scispace - formally typeset
Search or ask a question

Showing papers on "Bandwidth (signal processing) published in 1994"


Journal ArticleDOI
28 Nov 1994
TL;DR: It is shown that the DS-CDMA multi-carrier system over-performs the RAKE receiver when the system parameters are selected properly and the spread spectrum processing gain is increased, the effect of multipath interference is removed, and frequency/time diversity is achieved.
Abstract: A DS-CDMA multi-carrier system is proposed. The transmitted data bits are serial to parallel converted to a number of parallel branches. Each bit on each branch is DS-SS modulated and transmitted with a number of orthogonal and overlapping carriers. Given that sufficient interleaving is provided, this procedure provides many advantages. The system performance is compared to that of the conventional RAKE receiver. It is shown that the multi-carrier system over-performs the RAKE receiver when the system parameters are selected properly. The system utilizes a small number of carriers to solve the intersymbol interference (ISI). The data on each carrier is spread by a lower rate PN code. This reduces the effect of inter-chip interference (ICI). This technique is shown to provide the following advantages: the spread spectrum processing gain is increased, the effect of multipath interference is removed, and frequency/time diversity is achieved.

562 citations


Journal ArticleDOI
TL;DR: In this article, the problem of joint transmitter and receiver optimization for MIMO systems under the mean-squared error (MSE) criterion is revisited and analytical solutions for the optimal transmit-receive pair are derived.
Abstract: The problem of joint transmitter and receiver optimization for MIMO systems under the mean-squared error (MSE) criterion is revisited. We address the general problem of N (number of users) /spl ne/M (number of channel inputs) /spl ne/P (number of channel outputs) when the system is Nyquist bandlimited and obtain analytical solutions for the optimal transmit-receive pair. Next, we demonstrate how the above result is directly applicable to the problem where the system has excess bandwidth, thereby generalizing the results of Salz (1985). In conclusion, several numerical examples are included to demonstrate the performance gains obtainable with jointly optimized MIMO systems vis-a-vis systems based only on receiver optimization. >

359 citations



Journal ArticleDOI
TL;DR: In this article, a technique to design the channel frequency allocation in order to minimize the crosstalk due to FWM is presented, which is obtained at the expense of some expansion of the system bandwidth.
Abstract: Crosstalk due to four-wave mixing (FWM) is the dominant nonlinear effect in long-haul multichannel optical communication systems employing dispersion-shifted fiber. A technique to design the channel frequency allocation in order to minimize the crosstalk due to FWM is presented. It is shown that suitable unequal channel separations can be found for which no four-wave mixing product term is superimposed on any of the transmitted channels. This is obtained at the expense of some expansion of the system bandwidth. Simulations are presented to show the effectiveness of this technique in a 10-channel, 10-Gb/s per channel, system. >

263 citations


Patent
16 Feb 1994
TL;DR: In this paper, the authors propose a method and modem for communicating serial input data over a transmission link, where the signal is demodulated and assembled into frames of parallel signal elements which are de-rotated by an inverse linear mapping.
Abstract: A method and modem for communicating serial input data over a transmission link. Serial input data is partitioned into parallel data elements prior to rotation by an invertible linear mapping. Resulting frames of parallel signal elements sequentially modulate a carrier, which is then transmitted over the link. After receipt of the modulated carrier from the link, the signal is demodulated and assembled into frames of parallel signal elements which are de-rotated by an inverse linear mapping. Thresholding the result of the inverse mapping recovers the parallel data elements, which are then re-assembled into serial output data. The linear mapping employs: 1) commuting rotation matrices for convolutionally rotating data vectors into signal vectors and vice-versa; 2) filter bank polyphase rotation matrices; or 3) computationally efficient multi-rate wavelet filter banks. Transmitter pre-emphasis places most of the information in lower baseband frequencies; complimentary de-emphasis occurs in the receiver. Logarithmic amplification of the baseband signal prior to carrier modulation improves modulation gain and transmit channel noise attenuation. Coefficients of the rotation matrix of the receiver are adaptively equalized to correct for transmission path distortion. FM double-side band is employed in systems requiring minimized cost and complexity. FM single-side band is employed in systems in which bandwidth reduction is desirable. AM is also employable.

249 citations


Journal ArticleDOI
TL;DR: In this article, a modal analysis and a uniform field approximation were presented for the fields in an idealized two-dimensional, rectangular cavity excited by an electric line source, which was used to evaluate the effectiveness of frequency stirring, an alternative to mechanical stirring in reverberation chamber immunity measurements.
Abstract: A modal analysis and a uniform-field approximation are presented for the fields in an idealized two-dimensional, rectangular cavity excited by an electric line source. The model is used to evaluate the effectiveness of frequency stirring, an alternative to mechanical stirring in reverberation chamber immunity measurements. Numerical results indicate that good field uniformity (standard deviation less than 1 dB) can be obtained with a bandwidth of 10 MHz at a center frequency of 4 GHz. The bandwidth requirement is determined primarily by the number of modes excited, and higher frequencies can achieve the same field uniformity with a smaller bandwidth because of the higher mode density. Cavity excitation by two single-frequency sources is also analyzed. >

225 citations


Proceedings ArticleDOI
30 May 1994
TL;DR: A photoreceptor circuit that can be used in massively parallel analog VLSI silicon chips, in conjunction with other local circuits, to perform initial analog visual information processing, and the connection between shot and thermal noise in a system governed by Boltzmann statistics is beautifully illustrated.
Abstract: We describe a photoreceptor circuit that can be used in massively parallel analog VLSI silicon chips, in conjunction with other local circuits, to perform initial analog visual information processing. The receptor provides a continuous-time output that has low gain for static signals (including circuit mismatches), and high gain for transient signals that are centered around the adaptation point. The response is logarithmic, which makes the response to a fixed image contrast invariant to absolute light intensity. The 5-transistor receptor can be fabricated in an area of about 70 /spl mu/m by 70 /spl mu/m in a 2-/spl mu/m single-poly CMOS technology. It has a dynamic range of 1-2 decades at a single adaptation level, and a total dynamic range of more than 6 decades. Several technical improvements in the circuit yield an additional 1-2 decades dynamic range over previous designs without sacrificing signal quality. The lower limit of the dynamic range, defined arbitrarily as the illuminance at which the bandwidth of the receptor is 60 Hz, is at approximately 1 lux, which is the border between rod and cone vision and also the limit of current consumer video cameras. The receptor uses an adaptive element that is resistant to excess minority carrier diffusion. The continuous and logarithmic transduction process makes the bandwidth scale with intensity. As a result, the total AC RMS receptor noise is constant, independent of intensity. The spectral density of the noise is within a factor of two of pure photon shot noise and varies inversely with intensity. The connection between shot and thermal noise in a system governed by Boltzmann statistics is beautifully illustrated. >

197 citations


Journal ArticleDOI
TL;DR: The adaptive process is considerably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules, and a constrained least mean-squared algorithm is used for the adaptive process.
Abstract: Investigates adaptive digital notch filters for the elimination of powerline noise from biomedical signals. Since the distribution of the frequency variation of the powerline noise may or may not be centered at 60 Hz. Three different adaptive digital notch filters are considered. For the first case, an adaptive FIR second-order digital notch filter is designed to track the center frequency variation. For the second case, the zeroes of an adaptive IIR second-order digital notch filter are fixed on the unit circle and the poles are adapted to find an optimum bandwidth to eliminate the noise to a pre-defined attenuation level. In the third case, both the poles and zeroes of the adaptive IIR second-order filter are adapted to track the center frequency variation within an optimum bandwidth. The adaptive process is considerably simplified by designing the notch filters by pole-zero placement on the unit circle using some suggested rules. A constrained least mean-squared algorithm is used for the adaptive process. To evaluate their performance, the three adaptive notch filters are applied to a powerline noise sample and to a noisy EEG as an illustration of a biomedical signal. >

187 citations


Proceedings ArticleDOI
13 Nov 1994
TL;DR: A robust algorithm for estimation of local signal frequency and bandwidth is described based on combining local estimates of instantaneous frequency over a large number of scales using a set of lognormal quadrature wavelets.
Abstract: This paper describes a robust algorithm for estimation of local signal frequency and bandwidth. The method is based on combining local estimates of instantaneous frequency over a large number of scales. The filters used are a set of lognormal quadrature wavelets. A novel feature is that an estimate of local frequency bandwidth can be obtained. The bandwidth can be used to produce a measure of certainty for the estimated frequency. The algorithm is applicable to multidimensional data and examples of the performance of the method are demonstrated for one-dimensional and two-dimensional signals. >

186 citations


Patent
15 Nov 1994
TL;DR: In this article, the average speeds for intervals of, for example, 15 seconds are stored, with the time and place of observation, and the data from all calibrant vehicles are then analyzed to determine patterns of mean speed and bandwidth.
Abstract: Monitoring of traffic on selected routes requires little communication time, through reporting only instances of abnormal speed. During a calibration phase calibrant vehicles are operated along the selected routes with sufficient frequency and for enough days to provide meaningful data. Each calibrant vehicle carries a differential GPS receiver for measuring location accurately. Average speeds for intervals of, for example, 15 seconds, are stored, with the time and place of observation. The data from all calibrant vehicles are then analyzed to determine patterns of mean speed and bandwidth. In the monitoring phase probe vehicles are deployed, each carrying similar GPS, a computer in which the patterns are stored, and a radio for automatically reporting speeds which are out of bandwidth for that time and place.

184 citations


Patent
11 Aug 1994
TL;DR: In this article, a method and apparatus for achieving symbol synchronization of digital data in an OFDM channel such as a OFDM/FM radio link is presented. But the required bandwidth overhead is less than 10 %.
Abstract: A method and apparatus are disclosed for achieving symbol (frame) synchronization of digital data in an OFDM channel such as an OFDM/FM radio link. The method and apparatus are suitable for use in a pure ALOHA environment because synchronization is achieved on a frame-by-frame basis. The required bandwidth overhead is less than 10 %. The bit-error-rate performance achievable with this technique is within 1.5 dB of the performance assuming ideal synchronization. The method and apparatus provide a three-stage synchronization process. First the onset of an ODFM frame is detected. Second, coarse synchronization is achieved by sampling the received signal, and measuring the correlation between the received signal and a reference signal. Coarse synchronization provides synchronization to within ±1/2 sample period. The correlation is preferably carried out in the frequency domain after carrying out a Fast Fourier Tranform on the sampled signal date. Third, synchronization is achieved by calculating the time-shift between the coarse synchronization point and the actual synchronization point and using the calculated time shift to determine the phase correction to apply to each data carrying sub-carrier. Finally the transmitted data is recovered by decoding the information obtained about the phase and amplitude of the data-carrying sub-carriers.

Proceedings ArticleDOI
08 Jun 1994
TL;DR: A propagation model which incorporates the angular distribution of the rays in the vicinity of the mobile is postulated and it is shown that it is possible to increase capacity between two and twelve times depending on the number of antennas in the arrays and the spread of the local scattering.
Abstract: The goal of this paper is to estimate the gain, in terms of system capacity at a given outage probability, which can be obtained by applying antenna arrays in the base stations of a mobile cellular network. For this purpose a propagation model which incorporates the angular distribution of the rays in the vicinity of the mobile is postulated. Also included in the model is the interference from co-channel cells. With the aid of the model, a weight selection algorithm is derived. The proposed system is simulated with different numbers of mobiles per channel in each cell and different numbers of antenna elements in the arrays. Also varied is the cluster size. This is done to determine the optimal trade-off between reduced cluster size and multiple mobiles per channel in each cell. The results show that it is possible to increase capacity between two and twelve times depending on the number of antennas in the arrays and the spread of the local scattering. >

Patent
14 Apr 1994
TL;DR: In this article, an improved discrete multi-tone transmission scheme is described that contemplates encoding digital data and modulating the encoded data onto a discrete multitone signal having a total bandwidth of at least 16 MHz.
Abstract: An improved discrete multi-tone transmission scheme is describe that contemplates encoding digital data and modulating the encoded data onto a discrete multi-tone signal having a total bandwidth of at least 16 MHz The modulation system is capable of dynamically updating the subcarriers used and the amount of data transmitted on each subcarrier during transmission in order to accommodate real time changes in the line quality over particular subcarriers In one preferred embodiment of the invention the multi-tone encoding and modulation is done in substantial compliance with the ATIS North American Asymmetric Digital Subscriber Lines standard although a total of 512 subchannels each having a bandwidth of approximately 43125 kHz are used In this system, the subchannels that occur at frequencies above those set forth in the standard are treated similarly to those within the standard range in terms of subcarrier selection criteria This embodiment contemplates the use of a discrete multi-tone signal having an available bandwidth of 2208 MHz The described system permits transmission of digital data at transmission rates of 6 Mbps over telephone lines at distances of two miles even on lines that experience significant T1 crosstalk noise In one application of the invention, it may be used with ordinary telephone lines such as twisted pair lines to transmit data to remote receivers located up to six thousand feet from the transmitter at digital data transmission rates of at least ten million bits per second (10 Mbps) With more subchannels provided, the number of subchannels available for upstream communications may also be increased

Journal ArticleDOI
TL;DR: An algorithm is presented for real-time estimation of the frequency and azimuth and elevation angles of each signal incident on an airborne antenna array system over a very wide frequency band (2-18 GHz) commensurate with electronic signal warfare.
Abstract: An algorithm is presented for real-time estimation of the frequency and azimuth and elevation angles of each signal incident on an airborne antenna array system over a very wide frequency band (2-18 GHz) commensurate with electronic signal warfare. The algorithm provides unambiguous frequency estimation despite severe temporal undersampling necessitated by cost/complexity of hardware considerations. The 2-18 GHz spectrum is decomposed into 1-GHz bands. The baseband output of each antenna is sent through two 250-MHz sampled channels where one is delayed relative to the other (prior to sampling) by 0.5 ns, which is the Nyquist interval for a 1-GHz bandwidth. Due to the high variance of the Direct ESPRIT frequency estimator, aliased frequencies are estimated via a simple formula and translated to the proper aliasing zone, utilizing eigenvector information generated by PRO-ESPRIT. The algorithm also provides unambigous 2-D angle estimate over the entire 2-18 GHz bandwidth, despite severe spatial undersampling at the higher end of this band necessitated by mutual coupling considerations and resolving power requirements at the lower end of the band. Eigenvector information generated by PRO-ESPRTT is used to facilitate computationally simple estimation of azimuth and elevation angles that are automatically paired with corresponding frequency estimates despite aliasing. Simulations are presented demonstrating the capabilities of the algorithm. >

Journal ArticleDOI
TL;DR: In this article, the characteristics of square, circular and diagonal quadruple-ridged waveguides, including cutoff frequencies, attenuation, impedance and modal field distributions, are for the first time systematically analyzed and reported.
Abstract: In a previous paper, a unified approach has been proposed for the analysis and design of single- and double-ridged waveguides by a magnetic field integral equation (MFIE) formulation (see ibid., vol. 41, no. 11, p. 1965-71, Nov. 1993). This paper presents a continuing work with emphasis on the design of quadruple-ridged waveguides. The characteristics of square, circular and diagonal quadruple-ridged waveguides, including cutoff frequencies, attenuation, impedance and modal field distributions, are for the first time systematically analysed and reported. Distinct to being in a single- or double-ridged waveguide, the fundamental-mode in a quadruple-ridged waveguide has a cutoff frequency very close to that of the second-lowest mode, thus the natural single mode bandwidth is very small. However, when the second-lowest mode is effectively suppressed or not excited, a very wide bandwidth (6:1) can be achieved. This unique property, plus the capabilities of dual-polarization, high power, and low impedance, makes the quadruple-ridged waveguides well-suited to many antenna and microwave applications. >

Journal ArticleDOI
TL;DR: The ability of a linear equalizer/combiner or decision-feedback equalizer to suppress all received adjacent-channel, intersymbol, and cochannel interference is described and the number of interferers that may be suppressible by a generalized zero-forcing linear equalizers/combiners is described.
Abstract: We describe the ability of a linear equalizer/combiner or decision-feedback equalizer to suppress all received adjacent-channel, intersymbol, and cochannel interference. The emphasis is on values among transmitter bandwidth, receiver bandwidth, carrier spacing, and antenna diversity which provide the best opportunities for interference suppression. Through analyses of the number of degrees of freedom and constraints in generalized zero-forcing equalizers, and partial comparisons to calculations of equalizer minimum-mean-square performance, four results are obtained. First, with one antenna and a linear equalizer, arbitrarily large receiver bandwidths allow for marginal improvements in spectral efficiency through decreased carrier spacing, because the carrier spacing cannot be reduced to a value below the symbol rate without incurring unsuppressible interference. Second, large receiver bandwidths assist multiple antennas in improving the spectral efficiency in that carrier spacing values may go below the symbol rate, even in the presence of cochannel interference. Third, the use of equalizers and linear combiners, together with large receiver bandwidths, allows large transmitter bandwidths to be used. Fourth, for cochannel interference and intersymbol interference, the number of interferers that may be suppressible by a generalized zero-forcing linear equalizer/combiner increases linearly with the product of the number of antennas and the truncated integer ratio of the total bandwidth to the symbol rate. >

Patent
01 Dec 1994
TL;DR: In this article, an apparatus and method is provided for modulating and transmitting full-motion, television-quality color video signals along with digital data signals over a pair of ordinary unshielded twisted pair telephone wires without interfering with normal telephone data on the wires.
Abstract: An apparatus and method is provided for modulating and transmitting full-motion, television-quality color video signals along with digital data signals over a pair of ordinary unshielded twisted pair telephone wires without interfering with normal telephone data on the wires. The invention is characterized by a transmission method involving frequency modulation of a baseband video signal and subsequent filtering to suppress an upper sideband corresponding to a color component of the original video signal. The filtered signal is received from the telephone wires at a different location, filtered, demodulated and provided to a display device. Full-duplex operation over the same pair of wires is possible, such that two video signals may be simultaneously transmitted, each signal having an approximate bandwidth of 6 MHz and shifted to a desirable non-interfering frequency location within the approximately 20 MHz of usable bandwidth on the telephone wires. No pre-emphasis or de-emphasis is required to achieve good quality video transmission. The system has many applications including video distribution, conferencing, and communications.

Patent
25 Feb 1994
TL;DR: In this article, it is proposed to minimize the number of signal lines and maximize the bandwidth of the signal lines interfacing to the DRAM in order to take advantage of the high performance of the signals in the interface.
Abstract: As interfaces to DRAMs become more advanced and higher performance, the interfaces and signal lines required to support the interface become more expensive to implement. Therefore, it is desirable to minimize the number of signal lines and maximize the bandwidth of the signal lines interfacing to the DRAM in order to take advantage of the high performance of the signal lines in the interface. In the DRAM memory system of the present invention, the address and control lines and are combined and the information multiplexed such that the DRAM pins have roughly equal information rate at all times.

Patent
17 Oct 1994
TL;DR: In this article, a digital radio transceiver uses a differential 4-ary frequency shift keying (D4FSK) modulation scheme to achieve a radio that is low cost, miniaturizable, low in power consumption and high in spectral efficiency.
Abstract: A digital radio transceiver uses a differential 4-ary frequency shift keying (D4FSK) modulation scheme to achieve a radio that is low cost, miniaturizable, low in power consumption and high in spectral efficiency. An adaptive digital 'slicer' (31) looks at a digitized FM video signal produced in the receiver to determine if the data sent is a 00, 01, 10 or 11. The digitized FM video signal is first processed by a differential decoder (31), the output of which is input to a peak detector. The peak detector outputs a signal upon the occurrence of a three-step transition. Two and three step transitions are separately detected and used to perform digital clock recovery. A carrier detect circuit uses a digital bit filter to produce a carrier detect signal (CD) that is reliable and glitch-free. The digital radio transceiver uses frequency hopping spread spectrum transmission (23). A switchable loop bandwidth frequency synthesizer provides for glitch-free switching between a wide hopping bandwidth and a narrow bandwidth between hops.

Patent
Jerry Dagher1
01 Jun 1994
TL;DR: In this article, the transmission lines are arranged in a symmetrical configuration so that their propagation characteristics permit frequency independent modes of propagation of a plurality of signals to be transmitted thereon.
Abstract: A system and method for decreasing the amount of bandwidth required to transmit a high bandwidth signal over electrically conducting transmission lines, wherein the transmission lines are arranged in a symmetrical configuration so that their propagation characteristics permit frequency independent modes of propagation of a plurality of signals to be transmitted thereon. This permits decomposing a high bandwidth signal into lower bandwidth signals, and then encoding these lower bandwidth signals in association with the frequency independent modes of propagation, driving the individual electrically conducting transmission lines with these encoded signals, and then decoding and recombining the signals at the receiving end to recapture the high bandwidth signal.

Journal ArticleDOI
TL;DR: In this article, a combination tutorial and research paper on the propagation aspects of transmission at infrared (IR) frequencies for wireless in-building communications are explored, where basic principles of propagation at IR, a comparison with indoor radio propagation, and derivation of the channel's baseband model are explored.
Abstract: In a combination tutorial and research paper, propagation aspects of transmission at infrared (IR) frequencies for wireless in-building communications are explored. The tutorial section of the paper presents basic principles of propagation at IR, a comparison with indoor radio propagation, and the derivation of the channel's baseband model. The research aspect of the paper reports on the results of recent frequency response measurements at eight different sites in a university building. A major result shows that the indoor wireless optical channel is very dynamic, with great variations in the channel's characteristics for data collected in different rooms, in different locations within the same room, and for different orientations of the optical receiver at the same location of the same room. Numerical values of the channel's relative path loss and 3 dB bandwidth, along with frequency response plots covering a wide range of conditions, are presented and discussed. Finally, on the basis of the results of measurements, schemes for improving the performance of future wireless in-building optical transceivers are proposed. >

Journal ArticleDOI
TL;DR: A design for an amplifier for bioelectric events is presented that has fewer parts, with reduced dimensions and with a lower power consumption, that allows the construction of amplifiers of a high quality in terms of noise and common mode rejection.
Abstract: A design for an amplifier for bioelectric events is presented that has fewer parts than conventional designs. The design allows the construction of amplifiers of a high quality in terms of noise and common mode rejection, with reduced dimensions and with a lower power consumption. Gain, bandwidth and number of channels are easily adapted to a wide range of biomedical applications. An application example is given in the form of a multichannel EEG amplifier (gain is 20000), in which each channel consists of three operational amplifiers (one single and one dual), six resistors and two capacitors. The equivalent input noise voltage and current are 0.15 μVrms and 1 pArms, respectively, in a bandwidth of 0.2–40 Hz, and a common mode rejection ratio of 136 dB is achieved without trimming.

Journal ArticleDOI
TL;DR: In this article, the authors describe and characterize a narrow bandwidth volume holographic optical filter operating at the Krypton transition line at 1547.82 nm, which corresponds to the center wavelength of the proposed International Telecommunications Union wavelength standard.
Abstract: We describe and characterize a narrow bandwidth volume holographic optical filter operating at the Krypton transition line (1s2‐2p8) at 1547.82 nm, which corresponds to the center wavelength of the proposed International Telecommunications Union wavelength standard. A reflectivity of 98% and a bandwidth full width at half‐maximum of 0.18 nm are measured. The filter exhibits clean sideholes with a −20 dB optical response 0.5 nm away from the peak. The filter can be fabricated and operated with an absolute wavelength precision better than 0.005 nm.

Patent
16 Jun 1994
TL;DR: In this article, a code-division multiple access spread-spectrum communication system using pairs of spreading codes with rates of N/2 chips per data symbol to provide a capacity equivalent to that obtained in a conventional system with N chips per symbol.
Abstract: A code-division multiple-access spread-spectrum communication system uses pairs of spreading codes with rates of N/2 chips per data symbol to provide a capacity equivalent to that obtained in a conventional system with N chips per symbol. In the transmitter, identical input data are spread in parallel by both spreading codes, then used to modulate two orthogonal carrier signals, and the resulting radio-frequency signals are combined for transmission from an antenna. In the receiver, the received signal is demodulated by parallel multiplication with the two carrier signals, the resulting baseband signals are correlated with the two spreading codes, and the results are added.

Journal ArticleDOI
TL;DR: Simulation results indicate superior vibration attenuation compared to the minimum-energy forcing function, especially when some error in natural frequency exists.
Abstract: Forcing functions are developed to produce vibration-free motions in flexible systems. These forcing functions are constructed from ramped sinusoid basis functions so as to minimize excitation in a range of frequencies surrounding the system natural frequency. Frequency domain attributes of a particular ramped sinusoid forcing function are compared with corresponding attributes of a minimum-energy optimal input and an impulse-filtered ramp signal. A closed-loop control system is developed that utilizes each of these forcing functions to generate a reference profile, and also feeds the particular forcing function forward directly to the system to enhance closed-loop bandwidth. The use of a direct feedforward signal in the closed-loop implementation results in significantly faster response times when the closed-loop bandwidth is otherwise constrained to be very low. Simulation results indicate that residual vibration has been nearly eliminated for all three forcing functions, even when some error in natural frequency exists. However, the ramped sinusoid input provides the most control over spectral energy near resonance and uses the least amount of energy to achieve vibration-free motions. >

Journal ArticleDOI
01 Jun 1994
TL;DR: In this article, a new radiating element is presented, which can provide simultaneously a large bandwidth and high gain, and it consists of four identical patches uniformly displayed within a rectangular aperture and fed electromagnetically by a driven patch etched on a lower substrate.
Abstract: A new radiating element is presented, which can provide simultaneously a large bandwidth and high gain. It consists of four identical patches uniformly displayed within a rectangular aperture (2*2) and fed electromagnetically by a driven patch etched on a lower substrate. It is shown that a good coupling with the parasitic patches is obtained, causing a large bandwidth, and the resonance modes of each patch are excited in phase, giving a high gain.

Patent
13 Jan 1994
TL;DR: In this paper, a waveform generator at the transmitter generates a phase-aligned multichannel frequency diversity waveform according to a data clock at a predetermined phase relationship to the digital data.
Abstract: A satellite communications system for dispersing energy over a wide bandwidth includes a transmitter, a communication link, and a receiver. The transmitter takes a digital data signal and modulates that signal at a prescribed carrier frequency. The modulated digital data signal is then spread over M adjacent digital channels (M≧2 and being an integer multiple of 2), each channel containing the same information, to disperse the energy over a wide frequency range. The spectral bandwidth of the adjacent digital channels is chosen with compressed spacing to conserve bandwidth. Next, the spread modulated data signal is transmitted via the communication link to the receiver. In particular, a waveform generator at the transmitter generates a phase-aligned multichannel frequency diversity waveform according to a data clock at a predetermined phase relationship to the digital data. At the receiver, the spread modulated data signal received is mixed with a despreading waveform generated in a similar manner to the waveform spectrum generated at the transmitter to recover the modulated data signal. The despreading waveform is generated according to a symbol clock signal recovered from the received modulated data signal. A demodulator recovers the original digital data from the modulated data signal. To achieve higher spreading factors, multichannel frequency diversity may be utilized with known spread spectrum techniques to achieve high data recovery rates during adverse weather (fading) conditions at high radio frequencies in the microwave and higher regions of the radio spectrum.

Journal ArticleDOI
TL;DR: A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed and it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid; however, for the noncoherent modulation formats, a hybrids can have a greater capacity if a high channel error rate can be tolerated.
Abstract: A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signalling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal. >

Proceedings Article
01 Jan 1994
TL;DR: In this paper, a tunable active inductor is presented where the novel topology enables both the inductance and series resistance to be varied, and the measured performance for a monolithic 2 GHz filter achieves a mean insertion loss of 0.9 dB, passband ripple of ± 0.7 dB, with a 3 dB bandwidth of 70 MHz, and an excellent out-of-band rejection which exceeds 50 dB up to 18 GHz.
Abstract: A tunable active inductor is presented where the novel topology enables both the inductance and series resistance to be varied. With a discrete MMIC realization of this active inductor, Q-factors in excess of 15 000 have been measured over a wide range of inductance values. Applications for these active inductors include high-performance narrow-band filters, voltage controlled oscillators, and analog phase shifters. Analytical equations for the novel active inductor and a 3-resonator filter are given. The measured performance for a monolithic 2 GHz filter achieves a mean insertion loss of 0.9 dB, passband ripple of ±0.7 dB, with a 3 dB bandwidth of 70 MHz, and an excellent out-of-band rejection which exceeds 50 dB up to 18 GHz

PatentDOI
TL;DR: In this article, the peak-level increase (PLI) caused by signal processing such as perceptual coding is considered. But the peak amplitude of the signal reproduced by the perceptual decoder may sometimes exceed the capabilities of the broadcast transmitter, even though the signal amplitude of input to the perceptual encoder is properly limited.
Abstract: The invention relates to limiting the peak amplitude of an audio signal in one or more frequency subbands while preserving the apparent loudness. Applications such as a Studio-Transmitter Link (STL) for broadcasting sometimes use perceptual coding to deliver an audio signal originating from a studio to a broadcast transmitter. The peak amplitude of the audio signal will have been limited by means of a limiter or otherwise, and a perceptual encoder reduces the informational capacity requirements of the audio signal for transmission across a link to a broadcast transmitter. A perceptual decoder receives the coded signal from the link and reproduces the audio signal for the broadcast transmitter. The peak-amplitude of the signal reproduced by the perceptual decoder may sometimes exceed the capabilities of the broadcast transmitter even though the peak amplitude of the audio signal input to the perceptual encoder is properly limited. This increase in peak level is referred to as "peak-level increase" or PLI. Transmitter overload resulting from PLI can create audible distortion and/or impermissible broadcast conditions such as excessive FM deviation. Various embodiments of apparatus and method are described which estimate PLI caused by signal processing such as perceptual coding and which apply corrective gain to the portions of the audio signal bandwidth so as to limit peak amplitude while preserving apparent loudness.