Showing papers on "Error detection and correction published in 1968"

Convolutional coding for channels with memory

Abstract: This paper discusses the use of two types of convolutional codes, diffuse threshold-decoded codes and Gallager codes, on channels with memory (burst channels) The operation of these codes is explained and test results are given for a variety of equipments operated over phone line, HF radio, and troposcatter channels Error propagation in the threshold-decoded codes is discussed and, in the Appendix, we prove that, for one important diffuse code, propagation is finite and small

Waveform error control in PCM telemetry

Abstract: An optimum system for transmitting a sample function from a stationary second order process over the BSC in real time is formulated under the mean-integral-square error criterion. The optimum number of channel bits and the optimum assignment of these bits to the samples is determined for the SGM process with R(\tau) = \exp(-|\tau}) . The system error is evaluated and compared to the error performances of systems using time sampling with and without data compression. Shannon's information rate is also computed for these systems and compared to the theoretical limit and to Goblick's BSQC digitizer. We also present a waveform representation technique based on Hotelling's method of principal components. The waveform-to-vector converter consists of a time sampler followed by a digital filter, and the vector-to-waveform reconstructor consists of a digita filter followed by a linear interpolator. Performance is shown to be comparable to KL sampling.

COMET--A New Meteor-Burst System Incorporating ARQ and Diversity Reception

Abstract: A system has been built to make efficient use of meteor-trail reflections for telegraph communications in the VHF band over distances up to 2000 kin. The information is transmitted over the circuit in both directions at an instantaneous rate of 2000 bauds whenever a radio path is established by reflection from a meteor trail. The control of the flow of information is not based on an assessment of the signal strength, as for instance in the JANET system, but on an error-detection scheme with automatic request (ARQ). This technique makes it possible to minimize starting delays and to carry on transmission until the end of the signal burst independently of the rate of decay. A special synchronization procedure has been developed to enable the system to cope with path length variations up to one character in length. The system also features frequency, space, and height diversity. For more than a year extensive measurements were carried out on a 1000-km path at frequencies in the 36- to 39-MHz band. The transmitter power was 200 watts and the antennas were five-element Yagis. Hourly average values of the traffic capacity were found to vary between four to eight 50-baud channels in the early morning and between one half to two channels in the late afternoon with the average over 24 hours approximately three channels. The error rate was less than one in 3000 characters for 90 percent of the time. Statistical data concerning bursts, interval between bursts, and delays in the transmission of messages are presented.

Error Distribution and Diversity Performance of a Frequency-Differential PSK HF Modem

Abstract: A 4800-bit/s digital data modem is operated over a simulated HF channel to determine the bit-error rate and error distributions of the received serial binary data stream. The measured error distributions for multipath-limited conditions are compared with back-to-back operation and theoretically determined random distributions, and are also used to evaluate forward acting error correction assuming half-rate random error-correcting block codes. This improvement in bit-error rate is compared with that measured by operating the modem at 2400 bit/s with dual in-band frequency diversity. The error distributions for back-to-back operation approach random except for small block lengths where the systematic error resulting from the frequency-differential PSK coding appears. The error distributions for multipath-limited operation deviate from random especially for small multipath delay spreads (low biterror rates) where the correlation bandwidth is large. Forward error correction produces larger improvement factors as the code block length is increased. However, the improvement factor barely exceeds two orders of magnitude for the largest block considered. In fact, the burst nature of the errors is such that improvement factors actually decrease in most cases for multipath-limited operation as the raw bit-error rate decreases. On the other hand, inband diversity is more effective for small multipath delay spreads than for large ones. However, forward error correction appears to offer more potential especially if the bit errors can be spread over a greater number of bits.

Error Control Techniques Using Binary Symbol Burst Codes

Abstract: Much has been written on the theoretical description of error correcting codes but, due to a lack of actual channel error patterns, little has been said of practical performance. In this paper the performance of three types of error control is evaluated for the case of independent random errors and for an actual channel exhibiting dense bursts. The selected codes are burst codes with high probabilities of error detection and correction.

Error-Checking Logic for Arithmetic-Type Operations of a Processor

Abstract: —A method of extending the usefulness of residue coding (or congruence checking) to check for errors in operations such as complement, shift, and rotate (or cycle) is presented. The checking logic and a practical method for its implementation are derived. The cost of check circuitry is only of the order of 30 to 40 percent of the part of the processor that is subjected to checking. In another paper presently under review, a method for single error correction using a new code called "bi-residue code" is presented.

Predicted performance of error-control techniques over real channels

Abstract: The clustering of errors on real channels seriously complicates the task of evaluating the performance of error-control techniques. A model is introduced that, in addition to having the ability to match error distributions, greatly simplifies the task of code evaluations. Having selected the parameters of the model by matching the statistics recorded by Townsend and Watts on the switched telephone network, the model is shown to predict the results of tests of an interleaved burst-error-correcting code. The utility of the model is demonstrated in the analysis of error-detection codes with delayed retransmissions.

Error Control in Duobinary Data Systems by Means of Null Zone Detection

Abstract: It is shown that duobinary data system performance can be improved at least 0.7 dB in the presence of Gaussian noise by using a null zone detection procedure. Most nulls can be replaced by correct values using the analog signal redundancy information. Nulls which cannot be replaced using the analog redundancy are restored to their most probable values on the basis of the received sample levels.

Memory with error correction

Abstract: This invention relates to a memory for a data processing system in which the data stored in the memory is encoded to form check bits that permit identifying and correcting an error in a word of data read from the memory. The specification teaches improved circuits for changing the check bits to agree with a corrected word after an error has been detected and corrected.

Error detection and correction in a photo-digital storage system

Abstract: An error-correction system has been implemented for data stored in the IBM Photo-Digital Storage System. Hardware is used for encoding and error detection, and a processor-controller is used, on a time-sharing basis, for error correction. A Reed-Solomon code is used to obtain a very low error rate in spite of flaws affecting the recorded bits. This approach is applicable to systems which require complex codes and have a data processor available on a time-sharing basis.

Error-correcting codes for a compound channel

Abstract: Many data-transmission and data-storage systems are corrupted by disturbances of both the burst type and the random type. In this paper two classes of error-correcting codes for use with these systems have been constructed analytically and with the aid of a computer. Although not optimal, these codes do have the advantage of ease of implementation,

The Improvement of Digital HF Communication Through Coding: II--Tandem Interleaved Cyclic Coding

Abstract: In previous work the technique of error correction of digital data through the use of interleaved cyclic codes and a set of probability functions for the evaluation of error patterns have been presented. In Part I of this paper [1] the performance of a wide range of Bose-Chaudhuri-Hocquenghem (BCH) codes and PMsymbol codes was evaluated on representative portions of the data. Here a method (identified as tandem interleaved cyclic coding) will be presented which allows for a significant increase in error-rate improvement at a reduction in the delay time introduced into the channel. It is demonstrated that it is possible to get almost I00 percent error correction for delays under three seconds for all channel conditions measured.

Random and burst error-correcting arrangement

Abstract: Error correction installation for a data transmission system, comprising an encoder (112) for encoding blocks of information in code words, these code words belonging to a block code (n, k) in which they they have information digits k and error correction digits nk, whose block code has a random error correction capability r where k/<= (b-1)/b is an integer, characterized by comprising a storage unit (116) to store a plurality of the newest encoded words and an adder (120) connected to the encoder and the storage unit to add the information digits k of a previously encoded word to the most recently encoded word to correct accumulations of errors. (Machine-translation by Google Translate, not legally binding)

Analysis of implementation errors in digital computing systems

Abstract: : This report discusses problems encountered with control networks in highly restructurable digital systems. In particular the treatment of implementation errors is covered with emphasis on concurrent processing. The implementation of concurrent processing networks may result in errors which will be quite complex to detect and systematic methods are warranted. A model representing a particular type of computing system is presented, and methods for introducing concurrent control into the model discussed. The automatic detection of a certain class of errors caused by improper design of these systems is investigated. Graph theoretic representation is employed in demonstrating several error detection techniques. The properties of these techniques are compared and it is concluded that one technique, of those investigated, is of sufficient generality, thoroughness, and simplicity in implementation to be used for automatic error analysis.

Error Patterns Measured On Transequatorial HF Communication Links

Abstract: As part of the MITRE Corporation's program for improvement of HF communication, the performance of coding and a means for evaluating coding equipment has been presented. It is, however, preferable to have a channel model upon which various error control techniques can be tried out as opposed to the direct approach, which is available only to the possessor of the data. This paper has been developed with the intention of presenting both the traditional channel modeling statistics (consecutive error distributions and gap distributions) and a set of new statistics against which modeling can be performed, The error statistics incurred in the transmission of high-frequency digital data at rates of from 600 to 2400 bit/s over various paths of the Eastern Test Range are presented herein. The data was transmitted on and parallel to the range using various modulation systems (modems). It is demonstrated that the errors occur in nonrandom fashion and in some cases are periodic. These error patterns (especially the periodic ones) present a new important problem for channel modeling of HF data From a heavily-used transequatorial circuit. While the basic approach is not new, the characteristics of the data are different from those previously reported and imply that channel performance is relatively independent of modulation technique. The error statistics presented herein should assist those, not having direct access to the data, who are interested in the problem of modeling this data which does not fit any known model (e.g. Gilbert, Berkovits, and Pareto[2]-[4]). Until such a model is available, this author will continue to report on error control performance using the direct simulation approach.

Partial modification and check sum accumulation for error detection in data systems

Abstract: This invention relates, in general, to error detection for blocks of binary data, and more particularly relates to the transmission of a uniquely modified and check sum accumulated error identifying word, together with detection circuitry at the receiver location which senses the unique word and thereby verifies or negates that a block of data was correctly transmitted and received. In one preferred embodiment of the invention disclosed herein, a method and apparatus is disclosed for generating at a transmitting station, an error-checking word. The error-checking word is generated by making, in response to random binary bit sequences, unique modifications in its content. For example, one such unique modification in the word''s content is made in response to the number of frames in the block of data to be transmitted. Another unique modification of the error word''s content is made each time a check sum on a bit-by-bit basis exceeds the modulus, i.e. total bit-plus-bit capacity available in the error word. The error word''s content is subject to yet another unique modification, in response to the occurrence of a multibit word, within an overall block of data words, containing all ZERO''s. In one particular embodiment the complement of this error word is generated and sent to the receiver as the final word after a data block has been transmitted. Another essentially identical error-check summing circuit at the receiver station accumulates another error word. The receiver error-check word, when summed with the complemented error-check word from the transmitter has a predictable total when all data in the block has been transmitted and received error-free. If a sum other than that predicted is obtained at the receiver, then the received data contained an error.

Clock for overlapped memories with error correction

Abstract: THIS DISCLOSURE TEACHES A CLOSK CIRCUIT THAT CAN BE SHARED BY SEVERAL MEMORIES. THE CLOCK CONTROLS THE MEMORIES TO OPERATE IN AN OVERLAPPING MODE AND TO SHARE ERROR CORRECTION CIRCUITRY AND OTHER COMMON CIRCUITS.

Use of Error Correcting Codes on Memory Words for Improved Reliability

Abstract: Application of error correcting coding is often employed to improve system operation and reliability. By means of suitable reliability models and simple analysis, the effect of error correcting coding of memory words on the overall reliability of the system is discussed. Introduction of error correcting facilities will generally have three significant effects on the system: 1) increased hardware, which is also subject to failures and hence tends to lower reliability; 2) the system's ability to function in the presence of a certain class of failures; and 3) quicker detection of errors, which also means an improved repair rate. To illustrate the extent to which the above three factors govern the reliability improvement due to coding, three types of systems are considered. These systems use the same basic processor and memory units but differ in their structure and complexity. Other factors besides the three above which control the reliability improvement due to coding are the system structure and the relative sizes of processor and memory hardware.

Performance of selected block and convolutional codes on a fading HF channel

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.

Early error detection system for data processing machine

Abstract: A SYSTEM IS PROVIDED FOR THE DETECTION OF ERRORS IN A DIGITAL COMPUTER SYSTEM DURING A MACHINE CYCLE IN WHICH THE UNITS GIVING RISE TO THE ERROR ARE NOT ACTIVELY CONTRIBUTING TO THE FUNCTION BEING PERFORMED. IF THE ERROR OCCURS IN A NONOPERATIONAL FUNCTIONAL UNIT, A WAIT CYCLE ROUTINE MAY BE ENTERED WHICH INSURES THAT THE FUNCTIONAL UNIT IN WHICH THE ERROR OCCURRED WILL NOT BE UTILIZED BY THE COMPUTER SYSTEM DURING THE NEXT CYCLE. THE FUNCTIONAL UNIT IS AGAIN TESTED DURING THE WAIT CYCLE AND IF FOUND TO BE IN ERROR AGAIN, THE ERROR ROUTINE IS ENTERED.

Automatic equalizer utilizing error control information

Abstract: AN AUTOMATIC PASSBAND EQUALIZER FOR DIFFERENTIALLY COHERENT PHASE-MODULATION DATA TRANSMISSION SYSTEMS IS MADE ADAPTIVE TO ERROR INFORMATION DERIVED BY CORRELATING PHASE DIFFERENCES BETWEEN SUCCESSIVE ADJACENT SIGNALING INTERVALS WITH PHASE DIFFERENCES BETWEEN NONADJACENT SIGNALING INTERVALS SPANNING SUCH ADJACENT INTERVALS. THE ERROR INFORMATION IS PERIODICALLY INTEGRATED AND QUENCHED. DIFFERENCES BETWEEN SUCCESSIVE MAXIMUM INTEGRATION LEVELS YIELD A DISTORTION INDEX BY THE AID OF WHICH INCREMENTAL ADJUSTMENTS OF TAP ATTENUATORS IN A TRANSVERSAL EQUALIZER IN SERIES WITH A DATA DEMODULATOR ARE DIRECTED TO MINIMIZE SUCH DISTORTION.

A decoding algorithm for some convolutional codes constructed from block codes

Abstract: A new decoding algorithm for some convolutional codes constructed from block codes is given. The algorithm utilizes the decoding algorithm for the corresponding block code. It is shown that the codes obtained from one-step orthogonalizable block codes are majority decodable. Error propagation in some of these convolutional codes is studied. It is shown that if decoded with moderately reduced capability, these codes exhibit limited error propagation. A mode switching decoding method is suggested to realize a larger error correction capability while maintaining limited error propagation.

Single-Channel Error Correction in an f-Channel System

Abstract: —This paper discusses a method of correcting almost unlimited errors1in a single channnel of an f-channel system. The method uses a two-dimensional variable-length code (2-DVL). The encoding and decoding systems are implemented by a parallel linear-feedback shift register (LFSR).

Experimental Studies in Computer-Assisted Correction of Unorthographic Text

Abstract: A study of the feasibility of applying an experimental dictionary and a digital computer to proofreading led to investigation of the nature of conversion errors and development of computer programs for correction of unorthographic machine-readable text. The correction programs were tested with a sample of unproofread technical abstracts with a large number of possible errors. The error-correction program has three levels: the first level corrects commonly misspelled words through watching with a stored dictionary; the second level treats common misspelling patterns not readily amenable to direct dictionary correction. Error patterns most probably associated with human operation of transcription devices, or with limitations or malfunctions of conversion equipment, are dealt with by the third level. Beyond the first level, the program can apply nine error-correction procedures. The general structure and organization of the program is illustrated in Fig. 1 of the text. Because selections of alternative spellings are combinatorial, the correction algorithms must test several hundred candidates per error, on the average. Hence a study explored system design characteristics to increase the efficiency of correction procedures.

Method and apparatus for providing error compensation in a data transmission system

Abstract: In a magnetic azimuth detector system employing a servo transmission network between the input and a remote readout, error correction is provided by inserting correction signals into the servo transmission system. The servo transmission system employs a control transformer having null and 90* output windings and error compensation is effected by summing index, one cycle and two cycle error correction signals with the signal across the null output winding.

Buffer Design for Data Compression Systems

Abstract: Design of the output buffer is one of the most important tasks in implementing an adaptive data compression system. Upon proper design of the buffer including such parameters as size, inputoutput data rates, and occupancy control, rests the overall compression efficiency and error performance of the system. The binomial distribution is used to derive an exact model for a synchronous buffer. The Poisson distribution, which provides a reasonable model for a high-speed asynchronous buffer, is shown to yield an error greater than 10 percent in required buffer length for synchronous buffers. Design requirements such as probabilities of overflow and underflow, buffer length, and average buffer fill are derived as functions of compression ratio φ and the ratio of input-output transmission rates C . It is shown that the buffer queuing behavior is a function of the ratio \rho = C/\phi , as well as C and φ independently. The derived results indicate that restricting buffer overflow by increasing the buffer size is inefficient. Control is suggested in which the aperture of the compression algorithm is changed to control the buffer fill. The design requirements are determined for the zero-order predictor and the first-order interpolator with two degrees of freedom. Using the buffer equations derived and the compression ratio-aperture relationship, the design of a buffer is described. It is shown that doubling the aperture with a resultant doubling in rms error reduces the buffer probability of overflow by a factor of 100.