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Showing papers on "Data transmission published in 1968"


Journal ArticleDOI
R. Chang1, R. Gibby
TL;DR: This paper presents a theoretical analysis of the performance of an orthogonal multiplexing data transmission scheme (parallel transmission scheme) subject to a number of degrading factors normally encountered by a practical operating system.
Abstract: This paper presents a theoretical analysis of the performance of an orthogonal multiplexing data transmission scheme (parallel transmission scheme) subject to a number of degrading factors normally encountered by a practical operating system. The factors considered jointly are sampling time error, carrier phase offset, and nonideal phase characteristics of transmitting and receiving filters. Performance is measured by the familiar criterion of eye opening of the received data signal. A closed-form expression for the eye opening is obtained. It is shown that the lengthy nonlinear functions in the solution can be closely approximated by simple piecewise linear functions for parameter values of interest. The optimum settings of the sampling time and the carrier phase are determined for given filter phase distortion. Also, considering all factors, simple formulas are developed for computing interchannel interferences, intersymbol interference, and the resulting eye opening. Simple relationships between the eye opening and filter phase distortion are explored, and a concept of parametric eye is introduced to aid in filter design. An illustrative example is considered which shows that the impairment of the system performance is not excessive for a reasonable range of system design parameters.

384 citations


Journal ArticleDOI
TL;DR: A systematic approach to the analysis and construction of channel codes for digital baseband transmission is presented and state-dependent coding of both fixed and variable length is a direct result.
Abstract: A systematic approach to the analysis and construction of channel codes for digital baseband transmission is presented. The structure of the codes is dominated by the set of requirements imposed by channel characteristics and system operation. These requirements may be translated into symbol sequence properties which, in turn, specify a set of permissible sequence states. State-dependent coding of both fixed and variable length is a direct result. Properties of such codes are discussed and two examples are presented.

129 citations


Patent
08 Oct 1968
TL;DR: In this article, the authors propose a method for transmitting data on a time-shared basis between a plurality of low-speed sources and a high-speed source over a communication circuit.
Abstract: Apparatus and method for transmitting data on a time-shared basis between a plurality of low-speed sources and a high-speed source over a communication circuit. Byte-serial data is initially transmitted at a relatively low rate from a plurality of remote sources (terminals) to a nearby peripheral computer which temporarily stores the incoming data in a memory unit and arranges it into strings of data blocks. The stored data is later transmitted as messages of one or more data blocks at a much faster rate over a communication circuit to a central computer. These data blocks may be either text blocks containing the temporarily stored data or control blocks containing information regarding the status of remote terminals. In addition, each message contains an acknowledge block whose purpose is to facilitate the detection and correction of data transmission errors. The central computer checks all incoming blocks for errors and acknowledges only those that have been correctly received. Blocks received in error by the central computer are not acknowledged, and are retransmitted by the peripheral computer until they are correctly received. Conversely, messages consisting of acknowledge, text, and control blocks are transmitted from the central computer to the peripheral computer over the communication circuit at high speed, the data is temporarily stored in the peripheral computer''s memory and is later transmitted to the correct remote destination (terminal) at low speed. Error detection and correction performed on these messages is similar to those performed on messages traveling in the opposite direction.

87 citations



Journal ArticleDOI
TL;DR: This paper presents a model which provides a reasonable approximation to observed error phenomena which is similar to the model developed by E. N. Gilbert, but several important modifications greatly simplify the estimation of parameters, and make the model correspond more closely to the physical phenomena involved.
Abstract: The nature of the errors in a regenerative digital transmission system is such that a memoryless channel is a poor model for predicting the error phenomena. In this paper we present a model which provides a reasonable approximation to observed error phenomena. The memory of the channel is represented by a Markov model. This model is similar to the model developed by E. N. Gilbert, but several important modifications greatly simplify the estimation of parameters, and make the model correspond more closely to the physical phenomena involved. Bounds for the channel capacity of the binary regenerative channel are obtained. Error separation, block error, and burst statistics are derived. Error model parameters are derived from available experimental data on the T1 digital transmission line and the switched telephone network. The Markov model is shown to provide a good representation of the observed error phenomena.

52 citations



Journal ArticleDOI
01 Oct 1968
TL;DR: In high-speed communication through a medium with time-frequency spread (such as in HF ionospheric, sonic underwater, and voice-quality telephone line transmission), the transmission speed and system errors are determined by an overall system variance which comprises the intersymbol interference variance from time spread, as well as the variance from frequency spread and the variance arising from channel noise.
Abstract: In high-speed communication through a medium with time-frequency spread (such as in HF ionospheric, sonic underwater, and voice-quality telephone line transmission), the transmission speed and system errors are determined by an overall system variance (or equivalent noise). This overall variance comprises: 1) the intersymbol interference variance from time spread (or dispersion in the unit impulse response of the medium); 2) the variance from frequency spread (or dispersion it the CW response of the medium); and 3) the variance from channel noise at the receiver. In order to mitigate intersymbol variance from time spread, after discussing some early and limited attempts, a review is made of the general synthesis of the infinite and finite Wiener optimal networks or equalizers using delay lines with feedforward and/or feedback taps (or their shift register digital network counterpart). Also considered are optimal finite feedforward delay line approximations to the Wiener networks, synthesized nonsequentially and sequentially using a steepest descent evolutionary network synthesis, resulting in a monotonically decreasing and convergent overall variance. Applications of these networks are shown in the transmission of speeded-up analog facsimile pictures over unconditioned voice-quality telephone lines. It is shown that the received smeared picture can be refocused or de-smeared, or its time spread mitigated, to allow overall satisfactory high-speed picture transmission. Moreover, in over-the-horizon HF ionospheric analog and/or data transmission, time spread occurs in the form of discrete multi-path reception, such as the familiar ghosts observed in television. A particularly stringent multipath comprises two equal or nearly equal magnitude paths, a situation which is actually observed in HF ionospheric communication between two ships at sea. For this case it is shown that serial data transmission with pulses thin enough to resolve the multipath achieves, with optimal equalization, an irreducible bit error ratio (BER) which is a number of orders of magnitude less than the irreducible BER of the parallel data transmission method used in all contemporary HF modems (modulators and demodulators). Design curves are given showing the intersymbol interference variance from time spread as a function of the number of taps it the delay line correction networks, along with the variance arising from channel noise, and the optimal allocation of both variances for minimal overall BER with a given number of taps for the finite realizable correction networks. Because of frequency spread, the ever-changing unit or impulse response of the medium (e.g., HF ionospheric) causes the correction or equalization networks to become aged, giving rise to frequency spread variance. This is formulated both for determinate and for random changes of the medium unit response. For transmission media having simultaneous time spread and frequency spread, the equivalent overall variance is a simple function of the time-frequency spread product of the medium. These formulas are applied to find the overall minimal BER as a function of the time-frequency product for a contemporary parallel data modem and for a new serial adaptive data transmission system (ADAPTICOM) which periodically in real time and with digital techniques rejuvenates the time spread digital correction networks. It is shown that the transmission limit of communication of the parallel data modem is for a time-frequency spread product of about 1/2000, while that for the new serial adaptive data modem is about ten times larger, or 1/200. As a result, new communication channels are opened up for serial adaptive transmission, such as the HF spectrum below the maximum usable frequency (MUF).

39 citations


Patent
Bruce D. Gavril1
11 Jul 1968
TL;DR: In this paper, a general purpose control unit is provided for controlling a wide variety of digital computer peripher devices and systems and for facilitating their attachment to the complex system I/O interface.
Abstract: A versatile, general purpose control unit is provided for controlling a wide variety of digital computer peripheral devices and systems and for facilitating their attachment to the complex system I/O interface. Programmable digital interfaces and control circuitry are provided in the control unit for affecting a wide variety of external device operations in addition to conventional data read and data write functions. Means are further provided for directly interconnecting two peripheral devices through the control unit without computer system activity during data transfer; this eliminates unnecessary interference with the system memory or with the I/O channel. An additional aspect allows the attached peripheral equipment to change the effective system address of the control unit in order to more effectively utilize control unit facilities.

39 citations


Journal ArticleDOI
TL;DR: A hybrid digital-analog method for approximating closely almost any reasonable digital signaling waveform via a shift-register version of a transversal filter is described.
Abstract: Data transmission (digital signaling) systems generally transmit continuous, essentially bandlimited signals that represent alphanumeric sequences. The transmitting apparatus in such systems must therefore convert discrete symbols-often binary pulses-into prescribed analog waveforms. Current commercial systems do this via simple filtering, gating, and conventional modulation. These practices limit the types of waveforms that can be used and they are not always amenable to variable rate signaling. This paper describes a hybrid digital-analog method for approximating closely almost any reasonable digital signaling waveform. The basic idea is very simple: a "staircase" approximation of the desired signal can be generated via a shift-register version of a transversal filter. Variations on this idea, such as derivative approximation and multirate shifting, enhance its accuracy without destroying its simplicity and time-frequency scalability.

31 citations


Patent
03 Jul 1968
TL;DR: In this article, a communications system comprised of a multiplexer and a plurality of unit adapters for transferring data characters between a high speed digital computer and a relatively low speed data transmission devices operating online with the computer is described.
Abstract: A communications system comprised of a multiplexer and a plurality of unit adapters for transferring data characters between a high speed digital computer and a plurality of relatively low speed data transmission devices operating online with the computer. A scanner circuit included in the multiplexer provides for sequential servicing, in turn, each of the unit adapters for transferring the data characters. The scanner circuit may be interrupted at any time such that the computer can transfer a function selector character to any of the unit adapters, the character determining whether the unit adapter will thereafter operate in an input or output mode. Monitor and control logic in each unit adapter has circuitry therein for detecting an overload condition resulting from online operation of the computer system during an input mode of operation, thereby detecting any loss of data in its real time operation and enabling the computer to monitor the circuits to correct the loss of data caused by the overload condition.

31 citations


Patent
01 Oct 1968
TL;DR: In this paper, a data acquisition interface system for translating real-time randomly occurring complex input signals into data processing usable form for transmission to an online data processing system is presented, which includes a plurality of interchangeable data acquisition components of the monitor register, scaler/timer and analogue to digital converter type.
Abstract: A data acquisition interface system for translating real-time randomly occurring complex input signals into data processing usable form for transmission to an online data processing system. The system includes a plurality of interchangeable data acquisition components of the monitor register, scaler/timer and analogue to digital converter type which are activated by external means for gathering data, counting inputs, measuring time and making analogue to digital conversions and an interface control unit for organizing the data transfer from the components to the data processing system. The occurrence of an input signal, the time coincidence of two or more input signals or the presence and absence of input signals or the like are termed events. In response to the occurrence of an event, the interface control unit initiates a sequential component data transfer from the components associated with the event preceded by a word identifying the event. Events are processed in numerical sequence, but processing may be selectively modified to permit processing in priority sequence. Events may be programmed to exclude other events which share a common component.

Journal ArticleDOI
TL;DR: It is shown that many permutation alphabets provide energy per bit advantage over binary FSK, although the best results are obtained with one-out-of-N alphABets.
Abstract: Performance characteristics are derived for an FSK data transmission scheme in which M frequencies out of N are used simultaneously. Noncoherent matched filters are applied at the N frequencies, and the filter outputs are compared as in a permutation modulation system. It is shown that many permutation alphabets provide energy per bit advantage over binary FSK, although the best results are obtained with one-out-of-N alphabets. Considering bits per unit bandwidth, many permutation alphabets perform as well as or better than binary; however, one-out-of-N alphabets carry less information per unit bandwidth when N > 4.

Patent
23 Jan 1968
TL;DR: In this paper, an adaptive transversal equalizer for a channel 13 carrying non-synchronous or analogue signals from a source 10, the attenuators 16 of the equalizer are adjusted by correlating, in 15, the signal appearing at the taps of the delay line 14 with an error signal derived by comparing the output of an equalizer in response to a pseudo random repetitive test signal applied to the channel from generator 11, with the output output of a filter 23, having a response equivalent to the desired equalized channel response, when fed with the same test
Abstract: 1,258,131. Adaptive transversal equalizers. WESTERN ELECTRIC CO. Inc. 23 Jan., 1969 [23 Jan., 1968], No. 3746/69. Heading H4R. In an adaptive transversal equalizer, for a channel 13 carrying non-synchronous or analogue signals from a source 10, the attenuators 16 of the equalizer are adjusted by correlating, in 15, the signal appearing at the taps of the delay line 14 with an error signal derived by comparing the output of the equalizer in response to a pseudo random repetitive test signal applied to the channel from generator 11, with the output of a filter 23, having a response equivalent to the desired equalized channel response, when fed with the same test signal as is applied to the channel. The test signal is transmitted with the message signal, the effect of the message signal being eliminated by delaying, in network 21, the error signal applied to the correlators 15 by an integral multiple of the test signal repetition period.

Journal ArticleDOI
TL;DR: Fourier coding method for coding images for digital transmission achieves bandwidth reduction for televised images by reducing the amount of data to be coded.
Abstract: Fourier coding method for coding images for digital transmission, achieving bandwidth reduction for televised images

Patent
23 Apr 1968
TL;DR: In this paper, a sampling of alternate data input pairs for one particular partial-response format is used to produce a two-level line signal which preserves transitions occurring at the basic signaling interval.
Abstract: Theoretically maximum equivalent binary data transmission rates are obtainable in partial-response channels; i.e., bandlimited channels with filter shaping which disperses the impulse response to individual data inputs over more than one signaling interval. However, the resultant multilevel line signals occasionally give rise to system start-up problems. These problems are eliminated by initial sampling of alternate data input pairs for one particular partial-response format to produce a two-level line signal which preserves transitions occurring at the basic signaling interval. The same technique provides means for signaling at half the design rate without changing channel filters or the basic clock rate.

Patent
George H Swan1
19 Dec 1968
TL;DR: In this article, a jittering idle channel is tracked to an active channel and diversity switching to the idle channel without loss of a bit is provided without any built-in preference for one channel.
Abstract: A jittering idle channel is tracked to a jittering active channel and diversity switching to the idle channel is provided without loss of a bit. The signal received in the idle channel is written into an elastic store bit-by-bit as it is received; the signal is read out in the order in which it was written at times determined by a timing signal derived from the active signal and modified under control of an error signal indicating a timing difference between the signals on the active and idle channels. There is no built-in preference for one channel, thus either channel may track the other.

Journal ArticleDOI
TL;DR: The use of a digital computer to calculate cardiac catheterization data has been studied and the equipment and programming logic used by the laboratory are described.


Patent
Wolfgang G. Stehr1
29 Apr 1968

Journal ArticleDOI
TL;DR: The basic equivalence of many of the linear data transmission design techniques is illustrated, showing the unifying feature of these techniques to be a generalization of Nyquist's original ideas relating time samples and frequency domain constraints.
Abstract: This paper illustrates the basic equivalence of many of the linear data transmission design techniques. It shows the unifying feature of these techniques to be a generalization of Nyquist's original ideas relating time samples and frequency domain constraints. It examines pulse amplitude (with and without constraints on the input data) and pulse shape modulation systems, and shows their relationships. It uses a number of previously-described systems to illustrate the range of possibilities of the very general design approach. This paper presents some new results on noise and channel parameter monitoring and on spectrum shifting by constraining the input data.

Patent
25 Jun 1968
TL;DR: In this article, a method of transmitting data over connection paths subject to signal distorting influences was proposed, where the transmitted message signals comprised parity bits interspersed according to a predetermined ratio with the individual information bits comprising the message signal.
Abstract: A method of transmitting data over connection paths subject to signal distorting influences wherein the transmitted message signals comprise parity bits interspersed according to a predetermined ratio with the individual information bits comprising the message signal. The message signals are transmitted in the form of two time spaced transmission signals of the above described type in different frequency channels.

Journal ArticleDOI
TL;DR: A new data-transmission method that has twice the speed capability of the duobinary technique over an identical bandpass transmission medium is presented, which is sufficiently general to be applicable to both voice anti broadband communication channels.
Abstract: A new data-transmission method that has twice the speed capability of the duobinary technique over an identical bandpass transmission medium is presented. Advantages of this method include promising performance and completely digital manner of signal generation, thus considerably reducing the circuit complexity. The system is based on correlative techniques in which the digital encoding forms an integral part of the carrier modulation. The process is sufficiently general to be applicable to both voice anti broadband communication channels.

Journal ArticleDOI
TL;DR: An adaptive filter, similar to that used in automatic equalization, for use as a predictor in data compression systems, is suggested and some of the applications of this adaptive predictor in digital data transmission are discussed.
Abstract: This paper suggests an adaptive filter, similar to that used in automatic equalization, for use as a predictor in data compression systems. It discusses some of the applications of this adaptive predictor in digital data transmission. In the event of redundant data input to the system the predictor could be used to lower the transmitted power output required for a given error rate or to decrease the error rate while maintaining constant transmitted power. The action of these redundancy-removal and restoration systems is analyzed in simple cases involving Markov inputs.

Patent
James M. Brown1
28 Jun 1968
TL;DR: In this article, a delta modulation transmission system is described in which the message signal is effectively compressed at the transmitter and, effectively, complementarily expanded at the receiver, and the transmitter includes a variable size step pulse generator to provide pseudocompression.
Abstract: A delta modulation transmission system is disclosed in which the message signal is, effectively, compressed at the transmitter and, effectively, complementarily expanded at the receiver. The transmitter includes a variable size step pulse generator to provide the pseudocompression and means are provided to vary the magnitude of the step pulse discretely over a part of the dynamic range of the message signal and continuously over another part of the dynamic range of the message signal.

Journal ArticleDOI
TL;DR: In this article, it was shown that quantizing noise is not a basic limiting factor in the error rate for all input levels, and the results were applied to a model of an existing VSB modem whereby the additional degradations resulting from data set imperfections were included as added baseband noise.
Abstract: Methods for calculating the power in the quantizing noise on digital transmission facilities have been known for some time. A more difficult but unavoidable problem is the effect that this noise has on data signals intended for analog transmission. This paper demonstrates that to assume that the noise will behave as a white Gaussian noise process will always (except for a simple factor) yield an upper bound on the probability of error when no companding is present. We assume that linear detection will be used, as for a PAM system, and the result is true whether or not filtering or demodulation is involved. Results are illustrated by applying them to a model of an existing VSB modem whereby the additional degradations resulting from data set imperfections are included as added baseband noise. A modem operating perfectly would make no errors at all at the higher transmission levels. For example, with no companding, a set with an eight-level eye closed by even 30 percent would not yield errors for input powers down to −15 dBm. Thus quantizing noise is not a basic limiting factor in the error rate for all input levels. A similar rigorous theory is not available for compandored systems, but for special situations reasonable estimates can be made. For logarithmic companding and eight-level VSB transmission, worst case estimates indicate error rates about 10−6 for one link of T1 carrier.

Journal ArticleDOI
TL;DR: The information rate of a hybrid coaxial cable transmission system using multilevel pulse amplitude modulation is studied, assuming that the additive repeater noise has a flat spectral density and that statistically independent message symbols are transmitted.
Abstract: The information rate of a hybrid coaxial cable transmission system using multilevel pulse amplitude modulation is studied, assuming that the additive repeater noise has a flat spectral density and that statistically independent message symbols are transmitted. Questions considered theoretically are: (i) Reduction in information rate when some repeaters in an “all digital repeater” system are replaced by analog repeaters, (ii) Number of digital repeaters required for converting an analog system to digital service, (iii) Information rate versus number of added analog repeaters in a fixed digital repeater section, (iv) System sensitivity to repeater output power and noise spectral density variations, and (v) Bit rate versus baud rate and achieving the greatest bit rate. Curves and tables answer these questions. It is economical and theoretically optimum to use identical analog repeaters and uniform repeater spacing for the coaxial cable systems considered. The optimum gain-frequency characteristic for the analog repeaters is the same for both analog and digital transmission. Analog cable systems can be adapted directly to hybrid digital service with no compromise in theoretical performance.

Journal ArticleDOI
TL;DR: Joint optimization of the analog and digital repeaters is considered, using minimum mean-square error between the transmitted and received symbols as the performance criterion, and it is concluded that in many practical systems it is not only economical, but also optimum, to use identical analog repeaters.
Abstract: A hybrid digital transmission system consists of analog repeaters placed between digital repeaters. Joint optimization of the analog and digital repeaters is considered in this paper, using minimum mean-square error between the transmitted and received symbols as the performance criterion. A general hybrid system is considered. The joint optimization problem is solved in closed form for deterministic sampling under two usually satisfied conditions. From the results the minimum mean-square error and the optimum repeater characteristics can be computed for given system parameters. Timing error is also considered. From a general result, it is concluded that in many practical systems it is not only economical, but also optimum, to use identical analog repeaters, and that hybrid systems can be used for either digital or voice transmission with no compromise in theoretical performance.


Journal ArticleDOI
L. Zegers1
TL;DR: The high accuracy required for synchronization in data systems is obtained here by a pseudoternary precoding of the transmitted data which is adapted to the spectral properties of the synchronization cross correlator.
Abstract: This paper describes methods for the simultaneous transmission of information signals and pseudonoise synchronization waveforms in a common bandwidth. For a relatively low level of the pseudonoise signal, a satisfactorily high synchronization accuracy is obtained by means of correlation techniques. Conversely, the information signal is detected with negligible interference due to the synchronization waveform. This permits a new approach to synchronization in speech systems and data transmission. The application to speech systems is quite straightforward. Emphasis is placed on design considerations for narrow-band systems with regard to output signal-to-noise ratio and acquisition performance. In data transmission the method is applied for bit and word synchronization. Thus, no restrictions are imposed on the transmitted data patterns and no inclusion of special synchronization words is required. In addition, the bandwidth of the system is not increased. The high accuracy required for synchronization in data systems is obtained here by a pseudoternary precoding of the transmitted data which is adapted to the spectral properties of the synchronization cross correlator. In this way the influence of the data signal on the received synchronization signal is minimized. Calculations of synchronization accuracy are given which include the effect of transmission noise.

Journal ArticleDOI
TL;DR: The application of selected block and convolutional coding techniques to digital transmission over an HF radio channel is described and various coding techniques studied are compared on the basis of achievable performance as well as certain factors affecting the feasibility of implementation.
Abstract: This paper describes the application of selected block and convolutional coding techniques to digital transmission over an HF radio channel. Performance results are presented for interleaved binary Bose-Chaudhuri-Hocquenghem (BCH) codes, interleaved two-stage concatenated codes, and diffuse convolutional codes. The performance results are based upon raw error data recorded in transmission over a 640-km HF path, with various data runs representing the typical effects of frequency-selective and non-selective fading, atmospheric impulse noise, and interference from other users of the HF band. The performance of binary BCH codes with bit interleaving is presented and the selection of a code to meet a specified performance criterion is described. The sensitivity of specific codes to changing channel conditions is presented, along with the cost, in terms of interleaving, of designing for one set of channel conditions rather than others. Concatenated codes are discussed as a means of effective error control on channels with clustered errors. Performance data are presented for selected two-stage codes used with inner-stage word interleaving and the effects of varying certain of the code parameters are shown. Emphasis is placed on code designs that use the inner-stage code only for error detection and the outer-stage code mainly for erasure filling with only a small amount of symbol error correction. The impact of error clustering on the performance of concatenated codes is discussed. Two diffuse convolutional codes are evaluated with the use of recorded error data in computer simulations of their threshold-decoding algorithms. Performance of various configurations of these convolutional codes is given and a comparison is made with that of a simple block coding scheme having the same decoder storage requirements. The various coding techniques studied are compared on the basis of achievable performance as well as certain factors affecting the feasibility of implementation.