Showing papers on "Bandwidth (signal processing) published in 1985"

Gain enhancement methods for printed circuit antennas

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

A minimal parameter adaptive notch filter with constrained poles and zeros

Abstract: A new algorithm is presented for adaptive notch filtering and parametric spectral estimation of multiple narrow-band or sine wave signals in an additive broad-band process. The algorithm is of recursive prediction error (RPE) form and uses a special constrained model of infinite impulse response (IIR) with a minimal number of parameters. The convergent filter is characterized by highly narrow bandwidth and uniform notches of desired shape. For sufficiently large data sets, the variances of the sine wave frequency estimates are of the same order of magnitude as the Cramer-Rao bound. Results from simulations illustrate the performance of the algorithm under a wide range of conditions.

Worst case analysis in the frequency domain: The H ∞ approach to control

Abstract: This paper describes an approach to frequency domain design using Hxmethods. We outline the main tools available and describe how these methods can be applied to control problems and to some gain optimization problems in circuits. In particular, we present a new method for combining several competing constraints which arise in control (such as tracking error and bandwidth constraints) into a single type of constraint which H^{\infty} methods analyze explicitly. A computer program which implements and teaches this method is on tape for a VAX. It is available on request.

The Amount of Noise Inherent in Bandwidth Selection for a Kernel Density Estimator.

Abstract: : Any practical method of constructing a bandwidth must depend only on a statistical sample, and should produce some sort of estimate of this bandwidth. The purpose of this paper is to show that there a well-defined limits to the accuracy of all data-driven bandwidth estimates. Put another way, there is an unbridgeable gap between the minimum integrated square error attained using a optimal bandwidth and the minimum achievable integrated square error using a data-driven bandwidth estimate. Additional keywords: stochastic processes; cross validation; and random variables.

The tone capture properties of CMA-based interference suppressors

Abstract: An earlier paper introduced the constant modulus algorithm (CMA), an adaptive filtering technique for correcting multipath and interference-induced degradations in constant envelope waveforms such as FM and QPSK signals This algorithm exploits the fact that both multipath propagation and additive interference disrupt the constant envelope property of the received signal By sensing the received envelope variations, the adaptive algorithm can reset the coefficients of an FIR digital filter so as to remove the variations and, in the process, suppress the various interference components from the desired signal This paper examines a problem that arises when using CMA to suppress narrow-band interference If both the interferer and the signal have constant envelope and are spectrally nonoverlapping, then it is possible to find two different filter solutions, one which suppresses the interferer and another which "captures" the interferer and suppresses the desired signal This paper examines how "capture, can occur and how it may be prevented This problem is studied by characterizing the algorithm's behavior to an input consisting of only two sinusoids Assuming slow adaptation, the N-dimensional adaptive weight recursion is shown to compress into a two-by-two recursion in the tone output amplitudes This simplified recursion is then analyzed to determine what combinations of input amplitudes (signal-to-interference ratios) and filter initial conditions lead to "lock" and which lead to the capture of the interferer The results are then broadened to include multiple input tones and signals with nonzero bandwidth

On the statistics of fixed-point roundoff error

Abstract: Roundoff error after fixed-point multiplication is commonly modeled as uniformly distributed white noise that is uncorrelated with the signal. This paper presents a statistical analysis of fixed-point roundoff error that identifies the conditions under which this model is valid, and examines the statistical behavior of roundoff error when these conditions are not satisfied. The results show that if the multiplier coefficient is expressed as a = N/M, where M is a positive integral power of two and N is an odd integer, then the errors generated by roundoff after multiplication can generally be modeled as uniformly distributed, white, and uncorrelated with the signal, if the signal has sufficiently wide bandwidth and has a dynamic range that extends over approximately M quantum steps. For narrow-band low-level signals, the roundoff error statistics can differ significantly from the uniform, white, uncorrelated model. In addition, these results show that statistical behavior of roundoff error can differ significantly from that of the quantization error that is generated when a continuous random variable is quantized.

On the fine-scale intermittency of turbulence

Abstract: This paper presents a simple theory for evaluating the several measures used to characterize the intermittency of fine-scale turbulence, and corroborates the theoretical results from comparison with experimental data, some of which are new. The basic analytical tool is the envelope of the narrow-bandpass-filtered turbulent signal, defined via its Hilbert transform and the analytic signal. The contribution of this paper is twofold. First, it correctly identifies the roles played by the filter characteristics (such as the bandwidth) in determining the intermittency factor, the width of the active regions (pulses) in narrow-bandpass-filtered turbulent signals, and the pulse frequency; it also reveals that all dynamical characteristics of the signal enter indirectly through the peak pulse frequency and the threshold setting. Secondly, the theory suggests that, in the far-dissipation range, the most important feature of signals exhibiting internal intermittency is the stronger-than-algebraic roll-off of the spectral density in that region; it is argued that this feature of turbulence essentially determines the peak pulse frequency in that region. The theory is incomplete in that it does not show how the threshold setting depends on the signal dynamics, but here the discussion is supplemented by experimental data.

8-Gbit/s transmission experiment over 68 km of optical fiber using a Ti:LiNbO 3 external modulator

Abstract: We describe the performance of an experimental 1.5-μm lightwave transmission system operating at 8 Gbit/s over 68.3 km of single-mode fiber. The dispersion penalty is limited to 1 dB through the use of external modulation and is attributable to the intrinsic information bandwidth.

A 6-Bit/200-MHz Full Nyquist A/D Converter

Abstract: This paper deals with the development of an extremely fast 6-bit flash A/D converter. To gain insight into the nature of speed limitations, the effects arising from operation at very high sampling rates have been investigated. This led to the implementation of an optimized double-stage comparator circuit. The chip has been fabricated in a fast standard oxide isolated bipolar process. At a sampling rate of 200 MHz, measurements show excellent dynamic performance (high signal-to-noise ratio, no error codes) up to input frequencies of 100 MHz.

Frequency multiplexed convolver communication system

Abstract: A spread spectrum communication system is described for decoding data from a signal having a carrier frequency and at least one of a plurality of predetermined orthogonal modulations thereon incorporating a frequency synthesizer for generating a plurality of frequencies, a plurality of mixers, a combiner, a broadband convolver, a second combiner coupled to a reference signal generator for generating respective orthogonal modulations on spaced apart carrier frequencies, a power divider coupled to the output of the convolver and filters each having a frequency passband for recovering or separating the output signals of the convolver. The invention overcomes the problem of requiring a plurality of broadband convolvers to decode a plurality of orthogonal modulations of lesser bandwidth.

The synchronous oscillator: a synchronization and tracking network

Abstract: The synchronous oscillator (SO) is a free-running oscillator which oscillates at its natural frequency in the absence of an externally applied signal. In the presence of a signal, the oscillator synchronizes with and tracks the input waveform with an acquisition time inversely proportional to the tracking bandwidth. The SO possesses a constant output signal amplitude in the tracking region and an adaptive tracking bandwidth proportional to the input signal level. The authors present the theory and experimental characterization of SOs in terms of selectivity, noise rejection, carrier-to-noise improvement, tracking range, and acquisition time. A specific application is described for SO carrier and clock recovery networks in 60- and 120-Mb/s QPSK modem with bit-error-rate (BER) performance approaching that of hard-wired connection.

Edge artifacts in MR images: chemical shift effect.

Abstract: The boundaries of some organs as seen in clinical magnetic resonance images appear to be asymmetric. This effect is caused by chemical shift differences between the resonant frequencies of the hydrogen nuclei of water and fat. The zeugmatographic technique maps resonant frequencies to unique spatial locations. These differences in resonant frequencies can appear as artifactual misplacement of information as this one-to-one correspondence is lost. Various phantoms are used to demonstrate that the boundary artifact appears only in the direction of the read (frequency-encoding) gradient when media of two different chemical shifts are separated by an interface. When the relative shift is less than the width of the interface, the boundary appears to be asymmetric; when the relative shift is greater than the width of the interface, a bright band is seen along one edge with a dark band along the other. This artifact is more pronounced in low resolution images than in high resolution images, and these effects are seen even when the relative chemical shift is smaller than a pixel bandwidth. These effects are explained both conceptually and analytically. The clinician should be aware of the potential presence of this artifact at boundary interfaces that bear diagnostic significance.

High-user-density digital cellular mobile radio systems

Abstract: Digital cellular mobile radio systems are described having partially overlapping cells that are based on road configurations, and in which the energy is radiated along the road from approximately street lamp elevations. One proposed system uses propagation frequencies in the vicinity of 900 MHz, employs adaptive differential pulse code modulation at 32 kbit/s and a minimum shift keying modem enabling a channel spacing of 25 kHz. One example of system performance shows that, for clusters of ten cells along a six-lane highway, the signal/interference ratio is 20 dB, the probability of error is 10 -3 , and the channel SNR is 10.8 dB. Given an allocated mobile radio bandwidth of 20 MHz, the system can support 80 users per cell. If the vehicles are travelling at 88 km/h (55 miles/h) and 10% of the drivers make a telephone call, the cell length is 4.8 km (3 miles), and the cochannel distance is 48 km (30 miles). In our deliberations we made comparisons with conventional analogue FM systems, and showed that they have approximately half the user density capacity of the new system. A digital microcellular mobile radio systems employing 60 GHz is also considered. The bit rate per segment of road was found to be vast, e. g. 100 Mbit/s per 100 m of road. This system is capable of providing portable communications to large numbers of pedestrians and drivers in congested city streets. Because of the configuration of the proposed cell structure, shadow fading is conjectured to have very little impact on system performance.

Optical local area network employing microwave modulation techniques

Abstract: The present invention relates to an optical communication system wherein the entire microwave frequency bandwidth of the optical source-to-detector system is subdivided into a plurality of non-overlapping frequency bands or channels, and each user transmits and/or receives information either (a) on a separate fixed one of the channels, (b) on a free channel selectively assigned via control signals transmitted on a separate control channel at the time of initiation of a communication, or (c) on a channel randomly selected at the receiver by an associated user to receive a particular program. The present optical communication system can be configured to simultaneously broadcast multiple programs over separate channels for random selection by each user, or to achieve local and/or external two-way communications with the associated system users.

Mutual interaction between solitons of unequal amplitudes in optical fibre

Abstract: An exact solution to the mutual interaction of two solitons propagating in a nonlinear single-mode fibre is given. From this, it is shown that the soliton separation can be effectively maintained by allowing the solitons to have unequal amplitudes. This provides a simple way to maintain the high bandwidth of a nonlinear fibre.

Reduction of finite-gain effect in switched-capacitor filters

Abstract: A simple technique for significantly reducing the effect of the finite gain of amplifiers on the performance of switched-capacitor filters is presented. The effectiveness of this technique has been established by extensive simulation studies. This technique has the potential for simplifying amplifier design and extending the frequency range of switched-capacitor filters by trading gain for bandwidth.

A bandwidth enhancement method for microstrip antennas

Abstract: Bandwidth enhancement methods for electromagnetically coupled microstrip dipoles are discussed. It is demonstrated that if parasitic metallic strips are incorporated in the structure either co-planar and parallel to the embedded microstrip transmission line open end, or between the transmission line and the microstrip dipole, then substantial bandwidth enhancement results. Experimental verification of this model is introduced for a bandwidth definition based on the frequency range which satisfies a voltage standing-wave ratio (VSWR) \bar{E} - and \bar{H} -plane patterns verify the theoretical model which accounts for radiation from the microstrip dipole, the parasitics, and the transmission line.

Detection of temporal gaps in bandlimited noise: Effects of variations in bandwidth and signal‐to‐masker ratio

Abstract: Thresholds were measured for the detection of a temporal gap in a bandlimited noise signal presented in a continuous wideband masker, using an adaptive forced‐choice procedure. In experiment I the ratio of signal spectrum level to masker spectrum level (the SMR) was fixed at 10 dB and gap thresholds were measured as a function of signal bandwidth at three center frequencies: 0.4, 1.0, and 6.5 kHz. Performance improved with increasing bandwidth and increasing center frequency. For a subset of conditions, gap threshold was also measured as bandwidth was varied keeping the upper cutoff frequency of the signal constant. In this case the variation of gap threshold with bandwidth was more gradual, suggesting that subjects detect the gap using primarily the highest frequency region available in the signal. At low center frequencies, however, subjects may have a limited ability to combine information in different frequency regions. In experiment II gap thresholds were measured as a function of SMR for several signal bandwidths at each of three center frequencies: 0.5, 1.0, and 6.5 kHz. Gap thresholds improved with increasing SMR, but the improvement was minimal for SMRs greater than 12–15 dB. The results are used to evaluate the relative importance of factors influencing gap threshold.

Adaptive Tracker Field-of-View Variation Via Multiple Model Filtering

Abstract: Adaptive estimation using multiple model filtering is investigated as a means of changing the field of view as well as the bandwidth of an infrared image tracker when target acceleration can vary over a wide range. The multiple models are created by tuning filters for best performance at differing conditions of exhibited target behavior and differing physical size of their respective fields of view. Probabilistically weighted averaging provides the adaptation mechanism. Each filter involves online identification of the target shape function, so that this algorithm can be used against ill-defined and/or multiple-hot-spot targets. When each individual filter has the form of an enhanced correlator/linear Kalman filter, computational loading is very low. In contrast, an extended Kalman filter processing the raw infrared data directly and assuming a nonlinear constant turn-rate dynamics model provides superior tracking capability, especially for harsh maneuvers, at the cost of a larger computational burden.

A minimal parameter adaptive notch filter with constrained poles and zeros

Abstract: A new algorithm is presented for adaptive notch filtering and parametric spectral estimation of multiple narrow-band or sine wave signals in an additive broadband process. The algorithm is of recursive prediction error (RPE) form and uses a special constrained model of proper infinite impulse response (IIR) with a minimal number of parameters. The convergent filter is characterized by highly narrow bandwidth and uniform notches of desired shape. For sufficiently large data sets, the algorithm approaches the Cramer-Rao bound in estimating the frequencies of the sine wave signals.

Communications satellite repeater

Abstract: A communications satellite repeater having input demultiplexers for demultiplexing input beams to a plurality of first channels each having a first bandwidth, switches for interconnecting each input channel to desired output channel on a channel by channel basis, amplifiers, and output multiplexers for multiplexing output channels to output beams is improved by the particular structure of the switch. The present switch (8) has filter banks (9) for providing a plurality of second channels each having a second bandwidth narrower than said first channels by dividing each of said first channels, which can also operate as bandwidth-variable filter banks by multiplexing the adjacent second channels, switches (10) coupled with said filter banks (9) to interconnect said second channels, and multiplexers (11) for multiplexing the second channels at the ouptut of said switches (10) to provide output channels. Thus, each transponder can interconnect a plurality of beams.

Converting and decoding receiver for digital data recorded in analog form on magnetic tape

Abstract: Multi-phase/multi-level modulation data signals recorded on tape after conversion from original digital data are first converted to complex digital signals in an analog-to-digital converter in which the sampling rate is set by a pulse generator frequency controlled by the received signals through a control loop which develops a frequency control voltage (A). The complex digital signals have their real and imaginary parts separately filtered by filters of variable propagation time, but of constant bandwidth to produce complex signals to which the nearest permissible output complex signal (reference signal) is selected by a decision circuit (17), for final conversion to binary signals by a decoder (19) and a shift register (20). Timing shift correction is based on comparison of the received signals and reference signals of the decision stage to produce a control signal (φ) which further processed by addition to its previous value to produce a timing correction signal (A) which is applied both to the pulse generator for the sampling frequency of the analog-to-digital converter and to control the propagation time of digital non-recursive filters (14, 15). The timing correction signal (A) control of the filter propagation time makes possible a rapid timing shift correction that overcomes tape jitter effects. It is not necessary to stabilize the received carrier frequency because the tap recording preserves the relation between the sampling/keying frequency and the carrier frequency.

Apparatus for providing a carrier signal with two digital data streams I-Q modulated thereon

Abstract: A digital I-Q modulator provides an analog signal at a desired frequency ω 1 with in-phase I and quadrature-phase Q modulation sidebands provided responsive to different associated ones of in-phase I and quadrature-phase Q digital data streams, each having the same number N of data bits. A multiplexer alternatingly selects a different one of the data streams to provide a first N-bit-wide data signal during each of a successive multiplicity of time intervals of duration T essentially equal to the reciprocal of the carrier signal frequency ω 1 . The bits of the data signal are inverted to provide another data signal during every other one of a multiplicity of inversion time intervals of duration T/2, with each commencing at one of the beginning and midpoint of each time interval T. A single digital-to-analog converter (DAC) uses the sequentially inverted data stream to provide an analog signal having an amplitude substantially established by the digital value of the second data signal during each of another multiplicity of conversion time intervals of duration T/4, each commencing at one of the beginning and midpoint of each inversion time interval T/2. A bandpass filter, having a center frequency substantially equal to the carrier signal frequency F and a bandpass of at least twice the baseband signal bandwidth of the digital data streams effectively removes all frequency components except those of the desired modulation envelopes at the desired carrier frequency.

Double frequency modulation spectroscopy: high modulation frequency with low-bandwidth detectors.

Abstract: In this paper, we describe experimental and theoretical investigations of two variations of frequency modulation (FM) spectroscopy that use two electrooptic modulators. In the first variation, both modulators are frequency modulators (FM–FM), and, in the second, one is a frequency modulator and one is an amplitude modulator (FM–AM). The essential advantage of FM–FM and FM–AM spectroscopy is that sensitive lowbandwidth detectors, such as photomultiplier tubes, can be used to detect signals generated by the absorption of sidebands displaced from the carrier by frequencies far above the detector cutoff frequency. These two variations are complementary in the sense that, in situations where optical power is at a premium, the FM–FM scheme is most appropriate, and in situations where modulator drive power is at a premium, the FM–AM scheme is most appropriate. Using either of these variations, we have detected the absorption of 700-MHz sidebands with photomultiplier tubes whose cutoff frequencies lie below 100 MHz.

Peak optical power control circuit for laser driver

Abstract: To compensate for variations in a laser's peak power output due to changes in slope efficiency, a feedback loop is provided to monitor light output and effect compensatory changes in the drive current. In the feedback loop, the light output is detected by a photodiode. The output of the photodiode is filtered by a bandpass filter. The mean power of the filtered signal is determined and compared with a reference to control the laser drive. The reference takes account of the relationship between the filtered signal power and the peak power in the frequency spectrum of the pseudo-random input signal. The use of this reduced-bandwidth signal allows a relatively cheap, low bandwidth photodiode to be used with a long-wavelength laser.

Quantitative results near the band edges of disordered systems

Abstract: By combining the coherent-potential approximation, the potential-well analogy, and theories for the near tail in the density of states, we obtain, for the first time, explicitly quantitative results for the various quantities of interest near the band edges of disordered systems. These results exhibit a certain universality and can be expressed in terms of simple analytic functions, provided that disorder is not larger than about (1/5) of the bandwidth.

Signal transmission apparatus for a multiple channel system and method for using the same

Abstract: Signal transmission apparatus is provided for a communications system having a plurality of transmitters for transmitting information signals over any one of several transmission channels, and further having a plurality of receivers for receiving the information signals over any one of the transmission channels. In order to establish a selected transmission channel between a particular transmitter and a particular receiver, the transmitter selects an unoccupied transmission channel and transmits thereon a code identifying the receiver using a wide band signal for high speed bit transmission. When the receiver detects the presence of the identifying code over a particular channel, it first determines that the transmitter is the particular transmitter and, if so, establishes the transmission channel therebetween. The transmitter confirms that the transmission channel has been established, and then continues to transmit the identifying code repeatedly over the transmission channel using a narrow band signal with a low bit transmission rate. Both the wide band and narrow band signals containing the identifying code are included within the audio signal transmission band, so that no extra bandwidth is required for transmission of the identifying code.

Error-rate floor in optical ASK heterodyne systems caused by nonzero (semiconductor) laser linewidth

Abstract: Using a simple model to account for the effects of non-negligible linewidths for the transmitter and local oscillator lasers in a heterodyne ASK system, we show that there is an error probability floor which is a function of the IF bandwidth and the relative decision threshold level. We describe the physical reason for this behaviour and present some calculated results for total error probability in terms of signal power, IF linewidth and bandwidth, and threshold setting. The implications of this ‘floor’ for practical receiver design are discussed.