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Showing papers on "Bandwidth (signal processing) published in 2004"


Proceedings ArticleDOI
07 Nov 2004
TL;DR: To improve radio sensitivity of the sensing function through processing gain, three digital signal processing techniques are investigated: matched filtering, energy detection and cyclostationary feature detection.
Abstract: There are new system implementation challenges involved in the design of cognitive radios, which have both the ability to sense the spectral environment and the flexibility to adapt transmission parameters to maximize system capacity while coexisting with legacy wireless networks. The critical design problem is the need to process multigigahertz wide bandwidth and reliably detect presence of primary users. This places severe requirements on sensitivity, linearity and dynamic range of the circuitry in the RF front-end. To improve radio sensitivity of the sensing function through processing gain we investigated three digital signal processing techniques: matched filtering, energy detection and cyclostationary feature detection. Our analysis shows that cyclostationary feature detection has advantages due to its ability to differentiate modulated signals, interference and noise in low signal to noise ratios. In addition, to further improve the sensing reliability, the advantage of a MAC protocol that exploits cooperation among many cognitive users is investigated.

2,806 citations


Journal ArticleDOI
TL;DR: A memory polynomial model for the predistorter is proposed and implemented using an indirect learning architecture and linearization performance is demonstrated on a three-carrier WCDMA signal.
Abstract: Power amplifiers (PAs) are inherently nonlinear devices and are used in virtually all communications systems. Digital baseband predistortion is a highly cost-effective way to linearize PAs, but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA) or wideband orthogonal frequency-division multiplexing (W-OFDM), PA memory effects can no longer be ignored, and memoryless predistortion has limited effectiveness. In this paper, instead of focusing on a particular PA model and building a corresponding predistorter, we focus directly on the predistorter structure. In particular, we propose a memory polynomial model for the predistorter and implement it using an indirect learning architecture. Linearization performance is demonstrated on a three-carrier WCDMA signal.

1,160 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed an orthogonal frequency-division multiplexing (OFDM) system optimized for very high bit-rate, low-cost, and low-power wireless networks for personal computing (PC), consumer electronics (CE), and mobile applications.
Abstract: In February 2002, the Federal Communications Commission allocated 7500 MHz of spectrum for unlicensed use of commercial ultra-wideband (UWB) communication devices. This spectral allocation has initiated an extremely productive activity for industry and academia. Wireless communications experts now consider UWB as available spectrum to be utilized with a variety of techniques, and not specifically related to the generation and detection of short RF pulses as in the past. There are many differences between real-world behavior of narrow-band and UWB systems. All wireless systems must be able to deal with the challenges of operating over a multipath propagation channel, where objects in the environment can cause multiple reflections to arrive at the receiver (RX). For narrow-band systems, these reflections will not be resolvable by the RX when the narrow-band system bandwidth is less than the coherence bandwidth of the channel. The large bandwidth of UWB waveforms, instead, significantly increases the ability of the RX to resolve the different reflections in the channel. The UWB channel model developed by the IEEE 802.15.3a standard body is described in this paper. For highly dispersive channels, an orthogonal frequency-division multiplexing (OFDM) RX is more efficient at capturing multipath energy than an equivalent single-carrier system using the same total bandwidth. OFDM systems possess additional desirable properties, such as high spectral efficiency, inherent resilience to narrow-band RF interference, and spectral flexibility, which is important because the regulatory rules for UWB devices have not been finalized throughout the entire world. This paper describes the design of a UWB system optimized for very high bit-rate, low-cost, and low-power wireless networks for personal computing (PC), consumer electronics (CE), and mobile applications. The system combines OFDM modulation technique with a multibanding approach, which divides the spectrum into several sub-bands, whose bandwidth is approximately 500 MHz. The system described in this paper has been selected by several key industry organizations [Mulitband OFDM Alliance, WiMedia, Wireless Universal Serial Bus (USB)] because of its very good technical characteristics for the diverse set of high performance short-range applications that are eagerly anticipated for CE, PC, and mobile applications.

761 citations


Proceedings ArticleDOI
17 May 2004
TL;DR: A quantitative comparison of both approaches to spectrum pooling aims at enabling public access to these spectral ranges without sacrificing the transmission quality of the actual license owners, and it is obvious that both approaches sacrifice bandwidth of the rental system.
Abstract: The public mobile radio spectrum has become a scarce resource while wide spectral ranges are only rarely used. Here, the new strategy called spectrum pooling is considered. It aims at enabling public access to these spectral ranges without sacrificing the transmission quality of the actual license owners. Unfortunately, using OFDM modulation in a spectrum pooling system has some drawbacks. There is an interaction between the licensed system and the OFDM based rental system due to the non-orthogonality of their respective transmit signals. This interaction is described mathematically, providing a quantitative evaluation of the mutual interference that leads to an SNR loss in both systems. However, this interference can be mitigated by windowing the OFDM signal in the time domain or by the adaptive deactivation of adjacent subcarriers providing flexible guard bands between licensed and rental system. It is obvious that both approaches sacrifice bandwidth of the rental system. A quantitative comparison of both approaches is given as a tradeoff between interference reduction and throughput in the rental system.

642 citations


Journal ArticleDOI
TL;DR: In this article, an all-optical adiabatic and reversible pulse bandwidth compression process was proposed, which can generate arbitrarily small group velocities for any light pulse with a given bandwidth, without any coherent or resonant light-matter interactions.
Abstract: We show that light pulses can be stopped and stored coherently, with an all-optical adiabatic and reversible pulse bandwidth compression process. Such a process overcomes the fundamental bandwidth-delay constraint in optics and can generate arbitrarily small group velocities for any light pulse with a given bandwidth, without any coherent or resonant light-matter interactions. We exhibit this process in optical resonators, where the bandwidth compression is accomplished only by small refractive-index modulations performed at moderate speeds.

566 citations


Journal ArticleDOI
TL;DR: In this paper, the author illustrates why telecommunications data rates are as predictable as Moore's Law and illustrates why it is possible to predict the rate of data acquisition in the USA asymptotically.
Abstract: The author illustrates why telecommunications data rates are as predictable as Moore's Law.

359 citations


Journal ArticleDOI
TL;DR: Theoretical analysis and computer simulations are used to assess the performance of the proposed synchronizers and it is found that the degradations due to residual frequency and timing errors are negligible at signal-to-noise ratios of practical interest.
Abstract: This paper deals with timing and frequency recovery for the uplink of an orthogonal frequency-division multiple access (OFDMA) system. The frequency estimator is derived from ad hoc reasoning, whereas the timing estimator is based on the maximum-likelihood criterion. Both schemes rely on the repetition of a fixed pilot symbol. Their main feature is that they provide feedforward estimates and allow synchronization in only two OFDM blocks. In contrast to other existing methods, they do not require that the subcarriers of a given user occupy adjacent positions in the signal bandwidth. This makes it possible to interleave subcarriers of different users so as to optimally exploit the frequency diversity of the channel. Theoretical analysis and computer simulations are used to assess the performance of the proposed synchronizers. It is found that the degradations due to residual frequency and timing errors are negligible at signal-to-noise ratios of practical interest.

345 citations


Journal ArticleDOI
TL;DR: A repetitive-based controller for active power filters, which compensates selected current harmonics produced by distorting loads using a closed-loop repetitive- based control scheme based on a finite-impulse response digital filter, which allows full compensation of selected frequencies, even if the active filter has limited bandwidth.
Abstract: This paper proposes a repetitive-based controller for active power filters, which compensates selected current harmonics produced by distorting loads. The approach is based on the measurement of line currents and performs the compensation of selected harmonics using a closed-loop repetitive-based control scheme based on a finite-impulse response digital filter. Compared to conventional solutions based on stationary-frame current control, this approach allows full compensation of selected frequencies, even if the active filter has limited bandwidth. Compared to synchronous-frame harmonic regulations on line currents, the complexity of the proposed algorithm is independent of the number of compensated harmonics. Moreover, it is more appropriate for digital signal processor implementation and less sensitive to rounding and quantization errors when finite word length or fixed-point implementation is considered. Experimental results on a 5-kVA prototype confirm the theoretical expectations.

341 citations


Journal ArticleDOI
TL;DR: In this article, a broadbandwidth femtosecond pulses are used to achieve high spectral resolution in nonlinear spectroscopy and microscopy, based on chirping the excitation pulses in order to focus their entire bandwidth into a narrow spectral region.
Abstract: In this work, we show how broad-bandwidth femtosecond pulses can be used to achieve high spectral resolution in nonlinear spectroscopy and microscopy. Our approach is based on chirping the excitation pulses in order to focus their entire bandwidth into a narrow spectral region. We show that spectral features which are 100 times narrower than the excitation light can be resolved with this simple spectral focusing. The gain in spectral selectivity and sensitivity makes its application to nonlinear microscopy very convenient. This is demonstrated with diffraction-limited coherent anti-Stokes Raman scattering microscopy.

337 citations


Journal ArticleDOI
19 Mar 2004-Science
TL;DR: In this article, a femtosecond laser-based optical frequency synthesizer is used to demonstrate the generation and control of the frequency of electromagnetic fields over 100 terahertz of bandwidth with fractional uncertainties approaching 1 part in 1019.
Abstract: A femtosecond laser–based optical frequency synthesizer is referenced to an optical standard, and we use it to demonstrate the generation and control of the frequency of electromagnetic fields over 100 terahertz of bandwidth with fractional uncertainties approaching 1 part in 1019. The reproducibility of this performance is verified by comparison of different types of femtosecond laser–based frequency synthesizers from three laboratories.

285 citations


Patent
19 Mar 2004
TL;DR: In this article, a configurable vibration sensor consisting of a sensor circuit, an analog-to-digital converter and a processor is presented, where each sensor circuit comprises a vibration sensing element and a variable bandwidth filter controllable by the processor.
Abstract: A configurable vibration sensor comprising a sensor circuit, an analog-to-digital converter and a processor, where each sensor circuit comprises a vibration sensing element and a variable bandwidth filter controllable by the processor. In addition to the variable bandwidth filter, other configurable elements may also be employed in the sensor circuit, including a variable gain amplifier. These configurable elements allow the configurable vibration sensor to be configured for different vibration measurement applications when measuring vibrations from vibrating structures such as machinery and the like.

Proceedings Article
H. Yamaguchi1
01 Jan 2004
TL;DR: In this paper, a new approach that enables the accurate notch bandwidth and depth control for the general OFDM transmitter is discussed, which demonstrates the fundamental advantage of the OFDM-based UWB solution for the future cognitive ratio.
Abstract: Ultra Wideband transmit power (in-band) is regulated to be -41.25 dBm/MHz (in the United States), but in the future, it may be flexibly relaxed subject to the cognitive-radio spectrum policy. However, in close proximity of a protected radio service, transmission at the relaxed power might inflict an excessive degradation on the service quality. Applying the general analog or digital notch filter in the UWB transmitter (baseband) is the simplest but not a favorable approach due to the increased cost and the power consumption of the device. In OFDM, turning off the interfering tones has been studied as the alternative solution, but the inter-carrier interference may limit the notch depth to 5-10 dB. This paper discusses a new approach that enables the accurate notch bandwidth and depth control for the general OFDM transmitter. The technique demonstrates the fundamental advantage of the OFDM-based UWB solution[l] for the future cognitive ratio.

Journal ArticleDOI
TL;DR: In this paper, the effects of several phone chassis-related parameters-length, width, thickness, and distance between the head and phone-on the bandwidth, efficiency, and specific absorption rate (SAR) characteristics of internal mobile phone antennas are investigated.
Abstract: This paper presents a thorough investigation into the effects of several phone chassis-related parameters-length, width, thickness, and distance between the head and phone-on the bandwidth, efficiency, and specific absorption rate (SAR) characteristics of internal mobile phone antennas. The studied antenna-chassis combinations are located beside an anatomical head model in a position of actual handset use. The effect of the user's hand is also studied with two different hand models. The main part of the study is based on FDTD simulations, but also experimental results, which support the computationally obtained conclusions, are given. The presented analysis provides novel and useful information for future design of mobile handset antennas. The results show the general trends of bandwidth, SAR, and efficiency with different chassis parameters. The results also reveal a connection between these three performance parameters: an increase in SARs and a decrease in radiation efficiency occur compared to the general trend when the bandwidth reaches its maximum. This happens when the resonant frequency of the chassis equals that of the antenna.

Journal ArticleDOI
TL;DR: In this paper, a low-pass filter component values are used to improve the bandwidth of a CMOS transimpedance amplifier, which achieves 3 dB bandwidth of 9.2 GHz in the presence of a 0.5-pF photodiode capacitance.
Abstract: A technique for bandwidth enhancement of a given amplifier is presented. Adding several interstage passive matching networks enables the control of transfer function and frequency response behavior. Parasitic capacitances of cascaded gain stages are isolated from each other and absorbed into passive networks. A simplified design procedure, using well-known low-pass filter component values, is introduced. To demonstrate the feasibility of the method, a CMOS transimpedance amplifier (TIA) is implemented in a 0.18-/spl mu/m BiCMOS technology. It achieves 3 dB bandwidth of 9.2 GHz in the presence of a 0.5-pF photodiode capacitance. This corresponds to a bandwidth enhancement ratio of 2.4 over the amplifier without the additional passive networks. The transresistance gain is 54 dB/spl Omega/, while drawing 55 mA from a 2.5-V supply. The input sensitivity of the TIA is -18 dBm for a bit error rate of 10/sup -12/.

Proceedings ArticleDOI
01 Dec 2004
TL;DR: In a relay network with a single source-destination pair, the achievable rates with amplify-and-forward (AF) relaying strategy are examined and it is shown that transmitting in the optimum bandwidth allows the network to operate in the linear regime where the achieved rate increases linearly with the available network power.
Abstract: In a relay network with a single source-destination pair, we examine the achievable rates with amplify-and-forward (AF) relaying strategy. Motivated by applications in sensor networks, we consider power-constrained networks with large bandwidth resources and a large number of nodes. We show that the AF strategy does not necessarily benefit from the large available bandwidth. We characterize the optimum AF bandwidth and show that transmitting in the optimum bandwidth allows the network to operate in the linear regime where the achieved rate increases linearly with the available network power. We then present the optimum power allocation among the AF relays. The solution, which can be viewed as a form of maximum ratio combining, indicates the favorable relay positions in the network. Motivated by the large bandwidth resources we further consider a network that uses orthogonal transmissions at the nodes. While the above result for the optimum bandwidth still holds, a different set of relays should optimally be employed. In this case, the relay power solution can be viewed as a form of water-filling. The optimum AF bandwidth and the relay powers can be contrasted to the decode-and-forward (DF) solution. In a network with unconstrained bandwidth, the DF strategy will operate in the wideband regime to minimize the energy cost per information bit (S. Verdu, 2002), (O. Oyman et al., 2004). The wideband DF strategy requires again a different choice of relays; in the case of orthogonal signaling, the data should be sent through only one DF relay (I. Maric et al., 2004). Thus, in general, in a large scale network, a choice of a coding strategy goes beyond determining a coding scheme at a node; it also determines the operating bandwidth as well as the best distribution of the relay power.

Journal ArticleDOI
TL;DR: A wide-bandwidth continuous-time sigma-delta ADC is implemented in a 0.13-/spl mu/m CMOS circuit that achieves a dynamic range of 11 bits over a bandwidth of 15 MHz.
Abstract: A wide-bandwidth continuous-time sigma-delta ADC is implemented in a 0.13-/spl mu/m CMOS. The circuit is targeted for wide-bandwidth applications such as video or wireless base-stations. The active blocks are composed of regular threshold voltage devices only. The fourth-order architecture uses an OpAmp-RC-based loop filter and a 4-bit internal quantizer operated at 300-MHz clock frequency. The converter achieves a dynamic range of 11 bits over a bandwidth of 15 MHz. The power dissipation is 70 mW from a 1.5-V supply.

Proceedings ArticleDOI
20 Jun 2004
TL;DR: In this paper, a new exact small-signal z-domain model for the combination modulator and converter is derived, which is characterized by its capability to quantify the different dynamics of the converter for different modulators, its ease of use and its ability to predict the values of the control variables at the true sampling instants of the real system.
Abstract: As the performance of digital signal processors has increased rapidly during the last decade, there is a growing interest to replace the analog controllers in low power switching converters by more complicated and flexible digital control algorithms. Compared to high power converters, the control loop bandwidths for converters in the lower power range are generally much higher. Because of this, the dynamic properties of the uniformly-sampled pulse-width modulators used in low power applications become an important restriction to the maximum achievable bandwidth of control loops. Though frequency- and Laplace-domain models for uniformly-sampled pulse-width modulators are very valuable as they improve the general perception of the dynamic behavior of these modulators, the direct discrete design of the digital compensator requires a z-domain model for the combination modulator and converter For this purpose a new exact small-signal z-domain model is derived. In accordance with the zero-order-hold equivalent commonly used for 'regular' digital control systems, this z-domain model gives rise to the development of a uniformly-sampled pulse-width-modulator equivalent of the converter. This z-domain model is characterized by its capability to quantify the different dynamics of the converter for different modulators, its ease of use and its ability to predict the values of the control variables at the true sampling instants of the real system.

Journal ArticleDOI
TL;DR: Some plug-in type of bandwidth selectors, which are based on non-parametric estimation of an approximation of the mean integrated squared error, are proposed and it is concluded that an appropriately chosen PI bandwidth selector and the BT bandwidth selector perform comparably and both outperform the CV bandwidth.

Journal ArticleDOI
TL;DR: In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constant within the tuning range.
Abstract: In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constant within the tuning range. The difference between the odd- and even-mode characteristics of the coupled microstrip line makes it difficult to design a tunable bandpass filter with minimum degradation in passband performance. By using step-impedance microstrip lines, couplings between resonators can be controlled so that the constant bandwidth requirement could be satisfied with reasonable design parameter values. Lumped inductors are used for input and output coupling networks. Design equations are derived, and experimental results are compared with theoretical ones based on these equations.

Journal ArticleDOI
TL;DR: In this paper, a /spl Sigma/spl Delta/ fractional-N frequency synthesizer targeting WCDMA receiver specifications is presented, where spurs compensation and linearization techniques, the PLL bandwidth is significantly extended with only a slight increase in the integrated phase noise.
Abstract: A /spl Sigma//spl Delta/ fractional-N frequency synthesizer targeting WCDMA receiver specifications is presented. Through spurs compensation and linearization techniques, the PLL bandwidth is significantly extended with only a slight increase in the integrated phase noise. In a 0.18-/spl mu/m standard digital CMOS technology a fully integrated prototype with 2.1-GHz output frequency and 35 Hz resolution has an area of 3.4 mm/sup 2/ PADs included, and it consumes 28 mW. With a 3-dB closed-loop bandwidth of 700 kHz, the settling time is only 7 /spl mu/s. The integrated phase noise plus spurs is -45 dBc for the first WCDMA channel (1 kHz to 1.94 MHz) and -65 dBc for the second channel (2.5 to 6.34 MHz) with a worst case in-band (unfiltered) fractional spur of -60 dBc. Given the extremely large bandwidth, the synthesizer could be used also for TX direct modulation over a broad band. The choice of such a large bandwidth, however, still limits the spur performance. A slightly smaller bandwidth would fulfill WCDMA requirements. This has been shown in a second prototype, using the same architecture but employing an external loop filter and VCO for greater flexibility and ease of testing.

Journal ArticleDOI
30 Nov 2004
TL;DR: In this article, a 2-2 cascaded continuous-time sigma-delta modulator is proposed, which consists of two stages with second-order continuous time resonator loopfilters, 4-bit quantizers, and feedback digital-to-analog converters.
Abstract: This paper presents the design of a 2-2 cascaded continuous-time sigma-delta modulator. The cascaded modulator comprises two stages with second-order continuous-time resonator loopfilters, 4-bit quantizers, and feedback digital-to-analog converters. The digital noise cancellation filter design is determined using continuous-time to discrete-time transformation of the sigma-delta loopfilter transfer functions. The required matching between the analog and digital filter coefficients is achieved by means of simple digital calibration of the noise cancellation filter. Measurement results of a 0.18-/spl mu/m CMOS prototype chip demonstrate 67-dB dynamic range in a 10-MHz bandwidth at 8 times oversampling for a single continuous-time cascaded modulator. Two cascaded modulators in quadrature configuration provide 20-MHz aggregate bandwidth. Measured anti-alias suppression is over 50 dB for input signals in the band from 150 to 170 MHz around the sampling frequency of 160 MHz.

01 Jan 2004
TL;DR: A fast, easy-toimplement algorithm for localizing a source using received signal strength measurements is presented, based on incremental subgradient optimization methods, that is much lower than that used by other schemes, especially as network size grows.
Abstract: This paper describes a new approach to the source localization and tracking problem in wireless sensor networks. A fast, easy-toimplement algorithm for localizing a source using received signal strength measurements is presented. The algorithm is based on incremental subgradient optimization methods. Using theory on the convergence rates of these methods we characterize the amount of in-network communication required to achieve an accurate estimate of the source’s location. In comparison to other localization and tracking algorithms described in the literature, the amount of communication (and thus energy and bandwidth) used by our algorithm is much lower than that used by other schemes, especially as network size grows.

Journal ArticleDOI
TL;DR: In this article, a high-speed CMOS adaptive cable equalizer using an enhanced low-frequency gain control method is described, which alleviates the speed bottleneck of the conventional adaptation method.
Abstract: This paper describes a high-speed CMOS adaptive cable equalizer using an enhanced low-frequency gain control method. The additional low-frequency gain control loop enables the use of an open-loop equalizing filter, which alleviates the speed bottleneck of the conventional adaptation method. In addition, combined adaptation of low-frequency gain and high-frequency boosting improves the adaptation accuracy while supporting high-frequency operation. The open-loop equalizing filter incorporates a merged-path topology and offers infinite input impedance, which are suitable for higher frequency operation and cascaded design. This equalizing filter controls its common-mode output voltage level in a feedforward manner, thereby improving bandwidth. A prototype chip was fabricated in 0.18-/spl mu/m four-metal mixed-mode CMOS technology. The realized active area is 0.48/spl times/0.73 mm/sup 2/. The prototype adaptive equalizer operates up to 3.5 Gb/s over a 15-m RG-58 coaxial cable with 1.8-V supply and dissipates 80 mW. Moreover, the equalizing filter in manual adjustment mode operates up to 5 Gb/s over a 15-m RG-58 coaxial cable.

Journal ArticleDOI
TL;DR: In this paper, a review of the main filter requirements, highlighting the technologies that are being currently employed, and emerging filter technologies that have the potential to replace the existing technologies are then described.
Abstract: Phenomenal growth in the telecommunication industry in recent years has brought significant advances in filter technology as new communication systems emerged, demanding more stringent filter characteristics. In particular, the growth of the wireless communication industry has spurred tremendous activity in the area of microwave filter miniaturization and has been responsible for many advances made in this field. The filters that are currently being used in wireless base stations can be divided into two main categories: coaxial cavity resonator filters and dielectric resonator (DR) filters. While coaxial cavity filters have limited quality factor (Q) values, they offer the lowest cost design and are still being widely employed, particularly in wide bandwidth applications. With increased demands for high performance wireless systems, dielectric resonator filters are emerging as the baseline design for wireless base stations. Over the next five years, dielectric resonator filters are expected to have a significant share of the overall wireless base station filter market. High-temperature superconductor (HTS) filters are also expected to have a share of this market, particularly for systems, which have very stringent requirements for out-of-band interference. In this article, we begin by reviewing the main filter requirements, highlighting the technologies that are being currently employed. Emerging filter technologies that have the potential to replace the existing technologies are then described.

Journal ArticleDOI
TL;DR: Analysis of the Cramer-Rao bound (CRB) on source localization accuracy reveals that a distributed processing scheme involving bearing estimation at the individual arrays and time-delay estimation between sensors on different arrays performs nearly as well as the optimum scheme while requiring less communication bandwidth with a central processing node.
Abstract: Multiple sensor arrays provide the means for highly accurate localization of the (x,y) position of a source. In some applications, such as microphone arrays receiving aeroacoustic signals from ground vehicles, random fluctuations in the air lead to frequency-selective coherence losses in the signals that arrive at widely separated sensors. We present performance analysis for localization of a wideband source using multiple, distributed sensor arrays. The wavefronts are modeled with perfect spatial coherence over individual arrays and frequency-selective coherence between distinct arrays, and the sensor signals are modeled as wideband, Gaussian random processes. Analysis of the Cramer-Rao bound (CRB) on source localization accuracy reveals that a distributed processing scheme involving bearing estimation at the individual arrays and time-delay estimation (TDE) between sensors on different arrays performs nearly as well as the optimum scheme while requiring less communication bandwidth with a central processing node. We develop Ziv-Zakai bounds for TDE with partially coherent signals in order to study the achievability of the CRB. This analysis shows that a threshold value of coherence is required in order to achieve accurate time-delay estimates, and the threshold coherence value depends on the source signal bandwidth, the additive noise level, and the observation time. Results are included based on processing measured aeroacoustic data from ground vehicles to illustrate the frequency-dependent signal coherence and the TDE performance.

Journal ArticleDOI
01 Jan 2004
TL;DR: In this paper, a nonlinear interaction of the source under test with a quasimonochromatic source followed by an optical spectrum measurement has been proposed to measure the radiofrequency spectrum of an optical signal based on nonlinear optics.
Abstract: We study a technique to measure the radio-frequency (RF) spectrum of an optical signal based on nonlinear optics. The conventional approach, based on fast photodetection and analysis of the generated photocurrent via electronics means, is replaced by a nonlinear interaction of the source under test with a quasimonochromatic source followed by an optical spectrum measurement. Our technique has the advantage of an all-optical measurement that can provide a much larger bandwidth than electronic alternatives. The properties of this diagnostic, such as resolution and bandwidth, are studied. Typical applications to the monitoring of optical signals are presented.

Journal ArticleDOI
TL;DR: A novel parametric approach for constructing families of intersymbol-interference (ISI)-free pulses is presented and examined, and a number of theorems that relate time-domain behaviors of a pulse to the pulse's frequency spectrum are proved.
Abstract: A novel parametric approach for constructing families of intersymbol-interference (ISI)-free pulses is presented and examined. Some new pulses so constructed have smaller maximum distortion, a more open receiver eye, and a smaller probability of error in the presence of symbol-timing error than the Nyquist raised-cosine pulse for the same excess bandwidth. The parametric approach gives more degrees of freedom in the design of ISI-free pulses, and subsumes previous ISI-free pulses as special cases. A number of theorems that relate time-domain behaviors of a pulse to the pulse's frequency spectrum are proved. A previously known result relating pulse tail-time decay to discontinuity of the pulse-frequency spectrum is corrected and clarified.

Book
01 Jan 2004
TL;DR: In this paper, the authors present a framework for bandwidth extension for low-frequency audio signals, based on physics and psychophysics, with a focus on the effect of pitch and amplitude.
Abstract: Preface.I Introduction.I.1 Bandwidth Defined.I.2 Historic Overview.I.2.1 Electroacoustic Transducers.I.2.2 Sound Quality.I.3 Bandwidth Extension Framework.I.3.1 Introduction.I.3.2 The Framework.1 From Physics to Psychophysics.1.1 Signal Theory.1.1.1 Linear and Non-linear Systems.1.1.2 Continuous-time LTI (LTC) Systems.1.1.3 Discrete-time LTI (LTD) Systems.1.1.4 Other Properties of LTI Systems.1.1.5 Digital Filters.1.2 Statistics of Audio Signals.1.2.1 Speech.1.2.2 Music.1.3 Loudspeakers.1.3.1 Introduction to Acoustics.1.3.2 Loudspeakers.1.3.3 Bessel and Struve Functions.1.4 Auditory Perception.1.4.1 Physical Characteristics of the Peripheral Hearing System.1.4.2 Non-linearity of the Basilar Membrane Response.1.4.3 Frequency Selectivity and Auditory Filters.1.4.4 Loudness and Masking.1.4.5 Pitch.1.4.6 Timbre.1.4.7 Auditory Scene Analysis.1.4.8 Perceptual Modelling - Auditory Image Model.2 Psychoacoustic Bandwidth Extension for Low Frequencies.2.1 Introduction.2.2 Psychoacoustic Effects for Low-frequency Enhancement of Small Loudspeaker Reproduction.2.2.1 Pitch (Harmonic Structure).2.2.2 Timbre (Spectral Envelope).2.2.3 Loudness (Amplitude) and Tone Duration.2.3 Low-Frequency Psychoacoustic Bandwidth Extension Algorithms.2.3.1 Overview.2.3.2 Non-Linear Device.2.3.3 Filtering.2.3.4 Gain of Harmonics Signal.2.4 Low-Frequency Psychoacoustic Bandwidth Extension with Frequency Tracking.2.4.1 Non-Linear Device.2.4.2 Frequency Tracking.2.5 Subjective Performance of Low-Frequency Psychoacoustic Bandwidth Extension Algorithms.2.5.1 'Virtual Bass'.2.5.2 'Ultra Bass'.2.6 Spectral Characteristics of Non-Linear Devices.2.6.1 Output Spectrum of a Rectifier.2.6.2 Output Spectrum of Integrator.2.6.3 Output Spectra in Discrete Time.2.6.4 Output Spectrum of Clipper.3 Low-frequency Physical Bandwidth Extension.3.1 Introduction.3.2 Perceptual Considerations.3.2.1 Pitch (Spectral Fine Structure).3.2.2 Timbre (Spectral Envelope).3.2.3 Loudness (Amplitude).3.3 Low-frequency Physical Bandwidth Extension Algorithms.3.3.1 Systems with Low-frequency Extension.3.3.2 Non-linear Device.3.3.3 Filtering.3.3.4 Gain of Harmonics Signal.3.4 Low-frequency Physical Bandwidth Extension Combined with Low-frequency Psychoacoustic Bandwidth Extension.4 Special Loudspeaker Drivers for Low-frequency Bandwidth Extension.4.1 The Force Factor.4.2 High Force Factor Drivers.4.3 Low Force Factor Drivers.4.3.1 Optimal Force Factor.4.4 Transient Response.4.4.1 Gated Sinusoid Response.4.4.2 Impulse Response.4.5 Details of Lumped-element Parameters and Efficiency.4.6 Discussion.5 High-frequency Bandwidth Extension for Audio.5.1 Introduction.5.2 The Limits of Deconvolution.5.3 Perceptual Considerations.5.3.1 Pitch (Harmonic Structure).5.3.2 Timbre (Spectral Envelope).5.3.3 Loudness (Amplitude).5.3.4 Effects of Hearing Loss.5.3.5 Conclusions.5.4 High-frequency Bandwidth Extension for Audio.5.4.1 Non-linear Device.5.4.2 Filtering.5.4.3 Gain of Harmonics Signal.5.5 Spectral Band Replication (SBR).5.6 High-frequency Bandwidth Extension by Instantaneous Compression.5.6.1 Introduction and Algorithm.5.6.2 Analysis of Harmonics Generation.5.6.3 Implementation.5.6.4 Examples.5.6.5 Approximation of the Function tanh(Z).6 Bandwidth Extension for Speech.6.1 Applications.6.2 From a Speech Production Model to the Bandwidth Extension Algorithm.6.2.1 Model of the Process of Speech Production.6.2.2 Bandwidth Extension Algorithm.6.2.3 Alternative Structures.6.3 Extension of the Excitation Signal.6.3.1 Explicit Signal Generation.6.3.2 Non-linear Processing.6.3.3 Modulation in the Time Domain.6.3.4 Pitch Scaling.6.3.5 Discussion.6.4 Estimation of the Wideband Spectral Envelope.6.4.1 Representations of the Estimated Spectral Envelope.6.4.2 Instrumental Performance Measure.6.4.3 Theoretical Performance Bound.6.5 Feature Selection.6.5.1 Mutual Information.6.5.2 Separability.6.5.3 Linear Discriminant Analysis.6.5.4 Primary Features.6.5.5 Evaluation.6.6 Codebook Mapping.6.6.1 Vector Quantization and Training of the Primary Codebook.6.6.2 Training of the Shadow Codebook.6.7 Linear Mapping.6.7.1 Training Procedure.6.7.2 Piecewise-linear Mapping.6.8 Gaussian Mixture Model.6.8.1 Minimum Mean Square Error Estimation.6.8.2 Training by the Expectation-maximization Algorithm.6.9 Hidden Markov Model.6.9.1 Statistical Model of the Markov States.6.9.2 Estimation Rules.6.10 Discussion.7 Noise Abatement.7.1 A Special Kind of Noise Reduction.7.2 The Noise Pollution Problem - Case Study.7.3 The Application Low-frequency Psychoacoustic Bandwidth Extension to Noise Pollution.8 Bandwidth Extension Patent Overview.Appendix A Multidimensional Scaling.A.1 Introduction.A.2 Scaling.A.3 Example.A.4 Procedure.A.5 Precautions Concerning the Solution.A.6 Significance of Stress.A.7 Univariate Scaling.References.Index.

Journal ArticleDOI
TL;DR: In this paper, the authors summarized the topics of array processing for wideband signals in smart antenna-based applications, and proposed two main approaches based on the CSS method and beam-space processing has been introduced.
Abstract: In this article, we summarized the topics of array processing for wideband signals in smart antenna-based applications. For wideband beamforming, the TDF1B and FDFIB methods can provide the frequency-invariant beam-pattern over an arbitrarily wide bandwidth. The FDFIB method is applicable with arbitrary antenna arrays and suitable for switched beams and direction-finding approaches. The frequency-invariant beam-pattern can be designed with prescribed narrow main beam width and low SLL over a wide bandwidth by using two FDFIBs in a spatial interpolation process. For wideband DOA estimation, two main approaches based on the CSS method and beam-space processing has been introduced. The latest approach can provide lower resolution threshold, lower RMSE of estimate, and lower computational complexity. Finally, practical considerations in implementation of an antenna array regarding to array errors and mutual coupling have been considered. In the presence of array errors and mutual coupling, the performance of wideband DOA estimation is strongly degraded.

Proceedings ArticleDOI
20 Jun 2004
TL;DR: Small-signal frequency- and Laplace-domain models for the different types of uniformly-sampled pulse-width modulators are derived theoretically and the results obtained are verified by means of experimental data retrieved from a test setup.
Abstract: As the performance of digital signal processors has increased rapidly during the last decade, there is a growing interest to replace the analog controllers in low power switching converters by more complicated and flexible digital control algorithms. Compared to high power converters, the control loop bandwidths for converters in the lower power range are generally much higher. Because of this, the dynamic properties of the uniformly-sampled pulse-width modulators used in low power applications become an important restriction for the maximum achievable bandwidth of control loops. After the discussion of the most commonly used uniformly-sampled pulse-width modulators, small-signal frequency- and Laplace-domain models for the different types of uniformly-sampled pulse-width modulators are derived theoretically. The results obtained are verified by means of experimental data retrieved from a test setup.