overcome by applying the dithering quantization process in each subband. Consequently, the quantization noise is rendered into a signal-independent white noise; this noise is then estimated and removed by spectral subtraction at the decoder. Experimental results show an effective improvement by the proposed method over the conventional one in terms of better SNR and human listening test results. The proposed method can be combined with other existing or future coding methods such as perceptual coding to improve their performance at low bit rates.

In this paper, we develop a fast dynamic programming technique to construct the subband decomposition yielding the maximum coding gain. We first derive a unified coding gain applicable to arbitrary subband decompositions and arbitrary filter bases. Then, we prove that the unified coding gains are monotonically increasing function for the implementation complexities. Based on this phenomenon, we treat the implementation complexity and the coding gain in the same way as the rate and distortion function. Finally, we applied the developed algorithm to the wavelet packet based image coding, so as to verify coding performance improvement by the proposed algorithm.

We have developed a low bit-rate video coding using a video digital signal processor (DSP) called VDSP1χ, which performs real-time encoding and decoding for discrete cosine transform-(DCT-) based algorithms, such as ITU-T H. 261, H. 263 and wavelet-based subband encoding algorithms. This LSI features a processing unit which implements wavelet filters at high speeds, a compact DCT circuit, and a fast, flexible DRAM interface for low-cost systems. This system is capable of processing quarter common intermediate format (QCIF)(176144 pixels) size pictures at a rate greater than 15 frames/s.

This work addresses the problems of bit allocation and coding gain in subband coding system with non-paraunitary filter banks. Since energy conservation does not hold in non-paraunitary filter banks, the model to be adopted for quantizers is important to evaluate the output distortion introduced by subband signal quantization. To evaluate the overall distortion we start with adopting the gain plus additive noise model for quantizers, which is more reliable than the additive noise model. With this model, the expression for overall reconstruction error variance becomes so complicated that the problem of optimum bit allocation, as required for evaluation of the coding gain, must be numerically solved. So, we propose an approximation method in which we neglect the terms due to correlation among quantization errors in calculating the bit allocation but take them into consideration in evaluating the coding gain, assuming sufficiently high bitrate coding. Application of this approximation method to the SSKF subband coding systems with AR (1) input source shows that the method is very accurate even at low bit rate coding (1 bit/sample).

We propose a design method for a two-channel perfect reconstruction FIR filter banks employing linear-phase filters. This type of filter bank is especially important in splitting image signals into frequency bands for subband image cording. Because in such an application, it is necessary to use the combination of linear-phase filters and symmetric image signal, namely linear phase signal to avoid the increase in image size caused by filtering. In this paper, first we summarize the design conditions for two-channel filter banks. Next, we show that the design problem is reduced to a very simple linear equation, by using a half-band filter as a lowpass filter. Also the proposed method is available to lead filters with fewer complexity, which enable us to use simple arithmetic operations. For subband coding, the property is important because it reduces hardware complexity.

This paper discusses the bit-rate compression of super high definition still images with subband coding. Super high definition (SHD) images with more than 20482048 pixels or resolution are introduced as the next generation imaging system beyond HDTV. In order to develop bit-rate reduction algorithms, an image evaluation system for super high definition images is assembled. Signal characteristics are evaluated and the optimum subband analysis/synthesis system for the SHD images is clarified. A scalar quantization combined with run-length and Huffman coding is introduced as a conventional subband coding algorithm, and its coding performance is evaluated for SHD images. Finally, new coding algorithms based on block Huffman coding and entropy coded vector quantization are proposed. SNR improvement of 0.5 dB and 1.0 dB can be achieved with the proposed block Huffman coding and the vector quantization algorithm, respectively.

A novel coding scheme using orthonormal wavelet transform is proposed. Various forms of transform coding and subband coding are first reviewed. Then a wavelet coding method is proposed adopting a new approach similar to the one used for transform coding. The approach differs to conventional ones which considers wavelet coding as a class of subband coding. Simulation work is carried out to evaluate the proposed coding method. Significant improvement is obtained in subjective quality, and some improvement is also obtained in signal to noise ratio. Wavelet coding is still in its early stage of development, but can be considered to be a promising technique for image coding.