Showing papers on "Bandwidth (signal processing) published in 1984"

Gain enhancement methods for printed circuit antennas

Abstract: Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Detection in noise by spectro-temporal pattern analysis

Abstract: Detectability of a 400-ms, 1000-Hz pure-tone signal was examined in bandlimited noise where different spectral regions were given similar waveform envelope characteristics. As expected, in random noise the threshold increased as the noise bandwidth was increased up to a critical bandwidth, but remained constant for further increases in bandwidth. In the noise with envelope coherence however, threshold decreased when the noise bandwidth was made wider than the critical bandwidth. The improvement in detectability was attributed to a process by which energy outside the critical band is used to help differentiate signal from masking noise, provided that the waveform envelope characteristics of the noise inside and outside the critical band are similar. With flanking coherent noise bands either lower or higher in frequency than a noise band centered on the signal, it was next determined that the frequency relation and remoteness of the coherent noise did not particularly influence the magnitude of the unmasking effect. An interpretation in terms of nonsimultaneous masking was reconciled with some aspects of the data, and with an interpretation in terms of across-frequency temporal pattern analysis. This paradigm, in which detection is based upon across-frequency temporal envelope coherence, was termed "comodulation masking release." Comodulation offers a controlled way to investigate some of the mechanisms which permit signals to be detected at adverse signal-to-noise ratios.

High-Level Modulation and Coding for Nonlinear Satellite Channels

Abstract: Currently, 4-PSK is the prevalent modulation format in use for digital satellite communications. To improve bandwidth efficiency, 8PSK could be used instead, but a higher power would be needed; to improve power efficiency, error-correcting codes could be used, but at the expense of a larger bandwidth. Recently, Ungerboeck [1] has proposed a class of codes in which a constellation of 2M signals is used to transmit information at the rate of log_{2} M bits per symbol, and has shown that coding gains of up to several decibels can be achieved on the additive white Gaussian noise (AWGN) channel with no increase in bandwidth occupancy and a relatively small added complexity. Thus, these codes seem to be particularly attractive for application in the band-limited environment typical of satellite communication systems, provided that the performance gain that they provide on the AWGN channel is not lost over a satellite channel. The goal of this work is to assess the performance of this class of codes when used to transmit 3 information bits per symbol on a band-limited, nonlinear satellite channel. Three modulation formats are considered, namely 16-PSK, 16-QAM, and a 16-ary amplitude-phase keying scheme with two amplitude levels. It is found that 16-PSK outperforms the two other modulation formats, and that the use of these codes can provide a substantial performance improvement even on a satellite channel.

Digital methods for conversion between arbitrary sampling frequencies

Abstract: The paper presents filtering methods for interfacing time-discrete systems with different sampling frequencies. The methods are applicable for sampling rate conversion between any two sampling frequencies; the conversion ratio may even be irrational or slowly time varying. Interpolation by irrational factors requires digital filters with nonperiodically varying coefficients. This is dealt with in two ways. 1) All possible coefficient values are precalculated. This is, in a sense, possible because of the finite resolution needed. Or 2), the coefficients can be updated in real time using either FIR or IIR filters. The first solution requires a huge coefficient memory; the second scheme, on the other hand, is computationally intensive. While discussing both of these solutions, more practical intermediate schemes incorporating both FIR-and IIR-type filters are suggested. The suggested practical implementations are either based on analog reconstruction filters where the derived digital filter coefficients are functions of the distances between current input and output samples or digital interpolators combined with simple analog interpolation schemes for finding the desired values in between the uniform output samples from the digital interpolator.

Velocity-matching techniques for integrated optic traveling wave switch/modulators

Abstract: We propose and analyze a new technique for achieving velocity match between the traveling wave electrical drive and guided optical signal for modulators in substrates for which there is an inherent mismatch. The traveling wave electrodes are laterally shifted periodically to reverse the direction of the applied electric field within the optical waveguide which exactly compensates for the polarity reversal caused by the microwave-optical walkoff. Consequently, the electrooptically induced phase shifts of each section add in phase and several sections can be used to reduce the required drive voltage at the design frequency. This artificial velocity-matching technique moves the mismatch-limited bandwidth to an arbitrarily high design frequency. In addition, we extend the new concept of phase reversal and the previously suggested technique of intermittent interaction by proposing electrode structures with large inactive to active aspect ratios. This generalization provides increased flexibility for manipulating the total available bandwidth to, for example, allow efficient modulation by a train of arbitrarily short electrical pulses. These techniques are ideally suited for several proposed integrated optic devices, including picosecond samplers and gates, which require strong overmodulation at a single high frequency.

Phase-Locked Transparent Tone-in-Band (TTIB): A New Spectrum Configuration Particularly Suited to the Transmission of Data Over SSB Mobile Radio Networks

Abstract: The paper describes a new pilot tone SSB configuration, transparent tone-in-band (TTIB), which may be used in mobile radio systems from low-band VHF to microwave frequencies. By utilizing audio signal processing techniques in the transmitter and receiver, the pilot reference tone may be positioned centrally within the RF channel bandwidth without losing the property of data transparency and also retains the many system advantages of tone-in-band SSB over the pilot carrier and tone-above-band schemes. Besides speech transmissions, results are presented for noncoherent FSK and DPSK data formats under white noise and Rayleigh fading conditions. Finally, a new technique utilizing TTIB is suggested to facilitate the use of coherent data systems.

Hybrid subband coder/decoder method and apparatus

Abstract: The subband channels of a subband coder/decoder utilize different encoding/decoding algorithms so as to maximize overall signal transmission quality using a digital signal processor having limited digital memory capability. In the exemplary embodiment, a digitized 180-2900 Hz voice band signal is divided into four octave-spaced subbands. The highest frequency subband (1450-2900 Hz) is encoded/decoded using a block companded pulse code modulation (BCPCM) algorithm while each of the lower frequency subbands is encoded/decoded using an adaptive pulse code modulation (APCM) or an adaptive differential pulse code modulation (ADPCM) algorithm. The resulting "hybrid" vocoder tends to maximize the quality of transmitted voice signals while yet permitting implementation within constrained digitial memory capacity and/or constrained transmission channel bandwidth.

Image gathering and processing for enhanced resolution

Abstract: Traditional approaches to optical resolution enhancement have involved either the design of appropriate image-formation systems or some type of postprocessing of an image that has already been formed. Results presented in this paper suggest that improved images can be obtained if the image-gathering system is designed specifically to enhance the performance of the image-restoration algorithm to be used. We consider a class of problems in which the total available spatial bandwidth is fixed but the location of this bandwidth along the spatial-frequency axis is to some extent under our control. For example, we might consider either a low-pass system or a bandpass system of the same total bandwidth. We show that system performance can be substantially improved by proper allocation of the available bandwidth in the spatial-frequency domain. The optimum allocation is shown to be a function of the signal-to-noise ratio. We also describe coherent and incoherent optical image-gathering systems that can achieve the desired spatial-frequency passbands.

Embedding Data Into Pictures by Modulo Masking

Abstract: Three systems are proposed for embedding data into industrial quality monochrome analog pictures. The video signal on each scan line is sampled, and a data bit is inserted into a block of three or five pels by modulo masking scrambling the luminance level of only one pel in the block. Prior to transmission, the combined data and video sequence is converted into a continuous signal with a bandwidth that is no greater than that of the original video signal. Using six images each containing 65 536 pels, Systems 1 and 2 embedded an average of 17 430 and 8713 bits per image, while System 3 accommodated data at a constant rate of 21 760 bits/image. The data embedding procedures of Systems 1, 2, and 3 operated with average picture SNR's of 41, 44, and 30 dB, respectively, when the transmission channel was ideal. When the transmission was over a channel composed of a second-order Butterworth filter plus additive noise that yield a channel SNR of 40 dB, no bit errors occurred but System 3 offered the greater safety margin to bit errors than Systems 1 and 2.

Satellite communications system and method therefor

Abstract: A satellite communications system and method of communication which results in increased frequency-reusage within assigned frequency bands and allows for a reduction in satellite transponder requirements per unit of bandwidth employed The disclosed system employs a satellite in a geostationary orbit having transponders and one or more large-aperture, high-gain antennas that provide a broad-area beam for a relatively wide service area and for transmitting to and receiving signals from N narrow-area beams for N respective sub-areas, the sub-areas corresponding to the high-traffic nodes Both beam types operate in the same allocated frequency bands but with opposite linear or opposite handed circular polarizations, or, alternatively, with arbitrarily determined portions of the allocated frequency band pairs with dual polarization so that the allocated frequency spectrum is used at least N+1 times Since the narrow-area beams provide a substantially smaller illumination pattern than the broad-area beam, substantially less power is required to form each narrow-area beam at the satellite antenna so that each additional narrow-area beam results in a frequency reuse with only a relatively small incremental increase in drive power requirements Because of the reduced incremental satellite power requirements associated with the multiple additional frequency reusages, the high power amplifiers (HPA's) of the satellite transponders for the narrow-area beams can be backed-off from non-linear operation into their linear regions to allow multiple signal carrier amplification in each HPA to thus reduce the total HPA requirements for the system

Wide band bar detectors of gravitational radiation

Abstract: "Five-mode" massive aluminum gravitational radiation detectors cooled to millikelvin temperatures are considered for the purpose of approaching quantum sensitivity over a large bandwidth. A five-mode detector with a center frequency at 800 Hz would have a two-sided usable bandwidth of the order of 400 Hz. A five-mode detector with a center frequency at 1660 Hz would have a usable two-sided bandwidth of the order of 1000 Hz.

Large-signal theory of a two-stage wideband gyro-TWT

Abstract: A self-consistent large-signal theory is used to obtain gain and efficiency of the two-stage tapered gyro-TWT in a nonuniform external magnetic field. Calculations show that it is possible to design a device having 45 percent bandwidth at 45-dB gain and 25 percent efficiency if the axial velocity spread of the beam electrons is zero. It is found that the gain and bandwidth are very sensitive to the degree of beam velocity spread, the external magnetic field profile, and the various beam and circuit parameters. We also derive an expression for the efficiency under quasi-linear approximation in order to get a physical understanding of the device performance.

SBPSK: A Robust Bandwidth-Efficient Modulation for Hard-Limited Channels

Abstract: A family of constant-envelope modulation formats is described in which good spectral containment is achieved through the use of controlled phase trajectories. The phase trajectory of shaped BPSK (SBPSK) in particular is such that it can be considered a PSK/FSK hybrid. For one member of this family, 50% SBPSK, extensive analytical results are presented, including sensitivities to filter bandwidths, timing jitter, phase jitter, and frequency error. In addition, performance in the presence of multiple adjacent channel interferers in a hard-limited satellite channel is analyzed and performance comparisons to conventional modulations are presented.

Call progress monitor for a computer telephone interface

Abstract: A call progress monitor for a computer telephone interface system. Energy detectors are connected to receive signals from a telephone line. A bandpass filter is connected to the telephone line, having selectable center frequency. A counter-timer connected to count clock pulses is reset by the energy detector and timing commences in response to the presence of a signal on the telephone line. The counter will result in a center frequency control means for the filter being slewed over a bandwidth of interest, in synchronism with the counting of the timer-counter. A signal detector connected to the filter indicates the presence of a pair of signal tones passing through the filter as it is slewed. Decoding means are connected to the counter-timer and the signal detector for generating a binary signal indicating the frequency of the bandpass filter which passes each signal tone. The binary signal is entered in a data register, and an interrupt posted to a host computer. During the remaining portion of a counting cycle, a cadence interval is detected and the data register is loaded with cadence data. An interrupt is posted at the end of the cadence measuring interval for signalling the computer to read the contents of the data register.

Generalized tamed frequency modulation and its application for mobile radio communications

Abstract: Continued investigation of tamed FM (TFM) has led to an extension called generalized tamed FM (GTFM). The very narrow spectral property of a GTFM signal meets the stringent requirements on bandwidth utilization in modern mobile radio applications. The principle of GTFM is first described. It is then shown that the generation of GTFM signals can be made very simple by the use of an ROM table-lookup technique. By an appropriate choice of parameters in GTFM signal generation at the transmitter, a joint optimization for coherent and noncoherent detection with regard to BER performance in the presence of additive white Gaussian noise can be achieved. For mobile radio applications, the robustness of the detection scheme to fast fading is important. A low-complexity noncoherent receiver is presented, comprising a frequency discriminator and a simple maximum-likelihood sequence estimator. This receiver performs well in a fast fading environment. Computer simulated results of BER performance of this scheme are given. These results are confirmed by experimental measurements.

Performance of minimum-variance deconvolution filter

Abstract: Recently, we observed zero phase and undershoot patterns in data processed by a minimum-variance deconvolution (MVD) filter. These observations motivated a careful analysis of the MVD filter, which, as we demonstrate in this paper, explains both the zero phase and undershoot patterns. This analysis also connects the MVD filter with the well-known prediction-error filter [6], and Berkhout's two-sided least-squares inverse filter [7]. We show that the performance of the MVD filter depends heavily on the bandwidth of the source wavelet and signal-to-noise ratio, and only slightly on data length.

Speech coding system

Abstract: A speech signal coding system comprises a prediction filter coupled with an output of a quantizer for prediction of a signal. A subtractor provides the difference between an input signal and an output of the prediction filter. A quantizer quantizes the residual signal, which is the difference provided by the subtractor. The quantizer is improved by adaptively adjusting step size for quantization. Thus, the coded outputs, according to the present invention, are the parameter information of the prediction filter, quantized output of the residual signal, and step information for quantization. The quantization step is determined according to the fundamental step size which provides the statistical variance, equal to one, to the quantized signal, and/or the power of the residual signal. Because of an efficient encoding with an adaptive control of the quantization step, the bandwidth for transmission of the coded signal in a communication system or transmission rate of coded speech signal is minimized. Excellent speech is reproduced through a narrow band channel, or low bit rate digital channel like 16 kbits/second digital channel.

A New Frequency Domain Speech Scrambling System Which Does Not Require Frame Synchronization

Abstract: Communication security is becoming more and more important today. There is thus an increasing interest in analog scramblers due to the desire for secure speech communications over existing telephone channels with standard telephone bandwidth at acceptable speech quality and reasonable cost. The concept of scrambling the sample values of the speech waveforms becomes attractive due to its higher degree of security compared to the traditional scramblers. But all these sample value scramblers require frame synchronization, i.e., the signal segments used in scrambling and descrambling processes have to be exactly the same for signal recovery. This complicates the implementation and makes the transmission very sensitive to channel conditions. In this paper, a new frequency domain scrambling algorithm is presented, which is an extension of the DFT scrambler previously proposed. The use of short-time Fourier analyis and the filter bank concept leads to the special feature that frame synchronization is completely unnecessary. This simplifies the implementation and improves the reliability and feasibility. The theoretical developments, simulation results, hardware implementation, and test results are all discussed in detail.

Digital-to-analog conversion system as for use in a digital TV receiver

Abstract: A digital-to-analog converter system includes two DAC's operated in ping pong fashion with their analog output signals linearly summed. To preclude bandwidth limiting inherent in the summing operation the applied digital input signal is preconditioned in accordance with the transfer function 1/(1+Z-1).

High resolution noncollinear acoustooptic filters with variable passband characteristics: design

Abstract: A generalized method for designing a high resolution acoustooptic filter with variable passband characteristics is described and experimentally verified in crystalline quartz. The optical passband of this filter configuration is made insensitive to acoustic divergence by canceling the wave vector mismatch caused by acoustic divergence by the similar effect introduced by the anisotropy of the acoustic velocity within the acceptance angle. About 0.4-nm half-power bandwidth with an external half-angular aperture of ~3° was obtained at 488 nm in a quartz filter. By changing the effective interaction length from 47 to 6 mm the passband was varied approximately from 0.4 to 3.5 nm. The possibilities of finding suitable filter orientations in Tl3AsSe3 and TeO2 are also discussed.

Laser trimming monolithic crystal filters to frequency

Abstract: An improved method of adjusting piezoelectric devices to frequency by particularized laser trimming is disclosed. The laser removes a single contiguous area in the center of the electrodes to appropriately increase the individual resonator frequency without significantly degrading the filter "Q". In an AT-cut monolithic crystal filter, the particularized laser trimmed area can be positioned such on the face of the electrodes to simultaneously control frequency and bandwidth. This method can be substituted for the more cumbersome process of frequency adjustment by vapor deposition to provide a rapid inexpensive technique for monolithic crystal filter manufacture.

On the frequency limitations of SC filters

Abstract: Representative closed-form expressions are derived for a stray-insensitive integrator which describe the combined influence of the amplifier finite gain and finite bandwidth and of the nonzero on-resistance of the switches. In this way, a technology-dependent upper frequency limit is obtained for the application of typical stray-insensitive switched-capacitor circuits. The deteriorating effect of switch-on resistance and stray capacitance is also derived for integrator circuits comprising unity-gain amplifiers. However, the results obtained shown that they are too much affected by the parasitic capacitances to be a serious alternative for monolithic high precision filters.

Transimpedance amplifier having an improved gain/bandwidth product

Abstract: A transimpedance amplifier having improved gain/bandwidth product utilizes a direct current feedback circuit to provide improved stability of bandwidth and frequency response flatness as well as a much higher gain times bandwidth product than prior art circuits.

Can a resonant-mass gravitational-wave detector have wideband sensitivity?

Abstract: In principle, for an impulsive gravitational-wave signal, the signal-to-noise ratio for a resonant-mass antenna is independent of frequency if the limiting noise source is the antenna thermal noise. A gain-bandwidth restriction only arises when the coupling of the resonant antenna to the output amplifier is considered. Applying Bode's gain-bandwidth theorem we are able to derive in a general way the linear amplifier sensitivity limit for a resonant-mass detector. The practical bandwidth limits for a detector utilizing a superconducting inductive transducer are discussed. A fractional bandwidth of approx.0.17 appears feasible with current technology. Additional bandwidth and sensitivity can be achieved with an array of detectors.

Signal processor (system) for reducing bandwidth and for multiplexing a plurality of signals onto a single communications link

Abstract: The bandwidth required for a regularly occurring signal, such as a television signal, as received from a signal source can be substantially reduced by not transmitting each and every one of the horizontal scan lines. Rather, firstly, one or more selected lines may be transmitted and, secondly, instead of transmitting the remaining, unselected lines, a signal representing a predetermined arithmetic difference among predetermined ones of the scan lines may be transmitted. The bandwidth may be further reduced by a time expansion of the time interval of the selected line signal and by a time compression of the time interval of the differential signal. The bandwidth required for each regularly occurring signal as received from each of a plurality of N signal sources may be more efficiently used by time compression multiplexing the respective time expanded and time compressed signals.

Method for digital transmission of a broadcast radio programme signal

Abstract: For digital transmission of a broadcast radio programme signal, the frequency band of the broadcast radio programme signal is split into sub-bands. The individual sub-bands are differently quantised and are subsequently transmitted using time-division multiplex. In this case, the quantisation of each sub-band is carried out on the basis of the quiescent audibility threshold and/or on the basis of the monitoring threshold which is applicable to the respective bandwidth of the sub-band, and/or on the basis of the amplitude statistics of the broadcast radio programme signal which are applicable to the respective frequency of the sub-band.

Tissue signature tracking transceiver

Abstract: An ultrasound transceiver providing enhanced imaging by selective filtering of the received signal to provide a variable frequency, constant bandwidth filtering of the received echo signals. The resulting signals are then detected to produce a signal, which when displayed, has a reduced number of false multiple images and enhanced signal quality from the deeper tissue discontinuities. Additionally, the received signal is detected in quadrature by reference to a simulated carrier pilot tone having a nonconstant frequency relationship to the transmitted signal. The resulting signal is post-processed to provide information which is used to display structural features, and in addition, the velocity profile of blood flow. The structure and velocity image information is superimposed to provide a composite signal wherein the static and dynamic characteristic of a patient is completely reported to the observer.

Simulation of wide bandwidth signals that have propagated through random media

Abstract: A numerical technique is described to generate realizations of the received signal after propagation of a wide bandwidth waveform through a layer of strongly turbulent media. These signal realizations are generated to have Rayleigh amplitude statistics and to have spatial and frequency correlation properties which obey the parabolic wave equation in the strong scatter limit. This technique is based upon the solution for the two-frequency mutual coherence function Γ for spherical wave propagation with transmitter and receiver located on opposite sides of a finite layer of ionized electron density irregularities. An analytic solution may be obtained for Γ in the strong scatter regime by use of the quadratic approximation for the phase structure function. The thin phase screen approximation to the thick layer is then utilized, and great simplification to the analytic expression for Γ is obtained. The relationship between the impulse response function of the propagation channel and the two-frequency mutual coherence function and its Fourier transform is then used to directly obtain statistical realizations of wide bandwidth signals. These statistical realizations may be used as direct input to digital receiver modems to represent the effect of propagation through an ionospheric environment disturbed by barium releases or other sources of enhanced ionization. Although these statistical signal realizations apply only to the case of strong scattering, their generation requires only a fraction of the computer resources required for signal generation by wide bandwidth multiple phase screen calculations.

Design and Performance of Sampled Data Loops for Subcarrier and Carrier Tracking

Abstract: Design parameters and resulting performance are presented for the sampled data analogies of continuous time phase locked loops of second and third order containing perfect integrators. Expressions for noise equivalent bandwidth and steady state errors are given. Stability and gain margin are investigated using z plane root loci. Finally, an application is presented for Voyager subcarrier and carrier tracking under the dynamics of the encounters with Uranus and Neptune. For carrier tracking, loop bandwidth narrow enough for satisfactory loop signal to noise ratios can be achieved using third order loops without rate aiding, whereas second order loops would require aiding. For subcarrier tracking, third order loops can be used when the sampling rate is limited to approximately once per second, as in the Baseband Assembly, whereas second order loops sufficiently wide to track the dynamics have stability problems at that sampling rate.