Showing papers on "Bit error rate published in 1985"

Code Combining--A Maximum-Likelihood Decoding Approach for Combining an Arbitrary Number of Noisy Packets

Abstract: It is well known that if the data rate is chosen below the available channel capacity, error-free communication is possible. Furthermore, numerous practical error-correction coding techniques exist which can be chosen to meet the user's reliability constraints. However, a basic problem in designing a reliable digital communication system is still the choice of the actual code rate. While the popular rate-1/2 code rate is a reasonable, but not optimum, choice for additive Gaussian noise channels, its selection is far from optimum for channels where a high percentage of the transmitted bits are destroyed by interference. Code combining represents a technique of matching the code rate to the prevailing channel conditions. Information is transmitted in packet formats which are encoded with a relatively high-rate code, e.g., rate 1/2, which can be repeated to Obtain reliable communications when the redundancy in a rate-1/2 code is not sufficient to overcome the channel interference. The receiver combines noisy packets (code combining) to obtain a packet with a code rate which is low enough such that reliable communication is possible even for channels with extremely high error rates. By combining the minimum number of packets needed to overcome the channel conditions, the receiver optimizes the code rate and minimizes the delay required to decode a given packet. Thus, the receiver adapts to the actual jammer-to-signal (J/S) ratio which is critical when the level of interference J is not known a priori.

Error-control techniques for digital communication

Abstract: This practical handbook provides communication systems engineers with guidance in the application of error-control coding It emphasizes the fundamental concepts of coding theory while minimizing the use of mathematical toolsdemonstrates the role of coding in communication system designshows the performance gains achievable with codingillustrates how codes should be used and how to select the right code parametersdiscusses the decoding techniques that should be considered and how they are implementedand examines how detailed performance results are obtained

Performance of Noncoherent Direct-Sequence Spread-Spectrum Communications Over Specular Multipath Fading Channels

Abstract: The performance of coherent direct-sequence spread-spectrum communications over specular multipath fading channels is investigated. The average probability of error of the correlation receiver is derived for an arbitrary number of paths with deterministic or random gain coefficients. The gain coefficients, delays, and phase angles of any two distinct paths are modeled as mutually independent random variables. Numerical results for several values of the system and channel parameters are presented.

Performance of Reed-Solomon Coded Frequency-Hop Spread-Spectrum Communications in Partial-Band Interference

Abstract: This paper is concerned with the performance of a Communications system which utilizes frequency-hop spread spectrum, diversity transmission, Reed-Solomon coding, and parallel error-correction and erasure-correction decoding. Both binary signaling and M -ary orthogonal signaling are considered. The goals are twofold. First, it is desirable to provide good performance in partial-band Gaussian noise interference by use of coding and diversity with an efficient error-correction algorithm. Second, it is necessary to totally neutralize narrow-band interference (regardless of the power level or statistical distribution of the interference) in order to have an effective spread-spectrum system. Through an analysis of the effects of partial-band interference on a frequency-hop spread-spectrum system with diversity, it is shown that the use of ReedSolomon coding with a parallel errors and erasures decoding algorithm accomplishes these goals. The paper also investigates the accuracy of the Chernoff bound as an approximation to the true performance of a frequency-hop spreadspectrum communication system with diversity; side information, M -ary orthogonal signaling, and Reed-Solomon coding. The performance results presented in the paper are based on analysis and computer evaluation. Approximate results based on the Chernoff bound are also given. It is shown that the Chernoff bound for M -ary orthogonal signaling gives a very poor approximation for many cases of interest. This is largely due to the looseness of the union bound.

On the Undetected Error Probability for Shortened Hamming Codes

Abstract: Shortened Hamming codes are widely used for error detection in data communications. In this paper, a method for computing the probability of an undetected error for these codes is presented. This method is then used to evaluate the error-detection performance of the shortened codes obtained from the two distance-4 Hamming codes adopted by CCITT X.25 for error control for packet-switched networks. We show that shortening a code does affect its error-detection performance.

An Approximate Statistical Analysis of the Widrow LMS Algorithm with Application to Narrow-Band Interference Rejection

Abstract: The Widrow LMS algorithm is considered for the implementation of an adaptive prewhitening filter in a direct-sequence (DS) spread-spectrum receiver. Exact expressions for the steady-state tapweight covariance matrix and resulting average excess mean square error are developed for the real LMS algorithm when the input contains a random binary sequence (used to model a pseudonoise spreading sequence). It is shown here that the output samples of the adaptive filter possess approximately Gaussian statistics under the conditions of slow convergence and a large number of filter taps. Using this approximation, expressions for the resulting bit error rate (BER) when the adaptive algorithm is used to suppress a fading gone jammer are developed, and numerical results obtained from these expressions are compared to simulation results for the DS receiver.

Binary Code-Division Multiple-Access Systems Operating in Multipath Fading, Noisy Channels

Abstract: Binary code-division multiple-access (CDMA) systems operating in multipath fading, noisy channels (MFNC) are studied. Interference from undesired users and multipath are analyzed; these are modeled as equivalent noise. The error probability is given as a function of channel parameters and system parameters. The maximum possible number of users is estimated as a function of the tolerable error probability.

The synchronous oscillator: a synchronization and tracking network

Abstract: The synchronous oscillator (SO) is a free-running oscillator which oscillates at its natural frequency in the absence of an externally applied signal. In the presence of a signal, the oscillator synchronizes with and tracks the input waveform with an acquisition time inversely proportional to the tracking bandwidth. The SO possesses a constant output signal amplitude in the tracking region and an adaptive tracking bandwidth proportional to the input signal level. The authors present the theory and experimental characterization of SOs in terms of selectivity, noise rejection, carrier-to-noise improvement, tracking range, and acquisition time. A specific application is described for SO carrier and clock recovery networks in 60- and 120-Mb/s QPSK modem with bit-error-rate (BER) performance approaching that of hard-wired connection.

Beam pointing error as a significant design parameter for satellite-borne, free-space optical communication systems

Abstract: The issue of pointing errors between satellite-borne, free-space optical communication systems is examined. The single-axis pointing error distribution is described as a Gaussian function and is used to define a probability of burst error for the pointing subsystem. A relationship between the rms standard deviation of the pointing error distribution, the probability of burst error, and the Airy far field beamwidth is deduced. It is shown that the system beamwidth and antenna diameter are limited by the probability of burst error. Additionally, it is found that typical terminal designs have less temporal communication system availability than one specifically designed to account for the influence of burst errors.

Synchronization sequence decoder for a digital radiotelephone system

Abstract: A decoding system and method is disclosed for a radiotelephone system carrying digital messages. A set of multibit high auto-correlation, low cross-correlation synchronization words and their ones complement inverses are employed for message synchronization and supervisory functions. System state communication is achieved by utilizing a sequence of normal synchronization words and their ones complement inverses. Reliability of the coding is achieved by detecting normal or inverse words as binary levels when fewer than a predetermined number of bit errors exist in the bit sequence. If the predetermined number of bit errors is exceeded, a selected binary one or zero is substituted. This selected sequence of binary levels is decoded and the Hamming distance between a masked decoded sequence and a masked selected sequence is calculated. If the Hamming distance calculated yields a number less than or equal to a number equal to the synchronization error correction capability of the coding function, the decoded sequence is accepted as correct. If the Hamming distance calculation yields a number greater than the error correction capability value, a new set of substituted binary levels is tried.

Data communication method and apparatus

Abstract: A data stream is impressed on a carrier by forming from the data stream a succession of binary symbol words which control the modulation level of the carrier during respective modulation time intervals. To generate the symbol words from the data stream, the latter is first divided into a base bit stream (14) and one or more second bit streams (15). These second streams (15) are then subjected to error control coding before being used to define the least significant bits of the symbol words; the most significant bits are provided by the base bit stream. As a result, although the least significant bits of the transmitted symbol words (IV,III,II,I) are more prone to noise corruption than the most significant bits this tendency is compensated for by the error coding employed. The overall effect is to minimize power requirements while retaining good bandwidth efficiency.

A low bit rate segment vocoder based on line spectrum pairs

Abstract: A new approach for low bit rate coding of speech in a pitch-excited vocoder context is presented in this paper. The new technique, which operates at about 800 bps, has quality equivalent to a 2400 bps fixed-rate LPC vocoder while requiring only slightly more storage and computational resources. The improved performance of this system is based on two specific developments. The first is a novel use of line spectrum pair (LSP) coefficients in a structure which allows a low average bit rate while constraining the resulting distortion to have a low perceptual impact. The second is a frame-to-frame parameter interpolation algorithm which both reduces the bit rate and simultaneously insures more speech-like formant trajectories than those derived from vector quantizers at comparable bit rates.

Local and remote bit error rate monitoring for early warning of fault location of digital transmission system

Abstract: In-service line monitoring apparatus to detect and isolate marginal and failed digital transmission equipment within a digital telecommunication system having at least two end terminals. At selected terminal and repeater locations, a digital error detector monitors the bit error rate for each location. The detected BER is truncated to include at least the most significant digit and the exponent of the BER. The truncated BER is stored and then encoded for transmission back to the command center usually located at an end terminal. At the one end terminal the encoded BER is stored and displayed upon request. By being able to monitor the truncated BER at any location or direction, maintenance personnel are able to determine when a link in the system begins to deteriorate well before a complete path failure occurs.

New Short Constraint Length, Rate 1/N Convolutional Codes Which Minimize the Required SNR for Given Desired Bit Error Rates

Abstract: New, good ( K, 1/N ) convolutional codes are tabulated for 3 \leq K \leq 7 and 2 \leq N \leq 8 , which were selected based on the criterion of minimizing the required signal-to-noise ratio (SNR) for given desired bit error rates (BER). A transfer function upper bound was used to find the BER performance. Partial searches were performed using the idea that "good codes generate good lower rate codes." The new codes save signal energy up to 0.4 dB compared to previously reported codes of the same parameters.

Method of multiplexing digital signals

Abstract: A multiplexed bit stream consists of interleaved words all of the same number of bits, the words corresponding to respective channels (CH.0 to CH.24) one of which is a synchronizing channel (CH.0). A predetermined one of the bits (bit 9) of the words is used to identify the synchronizing channel, and may be used in the other, information, channels to carry service-related overhead and signalling information (B). The bit rate of the multiplexed bit stream is a harmonic of the bit rate of the individual channels. Such bit streams can be further multiplexed (Fig. 5, Fig. 7) together in a word-interleaved harmonic manner, whereby a harmonic structure of signals at different levels of multiplexing is built up.

Error detection and correction system

Abstract: An error detection and correction system includes a data transmission bus (196, 198) for transmitting data signals and error correction code (ECC) signals between a memory (28) and a processing unit (10). The ECC signals are in accordance with a modified Hamming code. An error detection and correction circuit (264) corrects single bit errors in data read from the memory (28). Also connected to the bus (196, 198) is a single bit error detection circuit (262) including a plurality of parity generators arranged to receive the data signals and selected ECC signals and adapted, when a single bit error is detected, to cause the blocking of a clock generator (94) thereby interrupting the operation of the processing unit (10). After a predetermined time period sufficient to enable the error detection and correction circuit (264) to correct the single bit error, operation of the clock generator (94) is resumed. The transmission bus includes a pair of individual buses (196, 198) and if both buses are utilized in a memory fetch operation, the error detection and correction circuit (264) operates successively on the data carried on the individual buses (196, 198).

Error logging memory system for avoiding miscorrection of triple errors

Abstract: Miscorrection of triple errors is avoided in a memory system equipped with a single bit error detection and correction/double bit error detection code by providing a double bit error logging technique. The address of each fetched word is logged in which a double bit error is detected. The address of each fetched word in which a single bit error is detected is compared with all logged addresses. If a coincidence is found between the compared addresses, a triple bit error alerting signal is generated and error recovery procedures are initiated.

BPSK system with sounder to combat Rayleigh fading in mobile radio communication

Abstract: A simple method is proposed to remove random FM from a fast Rayleigh faded binary phase shift keying (BPSK) signal and the great improved performance of reducing the irreducible error is presented. In the mobile radio environment, there happens inevitably a fast Rayleigh fading which causes random FM. The phase error of the reference signal due to random FM will degrade the bit error rate (BER) performance, even if the signal-to-noise ratio is sufficiently high. In the realization of reliable mobile communication, removal of this random FM is an unavoidable theme. Proposed strategy is to transmit a sounding continuous wave (CW) together with a BPSK signal, each phase being kept orthogonal and each power being kept the same. This CW wave is also used as the reference signal in coherent reception. The BER performance of this system is worse by 3 dB than that of the coherent BPSK in a slow Rayleigh fading environment.

Transmission of wideband speech signals

Abstract: Speech signal components in a high band of frequencies between 4 and 8 kHz are transmitted via a digital transmission channel, which carries speech signal samples at frequencies below 4 kHz and sampled at a rate of 8 kHz, by replacing the least significant bit of the samples with bits of information derived from the high band by linear predictive coding. These information bits are transmitted in frames, each frame comprising a synchronizing bit and bits representing the power of and a set of filter coefficients for the high band signal components occurring in a period corresponding to the frame duration. Each such bit is transmitted redundantly three or six times in view of bit stealing techniques already used for signalling on digital transmission links. The resulting wideband speech signal transmission is compatible with existing limited bandwidth voice channel transmission arrangements.

Error Performance Analysis for Narrow-Band Duobinary FM with Discriminator Detection

Abstract: Of the more band-efficient constant envelope digital modulations, duobinary FM is attractive in terms of its potential error performance, as indicated by the minimum distance of the signal structure. In this paper, the error performance of narrow-band duobinary FM, with discriminator detection in an additive Gaussian noise background, is evaluated for a range of system bandwidths BT and frequency deviation ratios h . The effects of intersymbol interference, due to the restricted bandwidth, are taken into account in the analysis. In addition, at the narrower bandwidths, 0.5 \leq BT , the filtered background noise is correlated, and these effects are included. It is shown that with the usual duobinary detector, "clicks," which are a major contributor to errors in conventional digital FM, do not contribute significantly to errors for the low frequency deviation ratios which are commonly used. The error rate theory agrees well with results obtained experimentally. The deviation ratios that give the best error performance for a given system bandwidth are presented. In a narrower bandwidth such as BT = 1/2 , where duobinary FM is proposed, duobinary FM with a frequency deviation ratio of h = 0.7 performs better than binary FM.

Method for improving the reliability of data transmission over Rayleigh fading channels

Abstract: A method and apparatus for reducing the bit error probability of data transmitted over a Rayleigh fading channel are disclosed. A relatively high bit rate serial stream of data is divided into N parallel relatively low bit rate streams of data. A controlled amount of intersymbol interference is introduced in the parallel streams. The N parallel streams are then transmitted simultaneously over the Rayleigh fading channel. Each bit in the N parallel stream of data has a duration longer than the duration of the typical Rayleigh fade. Thus there is a reduced probability that a Rayleigh fade will cause a bit error.

Fade margin calculation for channels impaired by Rician fading

Abstract: Excess path loss due to multipath severely restricts the performance of power limited mobile networks such as those using satellite-aided links. To reduce multipath related losses, the higher elevation angle of the spacecraft can be exploited by utilizing mobile antennas which reduce the strength of the multipath reflections in favor of the line-of-sight signal. The presence of a strong and stable path in a fading link will change the envelope statistics of the received waveform from Rayleigh to a more favorable Rician distribution. It is determined that the excess path loss, or fade margin, of a Rician channel when coherent detection of binary phase shift keying (BPSK) or quaternary phase shift keying (QPSK) signals is considered. The results are presented parametrically such that they can be applied to a wide range of propagation characteristics from heavy fading to nonfading situations. Furthermore, similar results are also given for the case where only limited coverage is provided.

Synchronizer for time division multiplexed data

Abstract: A circuit which finds a synchronization pattern and provides synchronized data from incoming time division multiplexed data is disclosed. The incoming data includes an incoming clock signal used in saving the incoming data in a FIFO memory. A local clock, which is isolated from the incoming clock but exhibits substantially the same rate as the incoming clock, retrieves output data from the FIFO memory. A series of bits from the output data which includes bits having relative bit positions that correspond to the bit positions of the synchronization pattern are examined for the occurrence of the synchronization pattern. If the synchronization pattern is not found, a dummy bit is added to the incoming data stream. The added dummy bit causes the quantity of data stored in the FIFO memory to increase the delays the output data by one bit relative to the output data prior to the addition of the dummy bit. The above described process repeats until synchronization is achieved.

Diagnostic technique for determining fault locations within a digital transmission system

Abstract: An in-service line monitoring technique to detect and isolate marginal and failed digital transmission equipment within a digital telecommunication system having at least two end terminals. At selected terminal and repeater locations, a digital error detector monitors the bit error rate for each location. The detected BER is truncated to include at least the most significant digit and the exponent of the BER. The truncated BER is stored and then encoded for transmission back to the command center usually located at an end terminal. At the one end terminal the encoded BER is stored and displayed upon request. By being able to monitor the truncated BER at any location or direction, maintenance personnel are able to determine when a link in the system is beginning to deteriorate well before a complete path failure occurs.

Application of Code Combining to a Selective-Repeat ARQ Link

Abstract: Various attempts have been made to devise ARQ schemes which maintain throughput at high channel bit error rates. Of these selective-repeat schemes, particularly hybrid verisons which employ error-correction coding, have proven most effective. However, even these schemes fail to provide useful throughput at very high bit error rates, despite a non-zero channel capacity. In this paper we demonstrate that a selective-repeat ARQ link employing code combining can maintain useful throughput at very high error rates (error rates approaching 50%). Moreover, with minor modifications this technique incurs no loss relative to previous schemes at low channel bit error rates. We substantiate these claims by comparing the throughput performance of code combining using a rate-?, constraint length 7 convolutional code on a selective-repeat ARQ link with other selective-repeat ARQ schemes.

Modelling the transfer function in medium bandwidth radio channels during multipath propagation

Abstract: A method to compute the effects of a multipath propagation channel on a line-of-sight link consists in establishing a statistical model of the channel transfer function. It is then possible to compute the outage time previsions for various communication systems, or to compare these systems by means of their signatures. To carry out this method, it is first necessary to choose a representation model of the transfer function, then to establish on an experimental basis the joint statistics of the model parameters. The authors discuss the various steps in the construction and validation of such a model and compare several proposed models from the point of view of their applications. These points are illustrated by means of results from thepacem Iexperiment.

Evaluation of the Probability Density Function and Bit Error Rate in Coherent Optical Transmission Systems Including Laser Phase Noise and Additive Gaussian Noise

Abstract: The gain of coherent optical transmission systems is deteriorated seriously by the phase noise of the transmitting and the local laser. In the present paper the non-gaussian probability density functions of the received baseband signals in coherent optical ASKand PSK-systems are calculated as a function of the phase noise and the additive gaussian noise. The probability density function will also be described by useful characteristic values. Finally a formula for the bit error rate is derived and evaluated.

Method and circuit arrangement for the transmission of data signal bits occurring with a first bit rate in a bit stream having a second bit rate which is higher than the first bit rate

Abstract: For the transmission of data signal bits occurring with a first bit rate from a transmission device by way of a transmission link to a receiving device in a bit stream having a second bit rate which is higher in comparison to the first bit rate, the data signal that is to be transmitted are combined in the transmission device with additional filler bits to form envelopes respectively comprising a prescribed plurality of bits, this being executed given non-transgression of the prescribed bit rate difference between the first bit rate and the second bit rate. The envelopes are transmitted via the transmission link with the second bit rate. Given transgression of the prescribed bit rate difference, the data signal bits, with first bit groups identifying the same as belonging to data signal envelopes, are combined with bits of separate envelopes which respectively contain a second bit group identifying them as blank envelopes and are transmitted via the transmission link with the second bit rate.