The technique of pulse-Position-modulation offers greater receiver sensitivity than PCM, and is ideally suited to optical sources. A broad analysis shows that more taps could be made available on an existing multi-poi...
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A differential pulse code modulation (DPCM) system provides a fast and inexpensive data compression technique for analog signals. Two methods of improving the performance of DPCM systems are studied: the introduction ...
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A differential pulse code modulation (DPCM) system provides a fast and inexpensive data compression technique for analog signals. Two methods of improving the performance of DPCM systems are studied: the introduction of delays using incremental tree coding techniques and the design of nonuniform quantizers based upon optimization theory. The performance of matched integrator, perfect integrator, and optimization-based DPCM systems are compared for first-order Gauss-Markov sources and mean square error using simulation techniques. Both methods improve system performance. The optimization-based DPCM system provides substantial improvement for high bit rates.
In DPCM (differential pulse code modulation) or HDPCM (hybrid DPCM) of coloured pictures consisting of three components, every component can be coded with three separate coders, each containing a scalar quantizer. How...
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In DPCM (differential pulse code modulation) or HDPCM (hybrid DPCM) of coloured pictures consisting of three components, every component can be coded with three separate coders, each containing a scalar quantizer. However, more compression can be obtained with one vector quantizer instead of three scalar quantizers. In the article, the attention is focused on the placement of the output vectors in the two-dimensional prediction error plane using visual masking functions.< >
The increasing availability of high capacity data communication networks has generated a demand for accurate, fast and low power dissipation analogue to digital signal converters. Such converters are now required to c...
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The increasing availability of high capacity data communication networks has generated a demand for accurate, fast and low power dissipation analogue to digital signal converters. Such converters are now required to convert a wide range of signals to binary weighted pulsecode modulated format. The use of sigma-delta modulation for the primary data conversion is very attractive, since it uses a one bit quantizer and requires no sample and hold. The sampling rate employed is much faster than the highest frequency in the message signal (oversampling). The high accuracy conversion is achieved as a result of the modulator operating as a self adaptive, fast limit cycling system. The digital output data from the modulator, containing quantization noise principally out of the signal band, is subsequently filtered and code converted digitally. A complete converter may be realised in integrated form using a combination of CMOS linear and digital circuitry.< >
The integration of voice and data switching using a packet based approach has been proposed in many forms. If speech coding is used in such a network, impairments such as lost packets affect the coder performance. The...
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The integration of voice and data switching using a packet based approach has been proposed in many forms. If speech coding is used in such a network, impairments such as lost packets affect the coder performance. The effect of packet loss on 3 toll quality speech coders is discussed. The coders are adaptive differential pulsecoded modulation (ADPCM), subband coding (SBC) and adaptive predictive coding (APC). Their configurations adopted in the simulations are described. Damage resulting from loss of a speech packet is two-fold: firstly a missing speech segment is introduced for the lost duration; secondly the adaptation logic is disrupted after the lost segment. Therefore any compensation technique should aim to fill the missing segment as well as restoring the adaptation after the loss. The use of side-information was suggested in the case of SBC-APCM. The results showed successful compensation in the case of ADPCM, and SBC.< >
In reviewing the growth and development of telecommunication services in New Zealand during the period 1978-87, the paper begins by examining the growth of digital technology and shows how the usual circuit switched s...
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In reviewing the growth and development of telecommunication services in New Zealand during the period 1978-87, the paper begins by examining the growth of digital technology and shows how the usual circuit switched services, as well as some of the traditional messaging-based systems such as telex and datex, have given way to the new digital services. The implementation of the Digital Data Network and packet switched related services which utilize this network, such as e-mail, videotex, Electronic Funds Transfer Point of Sale, intermational host connection, etc., have been significant mile-stones in telecommunications development in New Zealand. A number of other communication services such as the cellular radio and teletext are then briefly discussed, concluding with a look at Integrated Services Digital Network developments.
Presents a fast DPCM coder built around a ROM of feasible size, in which an elementary form of tree encoding is integrated, to improve the quality of the decoded picture. Simulations illustrate the improvements of thi...
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Presents a fast DPCM coder built around a ROM of feasible size, in which an elementary form of tree encoding is integrated, to improve the quality of the decoded picture. Simulations illustrate the improvements of this technique in comparison with normal DPCM encoding
The authors describe the design of a four-channel oversampled A/D (analog/digital) converter with transmit filter for voice-band application. The decimator filter is timeshared between the four channels and the archit...
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The authors describe the design of a four-channel oversampled A/D (analog/digital) converter with transmit filter for voice-band application. The decimator filter is timeshared between the four channels and the architecture of the sigma-delta coder is selected on the basis of minimizing the chip area. The analog front-end loop is fully differential to minimize the channel-to-channel crosstalk. The key issues in designing a multichannel oversampled A/D converter for area efficiency are addressed. It is concluded that for the multichannel telephony voice-band application implemented in CMOS technology, a first-order loop is most area-efficient. The performance of the coder has been evaluated and it is shown to have a dynamic range of 79 dB, to occupy a total active area of 33000 mils/sup 2/ or 8250 mils/sup 2/ per channel, and to meet the D3 specifications for the transmit filter. It runs on a 5-V supply and consumes 50 mW per channel.
A very high-quality sub-band ADPCM music coding scheme which compresses high-fidelity music signals, bandlimited to 15 kHz, to an equivalent PCM representation of only 4 bits per sample, is described. By processing mu...
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A very high-quality sub-band ADPCM music coding scheme which compresses high-fidelity music signals, bandlimited to 15 kHz, to an equivalent PCM representation of only 4 bits per sample, is described. By processing music sampled at 32 kHz, this coder exhibits a total bit rate of only 128 kbit/s and is consequently applicable to the ISDN. Subjective tests conducted with this coder have shown that music recovered from the compression scheme is essentially indistinguishable from the original material. The results obtained are of major importance, not only for ISDN and broadcasting, but also for other digital audio technology such as compact disc (CD) and digital audio tape
Skeletal muscle changes in PEM were studied in 70 children of both sexes below the age of 6 years. Fifty children were suffering from PEM of which 64 per cent were severely malnourished weighing < 60 per cent of th...
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Skeletal muscle changes in PEM were studied in 70 children of both sexes below the age of 6 years. Fifty children were suffering from PEM of which 64 per cent were severely malnourished weighing < 60 per cent of the reference weight for age. Twenty healthy children served as controls. The skeletal muscles were clinically assessed in all children. Then a histopathological study of the calf muscle was done in all the malnourished and four healthy children by standard methods. The flabbiness of the muscles was the earliest clinical manifestation followed by hypotonia. In extremely malnourished cases on the other hand, stiffness of the muscles was the prominent finding. Histopathological study revealed thinning of the muscle fibers, loss of sarcoplasm, and cross-striations leading to myotube or Sarcolemmal tube formation. The latter change was found in 75-90 per cent cases and was maximum in grade III PEM. The attenuated muscle fibers were found only in early malnutrition (subgroup A) whereas fatty degeneration of the muscle fibers was confined to moderate to severely malnourished cases (subgroup B). In chronic and severely affected cases significant fibrotic changes (P < 0.05) were also found in comparison to subgroup A. The shape and size of the subsarcolemmal nuclei were preserved, but their peripehral position was altered in a majority of the cases which can be described as ''no definite pattern of nuclear arrangement''. There was no pericapillary infiltration by lymphocytes, but we have, for the first time, observed perivascular oedema and hyalinization of the vessel wall in 5 per cent to 10 per cent of cases. These changes were inversely proportional to the severity of PEM. The size of the nerves and muscle spindles were normal in both malnourished and control cases.
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