Showing papers on "Bandwidth (signal processing) published in 1989"

An impedance-matching technique for increasing the bandwidth of microstrip antennas

Abstract: The nature of the inherent narrow bandwidth of conventional microstrip patch antennas is considered. It is observed that, except for single-feed circularly polarized elements, their bandwidth is limited only by the resonant behavior of the input impedance and not by radiation pattern or gain variations, which usually are negligible over a moderate 10 to 20% bandwidth. Therefore, broadband impedance matching is proposed as a natural to increase the bandwidth. The maximum obtainable bandwidth is calculated using Fano's broadband matching theory. It is found that by using an optimally designed impedance-matching network, the bandwidth can be increased by a factor of at least 3.9, the exact value depending on the degree of matching required. A transmission-line prototype for a proper matching network is developed. The translation of this prototype network into a practical structure (e.g. a microstrip or stripline circuit) is considered. Practical design examples and experimental results which clearly show the validity of the technique are given. >

MPPM: a method for improving the band-utilization efficiency in optical PPM

Abstract: Multiple pulse position modulation (MPPM) is proposed as a modulation method to improve the band-utilization efficiency in optical pulse position modulation (PPM). Optical PPM gives higher transmission efficiency (bit/photon) in optical communications but degrades band-utilization efficiency. The proposed method reduces the required transmission bandwidth in optical PPM to about half with the same transmission efficiency, thus increasing band-utilization efficiency. While in conventional optical PPM, only one optical pulse is transmitted in every signal block, multiple pulses are transmitted using this method. Information is represented by different combinations of the positions of these pulses. The principle of bandwidth reduction applied, the transmission characteristics of the proposed method, and examples of improvement in band-utilization efficiency are also shown. >

Industrial robot with servo

Abstract: A digitally controlled industrial robot comprises a set of unitized and integrated joint drive modules which can be assembled in series to form an arm. The joints are of two basic types, pitch joints and roll joints, with the roll joints providing rotation about the longitudinal axis of the manipulator and the pitch joints providing rotation about axes which are substantially perpendicular to and offset from the roll joint axes. Any number of joints may be assembled to comprise the manipulator, permitting the configuration of a kinematically redundant manipulator. A servocontrol derives feedback from sensing the motive force on a driven member and compensates the drive signal accordingly. More particularly, the torque exerted on each roll and pitch joint is measured and used for feedback to provide stability and optimum bandwidth for the servomechanism.

Three dynamic problems in robot force control

Abstract: Three dynamic problems which arise in robot systems are discussed: rigid-body bandwidth; dynamically noncolocated flexible modes; and dynamically colocated flexible modes. These effects combine to set the closed-loop bandwidth achievable in the individual joint control loops. Simple models of robot systems are presented to illustrate these three dynamic effects. Some laboratory data are then presented and analyzed in these terms. Finally, the implications for robot system design is discussed in the hope that these issues will be considered in the development of the next generation of robot systems and machine tools. >

Design principles of sequentially fed, wide bandwidth, circularly polarised microstrip antennas

Abstract: The technique of sequentially rotating the feed position of a microstrip patch antenna to improve the circular polarisation bandwidth of an array of such elements is briefly reviewed in the wider context of other known antenna parameter staggering concepts. A first order analysis then shows how the sequential technique significantly improves the axial ratio bandwidth in the relation to the number of patches in the array and the feeder connections. Unwanted effects such as feeder phase errors, multiple reflections in feeders, the presence of higher order modes and mutual coupling are then considered. Computations embracing these effects and measurements illustrate the various properties and topological options available. Finally, the application of the technique is briefly illustrated for a single patch and an array of patches. In conclusion the design principles are summarised and feeder effects are identified as the main limitation when implementing the sequential technique.< >

Blind separation and capture of communication signals using a multitarget constant modulus beamformer

Abstract: A multitarget least-squares CMA (constant modulus algorithm) that blindly adapts a narrowband beamformer to separate and capture multiple communication signals by exploiting only the low modulus variation of the communication waveforms is presented. It is shown that the algorithm can detect and classify transient and nontransient communication signals on the basis of modulus variation and extract those signals with maximum attainable output SINR (signal-to-interference and -noise ratio) in environments containing strong transient or nontransient cochannel interference. This is demonstrated via computer simulation for a narrowband (25 kHz bandwidth) four-element antenna array in environments containing FSK (frequency shift keying) bursts received at low ( approximately 4 dB signal-to-white-noise ratio) power levels in the presence of severe ( approximately -50-dB signal-to-interference ratio) interference. It is shown that the algorithm can capture the FSK bursts in less than 2 ms, and maintain capture on the signals as other signals appear and disappear over the signal ON times. >

Chattering reduction in the position control of induction motor using the sliding mode

Abstract: The induction motor position control system based on the sliding mode control is presented In the sliding mode control, control function is discontinuous on the hyper-plane, which causes harmful effects such as current harmonics and acoustic noise in the motor drive application. In this study, a low pass filter is introduced between the sliding mode controller output and the motor controller input to reduce these effects. The filter, however, makes the torque response be sluggish and the system performance may become poor in cost of chattering reduction. To overcome these problems, the bandwidth of the filter is varied according to the error function. It is shown that the proposed sliding mode control with variable-bandwidth filter shows good performance, which is confirmed through the computer simulation and experiments.

Selected-exponent signature systems

Abstract: Digital signature techniques are disclosed in which exponents may be selected by the message to be signed itself, by the signing party, by the party providing the message to the signing party for signature, and/or by a party to whom the signature is shown. When a message selects the exponent(s), the need for "hash functions" in known signature schemes is overcome. When the exponent is chosen by the party receiving the signature, to take another example, computation, storage and bandwidth requirements of known one-show blind signature systems may be improved. Also, the bank cannot falsely incriminate a payer for showing a signature more than once, even if the bank has unlimited computing resources.

An all digital receiver architecture for bandwidth efficient transmission at high data rates

Abstract: Using the maximum-likelihood approach, algorithms for detection and synchronization are derived that are well suited for VLSI implementation. Special emphasis is placed on an all-digital implementation where carrier and clock synchronization do not require a feedback of signals to the analog part, which simplifies the analog front-end design (mixing oscillator and A/D converter sampling clock run at fixed frequency). An important advantage of the proposed algorithms is that a high clock rate is not required; only two-four times the symbol rate is needed, depending on amplitude quantization. Implementation aspects, e.g. architecture, and quantization, are considered. A prototype is described which was implemented to prove the feasibility of the concept and to evaluate the performance under practical conditions. >

Perceptual transform coding of wideband stereo signals

Abstract: The author reports on the extension of the entropy-coded perceptual transform coder (ECPTC) to stereo signals. The stereo ECPTC exploits both the redundancy in the stereo signal and the effects of acoustic mixing in the listening environment in order to encode the stereo signal at a bit rate much less than twice that for a monophonic signal. This coder uses the perceptual threshold developed by the author (IEEE J. Selected Areas in Commun. vol.6, no.2, p.314-23, Feb. 1988) along with a noiseless compression scheme to provide a bit-rate reduction of approximately one third compared to that for two independent monophonic channels. Typical rates available from the coder are 64 kb/s for a 6.6-kHz bandwidth, 14-kHz sampling rate transparent monophonic channel, 128 kb/s for a 15-kHz bandwidth, 32-kHz sampling rate stereo channel with FM or better quality, and 192 kb/s for a 20-kHz bandwidth, 44.1-kHz sampling rate stereo channel with perceived quality equal to that of the original signal. The 64-kb/s, 128-kb/s, and 192-kb/s rates correspond to ISDN (integrated services digital network) 1B, 2B, and 3B rates respectively, suggesting applications within the ISDN framework. >

Adaptive carrier recovery systems for digital data communications receivers

Abstract: Adaptive or predictive carrier recovery systems, which are essential in high-performance quadrature-amplitude-modulated (QAM) data communications systems to correct for phase jitter and frequency offset, are considered. Analytical and experimental results are presented for two structures that implement a predictive carrier recovery system. These systems, which adapt their structure to match the spectral properties of the impairments, avoid the conflict between a wide bandwidth (to track fast jitter) and a narrow bandwidth (to minimize output noise) inherent in most carrier recovery loops. Such a system increases the likelihood that very bandwidth-efficient modems (e.g., 7 b/s/Hz for 19.2 kb/s voiceband modem applications) can provide reliable transmission in the presence of severe phase jitter and frequency offset. In particular, the predictive carrier recovery systems can track sinusoidal jitter present at more than one frequency as well as generalized time-varying phase jitter processes. Both finite-impulse-response (FIR) and infinite-impulse-response (IIR) adaptive phase tracking systems are considered. Prior limitations on adaptive IIR filters are overcome by designing a structure that is guaranteed to be stable and to possess only a global minimum as the filter coefficients converge to their desired values. >

Frequency limitations on broad-band performance of shunt slot arrays

Abstract: Two methods are presented for the analysis of slot array performance as a function of frequency, taking mutual coupling into account. The first is a direct method, the other an iterative one. These are applied to a seven-slot resonant array and to a 21-slot traveling wave array. This analysis permits prediction of the bandwidth and provides comprehension of broadband limitations. The two examples presented show good agreement between theory and measurement. >

Wide bandwidth frequency doubler

Abstract: A single-transistor frequency doubler uses an elliptical filter on the collector of the transistor to improve the bandwidth of the doubler Bandwidths in excess of thirty five percent having relatively constant output power levels at frequencies over 200 MHz can be realized

Local Bandwidth Selection for Kernel Estimates

Abstract: A kernel estimate of a curve that uses an adaptive procedure for local selection of the bandwidth is considered here. A two-step procedure is proposed for estimating the local bandwidth that minimizes the mean squared error (MSE) of a kernel estimator for nonparametric regression. First, a consistent estimate of the exact MSE is constructed. Then the bandwidth that minimizes the estimate of the MSE is calculated. Sufficient conditions under which this bandwidth is asymptotically optimal and normally distributed are given. The local bandwidth selection procedure was implemented on some simulated data and compared to a global bandwidth selection procedure proposed by Rice (1984b). A 68%–91% reduction in the average MSE of a kernel estimator was realized with the local bandwidth selection procedure. Such a scheme was also studied by Muller (1985) and termed a direct pilot estimator approach. Muller derived sufficient conditions similar to those presented here, under which the direct pilot estimator ...

A new method of spectral analysis and its application to the Earth's free oscillations: The “Sompi” method

Abstract: A new and powerful method of spectral analysis, which is named the “Sompi” method after a Japanese word, is introduced and applied to low-frequency seismograms. The Sompi method is based on an autoregressive (AR) process model, which is different from an ordinary prediction type AR model. In the ordinary AR model the AR coefficients predict the present observation from the past observations so that they are determined by minimizing the prediction error. The model implicitly assumes that the past observations are noise-free and that only the present observation consists of signal and noise. The method thus gives an unbiased estimate of the linear relationship among the past data and the present signal. In our AR model the AR coefficients extract signals from the time series so that they are determined by minimizing the extraction residual. The model assumes that each observation, either past or present, consists of signal and noise. The method thus gives an unbiased estimate of the linear relationship among the successive signals. Those who wish to make an unbiased spectral estimation for the signal must therefore minimize the extraction residual, rather than the prediction error. Minimization of the extraction residual leads to an eigenvalue problem of a non-Toeplitz matrix of autocovariance. The minimum eigenvalue yields the extraction residual which is an estimate of the noise power. The corresponding eigenvector constitutes the AR coefficients whose characteristic equation gives the complex frequencies (frequencies and decay or growth rates) of the signals extracted. The complex amplitudes (amplitudes and phases) are then determined through a least squares procedure. The Sompi method thus first retrieves medium-sensitive parameters, frequencies, and Q and then excitation-sensitive parameters, amplitudes, and phases. From the practical point of view it is not feasible to apply the Sompi method directly to such data as the Earth's free oscillations in which spectral peaks are densely and nonuniformly distributed over the entire frequency domain. We propose an algorithm of aliased sampling which enables us to apply the Sompi method to such data. In this algorithm the time series is first narrowly and sharply band-pass filtered. The resultant time series is then decimated at a rate corresponding to the bandwidth of the filter. The contributions of all the decimated time series, which may mutually lag in time, are stacked into the matrix elements of autocovariance for the eigenvalue problem. The Sompi method with this algorithm is tested against a synthetic seismogram to see the resolvability of the two modes closely spaced in frequency. The Sompi method is next applied to the seismograms of the 1977 Sumbawa Island earthquake recorded in the International Deployment of Accelerometers network. First, the two radial modes 0S0 and 1S0 are analyzed to examine the uniformity of their spectral parameters among different stations. Second, the fundamental multiplets 0Sl (l = 5–43) are analyzed to see how their initial amplitudes and phases oscillate with respect to l at one station. Third, the gravest mode 0S2 is analyzed in an attempt to resolve the five singlets with their Q values. Fourth, the analysis is made for the coupled multiplets 0Sl-0Tl+1 (l = 10–12) to observe their mutual repulsion in frequency and their mutual attraction in decay rate. Fifth, the core mode 7S3, a mode with most of its energy confined to the inner core, is detected. All five experiments demonstrate remarkable accuracy and resolvability of the Sompi method.

Some implications of TCM for optical direct-detection channels

Abstract: Consideration is given to the optical direct-detection channel, and it is shown how simple trellis-coded modulation (TCM) can be used to improve performance or increase throughput (in bits per second) without bandwidth expansion or performance loss. In fact, a modest performance gain can be achieved. Although the approach can be used with other signal constellations, the authors concentrate on signals derived from the pulse-position modulation (PPM) format by allowing overlap. Theoretical motivation for using this signal set, known as overlapping PPM (OPPM), was recently given by I. Bar David and G. Kaplan (1984), who showed a capacity gain when overlap is introduced. >

9 GHz bandwidth, 8-20 dB controllable-gain monolithic amplifier using AlGaAs/GaAs HBT technology

Abstract: A wideband and controllable-gain amplifier utilising a new parallel feedback technique, which can enhance the bandwidth and can control the gain keeping output DC voltages constant, has been developed using AlGaAs/GaAs HBT technology in monolithic form. This IC achieves a wide bandwidth of DC-9 GHz, and a controllable gain range of 8–20 dB with a total power dissipation of 640 mW at a power supply voltage of 9 V.

Communication of a voice signal via continuous quadrature amplitude modulator

Abstract: A method and apparatus for communicating a voice conversation over a single telephone channel using continuously variable level quadrature amplitude modulation establishes and maintains two totally independent communication paths, each near perfect in amplitude and phase with respect to frequency over a bandwidth suitable for communication of continuously variable amplitude pulses. These pulses may be representations of any suitable bandlimited analog signal. The method establishes almost flawless QAM channels (real, imaginary), then allows switching to continuously variable amplitude analog transmissions.

Tuned front-end design for heterodyne optical receivers

Abstract: A theoretical analysis of the noise performance of optical receivers with front-end tuning, suitable for wideband coherent systems, is presented. An algorithm for choosing the values of the tuning components in the front end so as to minimize the thermal noise output power has been developed. This theory is applied to the well-known simple parallel and serial tuning configurations and also to three more advanced designs. It is shown that any tuning is better than none in the wide-bandwidth designs considered and that the more advanced designs yield up to 12-dB reduction in thermal noise power. Two of the designs can be implemented with discrete components and should yield shot-noise-limited detection with 50-100 mu W of local oscillator power in receivers with 5-GHz bandwidth. The practical problem of equalizing the front-end response is considered, and it is shown that good performance can be expected using realizable components. >

Two-stage integrated-optic acoustically tunable optical filter with enhanced sidelobe suppression

Abstract: Demonstrates a two-stage integrated-optic acoustically tunable infra-red optical filter with subnanometre bandwidth and -19 dB sidelobe suppression. This configuration also eliminates the optical frequency shift of one-stage devices.

An efficient modulation/coding scheme for MFSK systems on bandwidth constrained channels

Abstract: The performance of a bandwidth-efficient multiple-tone modulation scheme for M-ary frequency-shift keying (MFSK) is presented. The use of balanced incomplete block (BIB) designs is proposed to form the signaling frames. On each symbol interval the modulator selects a group of elements from a BIB design and divides its energy into the orthogonal waveforms corresponding to these elements. The multiple-tone FSK scheme based on these block designs is shown to increase greatly the bandwidth efficiency of a conventional M-ary FSK system. An implicit diversity is incorporated in the modulation scheme. Thus, a performance improvement comparable to that obtained by using time or frequency diversity is shown on a Rayleigh fading channel and also on an interference channel with partial-band Gaussian noise. The multiple-tone scheme based on this design is compared to a multiple-tone scheme based on Hadamard matrices suggested by J.F. Pieper et al. (1978). It is shown that similar performance is achieved on a fading channel, while an advantage close to 4 dB is obtained for the proposed scheme on an AWGN (additive white Gaussian noise) channel. >

Creating complex signal samples from a band-limited real signal

Abstract: A very efficient method of creating complex signal samples from a band-limited real signal is presented. Because the method employs a simple mixer followed by one analog-to-digital (A/D) converter, plus a finite-duration impulse response (FIR) filter for image band rejection, there is no phase distortion in the resulting sampled signal. The method is more efficient than competing methods based on infinite-duration impulse response (IIR) filters. >

Fast locking phase-locked loop utilizing frequency estimation

Abstract: A phase-locked loop compares the loop output clock (12) with the loop input clock in a digital phase detector (10) to provide lead/lag error signal samples (14). A microprocessor (15) utilizes the lead/lag error samples to track the input clock in a wideband mode (23) matching the bandwidth of the input and in a very narrow band mode (24). When the system in which the loop is utilized switches to a new input clock source, the microprocessor resets the loop devider chain (13) so that the loop feedback signal is phase coincident with the input reference. The microprocessor tracks the new clock for a predetermined number of error samples in the wideband mode and statistically estimates, from the samples, the frequency of the input. After the frequency estimation (25), the microprocessor controls the loop VCO (32) to output the computed frequency and switches to the narrow band tracking mode.

Mechanical bandwidth as a guideline to high-performance manipulator design

Abstract: The mechanical bandwidth of a manipulator ultimately limits its closed-loop bandwidth and so its response in both trajectory and force control. Here, mechanical design strategies are introduced to improve performance, including placing a distinct speed reducer at the joint rather than at the motor shaft, limiting the transmission ratio and properly selecting the contact compliance. The authors define simple models of the transmission for position-in-position-out and force-out and examine the corresponding transfer functions. The bandwidth of each of the simple models (which neglect damping) is approximately equal to the frequency of the first break point in the magnitude of the frequency response which, in turn, is equal to its lowest resonant frequency. The aim is for the open-loop bandwidth to be as high as possible to increase the quickness of the manipulator's response to commands. >

Theory of regenerative frequency dividers using double-balanced mixers

Abstract: Regenerative frequency halvers using double-balanced mixers are analyzed in terms of modified Bessel functions. Particular attention is given to a regenerative divide using a zero-memory double-balanced Schottky diode mixer. Closed-form solutions predict the threshold of turn on, the steady-state input-output amplitude relationship, and the operational bandwidth. Experimental results are also presented. >

A high-resolution CMOS sigma-delta A/D converter with 320 kHz output rate

Abstract: A third-order switched-capacitor sigma-delta A/D converter is presented. The converter consists of three cascaded first-order sigma-delta modulators, and achieves 88 dB pk/rms S/(N+D) in a 160-kHz passband with a 10.24-MHz sampling rate. The high signal-to-noise ratio is maintained over this wide bandwidth by attenuating the quantization noise with a third-order noise-shaping function and a fourth-order comb decimation filter. A special autozeroed integrator with low pole error is required to achieve the 10.24-MHz sampling rate and high-order noise shaping simultaneously. >

Tunable multiple-quantum-well distributed-Bragg-reflector lasers as tunable narrowband receivers

Abstract: We report a tunable receiver based on a MQW-DBR laser biased just below threshold. The device simultaneously integrates the functions of a tunable filter, optical amplifier, photodetectorand, if desired, an FSK discriminator. Using identical devices for both a transmitter and a receiver, we demonstrate FSK transmission up to 250 Mbit/s with sensitivities in the ˜- 30dBm range for 10−9 BER. Speed is limited by the transmitter FM response, and independentspeed measurements indicate a detection bandwidth of at least 1.7 GHz.

The coded orthogonal frequency division multiplexing (COFDM) technique, and its application to digital radio broadcasting towards mobile receivers

Abstract: A system which is able to broadcast at high data rates in a selective Rayleigh channel is presented. This technique combines an orthogonal frequency division multiplexing technique and a convolutional coding scheme associated with a Viterbi decoding algorithm. This system is able to benefit from wideband transmission by employing the information contained in all the echoes of the multipath channel while having a very good spectral efficiency and a low computational complexity. The authors present the theoretical principles of the system. They describe the realization of a complete COFDM (coded orthogonal frequency division multiplexing) system, designed within the framework of the DAB (digital audio broadcasting) EUREKA 147 project, which is able to broadcast at 5.6 Mb/s in a bandwidth of 7 MHz. At present, this rate corresponds to 16 high-quality stereophonic programs. Network aspects are pointed out as far as the introduction of a new radio broadcasting service is concerned. >