Showing papers on "Bit error rate published in 1988"

The design of trellis coded MPSK for fading channels: performance criteria

Abstract: It has been well established that the appropriate criterion for optimum trellis-coded modulation design on the additive white Gaussian noise channel is maximization of the free Euclidean distance. It is shown that when the trellis-coded modulation is used on a Rician fading channel with interleaving/deinterleaving, the design of the code of optimum performance is guided by other factors, in particular, the length of the shortest error-event path, and the product of branch distances (possibly normalized by the Euclidean distance of the path) along the path. Although maximum free distance (d/sub free/) is still an important consideration, it plays a less significant role the more severe the fading is on the channel. These considerations lead to the definition of a new distance measure of optimization of trellis codes transmitted over Rician fading channels. If no interleaving/deinterleaving is used, then once again the design of the trellis code is guided by maximizing d/sub free/. >

Noncoherent detection of coherent lightwave signals corrupted by phase noise

Abstract: Waves are treated that modulate by either on-off keying (OOK) or binary frequency-shift keying (FSK) and are further impaired by additive Gaussian noise. Heterodyne detection of such a waveform produces an electronic bandpass signal, which, to ease demodulation in the presence of phase noise, is noncoherently demodulated to extract the baseband pulse stream. The treatment goes beyond previous bit error rate (BER) analyses of optical heterodyne receivers for OOK and FSK. First, there is full adherence to the standard (Brownian motion) model of phase noise. Also, the receiver structure is formulated in such a way that the probability density function of the receiver output samples can be accurately determined. This permits calculations of the additive noise and phase noise tolerable when achieving bit error rates as small as 10/sup -9/. Finally, the study is comprehensive regarding the range of parameters explored. Filtering at an intermediate frequency (IF) alone, as well as IF filtering plus postdetection low-pass filtering, is considered. When the receiver parameters decision threshold (for OOK) and IF filter bandwidth are optimized, large amounts of phase noise can be accommodated with only minor increases in required signal-to-noise ratio. This is especially important when the bit rate is moderate compared to the laser linewidth. >

The design of trellis coded MPSK for fading channels: set partitioning for optimum code design

Abstract: A previous work on criteria for designing trellis-coded MPSK modulation to achieve minimum error probability performance on the Rician fading channel (see ibid., vol.36, no.9, p.1004-1012, Sep. 1988) is extended. It is demonstrated that allowing for multiple symbols per trellis branch, i.e., multiple trellis-coded modulation (MTCM), provides an additional degree of freedom for designing a code to meet the optimization on the fading channel. Diversities larger than those achievable with conventional trellis codes having the same number of trellis states are now attainable, it is under these conditions that MTCM achieves its full potential. >

Multiple trellis coded modulation (MTCM)

Abstract: The authors demonstrate a trellis coded modulation technique referred to as multiple trellis coded modulation (MTCM) wherein more than one channel symbol per trellis branch is transmitted. They have found simple two-state trellis codes for symmetric MPSK multiple phase-shift keying and AM modulations that can achieve 3-dB gain over uncoded modulation at very high signal-to-noise ratios without bandwidth expansion or reduction in information bit rate. The gain of these codes with respect to previously reported two-state trellis codes is between 1 and 2 dB at very high signal-to-noise ratios, depending on the number of bits per Hertz transmitted. These gains are achieved for those of the equivalent conventional trellis codes with the same number of states in the trellis diagram. The authors note that additional computations per branch are needed for the multiple trellis coding scheme. The concept can be extended to a higher number of states and other types of modulations. >

Method and apparatus for decoding multiple bit sequences that are transmitted simultaneously in a single channel

Abstract: Data bits are decoded from a composite signal that is formed by coding multiple bit sequences with respective spreading codes, and transmitting the coded bit sequences simultaneously and asynchronously over a single channel in which the bit sequences are added. This decoding involves a metric in combination with a repetitive decision process which is only linearly dependent on the number of bit sequences in the composite signal.

The performance of trellis coded multilevel DPSK on a fading mobile satellite channel

Abstract: The performance of a trellis-coded multilevel differential phase-shift keying (DPSK) modulation over a mobile satellite channel characterized by additive white Gaussian noise (AWGN) and slow Rician fading is presented. Both the optimum and Gaussian (suboptimum) decoding metrics are considered, with performance results given only for the latter. Analytical results (upper bounds on bit error rate) are obtained wherever possible and illustrated by several numerical examples. Also given are simulation results which are more indicative of the exact system performance. Comparisons with results previously obtained for coherent detection of the same coded modulations are presented. >

Forward error correction in dispersion-limited lightwave systems

Abstract: A rate 0.964 forward error correcting (FEC) code is integrated into the low-speed tributaries of a 565-Mb/s lightwave system as an exploratory system design approach toward relaxing requirements on laser sources in dispersion-limited operation. By virtually removing error rate floors, regardless of their cause, FEC is shown to provide an increasing advantage in conditions of greater degradation and to be effective against mode partition noise (MPN), mode jumping, and reflection impairments.The experimental FEC code is implemented in a standard gate array. The FEC code is described and its performance is analyzed. A new system design strategy is suggested for low-cost gigabit lightwave systems using FEC. >

Performance of DS/SSMA communications in impulsive channels. II. Hard-limiting correlation receivers

Abstract: For pt.I see ibid., vol.COM-35, no.11, p.1179-88 (1987). In part I it was demonstrated that impulsive channel noise can be a serious detriment to the performance of direct-sequence spread-spectrum multiple-access (DS/SSMA) communications when conventional linear correlation reception is used. Here, a hard-limiting correlator as an alternative for reception of multiple-access transmission in impulsive channels is considered. For K asynchronous binary PSK DS/SSMA users sharing a linear channel corrupted by impulsive noise that is modeled at the output of the front-end filter of the receiver, techniques are developed for analyzing bit error probabilities of this hard-limiting receiver by exact computation for short spreading sequences, by approximation for longer spreading sequences, and by asymptotic limits for infinitely long spreading sequences. Performance is compared to that of the linear correlator under a variety of conditions, showing that hard-limiting correlation reception can offer substantial improvement over conventional systems in impulsive channels. However, the linear receiver is more effective against multiple-access noise only, and so a tradeoff emerges between rejection of impulsive noise and rejection of multiple-access interference. >

Densely spaced FDM coherent star network with optical signals confined to equally spaced frequencies

Abstract: The results obtained with a fiber-optical star network using densely spaced frequency-division-multiplexing (FDM) and heterodyne detection techniques are discussed. The system consists of three optical sources transmitting around 1.28 mu m, frequency-shift keying (FSK) modulated at 45 Mb/s and spaced by 300 MHz. A 4*4 optical coupler combines the three optical signals. The FDM signals, received from one of the four outputs of the coupler, are demultiplexed by a heterodyne FM receiver. The minimum received optical power needed to obtain a bit error rate (BER) of 10/sup -9/ is -61 dBm or 113 photons/bit, which is 4.5 dB from the shot noise limit. Cochannel interference is negligible for the above channel spacing and modulation rate. The results indicate that such a system has a potential throughput of 4500 Gb/s. The results obtained with two frequency stabilization circuits used to confine these three FDM optical signals to a comb of equally spaced frequencies are also presented. >

PSK and DPSK trellis codes for fast fading, shadowed mobile satellite communication channels

Abstract: The performance of 8-PSK and 8-DPSK trellis codes is presented for a class of fast fading, land mobile satellite communication channels. The fading model is Rician but, in addition, the line-of-sight path is subjected to a fast lognormal attenuation that represents tree shadowing. The fading parameters used in this study represent the degree of shadowing and are based on measured data. The primary application considered is for digital speech transmission and thus, bit error probabilities in the order of 10/sup -3/ are emphasized. Sensitivity of the bit error probability to amplitude fading, amplitude and phase fading, and decoding delay is presented. Performance is determined via digital computer simulation. Optimal four- and eight-state codes are determined and optimality is found to be dependent on the presence of lognormal shadowing. >

Interleaved convolutional coding for the turbulent atmospheric optical communication channel

Abstract: The coding gain of a constraint-length-three, rate one-half convolutional code over a long clear-air atmospheric direct-detection optical communication channel using binary pulse-position modulation signalling is directly measured as a function of interleaving delay for both hard- and soft-decision Viterbi decoding. Maximum coding gains theoretically possible for this code with perfect interleaving and physically unrealizable perfect-measurement decoding were about 7 dB under conditions of weak clear-air turbulence, and 11 dB at moderate turbulence levels. The time scale of the fading (memory) of the channel was directly measured to be tens to hundreds of milliseconds, depending on turbulence levels. Interleaving delays of 5 ms between transmission of the first and second channel bits output by the encoder yield coding gains within 1.5 dB of theoretical limits with soft-decision Viterbi decoding. Coding gains of 4-5 dB were observed with only 100 mu s of interleaving delay. Soft-decision Viterbi decoding always yielded 1-2 dB more coding gain than hard-decision Viterbi decoding. >

Differential phase-shift keying demodulator

Abstract: A digital modem is provided for demodulation of differential phase-shift keyed (DPSK) signals in a land mobile satellite receiver. The DPSK demodulator comprises a coarse frequency and lock detect module for identifying and estimating the frequency of the input signal, a numerically controlled oscillator (NCO) for generating in-phase and quadrature signals from the input signal, one pair each of delayed and non-delayed integrate and dump (I&D) modules, a symbol timing module for achieving symbol synchronization by determining the dump time of the I&D modules, a dot product detector for receiving the output of the non-delayed I&D modules and providing a detected data output, and an AFC loop comprising a cross product detector and an AFC loop filter that provides feedback to the NCO and lock detect module. The DPSK demodulator achieves symbol synchronization independent of carrier phase or frequency and at low signal-to-noise ratios. Overall, the modem achieves the theoretical bit error rate capability of DPSK on a narrow band, white Gaussian noise channel with minimal implementation loss.

A 50-Mbit/s CMOS monolithic optical receiver

Abstract: A general-purpose CMOS optical receiver that operates at data rates from 1 to 50 Mb/s has been fabricated in a 1.75- mu m CMOS process. The technology choice resulted in a high level of integration compared with similar bipolar technology receivers. The measured minimum signal current for a 10/sup -9/ bit error rate at 50 Mb/s is 48-nA r.m.s. Automatic gain control gives the receiver an electrical input dynamic range of greater than 60 dB. The outputs are TTL (transistor-transistor logic)-compatible and the chip dissipates less than 500 mW when switching at maximum speed. The die area is 16 mm/sup 2/. A comprehensive noise analysis of the receiver front end provides insight into the design tradeoffs of optical receiver preamplifiers. A wideband precision amplifier used in the linear channel is discussed in detail. A simple method for recovering low-frequency signal information lost in AC coupling is described. >

Information-bit, information-symbol, and decoded-symbol error rates for linear block codes

Abstract: There are two types of bounded-distance decoders for linear block codes: erasing decoders that discard uncorrectable received words, and reproducing decoders that reproduce uncorrectable received words. Exact expressions for the information-symbol and decoded-symbol error rates are derived for both types. Necessary and sufficient conditions are derived for the quality of the information-symbol and decoded symbol error rates, It is formally proved that these two error rates are equal for cyclic codes with either erasing or reproducing decoders. For reproducing decoders, two approximations to the information-bit error rate and their applicability are examined. >

Alternatives for on-board digital multicarrier demodulation

Abstract: In this paper alternatives for digital multicarrier demodulators (MCD) suitable for advanced digital satellite communications systems are presented. The MCD permits the direct on-board interfacing of FDMA and TDM communication links by digital signal processing techniques. Two main functions are implemented by a MCD: demultiplexing (DEMUX) and demodulation (DEMOD). We focus here only on a digital implementation of the MCD, looking at its advantages, flexibility, better performance and VLSI integrability. The DEMUX may be implemented in a number of ways: the analytic signal method, fast Fourier transform with polyphase network technique, or multistage methods. For all the implementation methods considered it is shown that a certain degree of integration of DEMUX and DEMOD functions is possible. To this end, in the proposed MCD schemes the receiver pulse-shaping filter has been integrated in the DEMUX structure, reducing the overall implementation complexity. It is shown that, for the per-channel structure based on the analytic signal method, a highly modular and flexible implementation can also be achieved. Coherent demodulation is used to reduce the signal-to-noise ratio required to achieve a specified bit error rate. The coherent demodulation is carried out by using the maximum likelihood (ML) estimation method. Two different approaches to receiver synchronization have been studied. For the first, the carrier phase and symbol timing estimates are independently derived by suitable techniques. The second approach makes use of the maximum a posteriori probability method to estimate both the carrier phase and symbol timing of the receivied signal. In particular, for this technique it is shown that, by a suitable choice of the architecture of the digital coherent receiver, the ML demodulator can be integrated in the joint carrier and clock recovery circuit, with no increase in the overall system complexity. The digital architecture of the proposed MCD can be adapted to different digital modulation techniques. However, here we consider only the application for QPSK signals, as this modulation scheme is the most promising for digital satellite communications. A theoretical analysis and computer simulation have been used to evaluate the performance degradation of the proposed MCD, including finite-arithmetic implementation effects.

Indoor propagation and bit error rate measurements at 60 GHz using phase-locked oscillators

Abstract: The authors report propagation and bit error rate (BER) measurements that have been conducted within buildings using phase-locked oscillators at 60 GHz. The propagation measurements were conducted to study the envelope distribution, the power law with distance for different environments, the signal coverage, the received power spectrum, and edge diffraction effects. Measurements were also conducted to determine the BER performance in fading for FSK (frequency-shift keyed) modulation at 240 and 480 kb/s for both LOS (line-of-sight) and non-LOS conditions. >

Information handling system having serial channel to control unit link

Abstract: An information handling system includes a processor with one or more channels for communicating to peripheral devices controlled by peripheral device controllers, and one or more serial data links between the channels and the peripheral controllers. Data is transmitted over the serial data link between the channels and the controllers in a frame format, wherein each frame includes a number of eight-bit characters selected so that all standard parallel interface tag and data lines are transmitted in a single frame with a high degree of error immunity resulting from selection of idle characters and frame start characters having the mutual characteristic that single and double bit errors in the idle characters do not create an erroneous indication of a start character in the system.

Fourier-Bessel error performance analysis and evaluation of M-ary QAM schemes in an impulsive noise environment

Abstract: The authors derive closed-form expressions for the BER (bit error rate) performance of coherent M-ary quadrature amplitude modulated (QAM) system in the presence of an additive combination of Gaussian and highly impulsive noise by using a Fourier-Bessel series expansion method. The model used for the impulse noise, which closely models atmospheric and/or ignition noise, consists of a stream of Poisson impulses with areas distributed according to a bilateral Rayleigh probability distribution function. Although the methodology is general enough to accommodate any M-ary QAM scheme, they present analytical as well as some computer simulated results for 16-, 64-, and 256-QAM systems. An almost insignificant increase of the truncation error with the increase of the modulation levels verifies that the proposed method of analysis can be a useful tool in evaluating the performance of very large-alphabet M-ary QAM systems, e.g. M>or=256. >

Forward error correction of data transmitted via television signals

Abstract: An encoding technique for data that enables the data to be reliably transmitted via television signals, even when impulse noise may be present, uses a two-fold approach for forward error correction. As a first step, the data is assembled into blocks of suitable length and each block is encoded with an error correcting code to enable individual bit errors to be identified and corrected at the receiving end. In addition, the blocks of data are interleaved over several different lines of information. Each line of information is transmitted during the vertical blanking interval in a respective field of a video signal. At the receiving end, the individual lines of data are reassembled into the blocks of information. If impulse noise or other disruptions cause one of the lines to be lost, the result at the receiving end would only be the loss of one bit of data in each block. The error correcting code with which each block is encoded enables this individual bit error to be identified and corrected.

Modulation techniques for digital cellular systems

Abstract: A modulation technique is described that uses the properties of linear modulation techniques to achieve high spectral efficiency. When combined with high-quality low-bit-rate speech coding and channel coding, linear modulation provides a substantial increase in system capacity. A QDPSK system provides high-quality speech using a 10-kHz bandwidth, with better S/I protection ratios than the current analog system. A digital cellular system which uses QDPSK is discussed. Bit error rate and spectral efficiency data are presented. >

Satellite communication protocols-a performance comparison considering on-board processing

Abstract: A comparison is made of error control techniques for digital satellite communication by both analytical methods and simulations. Throughput and delays are studied as functions of the satellite channel bit error rate. Advantages of onboard processing (OBP) offered by future satellite systems are taken into consideration. It is shown that performance of link layer protocols on satellite links can be improved significantly applying OBP. Furthermore, the flexibility of OBP satellites allows protocols, transmission rates, and transmission power to be chosen separately on uplink and downlink, so that the specific conditions can be taken into account. >

Causes of burst errors in multipath fading channel (mobile radio)

Abstract: The so-called irreducible error due to frequency-selective fading is known to have a serious effect on mobile radio communication systems. Thus, the analysis of such errors is a prerequisite for making high-speed digital signal transmission over a fading channel feasible. The authors attempted to elucidate the physical mechanisms causing such errors using laboratory measurements of microscopic bit error rate. The results clarified some sources of burst errors in a multipath fading channel. In particular, large and rapid timing fluctuations of eye pattern due to severe delay distortion of the multipath channel was found to be the most dominant source of error. >

Error probabilities for DS spread-spectrum systems using an ALE for narrow-band interference rejection

Abstract: The effects of the least-mean-squares adaptive line enhancer (ALE) weight misadjustment errors on the bit error rate are investigated for a direct-sequence spread-spectrum binary communication system in the presence of strong narrowband interference. The converged ALE weights are modeled as the parallel connection of a deterministic FIR (finite impulse response) filter and a random FIR filter. The statistics of the random filter are derived, assuming the output of the random filter to be primarily due to the jammer convolved with random filter weights. This output is shown to be nonGaussian and to cause significant error rate degradation in comparison to a Gaussian model. Error probability expressions are derived for the bit error rate, evaluated numerically, and compared to the corresponding error probabilities for a Gaussian model for the random filter output. For some typical system parameter values and error probabilities it is shown that the Gaussian model yields performance results that are too optimistic by several decibels. >

An error protected 16 kbit/s voice transmission for land mobile radio channel

Abstract: Robust speech coding and an efficient error correction coding is indispensable for toll-quality voice transmission in mobile radio because of degradation due to multipath fading. A decision procedure for the bit-selective forward-error-correction (BS-FEC) scheme is proposed as a promising solution to this problem, and backward-type prediction speech coding is shown to be more robust against transmission errors than forward-type prediction. Combinations of BS-FEC (channel coding) and backward-type prediction speech coding are designed, and improvements in the SNRs of transmitted voice signals are examined. Simulation results show that BS-FEC can provide good speech quality even at a bit error rate (BER) of 10/sup -2/ in Rayleigh fading environments, at the cost of a slight degradation in the SNR (signal-to-noise ratio) at low BERs. >

Error resilience of a video codec for low bitrates

Abstract: Source coding and channel coding are embedded in a video coding algorithm for low bitrates (64 kb/s) to obtain a complete encoder which is resilient against channel errors. The bits retained for the channel coder are spent for synchronization words, error correction, and update of erroneous parts in the image. The performance of the complete codec is evaluated by simulations in which channels with different characteristics are modeled. >

Degradations in Gbit/s DFB laser transmission systems due to phase-to-intensity noise conversion by multiple reflection points

Abstract: Severe system degradations and bit error rate floors are observed in Gbit/s fibre transmission systems due to the interferometric conversion of laser phase noise to intensity noise by multiple reflections from connectors and splices. Studies of penalties as a function of both the magnitude and number of reflections indicate that fibre joints with guaranteed minimum return losses of better than 20 dB may be required for high-speed direct detection systems as well as future coherent systems, even though optical isolators may be employed in such systems.< >

Apparatus and method for secure digital communication

Abstract: The multiplexer in a multichannel, secure digital communication system repetitively embeds a sequence of byte length uniquely coded synchronizing signals in each of n successive frames of one channel of a multichannel, time multiplexed digital bit stream. Redundant protective relay data and associated parity check data are embedded in four of the n frames in a second, preferably adjacent channel, with the remaining of the n frames in the second channel containing additional of the uniquely coded synchronizing signals. The time multiplexed serial bit stream is transmitted to a remote station, preferably by fiber optic communications media. The most recent bits of the received serial bit stream equal in number to the number of bits spanned by the two channels in n frames are retained in n-1 serially connected serial in, serial out shift registers. Sixteen bit portions, a frame apart, of the retained most recent bits of the serial bit stream are applied to n serial in, parallel out shift registers. The parallel outputs of these shift registers corresponding to the frames of the two channels encoded with the synchronizing signals are compared with the sequence of uniquely coded signals stored in addresses in PROMs. When the compared signals match, which will occur once in every n frames, a synchronization signal is generated and the protective relay data and parity check data are read directly from the other parallel outputs of the serial in, parallel out shift registers. Similar rapid resynchronization of voice and data channels in the time multiplexed serial bit stream can be achieved by counting the number of bits in the bit stream from the generation of the synchronization signal in the relay protection channels to the beginning of the time slot for a selected voice or data channel.

Bit error rate estimation for channels with memory

Abstract: A method for deriving key parameters of a bit-error-rate (BER) estimate is presented. The method is based on a bursty channel model proposed by B.D. Fritchman (IEEE Trans. Inform. Theory, Vol. IT-13, pp.221-227, Apr. 1967). This model is used to derive the confidence levels and confidence intervals of an error-rate estimate. The theoretical results have been confirmed experimentally by using the data from a helical-scan digital magnetic-tape recorder. The experiments clearly demonstrate the inadequacy of the BER estimates based on an independent-error approach. >

Optimum bandwidth-distance performance in full response CPM systems

Abstract: The problem of minimizing the effective bandwidth of a binary full-response continuous-phase-modulation (CPM) signal with respect to the shape of the frequency pulse for a prescribed value of the minimum Euclidean distance, which is directly related to the error probability for high signal-to noise ratio, is considered. An analytical procedure is presented that allows the determination of the optimum pulse shape together with its bandwidth and the minimum-distance characteristics. The solution contains an unknown parameter that is determined by numerical of a nonlinear equation. The results are compared to some standard pulses in terms of bandwidth, spectral density, minimum Euclidean distance, and error probability. Some gain in bandwidth is obtained for high values of minimum distance. >

Simulated Viterbi decoding using importance sampling

Abstract: The simulation of Viterbi decoding often requires excessive computer time to estimate low bit error probabilities since large sample sizes are needed to produce the rare error events. In this paper, importance sampling for Viterbi decoding is featured as a means of reducing the number of samples required. This reduction is achieved by modifying or ‘biasing’ the noise statistics to produce more errors, and subsequently scaling the number of errors to produce the desired bit error probability. If the bias is chosen properly and the effective memory of the decoder is limited, a significant reduction in the sample size is shown to occur.