Showing papers on "Keying published in 1991"

On the bit error rate of lightwave systems with optical amplifiers

Abstract: The problem of evaluating the performances of communication systems with optical amplifiers and a wideband optical filter is addressed. Exact probability of error expressions for optical signals in presence of amplifier spontaneous noise and photodetector shot noise are given and compared with those predicted by Gaussian approximations for amplitude shift keying (ASK), frequency shift keying (FSK), or differential phase shift keying (DPSK) modulations, both for ideal photodetectors and for the case where shot noise is significant. >

Computer models for fading channels with applications to digital transmission

Abstract: The authors describe computer models for Rayleigh, Rician, log-normal, and land mobile satellite fading channels. All computer models for the fading channels are based on the manipulation of a white Gaussian random process. This process is approximated by a sum of sinusoids with random phase angle. These models compare very well with analytical models in terms of their probability distribution of envelope and phase of the fading signal. For the land mobile satellite fading channel, results of level crossing rate and average fade duration are given. These results show that the computer models can provide a good coarse estimate of the time statistic of the faded signal. Also, for the land mobile satellite fading channel, the results show that a 3-pole Butterworth shaping filter should be used with the model. An example of the application of the land mobile satellite fading channel model to predict the performance of a differential phase-shift keying signal is described. >

Bit error rate performance of pi /4-DQPSK in a frequency-selective fast Rayleigh fading channel

Abstract: The bit error rate (BER) performance of pi /4-differential quadrature phase shift keying (DQPSK) modems in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). The probability density function of the phase difference between two consecutive symbols of M-ary differential phase shift keying (DPSK) signals is first derived. In M-ary DPSK systems, the information is completely contained in this phase difference. For pi /4-DQPSK, the BER is derived in a closed form and calculated directly. Numerical results show that for the 24 kBd (48 kb/s) pi /4-DQPSK operated at a carrier frequency of 850 MHz and C/I >

Performance of an RCPC-coded OFDM-based digital audio broadcasting (DAB) system

Abstract: A system proposal for DAB is investigated. The kernel is orthogonal frequency division multiplexing (OFDM) with 4-DPSK (differential phase shift keying) modulation, rectangular pulse-shaping, and a guard interval to reject multipath distortions. Emphasis is on the use of source-adapted channel coding with rate-compatible punctured convolutional (RCPC) codes. Based on analytical and simulated BER (bit error rate) curves for several propagation conditions and on preliminary source significance information (SSI), a static code design with unequal error protection (UEP) is presented that also takes auxiliary data services into account. The gain due to UEP is on the order of 8dB in signal power or 25% in bandwidth. >

Digital video effects generator

Abstract: A digital video effects generator includes: means for up-sampling the digital video component signals prior to their spatial transformation and linear interpolation, thereby reducing losses due to the (sin x)/x frequency response of the sampled video signal; means for spatially-mapping video motion data representing the degree of video data motion between temporally adjacent video frames and for motion adaptive interpolation to selectively blend interpolated video field data in accordance therewith; means for pre-transform keying, thereby allowing two video signal transformations to be keyed simultaneously; means for selectively transforming portions of input video signals, thereby allowing selective keying of non-spatially transformed video into selected regions of the video image; means for selectively linking keyframes within separate effects and providing smooth parametric transitions therebetween, thereby allowing several separate effects to be combined into a single effect with smooth parametric transitions between the linked (inter-effect) keyframes; and means for maintaining "pinned" image corners during parametric transitions between keyframes.

Laser linewidth requirements and improvements for coherent optical beam forming networks in satellites

Abstract: A coherent optical beam forming network using phase-locked semiconductor lasers as sources is presented. For this scheme the spectral purity of the intermediate frequency derived from mixing the signals from two semiconductor lasers is considered. The relationship between the linewidths of the lasers in a satellite transmitter and the phase error at the detector of a microwave differential quaternary phase-shift keying earth station receiver is analyzed. The demands placed on the linewidths from the point of view of phase stability requirements are calculated using quaternary phase-shift keying modulation at data rates of 33 and 131 Mb/s. It is shown that a substantial improvement in performance can be achieved when phase locking the two lasers to each other is feasible. >

Chromatic dispersion limitations for FSK and DPSK systems with direct detection receivers

Abstract: Chromatic dispersion limitations for frequency-shift keying (FSK) and differential phase-shift keying (DPSK) systems using narrow-linewidth lasers and direct-detection receivers are discussed. The limitations are found to depend strongly on the receiver configuration. The receiver must include an optical frequency discriminator, such as a Mach-Zehnder interferometer, and either a balanced photodetector pair or a single photodetector at the interferometer output. For transmission at 1550 nm over 1310-nm optimized single-mode fiber, the distance for 1-dB eye closure penalty at 10 Gb/s ranges from 20 to 70 km, depending on the modulation format and the receiver configuration. >

GMSK with limiter discriminator detection in satellite mobile channel

Abstract: Formulas are derived to find the error probability of partial-response frequency-shift keying with limiter discriminator detection, with and without decision feedback, for a satellite-mobile channel. The special cases of a Gaussian channel and a land-mobile channel are discussed. The formulas are applied to Gaussian minimum shift keying, and the error probability is computed as a function of energy-to-noise ratio, Gaussian filter bandwidth, Doppler frequency, maximum Doppler frequency, the ratio of powers in the specular and diffuse signal components, and the time delay between specular diffuse components. >

An adaptive combiner for co-channel interference reduction in multi-user indoor radio systems

Abstract: An efficient technique for co-channel interference suppression in multi-user indoor radio communication systems is presented. The proposed approach makes use of an antenna array in conjunction with an adaptive combiner that employs a training sequence to adjust the receiver to the desired co-user. A different training sequence known to the receiver is transmitted periodically with the information sequence of each co-user. Signals received at the diversity antennas are weighted and summed to produce a combined signal. The weight coefficients are adjusted such that the reception of the desired signal is enhanced and all interfering signals are attenuated. A complex least-mean-square algorithm based on the method of steepest descent is used for weight adjustment. Computer simulations are presented for a two-antenna system with coherent QPSK (quadrature phase-shift keying) signaling over frequency-nonselective Rayleigh fading channels, and in the presence of a single interferer. >

Error floors in the satellite and land mobile channels

Abstract: In a satellite mobile channel (SMC) and land mobile channel (LMC) because of fading and nonlinear power amplifiers, constant envelope modulation and noncoherent detection methods may outperform other schemes. It is shown how to compute the error floor for four noncoherent digital communication systems in satellite and land mobile channels. Differential phase shift keying (DPSK) with differential phase detection (DPD) or frequency shift keying (FSK) with DPD, limiter discriminator integrator detection. (LDID), or limiter discriminator detection (LDD) are studied. The error floor is the residual error probability when SNR is infinity, i.e. the error probability in the system is limited by the error floor. The error floor is computed as a function of Doppler frequency, modulation index, and ratio of powers in the specular and diffuse signal components for DPSK-DPD, FSK-DPD, FSK-LDID and FSD-LDD systems. >

New signature code sequence design techniques for cdma systems

Abstract: New design techniques are presented for carefully selecting subsets of signature code sequences with small crosscorrelation magnitudes for applications in code inversion keying (CIK) direct-sequence spread-spectrum multiple-access systems Also, a new class of code sequences, which has been called the class of “structured code” sequences, with small crosscorrelation magnitudes is presented The performance measure considered is the average probability of data-bit error at the output of a correlator receiver The results presented are applicable to various applications of code-division multiple-access (CDMA) systems including optical fibre local area networks and indoor radio communications

Combining digital video key signals

Abstract: A mixer for combining digital video signals allows four real-time signals to be combined. At each layer, a digital key signal may be generated from the input video signal using chroma or luminance keying. In addition, the video signal may be combined with drop shadows, a border and a fill to produce first-stage composite video and composite key signals. A composite key signal is produced by supplying two key signals to a comparator and a selector via respective switchable invertors. The comparator produces a selection signal which is supplied to the selector via a switchable invertor. The selector switches an input signal to produce an output signal which is supplied to an output port via a switchable converter.

Simulation of bit error performance of FSK, BPSK, and pi /4 DQPSK in flat fading indoor radio channels using a measurement-based channel model

Abstract: The results of a simulation study that provides insight into the simulation methodology and bit error rate (BER) performance of frequency-shift keying (FSK), binary phase-shift keying (BPSK), and pi /4 differential phase-shift keying ( pi /4 DQPSK) in flat fading channels inside open plan buildings are presented. A detailed measurement-based propagation channel model, SIRCIM (simulation of indoor radio channel impulse response models), which generates over 1000 closely spaced baseband equivalent complex impulse responses for a mobile radio operating at 1.3 GHz and traveling over a 1-m path, is used. The small-scale channel model, the communication system models used in the analysis and the methods used to predict BER are described. The channel simulator and the systems models have been thoroughly tested, and results from average instantaneous BER simulations are shown. The BER performances of the modulation techniques are presented. It is found that BPSK offers between a 2.8-dB and 3.0-dB improvement over pi /4 DQPSK, although the latter offers a 3-dB increase in capacity for a given spectrum allocation. >

Keying methods for digital video

Abstract: A digital video key signal generator for digital video special effects uses two cascaded programmable lookup tables. One table is addressed by the two chroma component signals and the second table is addressed by the luma signal and the output of the first table. The generator is particularly suitable for use with CCIR Rec. 601 digital signals, and can be used for a wide variety of compositing functions, using luma keys, chroma keys, combinations thereof, and multiple chroma keys simultaneously.

Recursive Bayesian algorithms for blind equalization

Abstract: A novel blind equalization algorithm based on a suboptimum Bayesian symbol sequence estimator is presented. It is shown that a parallel bank of Kalman filters can be used to update a suboptimum Bayesian formula for the sequence possibilities. Two methods are used to reduce the computational complexity of the algorithm. First, it is shown that the Kalman filters can be replaced by simpler least-mean-square (LMS) adaptive filters. Second, the technique of reduced-state sequence estimation is adopted to reduce the number of symbol subsequences considered in the Bayesian updating, and hence the number of parallel filters required. The performance properties of the resulting algorithms are evaluated through bit error simulations, and these are compared to the bounds of optimum maximum-likelihood sequence estimation. It is shown that the Kalman filter and LMS-based algorithms achieve blind start-up and rapid convergence (within 200 iterations) for both binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulation formats. >

Bit error probability for fading DPSK signals in microcellular land mobile radio systems

Abstract: Bit error probability is evaluated as a function of reuse distance in a microcellular land mobile radio system with differential phase shift keying (DPSK) modulation in the presence of cochannel interference and thermal noise. Spectrum efficiency of the conventional macrocellular and microcellular networks is also compared.

Performance of convolutional codes with interleaving in the interference limited Rayleigh fading channel

Abstract: The authors discuss and characterize factors affecting the use of error-correcting codes with bit interleaving for a channel model which includes antenna diversity in interference-limited fading radio environments. The coding gain required to compensate for the bandwidth expansion due to channel coding is investigated for binary phase-shift keying (BPSK) with coherent and with differential detection, and for orthogonal signaling with noncoherent detection. In some radio communication systems where the overall interleaving delay that can be tolerated by a user is limited, it is found that channel coding may not be practical from the viewpoint of spectrum efficiency. >

Vehicle-guidance and target-tracking system

Abstract: Proposed is a vehicle-guidance and target-tracking system in which a destination is entered into a vehicle-mounted terminal by keying in the place and street name in clear text. The vehicle-mounted terminal is connected by communications link with a beacon in which the street names in the various places, and the corresponding map coordinates, are stored. When requested by the vehicle-mounted terminal, the beacon extracts the appropriate map coordinates and transmits them to the vehicle. Other data can also be transmitted in the transmitted message, such as traffic information or street maps. The system can also be used for the automatic calculation of road tolls.

Technique for demodulating and decoding mls dpsk transmissions using a digital signal processor

Abstract: A system for demodulating and decoding differential phase shift keying (DPSK) transmissions utilizes a bandpass filter (11), an analog to digital converter (12) and a digital signal processor (13) Removal of the effects of unknown frequency component is achieved by applying a complex phase correction/rotation factor after DPSK demodulation The actual phase of the complex signal is never computed directly All of the processing from Rader decomposition (14) through carrier tracking filter is performed on the complex values and therefore requires only multiplication and addition operations which can be performed at high speed in a microcomputer or in dedicated arithmetic hardware

BER performance evaluation for CPFSK phase and polarization diversity coherent optical receivers

Abstract: The following methods of continuous phase frequency shift keying (CPFSK) signal demodulation are compared for phase and polarization diversity receivers: single filter, dual filter, delay and multiply. Bit error rate (BER) values are obtained in each case showing that for negligible laser linewidths the delay demodulation method outperforms the dual-filter method by approximately 3 dB, and the single-filter method by 6 dB. Since the noise bandwidth for minimum-shift keying (MSK) and delay demodulation is approximately twice as small as for the other methods, one should add another 3 dB to get the gain for that modulation/demodulation method. The influences of nonzero laser linewidth, noise correlation, and the nonGaussian character of the probability density functions of the noise at the sampler are taken into account. >

Design of optical matched filters

Abstract: A study is made of the design and the performance of receivers using optical matched filters and direct detection, when the basic pulse shape consists of a rectangular pulse of monochromatic light. The modulation format can be ASK (amplitude-shift keying), FSK (frequency-shift keying), or DPSK (differential phase-shift keying). Such receivers are useful when amplifier noise is the main source of uncertainty as they optimally reject additive white Gaussian noise. The performances of ASK and FSK receivers are reported, taking into account shot noise and the effects of postdetection filtering. >

Frequency shift keying modulator

Abstract: The present invention provides a modulator/generator circuit which includes the following features: a 1200 baud 4-phase differential phase shift keying (DPSK) modulator, a 300 baud frequency shift keying (FSK) modulator, a dual tone multi-frequency (DTMF) generator and 2100/2225 Hz answer tone generators. The DPSK modulator utilizes time-domain filtering techniques. It includes a spectrum controller that shapes the in-band frequency spectrum and attenuates the adjacent channel frequency components to eliminate the conventional requirement of band-pass filters after the modulator. The FSK modulator also utilizes a spectrum controller which, during each data transition, sends out six intermediate frequencies to smooth the frequency changeover. DTMF generation is accomplished by multiplexing two sine-wave counters into a DPSK sinewave look-up ROM. By varying the duty cycle of the multiplexing control signal, the DTMF generator provides a digital pre-emphasis function that boosts the amplitude of the high-band frequencies as referenced to the low-band frequencies. The answer tone section of the circuit is accomplished by sharing portions of the FSK section since the two tones are embedded in the FSK frequencies. A digital DAC is provided for converting the modulated signal (parallel) to a serial bit stream. The modulated signal in analog form is available after a low cost low pass filter.

On the performance of bandwidth efficient RS coded MPSK signaling over a Rayleigh fading channel

Abstract: The idea of combining RS (Reed-Solomon) codes with multiphase signaling schemes on fading channels is introduced. The performance of these schemes over a Rayleigh fading channel is evaluated. The lower bound of the post decoding bit error probability for three RS-coded 8-PSK (phase-shift keying) schemes for both errors-only decoding and erasures-and-errors decoding techniques are obtained through the analysis and computer simulation. These results show that substantial coding gains can be obtained relative to uncoded QPSK. The coding gain for a very simple RS

Applications of trellis coding to coherent optical communications employing polarisation shift keying modulation

Abstract: The application of the concept of trellis coded modulation to coherent optical communications using polarisation shift keying modulation is described and analysed. It leads to a receiver formed by a front end which performs the heterodyne detection and the Stokes parameters extraction cascaded with an electronic Viterbi processor operating the maximum likelihood estimate of the transmitted sequence. Results in terms of error event probability obtained analytically and confirmed by simulation show power gains of the order of 3-4 dB without sacrificing bandwidth.

Performance analysis of a slotted CDMA system for indoor wireless communication using a Markov chain model

Abstract: A performance analysis is outlined of a star-connected direct-sequence spread-spectrum slotted code-division multiple-access (CDMA) system with differential phase shift keying modulation in an indoor radio environment characterized by Rician fading. The performance is analyzed in terms of the throughput, delay, and stability of the CDMA network. The traffic load is described by a discrete time Markov chain model for a finite number of simultaneous users. Two types of diversity, namely selection diversity and maximal ratio combining, are used to combat multipath fading. Also, the influence of forward error correcting coding on the performance parameters is investigated. >

Digital carrier recovery with frequency offset in TDMA transmission

Abstract: Time-division multiple-access (TDMA) data transmission is used in various radio communication systems. In TDMA systems, demodulation requires the estimation of some parameters. In the systems considered, the phase is acquired at the beginning of each burst, while clock and frequency are tracked from burst to burst. Two classical algorithms are considered for phase estimation: the feedforward structure proposed by Viterbi & Viterbi (1983), and feedback structures like decision-directed loops. Their acquisition and tracking performance are compared both for coded and uncoded M-ary phase-shift keying (MPSK) modulations. The feedforward structure may be very sensitive to frequency offsets; therefore, the performance of a digital frequency estimator is analyzed in detail. All the algorithms considered are easily implemented with digital hardware. >

Keyed apparatus for providing ground, power or signal connections

Abstract: An arrangement for providing a connection for ground, power or signals for an electronic connector assembly which also provides a keying function.

Simulation of digital transmission over mobile channels at 300 kb/s

Abstract: Studies of digital transmission over typical urban and suburban mobile channels using simulations that employ a local area model for the time varying mobile channel impulse response are discussed. The digital transmission techniques of coherently detected and differentially coherent detected versions of quadrature phase-shift keying (QPSK), Gaussian minimum shift keying (GMSK), and coherently detected binary phase-shift keying (BPSK) over example mobile channels are presented. Two measures of performance are considered; the mean bit error ratio (and irreducible bit error ratio), which is used to compare the robustness of the various modulation methods to delay spread, and the outage probability, which provides a measure of the overall transmission quality as would be perceived by a user. Emphasis is placed on results obtained for GMSK, which is the modulation scheme to be employed in the Pan-European digital cellular mobile system. The effects of RMS delay spread on the mean bit error ratio, mean irreducible bit error ratio, and probability of outage are considered for different channel types. >

Simulated performance of coded digital transmission in a multi-user indoor radio communications environment

Abstract: The performance of error correction codes in conjunction with different diversity methods is investigated in a simulated multi-user indoor radio communications environment in the presence of a single interferer. Bit-error curves are presented for soft-decision convolution coding and for trellis coding with simple diversity methods. The degradation in bit error rate caused by CCI (co-channel interference) on uncoded QPSK (quadrature phase-shift keying), convolutionally coded QPSK, and trellis-coded 8-PSK is presented. The results indicate that the given trellis codes (without interleaving) have poor performance in a Rayleigh fading medium; their performance is even worse in the presence of both fading and CCI. The performance of soft-decision convolutional coding was much better than that of trellis, but at the expense of increasing the channel bandwidth. >