Original Bandwidth Research Articles

Route to broadband chaos in a chaotic laser diode subject to optical injection

We experimentally and numerically demonstrate a route to bandwidth-enhanced chaos that is induced by an additional optical injection for a chaotic laser diode with optical feedback. The measured and calculated optical spectra consistently reveal that the mechanism of bandwidth enhancement is the interaction between the injection and chaotic laser field via beating. The bandwidth can be maximized only when the injected light is detuned into the edge of the optical spectrum of the chaotic laser field and the beating frequency exceeds the original bandwidth. The simulated dynamics maps indicate that 20 GHz broadband chaos can be obtained by commonly used laser diodes.

Wideband two-layer SIW coupler: design and experiment

An original wideband two-layer substrate integrated waveguide directional coupler is presented. The structure provides attractive features including a flexible design with a wideband coupling and independent control of the transmission phase for arbitrary coupling levels. Characteristics of 18 dB isolation and 90° phase shift between direct and coupled ports are experimentally validated over 16% bandwidth.

Evaluation of an Artificial Speech Bandwidth Extension Method in Three Languages

Quality and intelligibility of narrowband telephone speech can be improved by artificial bandwidth extension (ABE), which extends the speech bandwidth using only information available in the narrowband speech signal. This paper reports a three-language evaluation of an ABE method that has recently been launched in several of Nokia's mobile telephone models. The method extends the speech bandwidth to frequencies above the telephone band by first utilizing spectral folding and then modifying the magnitude spectrum of the extension band with spline curves. The performance of the method was evaluated by formal listening tests in American English, Russian, and Mandarin Chinese. The results of the listening tests indicate that ABE processing improved the subjective quality of coded narrowband speech in all these languages. Differences between bandwidth-extended American English test sentences and their original wideband counterparts were also evaluated using both an objective distance measure that simulates the characteristics of human hearing and a conventional spectral distortion measure. The average objective error was calculated for different categories of speech sounds. The error was found to be smallest in nasals and semivowels and largest in fricative sounds.

Internal ultra‐wideband slot antenna with a stepped ground plane

AbstractThis article presents an ultra‐wideband antenna design useful for the internal application in compact mobile devices. It is a planar circular slot antenna fed by a 50‐Ω coplanar waveguide line through a circular patch. The antenna ground plane was bent and vertically connected to the system ground plane. Such fabrications make the whole ground plane like a step. The modified ground plane preserves the original ultrawide bandwidth (from 2.3 GHz to larger than 20 GHz) and radiation characteristics from the integration with the RF circuitry. Also, the experimental results indicate that the proposed antenna can be employed in very close proximity to the possible shielding metal cases for battery and associated RF circuitry, with almost no degradation in the antenna performances. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1487–1491, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23410

Hardware comb filter enhances dynamic range and noise performance of sensors in noisy environments

We present the results of combining a hardware implementation of an analog comb filter with an ultralow noise electromagnetic sensor. The comb filter is designed to attenuate mains related interference, at either 50 or 60 Hz, and related harmonics. The sensor chosen for this work is an induction magnetometer, but the method is applicable to any low noise high dynamic range sensor. The resultant system, in this case, uses only a single coil, not a gradiometric configuration, thus providing a magnetometer capable of sensing field as opposed to field gradient. This combination of filter and sensor allows additional gain to be added and the full sensitivity of the system to be achieved, previously only realized in an electromagnetically screened room. At the same time, the high dynamic range, low noise performance, and original bandwidth of the sensor are maintained. The technique is illustrated by using the system in an urban environment to observe Schumann resonance phenomena. This approach to acquiring small signals in a noisy environment is compared with conventional analog filter and digital signal processing techniques.

Amplitude and frequency anomalies in regional 3D seismic data surrounding the Mallik 5L-38 research site, Mackenzie Delta, Northwest Territories, Canada

Amplitude and frequency anomalies associated with lakes and drainage systems were observed in a 3D seismic data set acquired in the Mallik area, Mackenzie Delta, Northwest Territories, Canada. The site is characterized by large gas hydrate deposits inferred from well-log analyses and coring. Regional interpretation of the gas hydrate occurrences is mainly based on seismic amplitude anomalies, such as brightening or blanking of seismic energy. Thus, the scope of this research is to understand the nature of the amplitude behavior in the seismic data. We have therefore analyzed the 3D seismic data to define areas with amplitude reduction due to contamination from lakes and channels and to distinguish them from areas where amplitude blanking may be a geologic signal. We have used the spectral ratio method to define attenuation (Q) over different areas in the 3D volume and subsequently applied Q-compensation to attenuate lateral variations ofdispersive absorption. Underneath larger lakes, seismic amplitude is reduced and the frequency content is reduced to [Formula: see text], which is half the original bandwidth. Traces with source-receiver pairs located inside of lakes show an attenuation factor Q of [Formula: see text], approximately half of that obtained for source-receiver pairs situated on deep, continuous permafrost outside of lakes. Deeper reflections occasionally identified underneath lakes show low-velocity-related pull-down. The vertical extent of the washout zones is enhanced by acquisition with limited offsets and from processing parameters such as harsh mute functions to reduce noise from surface waves. The strong attenuation and seismic pull-down may indicate the presence of unfrozen water in deeper lakes and unfrozen pore water within the sediments underlying the lakes. Thus, the blanking underneath lakes is not necessarily related to gas migration or other in situ changes in physical properties potentially associated with the presence of gas hydrate.

ULTRA-WIDE BAND PULSE TRANSMITTING THROUGH RESONANT ANTENNAS

A novel concept called direct antenna modulation (DAM) is proposed for short pulse transmitting through resonant antennas. The essence is based on the nonlinear transient responses of the antenna. By integrating RF switches at particular positions on a resonant antenna such as a patch antenna, the modulating signal is able to turn on and off the antenna's radiation by means of opening or shorting the radiation slots directly. Therefore, the antenna behaves as an integrated pulse generator, modulator and radiator. It is observed that short pulses with rich spectrum components outside the antenna bandwidth can be radiated this way. The radiated signal bandwidth is no longer limited by the original antenna impedance matching bandwidth, but by the performance of the switching devices. The experimental results show that a patch antenna with a resonant frequency 2.4 GHz and a 30 MHz bandwidth can transmit a digitally modulated signal with more than 400 MHz bandwidth.

Dynamic inter-SLA resource sharing in path-oriented differentiated services networks

This paper proposes novel resource sharing schemes for differentiated services (DiffServ) networks, to achieve both high resource utilization and quality of service (QoS) guarantee. Service level agreements (SLAs) are negotiated at network boundaries and supported by path-oriented resource mapping within the network. The recently proposed SLA management scheme based on virtual partitioning (Bouillet et al., 2002) allows overloaded SLAs to exploit the spare capacity of underloaded SLAs for efficient resource utilization, however, at the the cost of possible SLA violation of the underloaders. In the bandwidth borrowing scheme proposed here, the dedicated bandwidth for underloaded SLAs is determined and adaptively adjusted at network boundaries according to the actual traffic load and QoS policies; the available spare capacity is then properly distributed to related links for lending to others. On the other hand, the traffic flows admitted with borrowed bandwidth are tagged and may be preempted later when the original bandwidth owner needs to claim back the resources. Through a detailed implementation design and extensive computer simulation results we show that, by bandwidth borrowing, both SLA compliance and high resource utilization can be achieved in various load conditions, with some side benefits such as call-level service differentiation, small admission overhead, and convenience for policy-based management. In addition, we propose a distributed bandwidth pushing scheme that can dynamically adjust the spare bandwidth distribution over the network. Combining bandwidth pushing with bandwidth borrowing, the resource utilization can be further improved.

A phase-shifted linearly chirped fiber Bragg grating with tunable bandwidth

We demonstrate a new method to broaden and adjust the transmission bandwidth of a phase-shifted linearly chirped fiber Bragg grating (PS-LCFBG) after its fabrication. A movable thermal head is used to heat the PS-LCFBG at a small contact point. The original ultra-narrow transmission bandwidth of the PS-LCFBG can be broadened due to both the presence of the passband peak caused by the thermally-induced temporary phase shift and the passband caused by the thermally-induced local Bragg wavelength shift. The transmission bandwidth of the new passband peak can be adjusted by changing the position of the thermal head. The transmission bandwidth of the PS-LCFBG can be broadened from <10pm to 0.16nm, and can be tuned from 0.16 to 1.05nm.

Blind compensation of nonlinear distortion for bandlimited signals

Nonlinear distortion of bandlimited signals results in spectral spreading. This paper develops a blind nonlinear compensation method for bandlimited signals by suppressing the spectral content of the distorted signal above the original signal bandwidth by means of adaptive nonlinear filtering. The nonlinear compensator is constructed using a power series filter with adaptive coefficients. The adaptive coefficients are identified blindly by applying a least-squares criterion to the out-of-band spectral content of the nonlinear compensator output. The extraction of the out-of-band signal is efficiently performed by the discrete cosine transform. The effectiveness of the blind nonlinear compensation method is demonstrated by way of simulation examples involving periodic, colored noise, and bandlimited speech signals.

Reservoir characterization using seismic data after frequency bandwidth enhancement

Reservoir characterization is a crucial prerequisite to predict the economic potential of a hydrocarbon reservoir or to examine different production scenarios. Unfortunately, it is impossible to determine the exact reservoir properties at the required scale. The most abundant seismic data have a resolution of around 30 m. Wells resolve the reservoir down to the centimetre scale, but only at some points in the vertical direction. This paper presents a method, referred to as frequency bandwidth enhancement (FBE), for enhancing the frequency bandwidth and restoring high frequencies. The method increases the resolution of seismic data by padding the frequency spectrum of seismic wavelets, thus pushing the notch corresponding to the time limit of resolution to a higher part of the spectrum. This approach (patent pending) results in sharper wavelets capable of identifying thinner beds. A by-product of extending the frequency spectrum is the elimination of the tuning effect of beds thinner than the new limit of resolution. When tuning curves before and after the process are compared, it is observed that although different, the differences are minuscule and insignificant compared to the benefits coming from being able to resolve thinner beds. The procedure enunciated here is robust and helps define trends better, leading to more confident interpretations. Such applications could redefine prospects, which in some cases may have been declared unsuccessful on the basis of interpretation of seismic data with the original bandwidth. The reservoir characterization is realized with the aid of coherence cube processing, which is an extremely powerful tool to efficiently exploit the wealth of structural and stratigraphic information encapsulated in the seismic waveforms of 3D seismic data volumes.

Repetition ‘‘pitch’’ in chinchillas

Repetition pitches are evoked in human listeners by rippled noises. Infinitely iterated rippled noise (IIRN) is generated when wideband noise is delayed, attenuated, and added to the original wideband noise through positive (+) or negative (−) feedback. In human listeners, the pitch of IIRN(+) is matched to the reciprocal of the delay, whereas the pitch of IIRN(−) is an octave lower. A stimulus generalization paradigm was used to characterize IIRN repetition pitch in chinchillas. Chinchillas were trained to discriminate IIRN(+) with a 4-ms delay from IIRN(+) with a 2-ms delay. In the generalization task, chinchillas were tested with IIRN(+) having delays between 2–4 ms. The pitches evoked by these IIRNs ranged from 500–250 Hz. The delayed noise attenuation for all IIRNs was fixed at −1 dB. A systematic gradient in behavioral response occurred along the dimension of delay for each animal tested, suggesting that a perceptual dimension of pitch exists. Responses to IIRN(−) evoking pitches between 500–250 Hz (delays of 1–2 ms) were also measured. Responses to IIRN(−) were more variable among animals, suggesting that other perceptual cues such as timbre differences may be stronger than the pitch cues. [Work supported by NIDCD R01 DC005596.]

A largely tunable CFBG-based dispersion compensator with fixed center wavelength

A largely tunable chirped fiber Bragg grating (CFBG)-based dispersion compensator with fixed center wavelength is demonstrated. Tunable dispersion ranging from 178 to 2126 ps/nm, corresponding to a large range of 3-db bandwidth from 0.42 to 5.04 nm, is realized by using a 10 cm-long CFBG with an original bandwidth of 1.61 nm. The variation in center wavelength is less than 0.2 nm.

TCP Westwood with adaptive bandwidth estimation to improve efficiency/friendliness tradeoffs

In this paper, we propose an extension of Transmission Control Protocol (TCP) Westwood allowing the management of the Efficiency/Friendliness-to-NewReno tradeoffs. We show that the extended TCP Westwood is able to achieve higher total link utilization, yet at the same time maintain friendliness. TCP Westwood (for short, TCPW) implements a novel window congestion control algorithm based on eligible rate estimation (RE). The performance of TCPW has been promising, exceeding that of TCP NewReno in ‘large leaky pipes’; i.e. network paths with high bandwidth-delay product and non-negligible random error rate. Consider the situation where TCPW and TCP NewReno connections coexist and share common bottlenecks. Friendliness in this shared environment is paramount. Under certain conditions TCP NewReno may experience some performance degradation since TCPW ‘learns’ more about connection performance and thus can take better advantage of available bandwidth. To manage the efficiency/friendliness tradeoffs, we propose to combine the original TCPW Bandwidth Estimation (BE) strategy with a new RE strategy. One finds that BE provides significantly higher utilization, but may, under certain conditions, overestimates a connection fair share. RE, on the other hand, tends to be closer to the achieved rate of a connection, but it may underestimate the connection fair share. The question is: which estimate—RE or BE—yields better throughput/friendliness tradeoffs? Our studies show that RE works best when packet loss is mostly due to congestion. If, on the other hand, packet loss is mostly due to link errors, BE gives better performance. To achieve the ‘best of all worlds’, we introduce a method we call Combined Rate and Bandwidth estimation (CRB.) A connection first infers the predominant cause of packet loss (buffer congestion or random error) and then uses the more appropriate estimation method. Simulation shows that the adaptive CRB provides a very effective compromise between efficiency and friendliness.

Synthetic aperture radar imaging by one-bit coded signals

Processing of synthetic aperture radar (SAR) data coded with one bit is considered. The one bit coding operation amounts to the retention of only the information about the sign of the signals involved (signum coding or SC). The paper reviews the theory of signum coding and evaluates its performance by computing some quality measures for real images. Numerical results, which are in accord with theory, show that only a slight degradation in the quality of the images obtained is introduced by the SC operation if the signal is sampled at a rate consistent with the original bandwidth. If the sampling frequency is increased, the quality obtained can be further improved. Since the data involved in the processing are binary sequences, the processing can be carried out in real time, on-board the moving platform carrying the SAR antenna, and by using dedicated hardware consisting of simple, small, low-cost devices, which can be on motherboards of small dimensions and absorb very little power.

Prediction of Radiative Heat Transfer in Laminar Flames∗

Abstract A detailed radiation model is proposed for radiative heat transfer calculations in laminar flames. The discrete transfer method is implemented in order to solve the equation of radiative transfer; the exponential wide band model is modified to avoid that thermal properties predicted by the original wide band model depend on the size of the numerical grid cells used in flame calculation. The overlapping correction among gases and mixture of soot and gases is considered. In addition, a phenomenological soot model for laminar premixed flat flame is formulated. The applications of the detailed radiation model in CO/H2/N2-Air and H2 — O2 laminar counterflow diffusion flames and C2H4-Ar premixed burner stabilized flame are presented.

A channelized-limiter approach to receiver front-end protection

The receiver protection scheme being presented relies on frequency channelization of incident signals to accomplish +amplitude limiting on a frequency-selective, self-induced, instantaneous basis. A demultiplexer separates signals into contiguous subbands for parallel processing, after which they are reunited by a multiplexer to yield a signal composite of original bandwidth. The scheme's attractiveness lies in its ability to combine the advantages of fast response, broadband, passive limiters with the benefits of narrowband signal rejection techniques that employ frequency-tunable or switched notch filters. The concept is demonstrated with an experimental five-channel modified-logarithmic-periodic limiter prototype circuit, configured as a 7.5- to 12.5-GHz channelized self-limiting amplifier. The measured results confirm the circuit's transparency to small-amplitude signals and illustrate its effectiveness in confining large-signal effects, such as gain compression and intermodulation products, to narrow frequency intervals.

Effects of amplitude envelope expansion and compression on nonsense sentence recognition

When spectral information in speech is obscured, listeners presumably fall back on secondary cues such as those contained within the gross waveform envelope. This study examined the extent to which listeners’ ability to use such cues is resistant to distortions of the envelope. Signal correlated noise samples, created individually to follow the amplitude envelopes of 200 nonsense sentences, were used as maskers of those sentences, with signal‐to‐noise ratios of −4, −2, 0, and +2 dB. The resulting waveforms preserved the original wideband envelopes, but spectral information was degraded to a degree determined by the S‐N ratio. The sentences were presented monaurally to normal hearing subjects at 70 dB SPL. Recognition of key words in these sentences was compared to that obtained for waveforms that had been processed with two different levels of amplitude expansion and two levels of compression. The results indicated that amplitude expansion severely reduced recognition scores, while compression had little effect. [Work supported by NIH ♯DC01533.]

Parallel tri- and bi-diagonalization of bordered bidiagonal matrices

We have previously presented various plane rotation patterns, which provide stable O( N 2) algorithms for reducing a b-band matrix of order N bordered by p rows and/or columns to ( b + p)-band) form, where b ⩾ 1 and p⩾ 1. By splitting the matrix into two similarly structured submatrices and chasing nonzeros to the corners in two directions, the newly proposed patterns reduce the computational cost by 50% compared to the other existing one-way chasing algorithms. In this paper, we show how these rotation patterns can be efficiently parallelized when reducing a one-bordered bidiagonal matrix to tridiagonal form possibly followed by bidiagonalization. Applications are found in updating total least squares solutions and signal or noise subspaces by means of a partial singular value decomposition. For each scheme, a linear systolic network and a parallel VLSI computing structure are presented. These architectures are able to reduce the overall computing time for the tridiagonalization from O( N 2) to O(N) using O( N) processors. In particular, it is shown that the best two-way chasing parallel implementation reduces the computation time of the tridiagonalization by 50% compared to the one-way chasing parallel implementation, using the same number of processors. If additionally the original bandwidth is restored, then all proposed two-way chasing parallel implementations achieve an 8% reduction in overall computing time compared to the one-way chasing scheme.

A Simple Root $n$ Bandwidth Selector

The asymptotically best bandwidth selectors for a kernel density estimator currently require the use of either unappealing higher order kernel pilot estimators or related Fourier transform methods. The point of this paper is to present a methodology which allows the fastest possible rate of convergence with the use of only nonnegative kernel estimators at all stages of the selection process. The essential idea is derived through careful study of factorizations of the pilot bandwidth in terms of the original bandwidth.