Showing papers on "Bandwidth (signal processing) published in 1990"

Comparison of Data-Driven Bandwidth Selectors

Abstract: This article compares several promising data-driven methods for selecting the bandwidth of a kernel density estimator. The methods compared are least squares cross-validation, biased cross-validation, and a plug-in rule. The comparison is done by asymptotic rate of convergence to the optimum and a simulation study. It is seen that the plug-in bandwidth is usually most efficient when the underlying density is sufficiently smooth, but is less robust when there is not enough smoothness present. We believe the plug-in rule is the best of those currently available, but there is still room for improvement.

A media-access protocol for packet-switched wavelength division multiaccess metropolitan area networks

Abstract: A dynamic time-wavelength division multiaccess protocol (DT-WDMA) is proposed for metropolitan-sized multichannel optical networks employing fixed wavelength transmitters and tunable optical receivers. Control information is sent over a dedicated signaling channel and data are sent over channels owned by the transmitters. Time is divided into slots on each channel and slots on the control channel are further split into mini-slots. Fixed time-division multiaccess (TDM) is used within each slot on the control channel. Transmitters indicate their intention to transmit a packet by transmitting the destination address during their appropriate mini-slot in the control channel and then transmit their packet in the next slot on their data channel. Receivers listen to the control channel and tune to the appropriate channel to receive packets addressed to them. A common but distributed arbitration algorithm is used to resolve conflicts when packets from many transmitters contend for the same receiver. Each receiver executes the same deterministic algorithm to choose one of the contending packets. Each transmitter uses the same algorithm to determine the success or failure of its packet. >

An analytic and experimental comparison of direct and external modulation in analog fiber-optic links

Abstract: Analytic lumped-element small-signal models of directly and externally modulated analog fiber-optic links are derived. Incremental modulation efficiency is defined and used to compare the performances of these modulation techniques. In experiments to optimize link RF-to-RF gain and noise figure, the measurements obtained agreed with calculations to within approximately=1 dB. The externally modulated link was operated with two different impedance matching circuits. With a low-pass match the bandwidth was 150 MHz, and the link transducer gain was 1 dB; with a bandpass match the bandwidth was 22 MHz, the link transducer gain was 11 dB, and the noise figure was 6 dB. The directly modulated link was operated with a low-pass match. In this case, the bandwidth was 1 GHz, the link transducer gain was -14 dB, and the noise figure was 33 dB. These experimental results were achieved with no amplification,. >

Cellular telephone service using spread spectrum transmission

Abstract: A spread spectrum processing system that employs wide bandwidth spread spectrum radio transmissions overlaid over the existing cellular voice signals to simultaneously provide additional cellular services without causing objectionable interference to current users of the cellular voice channel. The spread spectrum radio transmissions also support a large number of low rate digital messages. Both vehicle location and messaging functions are obtained without sacrificing any of the existing voice channel capacity. The cell site processor is designed to share the existing cellular frequencies, real estate, antenna towers, antennas, and low noise amplifiers used in the cell site radio frequency receiver chain. The only additional cell site equipment is the spread spectrum signal processor. The processing system provides a means for achieving vehicle location accuracies that are improved by greater than two orders of magnitude over that which is possible by the current transmissions in that band. It provides a means of achieving transmit power control of the vehicle transmitter to combat the extremely large variation (dynamic range) of radio signal path loss to the receiving sites. It also provides a means of excising at the receiver the excessively strong conventional voice cellular signals that are not under power control which ordinarily might interfere with the successful reception of the new broadband signals.

Technique for the evaluation of derivatives from noisy biomechanical displacement data using a model-based bandwidth-selection procedure.

Abstract: Smoothing and differentiation of noisy signals are common problems whenever it is difficult or impossible to obtain derivatives by direct measurement. In biomechanics body displacements are frequently assessed and these measurements are affected by noise. To avoid high-frequency noise magnification, data filtering before differentiation is needed. In the approach reported here an autoregressive model is fitted to the signal. This allows the evaluation of the filter bandwidth and the extrapolation of the data. The extrapolation also reduces edge effects. Low-pass filtering is performed in the frequency domain by a linear phase FIR filter and differentiation is performed in the frequency domain. The reported results illustrate the accuracy of the algorithm and its speed (mainly due to the use of the FFT algorithm). Automatic bandwidth selection also guarantees the homogeneity of the results.

Large bandwidth aperture-coupled microstrip antenna

Abstract: The feasibility of printed antennas which meet all the criteria for satellite communications antennas is considered. These criteria are a bandwidth greater than 20% for a VSWR of less than 1.5, crosspolar level lower than −30 dB over 20° solid angle, and gain better than 8 dB throughout the bandwidth.

A 400-MHz input flash converter with error correction

Abstract: An 8-b, 200-megasample/s flash converter with 400-MHz analog bandwidth and error correction circuitry is described. A cascoded input stage and a dense bipolar process make the wide bandwidth possible. Errors arising from high input slew rate and comparator metastability are reduced by means of the circuitry and the latching stages respectively. The final defense against errors is the second rank error suppression. Measured frequency and error rate performance are examined. >

Low probability of intercept communication system

Abstract: A low probability of intercept communication system (CCSK)--modulates information signals onto an inverse fast Fourier transformation of a large number of simultaneous frequencies that have been determined to be reasonably `quiet` within a given system bandwidth, so as to produce a time domain pulse waveform. The amplitude of each transmitted frequency is weighted. Within the receiver equipment of each participant in the system, the incoming pulse waveform produced by the inverse fast Fourier transformation mechanism at the source is coupled to a fast Fourier transform operator, so as to separate the time domain signal into a plurality of frequency components that contain the modulated data. These components are then convolved with a replica of the plurality of quiet channels to derive a time domain output waveform from which the data modulation can be identified and recovered. Even if a jamming threat is injected into one or more of the `quiet` channels that has been selected as a participating carrier, by virtue of the signal analysis and recovery process employed by each unit for incoming signals, jamming spikes are effectively excised.

Radio frequency receiver for a NMR instrument

Abstract: A receiver processes an NMR signal to produce a baseband image information signal from which two quadrature component signals are derived. An intermediate frequency section mixes the received NMR signal with two reference signals to shift the image information into a frequency band having a bandwidth BW and centered at a frequency that is 1.5 times the bandwidth BW. The resultant signal is filtered to remove extraneous signals outside the image information band. An analog to digital converter samples the filtered signal at a rate that is twice the bandwidth BW and digitizes the samples into a digital signal. A quadrature detector derives I and Q output signals from the digital signal by alternately selecting digital samples and negating every other sample selected for each of the I and Q output signals. The quadature detector also digitally filters the I and Q signals which are then used to construct an NMR image.

Delay, linewidth and bandwidth limitations in optical phase-locked loop design

Abstract: Maximum laser linewidth and loop gain in an optical phase-locked loop (OPLL) are calculated as a function of loop delay and filter bandwidth, using a cycle-slipping criterion. It is shown that a loop delay of less than 2 ns would permit the realisation of OPLLs using the recently reported submegahertz linewidth monolithic tunable semiconductor lasers.

Microcellular direct-sequence spread-spectrum radio system using N-path RAKE receiver

Abstract: A microcellular local area network (LAN) for indoor communications is proposed using code-division multiple access (CDMA) and differential phase-shift keying (DPSK) for data modulation. The pseudonoise (PN) codes in the transmitters of the base station are mutually synchronized. For this purpose, sets of Gold code sequences having low cross correlation have been found by an exhaustive computer search. Together with wideband measurements of the indoor radio channel at 900 MHz, a five-path RAKE receiver was designed to combat fading effects and to process the time diversity by using multipath signal reception. Each receiver path is demodulated independently. Several methods of diversity combining of these paths have been investigated. Acquisition and tracking of the spreading code in the receiver are controlled by a digital signal processor (DSP). Experimental results of the CDMA system are presented, showing the behavior in a multipath environment. >

P-code-aided global positioning system receiver

Abstract: Method and apparatus for use in a global positioning system (GPS), to obtain the benefit of L2 carrier signals and precise-code (P-code) signals transmitted from satellites in encrypted form. Received, encrypted P-code signals are correlated (96) with a locally generated (98) P-code sequence and the resulting signal is bandpass filtered (100) and squared (102), to separate one satellite signal from the others, to recover the carrier signal (106) and make accurate measurement of its phase and pseudo-range, even though the received P-code sequence is encrypted. Because the squaring step (102) is performed over a narrower bandwidth (100) than the original P-code (90), there is less degradation in the signal-to-noise ratio of the received signal, as compared with squaring over the entire P-code bandwidth. Therefore, performance is more reliable under weak signal conditions or when there are interference signals present, and the improvement in signal quality means that cycle ambiguity of the carrier signals can be resolved more rapidly. Moreover, the invention does not frustrate the intended purpose of P-code encryption.

Digital signal encoding apparatus

Abstract: A digital signal encoding apparatus in which input digital signals are divided into a plurality of frequency bands so that the bandwidth of each frequency band will be greater the higher the frequency band, the allowable noise level is set for each frequency band on the basis of the energy value of each frequency band, and components of each frequency band are quantized with the number of bits consistent with the level difference between the energy of each frequency band and the preset allowable noise level. The output information volume following the quantization is detected and the number of bits of allocation for quantization is corrected in dependence upon the error between the detection output and the target value to render the information volume constant over a predetermined time period to enable bit rate adjustment or bit packing with lesser signal deterioration by a simplified construction.

Optical fibre digital pulse-position-modulation assuming a Gaussian received pulse shape

Abstract: The abundance in bandwidth available in the best monomode fibres may be exchanged for improved receiver sensitivity by employing digital PPM. The paper presents a performance and optimisation analysis for a digital PPM coding scheme operating over a fibre channel employing a PIN-BJT receiver and assuming a Gaussian received pulse shape. The authors present original results for a 50 Mbit/s, 1.3 mu m wavelength digital PPM system and conclude that, provided the fibre bandwidth is several times that of the data rate, digital PPM can outperform commercially available PIN-BJT binary PCM systems.

Vertical resolution of thick beds, thin beds, and thin-bed cyclothems

Abstract: Resolution has two common definitions. The first of these relates to determination of the position of a reflector in time or space. Resolution by this definition is inversely related to pulse width or sharpness of the wavelet and, potentially, directly related to bandwidth of the frequency spectrum. The second definition of resolution relates to determination of the spacing of close features such as thin beds. This type of resolution is determined by the Rayleigh criterion which inversely relates resolution to wavelength. Resolution of thin beds improves with shorter wavelength, or higher frequency. In comparison to the Rayleigh criterion, the Ricker and Widess criteria improve the resolution potential of thin beds, but they rely on models of the reflectors and require that the beds be isolated.It is a long established and widely accepted axiom that the best wavelets contain bandwidths of at least a couple of octaves. This results in wavelets with reduced side lobes and ringiness, a more easily interpreted waveform. The concept of octaves does not figure into the equation of resolution according to either of the above definitions, but that is not to disagree with the axiom. For wavelets with bandwidths of at least a few octaves, the two definitions of resolution find a consensus in that resolution quality becomes dependent on the value of the highest frequency. That is, resolution is proportional to the highest frequency of the data when it contains several octaves of information.

Precise satellite ranging and timing system using pseudo-noise bandwidth synthesis

Abstract: A precise ranging and timing system using pseudo-noise bandwidth synthesis to provide precise orbit determination for geosynchronous and low earth orbit satellites, navigation of low earth orbiting satellite through signals transmitted through geosynchronous satellites and precise time-transfer. The system includes a novel signal structure which is comprised of disjoint, narrow band, spectral components spread over a wide bandwidth. The number of spectral components, their individual bandwidths, and their specific spectral locations over the end-to-end spread bandwidth determine the ultimate capabilities and performance achievable. The broad beam transmission of the precise ranging and timing system signal via a geosynchronous satellite provide the precise ranging and timing system capability to suitably equipped users for a multiplicity of purposes including: (1) precise orbit determination, (2) navigation of low-earth orbiting satellites through signals transmitted through geosynchronous satellites, and (3) precise time transfer.

Spread-spectrum multiple-access performance of orthogonal codes for indoor radio communications

Abstract: Direct-sequence spread spectrum, with its inherent resistance to multipath, is a promising technique for indoor wireless communication. To allow multiple users within a limited bandwidth, code division multiple access (CDMA) is needed. The bandwidth efficiency of M-ary CDMA systems in fading multipath indoor radio channels is analyzed. It is shown that M-ary signaling improves the bandwidth efficiency significantly when compared to binary signaling. >

Locally adaptive hazard smoothing

Abstract: We consider nonparametric estimation of hazard functions and their derivatives under random censorship, based on kernel smoothing of the Nelson (1972) estimator. One critically important ingredient for smoothing methods is the choice of an appropriate bandwidth. Since local variance of these estimates depends on the point where the hazard function is estimated and the bandwidth determines the trade-off between local variance and local bias, data-based local bandwidth choice is proposed. A general principle for obtaining asymptotically efficient data-based local bandwiths, is obtained by means of weak convergence of a local bandwidth process to a Gaussian limit process. Several specific asymptotically efficient bandwidth estimators are discussed. We propose in particular an, asymptotically efficient method derived from direct pilot estimators of the hazard function and of the local mean squared error. This bandwidth choice method has practical advantages and is also of interest in the uncensored case as well as for density estimation.

Instantaneous bandwidth for signals and spectrogram

Abstract: The concept of instantaneous bandwidth, which is an indication of the frequency spread at a given time, is developed. It is shown that the global bandwidth of a signal can naturally be broken up into an AM and an FM contribution and that the AM contribution comes from averaging the instantaneous bandwidth. The instantaneous bandwidth for the spectrogram is derived, and series expansions in terms of the derivatives of the phase are obtained. >

Data link controller with channels selectively allocatable to hyper channels and hyper channel data funneled through reference logical channels

Abstract: An integrated data link control device (IDLC) interfaces between a host computer system and external channels in a communication network. The device contains multiple internal channels allocatable individually to interface to the external channels, each internal channel having internal buffer memory reserved to it for storing data signals handled by it. The device also includes facilities for selectively configuring groups of its internal channels into "extended channels", some of which are termed Hyper Channels. Channels in each extended channel group interface collectively and in time coordination to one external channel, presenting an effective bandwidth to the external channel which is greater than the bandwidth of any single internal channel. One channel in each group is designated as a reference channel for the group, and all data signals transferred between the group and the assigned external channel are funneled through only the buffer memory assigned to the respective reference channel; in order to ensure that such signals are transferred between the external channel and the host system in their correct "message" sequence.

Dynamic calibration of waveform recorders and oscilloscopes using pulse standards

Abstract: The current methods used to calibrate oscilloscopes are briefly discussed, and the problems associated with oscilloscope vertical channel bandwidth testing are illustrated. A method is presented for the complete and correct calibration of an oscilloscope voltage channel. A solution that involves measuring and digitizing pulse signals and an NIST-developed deconvolution algorithm is shown. An example of the calibration of the vertical channel of a 20-GHz sampling oscilloscope is presented. >

GMSK with differential phase detection in the satellite mobile channel

Abstract: A formula is derived for the error probability of partial-response continuous-phase modulation (which contains Gaussian minimum shift keying (GMSK) as a special case) with N-b (N=1, 2) differential phase detection (DPD) for the satellite mobile channel, which contains as special cases the Gaussian and Rayleigh channels In the satellite mobile channel, the input signal is the sum of a direct component, a diffuse component, and white Gaussian noise The receiver is either with or without decision feedback, and the decision region is optimized for 2-b DPD to minimize the error probability The error probability for GMSK is computed as a function of signal-to-noise ratio and other system or channel parameters (Doppler frequency, Gaussian filter bandwidth, ratio of powers in the direct and diffuse signal components, etc) It is shown that decision feedback is more effective for GMSK with narrow bandwidth The 2-b DPD is superior to the 1-b DPD for low Doppler frequencies and signal-to-noise ratios For practical vehicle velocities and bit rates, a 2-b DPD with decision feedback outperforms all other analyzed schemes when the signal-to-noise ratio is low >

Interference reduction using an adaptive receiver filter, signal strength, and BER sensing

Abstract: A radio receiver having a variable bandwidth received channel filter (113,115) to reduce interference is disclosed. A interference is detected by comparing received signal strength and received signal BER. The bandwidth of the filter (113,115) is narrowed to improve BER when a received signal strength is greater than a threshhold value and BER is worse than a threshhold value.

System for scanning halftoned images

Abstract: A process for scanning halftoned images with a sampled or electronic imaging system includes the steps of first optically low-pass filtering the scene, then oversampling the scene at a rate several times that required for display bandwidth, and finally putting the resulting data through an electronic or digital low-pass filter/resampling operation to reduce the system data load. The oversampling advantageously shifts unwanted aliasing between the halftone and sampling frequencies to frequencies above the display bandwidth, so that the aliasing may then be filtered out without affecting signals within the bandwidth of the display.

A VLSI architecture for a high-speed all-digital quadrature modulator and demodulator for digital radio applications

Abstract: An all-digital architecture is presented for implementing the front-end signal-processing functions in a quadrature modulator and demodulator for high bit-rate digital radio applications. A pair of CMOS chips has been designed and submitted for fabrication in a 1.25- mu m process and is expected to accommodate symbol rates up to 35 MBd. The modulator chip accepts a pair of 8-b in-phase and quadrature data streams and generates a bandlimited IF output with an excess bandwidth factor of 35%. The demodulator chip accepts a digitized IF input signal and generates a pair of filtered in-phase and quadrature baseband signals. The modulator and demodulator chips each incorporate 40-tap multiplierless FIR (finite-impulse response) square-root Nyquist matched filters, and the cascade of the two chips achieves a peak intersymbol interference distortion of -54 dB. The modulator chip can generate any arbitrary signal constellation within a rectangular grid of 256*256 points. Thus, the all-digital implementation results in a generic chip set suitable for a wide variety of high bit-rate digital modem designs using formats such as M-ary PSK and QAM. >

Reconstruction of two-dimensional signals from level crossings

Abstract: Recent results indicate that reconstruction of two-dimensional signals from crossings of one level requires, in theory and practice, extreme accuracy in positions of the samples. The representation of signals with one-level crossings can be viewed as a tradeoff between bandwidth and dynamic range, in the sense that if the available bandwidth is sufficient to preserve the level crossings accurately, then the dynamic range requirements are significantly reduced. On the other hand, representation of signals by their samples at the Nyquist rate can be considered as requiring relatively small bandwidth and large dynamic range, because, at least in theory, amplitude information at prespecified points is needed, to infinite precision. An overview of existing results in zero crossing representation is presented, and a number of new results on sampling schemes for reconstruction from multiple-level threshold crossing are developed. The quantization characteristics of these sampling schemes appear to lie between those of Nyquist sampling and one-level crossing representations, thus bridging the gap between explicit Nyquist sampling and implicit one-level crossing sampling strategies. >

Modulation bandwidth of high‐power single‐mode semiconductor lasers: Effect of intraband gain saturation

Abstract: The effect of intraband gain saturation on the modulation bandwidth of single‐mode semiconductor lasers is discussed by using a nonperturbative form of the optical gain that is valid at high‐power levels. The small‐signal analysis of the modified rate equations is used to predict the power dependence of the modulation bandwidth. The results are used to discuss the ultimate modulation bandwidth of InGaAsP distributed feedback semiconductor lasers and its dependence on various device parameters.

A versatile vector modulator design for MMIC

Abstract: A single-chip, monolithic microwave integrated circuit (MMIC) vector modulator designed for use in an X-band, phased array radar system is described. The design principle is capable of addressing octave bandwidths and frequencies up into the millimeter-wave region. The circuit is novel in that it is purely passive, using unpowered FETs as the control elements. Therefore, it is low noise and should be able to handle relatively large RF signal levels of up to 1 W. Analog control of the vector extends over a range of more than 30 dB for amplitude and over 0-360 degrees for phase. Swept frequency, measured phase errors are lower than +or-10 degrees for a 10% instantaneous bandwidth anywhere in X-band (8-12 GHz). >

Frequency tracking using constrained adaptive notch filters synthesised from allpass sections

Abstract: New constrained adaptive notch filter structures are proposed. These structures are synthesised from allpass filter sections, which are realised as structurally lossless bounded real functions with a minimum number of delay elements and multipliers. Both structures admit orthogonal tuning of their notch frequency and bandwidth. Frequency tracking is achieved simply by the evaluation of a function of a filter parameter. Connections are shown with the structures used by other workers. Signal enhancement outputs are obtained from both structures and their signal-to-noise improvement ratios are given. The mirror-image pair of polynomials present in a real allpass transfer function is shown to provide a significant simplification in the generation of the necessary gradient terms used in parameter adaptation. Simulations are included to verify the performance of these structures when they are used to track both single and multiple sinusoids in additive broadband noise.