Detection and partial correction of isolated errors from the received data in a 1st-order d.p.c.m. codec

A detection and partial-correction (d.p.c.) system located at the receiver in a 1st-order d.p.c.m. system enables isolated transmission errors that would cause gross distortion in the recovered signal of a conventional d.p.c.m. decoder to be corrected from the received data, providing that the input signal does not exhibit a rapid change in its slope during a sampling period. The d.p.c. system is disabled when this occurs.     

High-performance c.c.d. channel filter for a p.c.m. codec

A monolithic c.c.d. filter for p.c.m. codec was fabricated employing both a minimum-phase design with a substantially reduced number of taps and almost perfect elimination of excess capacitances. Results, such as negligible degradation in frequency responses, considerable reduction of common-mode signal, low filter noise (?78 dBm) and wide dynamic range (84 dB) were successfully obtained.     

Optimised hybrid unidigit p.c.m. system

The coding efficiency of unidigit p.c.m. systems has been improved by using a secondary feedback loop, and the gain/frequency characteristic of the coder has been equalised. The overall signal/noise characteristic of this hybrid system is found to be better than those of all other unidigit systems; it is inferior to the conventional p.c.m. system only for bit rates higher than 60 × 103 bit/s.     

Meander-channel c.c.d. (m.c.c.d.) recursive filter

A modified input-weighting concept for a c.c.d. recursive filter is proposed; it has been implemented using an m.c.c.d. with a complementary input scheme which provides net weighting coefficients. This improved structure requires neither operational amplifiers nor resistors. The operation and performance of the fabricated 2nd-order bandpass filter are presented.     

Hybrid p.c.m.?an experimental video system

Hybrid pulse-code modulation (h.p.c.m.) is a variant o. multilevel p.c.m., in which the least significant digit(s) is made to describe the quantising noise exactly. A theoretical and practical feasibility study has been made of the application of h.p.c.m. to the transmission of 625-line Pal colour signals over low-quality narrowband circuits.     

Adaptive statistical encoding of d.p.c.m.-coded videotelephone signals

Adaptive statistical encoding of d.p.c.m.-coded video-telephone signals is considered. The need for an adaptive statistical encoder to operate on short-term batch statistics is explained and the effect on the bit rate of limiting the number of codes employed by the statistical encoder is reported.     

Meander channel c.c.d. (m.c.c.d.) transversal filter

A simple and compact m.c.c.d. transversal filter is presented. The device features (a) an input-weight technique to achieve a large output voltage, (b) a new `split-input-gate? weighting to provide accurate filter coefficients, and (c) a simplified electrode structure by using the m.c.c.d. as a summing register.     

Pitch synchronous differential predictive encoding system

A pitch synchronous differential predictive encoding system (p.s.d.p.e.) is described, which reduces the dynamic range of voiced speech to a value similar to that of unvoiced speech. As a consequence, the signal encoded has a smaller dynamic range than the speech signal and results in an improvement in the signal/noise ratio for a given transmitted number of bits per sample. This improvement is approximately 8 dB compared with an a.d.p.c.m. codec, when the p.s.d.p.e. system uses an adaptive p.c.m. encoder and the transmission rate is 3 bit/sample.     

Adaptive difference detection and correction system for partial correction of transmission errors in linear p.c.m.

An adaptive version of the difference detection and correction system for the partial removal of transmission errors in linear p.c.m. speech without the use of channel coding is presented. The improvement in s.n.r. compared to the nonadaptive system is approximately 3 dB for transmission bit error-rates between 0.5 and 5%.     

Application of c.c.d.s to f.d.m. channel filtering: a phase-cancellation system

A system is suggested for generating and demodulating single-sideband signals, based on the phase-cancellation method; it is particularly attractive for implementation by c.c.d.s, whose well known features it seems fully able to exploit.     

Stability of 1st-order thyristor-bridge control system

A nonlinear difference equation that corresponds to a 2-phase thyristor bridge supplying an inductor-resistor series load and using an inverse-cosine control scheme is shown to converge uniformly, and the global asymptotic stability of the system is established rigorously.     

Feasibility of using digital filters to interconnect p.c.m. and f.d.m. transmission systems

A time-division multiplex (t.d.m.) and a frequency-division multiple (f.d.m.) system may be interconnected by means of gates and lowpass filters. The use of digital filters (d.f.s) for this purpose appears attractive when the t.d.m. system uses pulse-code modulation (p.c.m.), because digital-analogue and analogue-digital conversion are unnecessary at the interface between the d.f. and the p.c.m. system. The problems involved in applying d.f.s in this application are discussed. It is concluded that the interconnection of p.c.m. systems with f.d.m. systems using quite low carrier frequencies requires the development of digital circuits operating at several hundred megahertz.     

Delta-modulation/p.c.m. convertor

A simple and sufficiently accurate digital convertor is suggested that converts a delta sequence of an exponential delta modulator into a sequence of digital numbers. Each number equals the height of the analogue signal at the input of the delta modulator at each moment. The system employs an up-down counter and some logic based on conventional full adders.     

Simple delay-line p.c.m. coder

A simple p.c.m. coder, using a delay line as the coding network and having signal/noise ratio and other characteristics similar to conventional p.c.m. systems, has been developed. The coder can easily be extended to ternary and multilevel working, and the reconstructed message, available at the transmitter, may be used for purposes of monitoring and further reducing quantising noise.     

Upper bound on signal/quantising-noise ratio for television d.p.c.m. systems

Consideration is given to an upper bound on signal/quantising-noise ratio for television d.p.c.m. systems. The 7.2 dB gain for entropy coding assumes ? entropy of the bit stream of the quantiser output. The calculations are based on Laplacian signals, because television signals at d.p.c.m. quantiser inputs are approximately Laplacian.     

Noninteger sampling to subcarrier frequency ratios in d.p.c.m. of PAL signals

A simple predictor having three coefficients is described for d.p.c.m. encoding of composite PAL colour signals. Noninteger ratios of sampling frequency fs to subcarrier frequency fsc can be selected. For a colour-bar signal, it is shown that the s.n.r. of the d.p.c.m. system using fs/fsc = 2.5 is approximately the same as when third-previous sample prediction is used, i.e. when fs/fsc = 3.0.     

Simulation of p.c.m. transmission system for use in subscriber network

The extension of p.c.m. techniques to telephone and data subscribers requires a cheap transmission system that works over a wide range of different cable lengths and diameters and that is compatible with existing analogue services. Simulation on a digital computer and interactive optimisation show the feasibility of such a system.     

Speech-transmission performance of p.c.m. systems

A method is described for calculating a quantity representative of the transmission performance of a p.c.m. system. The value obtained depends upon (a) the number of quantised output voltage states, (b) the companding law and (c) the volume of the input speech signal relative to the overload point of the system.     

Partial correction of transmission errors in d.p.c.m. without recourse to error correction coding

A method for partially correcting transmission errors in a 1st-order d.p.c.m. system, without recourse to channel coding, is described. A simple detection algorithm based on the statistical properties of a sequence of differences between adjacent samples of a modified decoded sequence is used to identify the erroneous samples. Three different correcting algorithms are described. Substantial improvements in the decoded waveform are achieved, and, for a Markov input process, an error rate of 0.04% in the first and second most significant digits, an improvement in s.n.r. of 7dB is achieved.     

Stability of p.c.m.-oscillator control systems

An extension of existing techniques allows a proof of the stability of two classes of linear oscillator control system for use in integrated p.c.m. systems. Stability is shown to depend on the response of various filters used in the system in a manner which should be easily realisable in a practical network.