Nonblocking, repackable, and rearrangeable Clos networks: fifty years of the theory evolution

The article gives an overview of major theoretical issues associated with a switching network structure proposed by C. Clos (1953). The concepts of strict-sense and wide-sense nonblocking as well as repackable and rearrangeable networks are described, showing the development of major research areas. A taxonomy of Clos switching networks and some important results for the basic network structure are given and discussed. Other research issues are enumerated.     

Digital pictures fifty years ago

Automatic translation of the lights and shades of a picture into a digital record tape and its reconversion to a picture were elements of the Bartlane picture transmission system in operation on telegraph circuits fifty years ago.     

Correlative coding: A bandwidth-efficient signaling scheme

In most transmission channels, bandwidth is at a premium and an important attribute of any good digital signaling scheme is its ability to make efficient use of the bandwidth. Conventional Nyquist-type pulse amplitude modulation signaling schemes, which are designed to eliminate intersymbol interference, achieve high data rates only at the expense of a large number of signal levels. In many applications, correlative coding or partial response signaling, which introduces intersymbol interference in a controlled way, is able to achieve high data rates with fewer levels and hence with better error rate performance. In addition to higher data rates, correlative schemes achieve convenient spectral shapes and have error-detecting capabilities without introducing redundancy into the data stream. This paper explains how correlative schemes work and why they are advantageous.     

The Radiation Laboratory, fifty years later [telecom and remotesensing]

The author gives his impressions of the Radiation Laboratory of MIT as it existed from 1940 to 1945. He explores relationships of developments at the lab to present activity in radiowave propagation and remote sensing. His comments relate primarily to telecommunications and nonmilitary applications of remote sensing     

多天线对角空频编码传输

将平坦衰落信道的对角代数空时码(DAST)推广到频率选择性衰落信道,提出了对角空频分组码(DSF).基于多输入多输出天线和正交频分复用(OFDM),DSF码将满秩的旋转信号星座和子载波分组结合起来,以对角发送方式(每时刻只有一个天线发射)发射旋转信息符号向量的每个分量.成对错误概率分析表明:在频率选择性信道中,通过选择最佳的旋转矩阵,这种DSF-OFDM系统能实现满分集增益和最大的编码增益.系统采用了球型解码器对DSF码实施最大似然解码,它的解码复杂性是中等的,并且,解码算法的复杂性与信号星座的维数无关.此外,和先前所提出的一些方法相比,提出的空频码还具有频谱效率高(1symbol/s/Hz)的性能特点.     

Multi-dimensional sub-band coding: Some theory and algorithms

A system is proposed in order to split a multi-dimensional signal into N sub-bands, which are then subsampled by N. Subsequent upsampling and filtering allows the recovery of the original signal. Main features are a good bandpass characteristic of the channels, automatic aliasing cancellation and spectral invariance of the overall system. The one dimensional case, known as the quadrature mirrir filter (QMF, [1]), is generalized for both the separable and the non-separable case. A parallel implementation, based on pseudo-QMF filters, is presented as an efficient way to split a signal into equal sub-bands.     

Combined coding and modulation: theory and applications

The theoretical aspects of the encoding process are investigated, resulting in a precise definition of linear codes together with theorems that clarify how they can be obtained. A particular subset of linear codes, called superlinear codes, for which the performance analysis is highly simplified is identified. The most relevant performance measures for the analysis of this class of codes are discussed. The minimum Euclidean distance and the event and bit error probabilities are found analytically using the uniform error property (when applicable) or variations on it. This yields accurate upper and lower bounds to the error rate at the price of reasonable computational complexity. The theory is then applied to the search for `good' codes and to their performance evaluation. The cases of 16- and 32-PSK codes, which are good candidates for use in digital satellite transmission, are considered. Several new results in terms of error event and bit error probabilities are presented, showing considerable gains in terms of SNR with respect to the uncoded case     

Ten years of art imaging research

This paper describes a decade of work on digital imaging for museums. From 1989 to 1992, the visual arts system for archiving and retrieval of images (VASARI) project produced a digital-imaging system that made color-calibrated images of up to 20000×20000 pixels directly from paintings. It used seven color-separation bands in the visible region, resulting in an average color error of around 1 ΔE*_ab unit. These images have since been used to monitor the condition of paintings, document paintings during conservation treatment, including predicting appearance after cleaning, reconstruct the original appearance of paintings in which pigments have faded, and assess whether paintings have been damaged during transportation, in estimations of the surface reflectance spectra and in the printing of high-quality reproductions. We have applied similar techniques to museum infrared and X-ray imaging. To manage the images produced by the VASARI system, an image-processing package has been developed that is tailored for very large colorimetric images. This package has since been used in several other projects, including a remote image viewer designed to provide internet access to high-resolution images. The paper explores these developments and gives details of the current generation of VASARI-derived systems, set in the context of the state of the art for museum imaging     

State of the art and trends in speech coding

An introductory review of some basic speech coding techniques covers the most important properties of speech production and hearing, the ubiquitous techniques of quantization and linear prediction, and a recital of the most important measures of coding performance. In the survey that follows, several standardized speech coding systems reflecting the state of the art in speech coding are discussed in terms of coding method, bit rate, performance, complexity and typical application areas. Major future trends are indicated on the basis of expected future standards. The paper, which primarily deals with narrowband speech coding systems, is concluded by a review of the state of affairs and an outline of the future trends in the area of wideband speech coding.     

Renewal theory and source coding

Renewal theory provides a wavy to derive fundamental results about source coding and is useful in the analysis and design of many lossless data compression algorithms. We consider two very different applications of renewal theory to source coding. The first one results in a variable-length counterpart to the asymptotic equipartition property for unifilar Markov sources. The second application leads to the first analysis of variable-to-fixed length codes with plurally parsable dictionaries     

LINC: a common theory of transform and subband coding

A common theory of lapped orthogonal transforms (LOTs) and critically sampled filter banks, called L into N coding (LINC), is presented. The theory includes a unified analysis of both coding methods and identity relations between the transform, inverse transform, analysis filter bank, and synthesis filter bank. A design procedure for LINC analysis/synthesis systems, which satisfy the conditions for perfect reconstruction, is developed. The common LINC theory is used to define an ideal LINC system which is used, together with the power spectral density of the input signal, to calculate theoretical bounds for the coding gain. A generalized overlapping block transform (OBT) with time domain aliasing cancellation (TDAC) is used to approximate the ideal LINC. A generalization of the OBT includes multiple block overlap and additional windowing. A recursive design procedure for windows of arbitrary lengths is presented. The coding gain of the generalized OBT is higher than that of the Karhunen-Loeve transform (KLT) and close to the theoretical bounds for LINC. In the case of image coding, the generalized OBT reduces the blocking effects when compared with the DCT     

Sample converses in source coding theory

The rate and distortion performance of a sequence of codes along a sample sequence of symbols generated by a stationary ergodic information source are studied. Two results are obtained: (1) the source sample sequence is encoded by an arbitrary sequence of block codes which operate at a fixed rate level R, and a sample converse is obtained which states that, with probability one, the lower limit of the code sample distortions is lower bounded by D(R), the value of the distortion rate function at R; (2) the source sample sequence is encoded by an arbitrary sequence of variable-rate codes which operate at a fixed distortion level D, and a sample converse is obtained which states that, with probability one, the lower limit of the code sample rates is lower bounded by R(D), the value of the rate distortion function at D. A novel ergodic theorem is used to obtain both sample converses     

DS-CDMA systems using q-level m sequences: coding map theory

GF(q) m sequences with complex spreading mapping are considered for DS-CDMA systems by referring to three different environments with increasing synchronicity levels. For all environments, performance evaluation is derived both with a deterministic approach requiring spreading sequence specification, and with a statistical derivation, based on the assumption of spreading sequence ergodicity, in order to give closed-form performance theory. The optimal mapping design criterion, through zero-mean complex code mapping, is computed for all environments and validated through several numerical tests. Performance invariance, with respect to sequence levels, has been demonstrated for low synchronous environments, where the proposed sequence gives better performance     

Fifty years of Shannon theory

A brief chronicle is given of the historical development of the central problems in the theory of fundamental limits of data compression and reliable communication     

An application of coding theory to document retrieval

In this paper, methods for document retrieval are derived from algebraic coding theory. It is shown that these methods are efficient in information representation and that the amount of computation required in implementation is quite reasonable.     

Gamma rate theory for causal rate control in source coding and video coding

The rate distortion function in information theory provides performance bounds for lossy source coding. However, it is not clear how to causally encode a Gaussian sequence under rate constraints while achieving R–D optimality. This problem has significant implications in the design of rate control for video communication. To address this problem, we take distortion fluctuation into account and develop a new theory, called gamma rate theory, to quantify the trade-off between rate and distortion fluctuation. The gamma rate theory implies that, to evaluate the performance of causal rate controls in source coding, the traditional R–D metric needs to be replaced by a new GRD metric. The gamma rate theory identifies the trade-off between quality fluctuation and bandwidth, which is not known previously. To validate the gamma rate theory, we design a rate control algorithm for video coding; our experimental results demonstrate the utility of the gamma rate theory in video coding.     

Continuous phase quadrature phase shift keyed signaling techniquewith coding

A continuous phase quadrature phase shift keyed (CPQPSK) modulation technique is presented. This method utilizes a conventional QPSK modulator and a phase trajectory converter to approximate M=4, h=1/4 continuous phase signal and allows low cost, low complexity, and high rate (>1 Gbit/s) CPM modem implementation for bandwidth efficient transmission through nonlinear satellite channels. Using a communications analysis computer program it has been found that CPQPSK has 99 percent out-of-band power of 0.8R (MSK has 99 percent out-of-band power of 1.2 R where R is defined as bit rate), continuous phase trajectories, and nearly constant envelope amplitude. Simulation of realistic hardware designs indicate that the CPQPSK will require an Eb/No of 14 dB to achieve a bit error rate (BER) of 10^-6. Forward error correcting techniques using block codes with an overhead of 10 percent indicate that the Eb/No requirements can be reduced to 11.2 dB for 10^-6 BER     

Source coding theory for a triangular communication system

A rate-distortion problem is considered for a triangular communication system (TCS), which has one encoder f and two decoders g _X and g_Y. The encoder f maps correlated source outputs (X^K,Y^K) to two codewords W_X and W_Y, which are sent to g_X and g_Y, respectively. The decoders g_X and g_Y can communicate with each other via rate-constrained channels as many times as they need, and g_X reproduces Xˆ^K while g _Y reproduces Yˆ^K. The admissible rate-distortion region is determined for this TCS. Furthermore, the relations between the TCS and the Gray-Wyner (1974) system, Wyner's (1974) common information, Yamamoto's cascade communication system (1981), and the successive refinement system are discussed