PCM systems are becoming increasingly popular because of certain inherent advantages such as repeatability without deterioration in the quality and the compatibility with other digital systems. Sampling and quantizing...
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PCM systems are becoming increasingly popular because of certain inherent advantages such as repeatability without deterioration in the quality and the compatibility with other digital systems. Sampling and quantizing are the two important steps in converting a voice signal into PCM. Companding in the PCM systems reduces the effect of quantization noise and improves the overall performance of PCM. Various digital modulation techniques such as amplitude shift keying, frequency shift keying and phase shift keying are employed when PCM data are required to be sent on an rf carrier. PCM communication systems require three types of synchronizations: bit, frame and network synchronizations. Hierarchy of PCM terminals are developed in the USA and Japan. PCM systems are now being introduced into the telecommunication networks in India. In this paper the use of PCM in modern communication has been outlined.
A description is given of a 2. 048 Mbit/s line unit, namely: the repeater-regenerator, the remote identification device for the repeater-regenerators, the remote identification control unit, the remote power supply wi...
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A description is given of a 2. 048 Mbit/s line unit, namely: the repeater-regenerator, the remote identification device for the repeater-regenerators, the remote identification control unit, the remote power supply with automatic rearming. Furthermore, a description is given of the functions of the telegraphic transmission equipment using the free bits in the P. C. M. frame;the functions of the data transmission equipment using the 64 kbit/s time slots in the P. C. M. frame, and of the functions of the time slot and free bit P. C. M. frame extraction equipment.
Methods of the synthesis of sequential logic circuits, with reference to designing linear transcoders in PCM systems are presented. The suitability of transforming digital binary signals prior to their introduction in...
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Methods of the synthesis of sequential logic circuits, with reference to designing linear transcoders in PCM systems are presented. The suitability of transforming digital binary signals prior to their introduction into the linear PCM trunk has been explained. The best known methods of transforming binary signals into linear ones have also been reviewed. The design of linear transcoders for two selected codes is considered.
The tasks of a subscriber channel status detector are established, along with the problems that must be solved for which a variant of a solution is formulated. The necessary three tests are combined into a realization...
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The tasks of a subscriber channel status detector are established, along with the problems that must be solved for which a variant of a solution is formulated. The necessary three tests are combined into a realization proposed by means of automotive means.
The channel error response of decoders in picture transmission with differential pulse code modulation (DPCM) is analyzed mathematically. This error response is derived for two-dimensional prediction using three pictu...
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The channel error response of decoders in picture transmission with differential pulse code modulation (DPCM) is analyzed mathematically. This error response is derived for two-dimensional prediction using three picture elements. Corresponding expressions for less than three picture elements are shown to be special cases of the solution obtained. From a discussion of the convergence, various conditions for the prediction coefficients are given. Based on the energy of the error response it is verified for a group of prediction algorithms that the extent of the associated error patterns decreases considerably when the sum of the coefficients is reduced only slightly below the limit for convergence. Examples of calculated and simulated error patterns are presented.
pulse code modulation (PCM) was first introduced into North America on a wide scale in 1962 by the Bell System with the introduction of the Western Electric Company's D1 channel bank and T1 line. The tremendous su...
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pulse code modulation (PCM) was first introduced into North America on a wide scale in 1962 by the Bell System with the introduction of the Western Electric Company's D1 channel bank and T1 line. The tremendous success of PCM in North America can best be illustrated by the more than 1,250,000 channels presently installed, the number expanding at the rate of 285,000 channels per year. To meet the increased demand, a number of other suppliers, including ITT, have developed comparable PCM systems;however, compatibility with the Bell System is still of major concern to the independent telephone companies and suppliers. Competition among various suppliers has caused the introduction of many new features and systems for special applications such as subscriber systems, data capability, increased channel capacity, and supervisory systems. Also, a number of independent digital networks are being developed that will provide service independent of the Bell System, particularly for full-time leased circuits and data transmission.
It is claimed that W. R. Bennett's approximation for the spectrum of quantizing noise is both numerically accurate and computationally economical, but apparently does not correspond to the physical mechanism of in...
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It is claimed that W. R. Bennett's approximation for the spectrum of quantizing noise is both numerically accurate and computationally economical, but apparently does not correspond to the physical mechanism of intermodulation producing the noise. On the other hand A. I. Velichkin's approach reveals this structure, but G. H. Robertson's computation of his formula becomes rather expensive for quantizers with more than 16 levels. In this paper, the authors derive Bennett's result by a new route, starting from the noise analysis of Blachman. It is shown that Velichkin's intermodulation series has a 'line-structure' which, when exploited for approximation leads to Bennett's B series. Bennett's approximation may now be reinterpreted as a genuine intermodulation series in which low-order terms are absent, and the authors show how this explains the experimentally observed flatness of quantizing noise spectra for arbitrary input spectra and for high sampling rates. Experimental results are presented which indicate that the noise/signal ratio defined in terms of Blachman's analysis is a better estimate of system performance than the conventional mean-squared-error analysis in cases where the quantizer is not globally linear, as for instance when compandor and expander are mismatched.
The aliasing effect associated with modulation is discussed, along with problems related to demodulation. The concepts of sampling and aliasing are considered. The experimental demonstration of aliasing is outlined.
The aliasing effect associated with modulation is discussed, along with problems related to demodulation. The concepts of sampling and aliasing are considered. The experimental demonstration of aliasing is outlined.
The advantages of PCM in telecommunication systems from the viewpoints of economy, reliability and transmission quality are pointed out. The application of a continuous progression chain code as a correcting transmiss...
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The advantages of PCM in telecommunication systems from the viewpoints of economy, reliability and transmission quality are pointed out. The application of a continuous progression chain code as a correcting transmission code of a PCM system is reported.
A study was made of combining two ways of reducing the redundancy in the digital representation of speech signals. Differential PCM encodes the signal into digital form and reduces the redundancy due to correlation in...
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A study was made of combining two ways of reducing the redundancy in the digital representation of speech signals. Differential PCM encodes the signal into digital form and reduces the redundancy due to correlation in adjacent sample values of the signal. Following this differential PCM operation, entropy coding is used to reduce redundancy due to the unequal probabilities of the quantizer levels to be transmitted.
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