Showing papers on "Bandwidth (signal processing) published in 1992"

Variable Bandwidth and Local Linear Regression Smoothers

Abstract: In this paper we introduce an appealing nonparametric method for estimating the mean regression function. The proposed method combines the ideas of local linear smoothers and variable bandwidth. Hence, it also inherits the advantages of both approaches. We give expressions for the conditional MSE and MISE of the estimator. Minimization of the MISE leads to an explicit formula for an optimal choice of the variable bandwidth. Moreover, the merits of considering a variable bandwidth are discussed. In addition, we show that the estimator does not have boundary effects, and hence does not require modifications at the boundary. The performance of a corresponding plug-in estimator is investigated. Simulations illustrate the proposed estimation method.

Increasing capacity in wireless broadcast systems using distributed transmission/directional reception (DTDR)

Abstract: A method and apparatus for increasing the capacity of wireless broadcast communications system from a central studio to a plurality of users in a service area is disclosed. Given a source signal whose high information rate exceeds the practical information carrying capacity of the available broadcast channel bandwidth, the invention increases the effective capacity of the broadcast system to effectively communicate such a source signal. The high-rate signal is split into several low-rate signals such that each can be accommodated within the allocated bandwidth. These low-rate signals are transmitted from spatially separated transmitters, all radiating into the service area in the same frequency channel. Each receiver uses a plurality of antennas to receive these multiple cochannel signals that arrive from different directions-of-arrival. The receiver exploits the directions-of-arrival differences of these cochannel signals to separate them into the individually transmitted signals. The separated signals are then demodulated to extract the information signals which are then combined to obtain the original high-rate source signal. Thus, the broadcast information capacity can be increased several-fold.

A 100-MHz 100-dB operational amplifier with multipath nested Miller compensation structure

Abstract: A multipath nested structure which overcomes the bandwidth reduction in the conventional nested structure by appending an independent feedforward path for high frequencies is presented. At low frequencies, the opamp behaves as a three-stage nested Miller-compensated amplifier, while at high frequencies the opamp has the nature and bandwidth of a two-stage amplifier with simple pole splitting. In this fashion, the concept circumvents the classical DC-gain/high-frequency-performance dilemma. No pole-zero doubles occur, because the two regions of operation can be independently and closely matched, unaffected by variations in the parameters of the IC process in which the amplifier is fabricated. >

Joint blind equalization, carrier recovery and timing recovery for high-order QAM signal constellations

Abstract: Two existing blind equalization tap update recursions for 64-point and greater QAM (quadrature amplitude modulation) signal constellations are studied, along with existing and novel carrier and timing recovery techniques. It is determined that the superior tap update recursion is the one known as the constant modulus algorithm. Carrier recovery requires a modified second-order decision-directed digital phase-locked loop. An all-digital implementation of band-edge timing recovery is used. With 14.4 kb/s outbound transmission using CCITT V.33 trellis-coded 128-QAM signals having 12.5% excess bandwidth, a prototype blind retrain procedure is developed to demonstrate the feasibility of the techniques for high-speed multipoint modems. A WE DSP32-based real-time digital signal processor was employed to test the retrain over a set of severely impaired channels. For each channel in the set, the retrain succeeded at least 90% of the time. >

Dual mode transmitter and receiver

Abstract: A dual-mode transmitter having an antenna (109), a mode controller (103), a source encoder, a tunable-frequency synthesizer (105), a chip-code generator (107), a spread-spectrum modulator (111), a narrowband modulator (113), a power amplifier (115), and an adjustable bandpass filter (117). Also provided is a dual-mode receiver having a mode controller (103), a tunable-frequency synthesizer (105), a chip-code generator (107), an antenna (109), an adjustable bandpass filter (117), a preamplifier (205), a frequency converter (209), an IF amplifier (211), a spread-spectrum despreader (215), a spread-spectrum demodulator (217), a narrowband modulator (213), and a source decoder. For the transmitter and receiver, the mode controller (103) selects receiving a narrowband modulation or a spread-spectrum modulation. The tunable-frequency synthesizer (105) generates a local oscillator signal for the receiver, and a carrier signal for the transmitter. The chip-code generator (107) generates a chip code signal for both the transmitter and the receiver. With a narrowband modulation setting of the mode controller (103), the transmitter and receiver have the adjustable bandpass filters (117) adjusted to a narrowband width for telephone communications. With a spread-spectrum setting of the mode controller, the adjustable bandpass filters (117) and the system are adjusted to transmit and receive a wide bandwidth for passing the spread-spectrum signal.

Location-based adaptive radio control

Abstract: A method (200) and apparatus (100)is provided for a radio having adjustable operating parameters to adjust at least one such adjustable operating parameter based on the current location of the radio. Operating parameters which may be so adjusted include, but are not limited to, the following: transmitting power, operating channel, operating band, modulation type, modulation index, frequency deviation, squelch setting, channel spacing, control channel (for trunked communications), noise blanker characteristic, and receive bandwidth. In another embodiment, transmissions by the radio can be inhibited as a function of the location when it is determined that the location is within a hazard area.

Data with video transmitter

Abstract: Signal processors for permitting the transparent, simultaneous transmission and reception of a data signal in the video bandwidth is disclosed. The signal processor in the transmitter rasterizes the data at the horizontal scanning rate and modulates the data with a data carrier at a non-integral multiple of the horizontal scanning rate to obtain frequency interleaving. The data is transmitted during the active video portion of each video line.

Method and apparatus for the transmission and reception of a multicarrier digital television signal

Abstract: A method and apparatus for encoding a television source signal having a first bandwidth, into a frequency multiplexed signal having a narrower bandwidth and comprising a plurality of subcarriers modulated with digital information. Each of said subcarriers has an amplitude, bandwidth and coding characteristic which reflects the relative importance of the digital information provided thereby. The frequency multiplexed signal is suitable for use in a broadcasting environment wherein a conventional television signal is also used and wherein said subcarriers are disposed in frequency, in positions which are least likely to result in interference to or from said conventional signal. The invention also includes a receiver for decoding the frequency multiplexed signal and for providing a high definition display.

Digital beamforming in ultrasound

Abstract: The effects on array gain and sidelobe level of a practical digital beamforming (DBF) processor under the wideband conditions typical of ultrasound is discussed. It is concluded that a relatively simple design that replaces each analog delay line with a tapped, digital shift register (DSR) and a digital phase shift operation adjusted for midband will provide the desired performance, provided that the sampling rate of the signal at the input to the DSR is 4 to 10 times the bandwidth. More realistically, when nonidealized passbands are taken into account and the typical condition whereby the transducer frequency is about twice the bandwidth is considered, the rule of thumb for the sampling rate is that it must be 4 to 10 times the transducer frequency. >

Signal detector employing mean energy and variance of energy content comparison for noise detection

Abstract: A signal detector discriminates between signals manifesting noise and signals manifesting information, both of which appear at an input. A analog-to-digital converter circuit samples the signals and a Fourier filter determines, for each signal sample, energy content of each of a plurality of frequency cells in the sample. A processor then determines the mean energy content and the average variance of energy content in all frequency cells in the signal sample. The mean energy content and average variance of energy content of the signal sample are then compared, and if the comparison indicates an approximate equality, the sample is declared to be noise. The processor further determines a centroid center frequency for the frequency cells in the sample which indicates, if it is on-center, that the sample is likely to be noise. The processor further determines the bandwidth of the Fourier components of the input signal, to determine if it is indicative of noise. The skew of the sample's Fourier components is also determined and if it is nearly zero (indicating the signal is symmetrical in frequency about the center frequency), a noise signal is indicated. The combined indications are then normalized and subjected to a threshold which indicates whether a signal or noise is present.

Dynamic capacity allocation CDMA spread spectrum communications

Abstract: A dynamic capacity allocation spread spectrum CDMA communications system for overlaying, at least in part, geographically and in frequency a radio-relay system A first receiver, located near the relay receiver of the radio-relay system, measures a first power level within the relay bandwidth of the radio-relay system A second receiver, located near the relay receiver, measures a second power level outside the relay bandwidth of the radio-relay system The first power level is compared to a predetermined threshold A ratio signal is generated from the first power level and the second power level When the first power level exceeds the predetermined threshold, the ratio signal is used to regulate the power level and dynamically allocate the capacity transmitted from each spread-spectrum-base station

The use of the wavelet transform in the detection of an unknown transient signal

Abstract: For the detection of a not-perfectly-known signal in noise, usually no uniformly most powerful test exists, and thus a detector performance depends on the signal representation. The use of the wavelet representation of signals to perform a new detection scheme is discussed. The advantage of using this particular representation is shown. It is shown that prior information regarding the relative bandwidth and the time-bandwidth-product of the signal to be detected is efficiently incorporated into the detection problem formulation. Thus, the proposed detection scheme is most suitable for detection of unknown transient signals when prior information about the signal time-bandwidth product and relative bandwidth exists. In these cases, the wavelet-representation-based detector performs better than any other. The structure of the proposed detectors is discussed and its performance is evaluated using Monte Carlo simulations. >

A class of frequency hop codes with nearly ideal characteristics for use in multiple-access spread-spectrum communications and radar and sonar systems

Abstract: The problem of constructing frequency hop codes for use in multiuser communication systems such as multiple-access spread-spectrum communications and multiuser radar and sonar systems is addressed. Previous frequency hopping techniques are reviewed. The construction of a new family of frequency hopping codes called hyperbolic frequency hop codes is given. The concepts of multiple-access spread-spectrum communication systems and multiuser radar and sonar systems are reviewed, and it is shown that the hyperbolic frequency hop codes possess nearly ideal characteristics for use in both types of system. Specifically, in multiple-access communications the codes achieve minimum error probability, while in radar and sonar systems the codes have at most two hits in their auto- and cross-ambiguity function. Examples of address assignment for multiple-access communications systems and radar and sonar auto- and cross-ambiguity functions are also given. >

Practical performance of several data driven bandwidth selectors

Abstract: Most recently proposed bandwidth selectors in kernel density estimation have been developed with intent to reduce the large sampling variability of Least Squares Cross-Validation. Their asymptotic superiority has been shown in many papers. Some of those selectors have even the fastest n-1/ 2 relative rate of convergence to their theoretical optimum. The aim of this paper is to see what is happening for small sample sizes. Several recently proposed methods of bandwidth selection are considered. These methods are compared to Least Squares Cross-Validation through simulations. Some qualitative measures of performance as well as quantitative ones are used for this comparison. It is seen that, while most of the bandwidth selectors gain some in terms of variance reduction, some of them lose a lot in terms of increased bias resulting in inferior overall performance when compared to Least Squares Cross-Validation.

Narrow-band optical channel-dropping filter

Abstract: Waveguide couplers are combined with lambda /4 shifted distributed feedback (DFB) resonators to produce narrowband channel dropping filters. The bandwidth of the filter can be made much narrower than the stopband of the grating. It is possible to remove the spurious responses of the grating filter by appropriate dispersion characteristics for the coupled waveguides. However, in some practical applications it may not be necessary to do this, if all channels can be accommodated within half the grating bandwidth of the filters. >

Dynamic channel allocation method and system for integrated services digital network

Abstract: Dynamic channel allocation in an ISDN line is implemented above a Level II link layer protocol (LAPD). The preferred embodiment comprises programming operating on a computing platform system including a communication coprocessor system. The programming includes a channel management module (CMM) and a virtual channel module (VCM) to implement dynamic channel Allocation. The modules cooperate to control bandwidth between communication partners by selective allocation and deallocation of virtual B-Channels between them in response to preassigned priorities and real time events. Voice and data channels are interrogated. Channel deallocation also takes place in response to high error rates in message transmission.

Digital down converter and method

Abstract: A digital down converter for extracting a signal from a complex digital signal wherein the real and imaginary components of the complex digital signal are each modulated to shift the center frequency of the desired signal to zero frequency, decimated digitally to limit the bandwidth of each to the bandwidth of the desired signal and filtered to alter the shape thereof. The digital down converter includes a formatter for arranging the output of the desired signal in one of multiple output formats and a controller for programmably controlling the modulation, decimation and filtering and for selecting the desired output format.

The detection of temporal gaps as a function of frequency region and absolute noise bandwidth.

Abstract: Temporal gap detection was measured as a function of absolute signal bandwidth at a low‐, a mid‐, and a high‐frequency region in six listeners with normal hearing sensitivity. Gap detection threshold decreased monotonically with increasing stimulus bandwidth at each of the three frequency regions. Given conditions of equivalent absolute bandwidth, gap detection thresholds were not significantly different for upper cutoff frequencies ranging from 600 to 4400 Hz. A second experiment investigated gap detection thresholds at two pressure–spectrum levels, conditions typically resulting in substantially different estimates of frequency selectivity. Estimates of frequency selectivity were collected at the two levels using a notched‐noise masker technique. The gap threshold‐signal bandwidth functions were almost identical at pressure–spectrum levels of 70 dB and 40 dB for the two subjects in experiment II, while estimates of frequency selectivity showed poorer frequency selectivity at the 70‐dB level than at 40 dB. Data from both experiments indicated that gap detection in bandlimited noise was inversely related to signal bandwidth and that gap detection did not vary significantly with changes in signal frequency over the range of 600 to 4400 Hz. Over the range of frequencies investigated, the results indicated no clear relation between gap detection for noise stimuli and peripheral auditory filtering.

Joint design of block source codes and modulation signal sets

Abstract: The problem of designing block source codes and modulation signal sets that are both energy and bandwidth constrained is considered. For the class of linear estimator-based decoders, necessary conditions for optimality for the encoder, decoder and modulation signal set are derived. An algorithm that iteratively solves these necessary conditions to converge to a locally optimum solution has been developed. By studying the performance of the previous class of digital communication systems in the limit of infinite encoding rates, it is demonstrated that the MSE of a bandwidth and energy constrained digital system is bounded from below by that of a block pulse amplitude modulation system. This bound is readily computable in terms of the eigenvalues of the source and channel covariance matrices. The results indicate that for a correlated source, a sufficiently noisy channel and specific source block sizes and bandwidths, the digital system performance coincides with the optimum performance theoretically attainable. Further, significant performance improvements over the standard VQ-based system are demonstrated when the channel is noisy. >

25 GHz bandwidth 1.55 mu m GaInAsP p-doped strained multiquantum-well lasers

Abstract: A modulation bandwidth of 25 GHz for InP based lasers, using devices with p-doped, strained multiquantum-well active regions is reported. The doping reduces the bandwidth limitations caused by hole transport in standard quantum-well lasers, as well as increasing resonance frequencies to over 30 GHz. The present 25 GHz bandwidth is limited by device parasitics, with a predicted intrinsic device bandwidth of over 40 GHz.

Wide bandwidth bandpass filter comprising parallel connected piezoelectric resonators

Abstract: A plurality of piezoelectric resonators (10,32,37,57,62,66,79,88,93) are utilized to form a bandpass filter (31,56,78). The resonators (10,32,37,57,62,66,79,88,93) are connected in parallel to form a plurality of parallel paths between an input (43,73,81) and an output (47,74,82) of the filter (31,56,78). A predetermined number of the piezoelectric resonators (10,32,37,57,62,66,79,88,93) provide a phase shift of approximately 180 degrees. Each parallel path has a passband and center frequency that is displaced from the passband and center frequency of other paths. Consequently, the passband of each parallel path algebraically sums and creates a filter passband that is wider than the passband of each of the filter's individual parallel paths.

Simulation and analysis of an adaptive predistorter utilizing a complex spectral convolution

Abstract: An adaptive predistorter for linearizing a power amplifier in a mobile transmitter is studied, and the analytical, simulation, and measured results are presented. This predistorter does not have the problems of loop delay or phase shifting in its feedback path. The feedback is used only periodically to update the predistorter parameters so that it adapts to changes in the amplifier characteristics. An adaptation method for predistorters of the polynomial type is described. Its complexity is significantly lower than that of the previously described methods and its convergence speed, though low, is more than sufficient to track amplifier drift. Analytical verification that the measurement of out-of-band power is sufficient to drive the adaptation, a complex convolution method for measuring the out-of-band power that requires no additional local oscillator or phase reference, and a demonstration of the system performance utilizing a 16-QAM signal in a 25-kHz bandwidth, centered at 850 MHz, are provided. >

Apparatus, system and method for transmitting secure signals over narrow spaced channels

Abstract: An encryption/decryption device, system and method for providing secure communication over a communication channel. The encryption device includes a radio interface unit connected to a conventional radio, wherein the interface unit selectively couples a codec, signal processor and modem to the transmit and receive path during secure operation. The codec digitally encodes non-secure analog signals and places them in pulse code modulated format. The signal processor then compresses the pulse code modulated signals into voice coded and then digitally encrypted NRZ signals which are then input into the conventional radio for modulating a carrier frequency on an occupied bandwidth approved for 15 KHz to 25 KHz, or as little as 11.4 KHz, spaced channels. The modem can input the digitally encrypted signals using modified frequency modulation to place the modified digitally encrypted signals substantially within the voice passband of 300 Hz to 3200 Hz. The device, system and method incorporates a master prologue sent prior to voice information at a BPS rate different from that of the voice BPS rate. The voice information is sent in blocks with a plurality of resynchronization data frames of bits interlaced between a plurality of voice frames of bits to allow highly reliable late entry and re-entry access. A conventional repeater system can be selectively controlled by a controller device of the present invention for demodulating, error correcting and recompressing the master prologue without descrambling the digitally encoded voice information.

Maximizing the Efficiency of Wave-Energy Plant Using Complex-Conjugate Control

Abstract: A method of determining the hydrodynamic coefficients of a floating wave-energy absorber is outlined, and the coefficients of a Salter's duck are measured experimentally. A complex-conjugate synthesizer, derived from these coefficients, is used both theoretically and experimentally to predict and to measure the efficiency of a duck in unidirectional monochromatic waves. The synthesis produces a higher efficiency over a greater bandwidth than has been achieved before. The reason for the improvement in efficiency is explained, and conclusions are drawn about the implications of complex-conjugate control for predicting practical engineering constraints on the design of a full-sized wave-energy absorber.

QAM: the modulation scheme for future mobile radio communications?

Abstract: With spectral congestion increasing, and plans announced to dramatically increase the number of mobile telephone users over the coming decade, many approaches are being considered to reduce the bandwidth requirements of each user. One approach is the use of quadrature amplitude modulation (QAM), a particular form of multilevel modulation where each symbol contains several bits of information. The use of QAM for mobile radio applications is considered and it is shown that this form of multilevel modulation can offer an attractive solution to current bandwidth restrictions in microcellular networks. An advanced variable-rate system is also considered and hardware development of a QAM modem discussed.

Digital filter-type frequency demultiplexing device

Abstract: After sampling a multicarrier signal, groups of multiplex modulated carriers with identical bandwidths are separated by group filters. Clock frequencies of the carriers are then reduced by decimators depending on their respective bandwidths. To separate each of the modulated carriers in each of the groups, a polyphase network architecture is combined with a stage of delay lines for processing separate groups of multiplexed modulated carriers with identical bandwidth by programming a Fourier transform complex multiplying circuit. The demultiplexing devices is programmed to process evolutive traffics of groups of multiplexed carriers by a switching stage linking outputs of the decimation filters to inputs of the delay line stage.

Asynchronous peak detection of information embedded within PRML class IV sampling data detection channel

Abstract: A digital peak detection circuit asynchronously detects embedded overhead information such as servo or sync pattern data within a PR4,ML synchronous data detection channel of a magnetic disk drive. The channel includes an analog to digital converter clocked by a data clock operating asynchronously with respect to playback of the embedded overhead information in the channel for converting an analog data stream into raw data samples, and an adaptive digital FIR filter for conditioning the raw data samples into conditioned data samples in accordance with programmable filter coefficients. The digital peak detection circuit includes a filter adaptation circuit for programming the digital FIR filter to a bandwidth characteristic selected for the embedded overhead information, a plurality of tapped clock delays each connected in tandem to receive and progressively by a period related to said data clock to delay conditioned data samples of the embedded overhead information, a first comparison logic array connected to predetermined taps of said tapped data clock period delays for comparing said conditioned data samples of the embedded overhead information at said taps and for generating a first logical condition therefrom, a second comparison logic array connected to a predetermined tap of said tapped clock delay means and to a threshold-providing circuit, for comparing the conditioned data samples of the embedded overhead information at the taps with threshold values provided by the threshold-providing circuit and for generating a second logical condition therefrom, and a digital combining circuit for combining the first logical condition and the second logical condition in order to detect and put out the embedded overhead information. A fault tolerant sync pattern detection method and apparatus is also disclosed.

Method and apparatus for dynamic bandwidth allocation in a digital communication session

Abstract: A dynamic and automatic method and apparatus for changing the bandwidth of a digital communication session is disclosed The communication session uses a plurality of channels (28, 30, 32, 34, 36, 38) for transmitting digital data between a first location and a second location The rate of data or non-data characters in the transmitting digital data stream is detected A utilization parameter is calculated by dividing the non-data rate by the overall transmission data rate The number of the plurality channels (28-38) is changed to maintain the utilization parameter in response to changes in the data rate

Bandwidth performance of linear adaptive arrays with tapped delay-line processing

Abstract: The nulling bandwidth of adaptive arrays with tapped delay-line processing is examined. Linear arrays with up to 10 elements are considered. It is shown how the number of taps in the delay lines and the amount of delay between taps affect the nulling bandwidth. For each size of array, the optimal number of delay-line taps and the optimal intertap delays are determined as functions of the required nulling bandwidth. >