Showing papers on "Frequency band published in 1991"

Spread spectrum for mobile communications

Abstract: The characteristics of spread spectrum that make it advantageous for mobile communications are described. The parameters that determine both the performance and the total capacity are introduced, and an analysis which yields (approximately) the number of users that can simultaneously communicate, while maintaining a specified level of performance, is presented. Spread spectrum overlay, wherein a code-division multiple-access (CDMA) network shares a frequency band with narrow-band users, is analyzed, and it is seen that excision of the narrowband signals from the CDMA receivers before despreading can improve both performance and capacity. >

A finite-difference time-domain near zone to far zone transformation (electromagnetic scattering)

Abstract: An efficient time-domain near-zone-to-far-zone transformation for FDTD (finite-difference-time-domain) computations is presented. The approach is to keep a running accumulation of the far-zone time-domain vector potentials due to the tangential electric and magnetic fields on a closed surface surrounding the scatterer at each time step. At the end of the computation, these vector potentials are converted to time-domain far-zone fields. Many far-zone bistatic directions can be included efficiently during one FDTD computational run. Frequency domain results can be obtained via fast Fourier transform. Wideband results for scattering from a perfectly conducting plate were obtained from a single FDTD computation transformed to the frequency domain, and compared with moment method results. This approach is significantly more efficient than computing many FDTD results using sinusoidally varying excitation if a wide frequency band is of interest. Coupled with recent advances in computing FDTD results for frequency-dependent materials, wideband results for far-zone scattering from targets including frequency-dependent materials can be obtained efficiently. >

A comparison of median frequency, spectral edge frequency, a frequency band power ratio, total power, and dominance shift in the determination of depth of anesthesia.

Abstract: Five numerical descriptors were derived from the electroencephalogram (EEG), recorded, and processed (Tracor Nomad) during emergence from isoflurane-nitrous oxide anesthesia The five descriptors (median frequency, spectral edge frequency-90%, total power, a frequency band power ratio, and the ratio of frontal to occipital power) were compared for their ability to predict imminent arousal Arousal was defined as spontaneous movement, coughing or eye opening All of the descriptors except the frontal-occipital power ratio underwent significant (P less than 005) changes between the initial recordings made intraoperatively during surgical stimulus under anesthesia and later recordings in the 40 s preceding arousal A post hoc analysis was performed to identify the threshold value for each parameter that best served to predict imminent arousal For median frequency, spectral edge frequency-90%, total power, and the frequency band power ratio, thresholds that predicted imminent arousal with sensitivities of 90% and specificities of 82-90% could be identified The data indicate that, even in the favorable circumstances of the present study (uniform anesthetic technique, post hoC identification of thresholds), none of several previously popularized EEG descriptors (median frequency, spectral edge frequency-90%, total power, a frequency band power ratio) can serve as a completely reliable sole predictor of imminent arousal As presently derived, these EEG descriptors at best provide trend information to be used in concert with other clinical signs of depth of anesthesia

Duplexing antenna for portable radio transceiver

Abstract: An antenna for use with portable duplex radio transceivers, such as those found in hand-held cellular telephones, which includes a pair of co-planar radiating patch elements elevated above a conductive surface by a conductive bar. The surface and bar define a reference ground plane which inherently isolates the patches. The patches are shaped so that they operate in a desired frequency band as well as band-pass filters--one of the patches is tuned to the transmit band and serves a transmit structure, and the other patch is tuned to the receive band and serves as a receive structure. Switching devices such as positive-intrinsic negative (PIN) diodes can be disposed along the space between the patches and the ground plane to allow each structure to be tuned. The antenna is efficient, because of inherent isolation between the receive and transmit patches, and eases the front end filtering functions traditionally performed by a duplexer. It can be completely enclosed within the chassis of a hand-held telephone.

Radio communication system using spread spectrum techniques

Abstract: A spread spectrum radio communication system includes a generator for generating a pseudo-random chipping sequence, a frequency spreader for combining digital data with the pseudo-random chipping sequence to produce a spread spectrum signal, a modulator for modulating the spread spectrum signal for broadcasting over a predefined frequency band, a demodulator for demodulating broadcast spread spectrum signals, a de-spreader that employs single bit quantization and oversampling for digitally correlating the output of the demodulator means with a pseudo-random chipping sequence, and an extractor for extracting clock and data signals from the output of the de-spreader The chipping sequence is normally selected from a set of codes including an eleven-bit Barker code, its inverse and reversals of the inverse and non-inverse code

TV signal receiving double conversion television tuner system having automatic gain control provisions

Abstract: A TV signal receiving system, in order to tune a broadcasting frequency of a desired channel after receiving a TV signal, converts the TV signal into an intermediate frequency having a frequency higher than the maximum frequency in a TV broadcasting frequency band and then converts again the frequency of the signal into another intermediate frequency in conventional TV systems so as to improve the rejection characteristics of image and IF signals. The system comprises a first converter for tracking a desired channel frequency from a TV RF signal and converting the frequency into a first IF of 2 GHz, a band-pass filter of the 2 GHz IF for filtering only the first IF frequency signal in the first converter, and a second converter for converting the filtered first IF into 45 MHz of the conventional TV IF.

A limit to the frequency stability of passive frequency standards due to an intermodulation effect

Abstract: It is shown that in passive frequency standards, the fre- quency noise of the probing signal, at Fourier frequencies equal to even multiples of the modulation frequency, is translated into the frequency band of the selectively amplified resonator response. Then an addi- tional perturbation of the slaved frequency source arises, which sets a limit to its achievable frequency stability. A quantitative estimate of this limit is given for the first and the third harmonic locking tech- niques. As an example, numerical values are given assuming a good crystal oscillator' as a frequency source. It is concluded that the limi- tation considered is very serious and may impinge on the expected fre- quency stability of newly developed frequency standards in which the resonance line can be observed with an enhanced signal to noise ratio. Such is the case, for instance, in devices using laser optically pumped cesium beam, rubidium cell, or stored ion(+

Listening bandwidths and frequency uncertainty in pure-tone signal detection.

Abstract: The effect of frequency uncertainty on the detection of tonal signals in noise was studied using a modified probe-signal method. Widths of the listening bands used during detection were measured directly, allowing for an analysis that separates the effects of having to monitor multiple independent bands from those due to limited frequency resolution. Uncertainty was varied by beginning each trial with a cue consisting of one, two, or four randomly chosen, simultaneously presented tones. An expected signal, whose frequency matched one of the components in a cue, was presented on a majority of trials. However, on remaining trials, the signal was a probe, which meant that its frequency differed from one of the components in the cue by a constant ratio. Performance as measured in percent correct declined for probes at increasingly distant ratios from the expected values. The results were converted to dB using individual psychometric functions for expected signals and listening bands were fitted using the rounded exponential filter of Patterson et al. [J. Acoust. Soc. Am. 72, 1788-1803 (1982)]. The obtained bandwidths are comparable to those reported using notched-noise maskers, but there is a small but consistent increase in bandwidth with increased numbers of components in the cues. The primary results is that the effects due to uncertainty are well described by a 1-of-M orthogonal band model, which takes into consideration limitations of the detector, including the widths of the listening bands.

Device and method for on-line adaptive selection of baud rate and carrier frequency

Abstract: Optimal baud rate and carrier frequency for data transmission using a modem on a communication channel (100) are determined by utilizing an on-line line probing technique. The technique utilizing the information from a decoder noise power spectrum estimated from the equalized received modulated signals and decoder output symbols to determine the decoder signal-to-noise ratios (SNRs) and supported bit rates for the available baud rates and carrier frequencies. These SNRs and bit rates together with a band edge SNR difference at each frequency band are utilized to select (110) the optimal baud rate and carrier frequency.

Communication system using spread spectrum and leaky transmission line

Abstract: A spread spectrum communication system uses a leaky coaxial cable for cost effective radio communication in enclosed areas. The system includes radio units which communicate with a transceiver, the transceiver being coupled to the leaky coaxial cable. Full-duplex communication includes a first frequency band for transmitting spread spectrum signals from the transceiver to the radio units at power levels which are adjusted to take advantage of the losses associated with leaky coaxial cable, and a second frequency band for transmitting spread spectrum signals from the radio units to the transceiver at the more conventional spread spectrum power levels speicified by the FCC. The present invention employs this split band configuration to accommodate communication over leaky coaxial cable without expensive and bulky filtering for isolation between the transmit and receive signals.

Full-duplex, sub-band spread spectrum communications system

Abstract: An improved spread spectrum communications system is provided for establishing full-duplex voice/data radio communications within a single specified FCC ISM band. Spectrum spreading is performed relative to a plurality of sub-bands respectively defined about the lower and upper band-edges of the prescribed ISM band and having spectral roll-off characteristics which satisfy FCC requirements for radio frequency radiation outside the ISM bands on the corresponding band-edges thereof. Full-duplex operation is implemented by the use of digital MSK modulation and associated filtering in order to conserve available bandwidth and accommodate the filtered, modulated signal within the sub-bands defined in the prescribed ISM frequency band, and the system is capable of being easily interfaced to related digital communications services.

Microcellular communications system using space diversity reception

Abstract: Microcellular stations are transceiving units covering a relatively small geographic area and adapted to establish bidirectional links between mobile telephone subscriber stations and a main base station. Each such microcellular station includes a transmitter for generating outgoing signals directed to the main base station over an optical fiber link. Radio signals received from a mobile station at a separate diversity antenna of the microcellular station are frequency shifted and combined with other signals received from the mobile station. The transmitter at the microcellular station generates an optical carrier signal which is modulated by the resulting combined signals. A frequency converter, located at the main base station, restores the frequency band of signals received from the microcellular station to its original frequency. Frequency shifting and conversion are implemented at the microcellular station and at the main base station by frequency mixing steps performed by oscillators at both locations, which oscillators use the same reference frequency thereby achieving channel coherency.

Soliton generation at 10 MW level in the very high frequency band

Abstract: Eletromagnetic solitions at a 10 MW level in a frequency band of several hundred megahertz are generated in a transmission line loaded by a nonlinear ceramic dielectric in the para‐ electric phase.

Optical cable television transmission system

Abstract: OF THE DISCLOSURE The invention is based on the problem of transmitting a frequency-division multiplex signal occupying a broad frequency band, e.g., the cable television frequency band of 47-440 MHz, over an optical waveguide transmission section. According to the invention, in the transmitting unit, the whole frequency band to be transmitted is divided into two sub-bands (FB1, FB2), and the lower sub-band (FB1) is converted by means of single-sideband amplitude modulation of a high-frequency carrier (f0) into a higher-frequency transmission frequency band, e.g. 497-688 MHz, which is less than one octave in width, based on its lowest frequency. The lower sub-band (FB1) and the transmission frequency band produced by the conversion are converted separately into optical signals with different wavelengths (.lambda.1, .lambda.2) and are transmitted in a wavelength multiplex procedure via the optical waveguide. Because of the limitation of less than one octave, second-order intermodulation products, which are usually formed during conversion into an optical signal, fall into unoccupied frequency regions. A corresponding reverse processing is carried out on the receiving side.

On adaptive multiband signal detection with GLR algorithm

Abstract: An adaptive multiband detector based on the principle of the generalized likelihood ratio test (GLR) is presented. Its detection performance is studied and compared with that of the corresponding single-band GLR detector. The multiband detector is shown to significantly outperform the single-band under the chosen system constraint, especially when the amount of data available from a single frequency band is severely limited by the environment. >

Waveform display apparatus for easily realizing high-definition waveform observation

Abstract: A measurement unit U100 measures an input signal to be measured by sweeping frequencies in a measurement range having a predetermined frequency band so as to obtain waveform data to be developed on the frequency axis such as spectrum data in, e.g., a spectrum analyzer. The waveform data obtained by the measurement of the measurement unit U100 is displayed by a display device 500 via a display data processor U20 included in a control unit U200 to be described later to be developed on the frequency axis of the display device, i.e., in correspondence with the measurement frequencies. The control unit U200 includes a measurement controller U30 for controlling the measurement unit U100 so as to display waveform data obtained by enlarging or reducing waveform data, before a measurement frequency condition is changed, at a predetermined magnification to have a predetermined point on the frequency axis as the center on the basis of a change in measurement frequency condition set by a condition setting unit U900, and an enlargement display/stable display processor U40 for controlling the display data processor U20. The enlargement display/stable display processor U40 realizes high-definition waveform observation as the gist of this invention, and substantially has a function of controlling the display device U500 as the control unit U200.

Digital signal encoding with quantizing based on masking from multiple frequency bands

Abstract: An allowable noise level is set for each frequency band of the input digital signal on the basis of the energy level of the respective frequency band and that of another frequency band. The energy level and the allowable noise level are non-linearly related so as to enable high data compression and to provide a satisfactory sound. The signal components of each of the frequency bands are quantized with a number of bits which correspond to the difference between the energy level of each frequency band and the allowable noise level. If the input digital signal is preemphasized, the signal is corrected for preemphasis prior to the setting of the allowable noise level, so that the quantization is performed on a signal which is free from the effects of preemphasis.

Method and circuit for automatic outphasing

Abstract: The invention refers to an automatic dephasing method with the phase φ= kx360 degrees/N, where k = 0,1,...N-1, in a narrow frequency band and with a dephasing circuit with 120 degrees, with application of the method for the case N=3, k=1. The method is based on an automatic control loop of the phase, where the control is made in order to maintain a constant dephasing of 0 degree between frequency multiples of order N of the inlet signal and the dephased signal.The 120-degree dephaser, achieved with a voltage controlled dephasing circuit (cell with "low pass" type transfer function and with TEC used with variable resistance), uses two identical PLL circuits for the multiplication by 3 of the frequency and the phases of the inlet and outlet signals. The correction signal from the phase sensitive detector ("with 3 states") amplified and integrated, commands the dynamic resistance of TEC and thus the dephasing inserted by the circuit, so that the frequency multiples of order 3 of the inlet and outlet signals to be in phase. The working domain of frequency of the dephaser is limited by the capture band of the PLL circuits.The circuit is not modifying the outlet signal amplitude and allows the maintenance of a constant dephasing (120 degree) between the inlet and outlet signals, independent of the frequency fluctuations of the signal or of the variation of the parameters, with temperature or in time, of the components, thus eliminating the need of control.The 120 degree dephased circuit can be used within the frame of devices which are measuring with precision the symmetrical components of voltage and current in a three-phased system with asymmetric sinusoidal magnitudes, for example in a wattmeter for three-phased alternating current in the range 35...75 Hz.

Technique for accurate carrier frequency generation in of DM system

Abstract: An Optical Frequency Division Multiplexing system achieves close channel spacings and thus high density of communications channels in a particular frequency band by providing a very precise carrier frequency stabilization technique. Each laser-generated local carrier signal is locked to a corresponding reference signal. All of the reference signals are generated by a common tunable laser circuit (2) that produces a sequence of bursts of successively higher frequencies determined by resonant points of single Fabry-Perot filter. Each transceiver of the Optical Frequency Division Multiplexing system includes a frequency tracking circuit (1) that converts received signals (P1 in (t)) from the optical domain to the electrical domain (P2) and utilizes an intermediate frequency filter circuit (10) and a servo control circuit (16) to adjust the tunable laser frequency and lock it to the present reference frequency.

Apparatus for encoding digital signals

Abstract: Apparatus for efficiently encoding a digital signal includes an arrangement (41, 42) for dividing the signal into a number of frequency band signals. The frequency band signals are segmented into blocks and the blocks are orthogonally transformed (43, 44, 45) to form coefficient data. The coefficient data is then quantized (58). A circuit (50) detects whether at least the lowest frequency one of the frequency band signals contains a transient. If so, a control circuit (57; 102; 100) controls processing of at least the lowest frequency band signal so as to reduce the perceptibility of noise in the processed signal. The control circuit may be operative, in the event of detection of a transient, to increase the number of bits used for quantizing at least the lowest frequency band signal, to reduce the block size of at least the lowest frequency band signal, and/or to reduce the level of at least the lowest frequency band signal.

Frequency division, energy comparison signal processing system

Abstract: A frequency division, energy comparison signal processing system for detecting the presence of, and separating the contributions from, sources that compose a wide-band sound signal, in which the system divides at least part of the wide-band sound signal into a number of discrete narrow frequency band components (12a), generates the energy envelope of each of those components (14a), normalizes the envelopes (29), multiplies each normalized envelope with each of the other normalized envelopes to obtain a plurality of envelope correlation coefficients for each frequency band (40), and then identifies from the correlation coefficients a sound source seed frequency band component and then, using the seed, identifies the remaining frequency components of a sound source.

Multifunctional aperture coupled stacked antenna

Abstract: A multifunctional aperture coupled stacked patch antenna that operates at dual-frequency bands is presented. At the lower frequency band, the antenna exhibits a 2:1 voltage standing wave ratio (VSWR) bandwidth of 20%. At the higher frequency band it behaves like a conventional narrowband patch antenna with a 2:1 VSWR bandwidth of 3%. Measured VSWR and far-field radiation patterns as well as numerical predictions are presented. A proper choice of the patch dimensions has been found critical to achieve this multifunctional performance. >

Video network system with computer LAN

Abstract: A bi-directional video signal transmission system is equipped with transmission lines having coupled upsteam and downstream segments. With the entire band of a RF signal being taken as a modulation frequency band, an image signal modulated to a frequency band and RF-multiplexed in the upstream segment is introduced into the downstream segment at the modulated frequency and is then branched to demodulate the same frequency band, thereby obtain one video signal transmission channel. In response to a request by a subscriber, a channel management section assigns and releases the transmission channels and further outputs a control command whereby a transceiver control section performs switching-control of the transmission frequencies to transceiver units.

Delayed-focus pulses for magnetic resonance imaging: an evolutionary approach.

Abstract: An evolutionary algorithm has been used to design a family of shaped radiofrequency pulses giving uniform absorption-mode excitation across a predetermined frequency band. By allowing a free precession interval before signal acquisition, time is left for field gradients to be switched and for undesirable transients to decay.

Photonic band gaps of transverse-electric modes in two-dimensionally periodic media

Abstract: A rigorous analysis of the propagation of transverse-electric modes in two-dimensionally periodic media is presented, based on an exact solution of the wave equation. The modulation functions studied lead to Mathieu and Hill equations. It is shown that the complete inhibition of the propagation of transverse-electric modes in a modulated plane is possible. Several modulation functions of the permittivity are studied in order to find the one for which the modulation depth necessary for the observation of a frequency band gap is minimized. In particular, thin grids and closely packed arrays of square rods are considered. The allowed angles of propagation of waves whose frequency is not contained within a forbidden band are also presented.

Monitoring device of plant equipment

Abstract: PURPOSE: To enable a variety of abnormalities to be processed with a simple device and in a short time by executing judgment of abnormality at high-frequency and low-frequency regions. CONSTITUTION: Sensors 11 are installed at measuring points of an equipment 10 to be monitored. These sensors 11 incorporate an AE sensor for high-frequency band and an acceleration sensor for low-frequency band and cables 12a and 12b from each sensor are connected to pre-amplifiers 13a and 13b. A signal from the amplifiers 13a and 13b is connected to a sensor switcher 14 and one set of signals for the high-frequency band and the low-frequency band are selected from a number of sensors 11. After the selected one set of signals are amplified and converted by an amplifier 15a for high frequency, an amplifier 15b for low frequency, an A/D converter 16a for high frequency, and an A/D converter 16b for low frequency, they are input to a judgment- processing part 17. The judgment-processing part 17 performs conversion for a data at each specified frequency band, performs comparison with a preset threshold, and then determines it to be a failure when the preset threshold is exceeded. COPYRIGHT: (C)1993,JPO&Japio