Showing papers on "Bit error rate published in 1975"

Odd-Bit Quadrature Amplitude-Shift Keying

Abstract: The selection of a particular signal set design for a bandwidth-constrained multiple amplitude-and-phase-amplitude-and-phase-shift-keyed (MAPSK) communication system with a linear additive Gaussian noise channel is influenced by a number of factors, such as average and/or peak signal-to-noise ratio for a given error probability, dynamic range of signal amplitudes, simplicity of generation and detection, and number of bit errors per adjacent symbol error (Gray code properties). This paper compares two possible quadrature amplitudes-shift-keyed (QASK) signal sets when the number of bits per symbol is odd (for the even-bit case, the square array is the only viable QASK choice). The "symmetric" QASK version outperforms the "rectangular" QASK set at a very modest implmentation penalty.

Digital time-division multiplexing system

Abstract: Disclosed is a digital multiplexer which combines N parallel bit-synchronized digital signals, each of bit rate f 1 , into a single composite line signal of bit rate f 2 , where f 2 > Nf 1 . Before the individual bits are interleaved, each digital signal is converted to a submultiple of the line frequency, f 2 . By inserting gaps having a predetermined duration and occurring at a fixed rate into each of the N digital signals, the bit rate f 1 of each bit stream is increased to f 2 /N. This is done without sampling any bit more than once. A multiplexer sequentially interleaves each bit from the N converted bit streams along with the gaps in each bit stream, forming the composite signal of bit rate f 2 . The interleaved gaps form empty time slots in the composite signal into which one or more signaling bits are added. Some of the added signaling bits carry framing information to lock the transmitter and receiver together. Thus, a composite higher-rate digital line signal consisting of interleaved information bits and signaling bits forms the time-division multiplex signal suitable for transmission over a single digital transmission path.

Asynchronous multiplexer and demultiplexer combination

Abstract: An asynchronous digital time division multiplexer and demultiplexer combination at one communication terminal is disclosed that will multiplex first N asynchronous source data signals having a first mixture of different bit rates into a transmitted synchronous data stream having a predetermined fixed data format and a given bit rate greater than the total of the bit rates of the source data and to demultiplex second N asynchronous source data signals having a second mixture of different bit rates from a received synchronous data stream having the predetermined fixed data format and the given bit rate. The combination includes an automatic channel assignment circuit to assign channels of the two data streams to the asynchronous source data signals in a manner to minimize temporary data memory regardless of the number of different bit rates by assigning the data signals to channels of the associated one of the two data streams so that the bits of each of the data signals tend to have equal spacing throughout the bits of the associated one of the two data streams. The channel assignment control circuit also includes a means to automatically indicate when the total of the mixture of bit rates has exceeded an allowable maximum.

Step-size transmitting differential coders for mobile telephony

Abstract: In using digital speech for mobile radio, we encounter the problem of severe bit-error bursts. Error clustering occurs because the bit duration is typically much smaller than that of a signal “fade,” and average bit-error probabilities greater than 1 percent are not uncommon. For speech communication over such channels, this paper proposes variable step-size differential coders based on explicit (and error-protected) transmission of quantizer step size. Specifically, we discuss delta and dpcm coders to be referred to as dm-aqf and dpcm-aqf, where aqf stands for adaptive quantization with forward estimation (and transmission) of step size. (Backward estimation, based on quantized-signal history, has the nice feature that the step-size information does not have to be explicitly transmitted. Furthermore, obtaining this information does not entail any encoding delay. However, due to the dependence of step size on reconstructed signal history, backward estimation is often less reliable in the presence of bit errors than a scheme based on aqf.) The studies reported in this paper cover the problem of step-size determination in aqf, the design of time-invariant first-order predictors for dpcm-aqf, and the performances of aqf encoders with and without burst-error-protecting ploys such as redundant time-diversity coding and bit scrambling. Judging from snr figures and informal listening tests, interesting results are obtained with the following 48-kb/s coders: three-bit dpcm-aqf with redundant error protection, and dm-aqf using bit scrambling.

Error coding communication terminal interface

Abstract: A communication terminal interface accepts, on different channels, information in a plurality of formats for communication purposes over a communication link which may be a TDMA satellite link. Each channel is accepted by a different interface unit which serves to format the information for communication over the system. This unit includes a compression-expansion buffer memory for allowing information received at a receive rate R s to be multiplexed and transmitted at a transmission rate T s which may be many times higher than the receive rate. In addition some units may include forward acting error correcting coding selected to provide the necessary corrected bit error rate for the type of information accepted by the unit and the capacity of the communication link over which the information is to be transmitted. The transmitter may employ differential encoding. To avoid increasing the error rate, which would normally result from this type of encoding, the encoded data is interleaved at the transmit side such that adjacent errors, after de-interleaving, on the receive side, are sufficiently displaced such that they may be corrected by the error decoding.

Differential Phase-Shift Keying Performance Under Time-Selective Multipath Fading

Abstract: Differential phase-shift keying (DPSK) performance analysis in the presence of multipath is extended to include cases in which the Doppler spread is on the order of the bit rate or greater. As the Doppler spread is increased from zero, the performance degrades below that predicted by Jones [1]. However, as the Doppler spread is increased beyond values on the order of the bit rate, performance improves. In the limit as the Doppler spread approaches infinity, with total multipath power held constant, performance approaches that of ideal DPSK as expected. Bit error rate performance in the presence of time-selective Rician fading is presented along with confirming experimental data obtained with a channel simulator.

A Bit Error Rate Monitor for Digital PSK Links

Abstract: This study is concerned with the problem of monitoring the performance of communication links, as indicated by bit error rate, with the objective of detecting as rapidly as possible failures or extreme degradation caused by any source The monitoring method is based on the use of an artificial threshold for the decision variable and the generation of a measurable "pseudoerror" The study relates pseudoerror probability to true-error probability for two models-one using an analytical-numerical approach and the other using a Monte Carlo simulation Variation of the parameters in the models adequately approximates the first-order effects of many types of link failure The results indicate that a monitor indication based on pseudoerror is feasible and has many desirable properties

Concatenation technique for burst-error correction and synchronization

Abstract: A system for processing a digital information bit stream and generating a data bit stream. The processing includes convolutional burst error correction encoding which is capable of correcting burst errors of length 2B, where B is any positive integer. Inherent in such systems are the requirements of 2B and 5B zero level bits at the beginning, and end, respectively, of the data bit stream. The processing further includes encoding n sync bits at the beginning of the data bit stream. The improvement includes encoder apparatus for replacing the 2B zero bits with the n sync bits; and, decoder apparatus for detecting a threshold number of sync bits and, in response thereto, replacing each sync bit with a zero bit. This improvement significantly reduces the number of bits otherwise required in the data bit stream. Modifications render the system suitable for processing time diversity data transmissions, or for concatenating sync bits at the conclusion of each message in a fixed length, sequential message transmission system.

Apparatus for demodulation of relative phase modulated binary data

Abstract: A digital system is disclosed for demodulating relative phase-shift modulated binary data using a delay circuit to store one data bit period of sample bits for phase comparison with the next data bit period of sample bits, and a cascaded delay circuit of the same length to effectively repeat the demodulation one data bit period later. An up-down counter effectively integrates the difference between current demodulated sample bits and the demodulated sample bits of the previous data bit period to enhance data bit detection. Such data demodulation is used from a selected one of three channels, a center channel for no Doppler shift compensation, and two channels for positive and negative Doppler shift compensation. All delay circuits are implemented with random access memory units, and all units in each channel are addressed by a single counter preset each time it overflows in response to counting clock pulses to set the length of the delay circuits according to the average of any expansion or contraction of a data bit period expected due to Doppler shift.

Signal Design for Digital Multiple Access Communications

Abstract: In this concise paper we examine the signal design problem associated with a multiple access communication channel in which several binary digital links are operated simultaneously over a common channel Receiver noise is neglected but the channel is confined in dimension, so that signal crosstalk is the only source of bit errors An encoder is assumed to exist prior to channel transmission for converting the bit waveforms from all transmitters into a common channel signal available to all receivers The encoder selects the channel signal during each bit so as to maximize the average detection probability per bit, where the average is taken over all links and all possible bit patterns Two classes of receivers are considered In the first the receivers are confined to only signal correlations with the corresponding transmitter signals In the second the encoder and receivers are matched to arbitrary signal sets For both type receivers, optimal channel signal selection is shown to be related to minimal hamming distance mappings Values and bounds for the resulting detection probabilities in terms of numbers of transmitters and channel dimension are reported

A Modified Receiver for Digital Optical Fiber Transmission Systems

Abstract: A Percival coil connected between the photodetector and amplifier in the receiver of a digital optical communication system offers the possibility of a reduced signal power requirement for a given bit error rate. When the photodetector is an avalanche diode, the modified receiver requires a lower value of avalanche gain for optimum performance.

Digital bit stream synchronizer

Abstract: A digital data communication system typically includes arrangements for achieving synchronization of the digital data processed by the system. However, known synchronizing arrangements are usually inefficient with respect to the time required to achieve bit synchronization. To shorten the time required for synchronization of two bit streams, an improved synchronizer including a sequential store, a plurality of comparators, a circulating memory having a plurality of memory registers, and a control circuit is disclosed. A first bit stream is extended through the sequential store into respective first inputs of the plurality of comparators. Each bit of a second bit stream jointly feeds all respective second inputs of the comparators. Using negative logic, each comparator output is NANDed with a first memory register output and fed into a second register input. When all but one of the memory register outputs are set, synchronization is achieved.

Short Constraint Length Rate 1/2 "Quick-Look" Codes

Abstract: Quick-look nonsystematic convolutional codes have the property that the information sequence may be recovered from the encoded sequence in straightforward fashion and with a minimum of error amplification. In this concise paper we investigate their relevant characteristics for constraint lengths less than eight and rate \frac{1}{2} and obtain a number of interesting and practically useful results. In particular, for the best of these codes, we derive their free distance and error amplification, their decoded bit error probability when used over the binary symmetric channel in conjunction with Viterbi decoding, and show how they can be employed to measure the channel bit error rate.

Two shift registers with feed-back in sender and receiver - has method for discrimination between bunch errors and synchronisation failure

Abstract: Both registers generate the same pseudo-random signal trains, and are parts of a bit error measuring device which compares the received signals with the locally generated pseudo-random signal train. Error signal train generated by the bit-by-bit comparison is examined in a special circuit for whether it itself corresponds to the pseudo-Random signal train on which the comparison is based. If it does, the synchronisation failure is confirmed when bit errors are at the same time delivered at the bit error measuring device output.

Threshold detection in an on-off binary communications channel with atmospheric scintillation.

Abstract: The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence was investigated assuming a poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength was analyzed and semi-empirical relationships to predict the optimum detection threshold derived. On the basis of this analysis a piecewise linear model for an adaptive threshold detection system is presented. The bit error probabilities for nonoptimum threshold detection systems were also investigated.

Voice-Band Data Modem Performance Over Companded Delta Modulation Channels

Abstract: This paper reports upon the results of tests of the transmission of data over single- and multiple-hop companded delta modulation (DM) systems. The DM coder-decoder (CODEC) was optimized for voice transmission. Modem bit error rate (BER) achievable over the range of 1200-9600 bits/s is presented. A comparison with the performance of pulse code modulation (PCM) is included. The comparison indicates that the two systems are comparable for error-free digital lines but favors the DM system for lines with errors.

Wide-Band Digital Transmission over Analog Radio Relay Links

Abstract: An experimental investigation has been performed to assess the feasibility of 8-phase phase-shift-keyed (PSK) signal transmission through a 6-GHz band microwave radio link with a 30-MHz nominal RF bandwidth. Only a portion of this bandwidth is currently being utilized to transmit one analog TV program or 1800channel frequency-division-multiplexed (FDM)/FM telephony. The link has been modified to have a 40-MHz bandwidth for this experiment. The digital modem is a 36-MHz bandwidth, 8-phase coherent PSK (CPSK), 36-Msymbol/s (108 Mbit/s) system. The work which has been performed includes the following: 1) study of the link bit error rate as a function of link carrier-carrier-to-noise ratio (C/N) with the transmitter TWT power output as a parameter; 2) study of the effects of an adjacent 1800-channel carrier (center-to-center separation of 36 MHz) on the error rate of the PSK carrier; and 3) perturbation of the 1800-channel FM carrier top channel noise power ratio (NPR) by an adjacent-channel 8-phase carrier (center-to-center separation of 36 MHz). In addition, experiments have been conducted through a four hop test simulator to examine the cumulative effect of transmission deviations such as group delay and TWT AM-PM transfer effect on the error rate performance for two different TWT power outputs, namely 2 and 4 W.

Error Detection in the Presence of Synchronization Loss

Abstract: Cyclic codes are very attractive for error detection because of their low cost encoding and decoding circuits, and because of their high guaranteed minimum distance, but they suffer from very poor protection when word frame synchronization is lost. This note suggests starting the encoder and decoder circuits in an essentially random state, instead of the usual all-zero state. Under this condition of operation it is shown that the undetected error rate against synchronization loss is 2^{-p} where p is the number of parity check bits.

On the Effect of Timing Errors in Run Length Codes

Abstract: Many redundancy removal algorithms employ some sort of run length code. Blocks of timing words are coded with synchronization words inserted between blocks. The probability of incorrectly reconstructing a sample because of a channel error in the timing data is a monotonically nondecreasing function of time since the last synchronization word. In this paper we compute the "probability that the accumulated magnitude of timing errors equal zero" as a function of time since the last synchronization word for a zero-order predictor (ZOP). The result is valid for any data source that can be modeled by a first-order Markov chain and any digital channel that can be modeled by a channel transition matrix. An example is presented.

A Half-Kilometer, 150 M BIT/SEC. Data Link Experiment Using A Striped-Geometry LED

Abstract: High-speed data links using laser-like LED's, single fiber graded index multimode waveguides, and avalanche photodiodes are described We describe a new stripe-geometry laser/LED source in which lateral current confinement is achieved by selective diffusion of the n-type substrate prior to the epitaxial growth of the GaAs/GaAlAs layers Using an H-P 3760A/3761A Bit Error Rate system, we observed no errors in a psuedo-random sequence of 1011 bits over a half kilometer fiber at 150 Mbits/sec, the bit rate limit of the H-P system Satisfactory eye diagrams were observed at somewhat higher bit rates A measurement of the broadening of single laser pulses set an upper limit to the pulse dispersion, for this particular h km fiber, of h nsec/km, which compares to 5 to 25 nsec/km for step-index fibers of similar diameters and index differences A status report will be presented on an experiment to install a 360 meter cable with six independent waveguide channels thru buried conduit between two laboratory buildings© (1975) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only