Search

Modern autonomous vehicles are being equipped with various automotive sensors to perform special functions. Especially, it is important to predict the heading direction of the front vehicle to adjust the speed of the ego‐vehicle and select appropriate actions. Here, we propose a method for estimating the instantaneous heading direction of a vehicle using automotive radar sensor data. First, using a frequency‐modulated continuous wave (FMCW) radar in the 77 GHz band, we accumulate the automotive radar sensor data for different movements of the front vehicle (e.g., stop, going ahead, reversing, turning left, and turning right). To distinguish the different movements of the vehicle, we use the convolutional neural network (CNN) and train it using the acquired radar sensor data. Because the CNN algorithm usually uses image data as input, it is essential to convert radar sensor data into image data. Therefore, we apply a high‐resolution angle estimation algorithm to the obtained radar data and convert it into a two‐dimensional range map. After the CNN model is trained with the obtained radar sensor data, various movements of the front vehicle can be classified with over 94% of accuracy. [ABSTRACT FROM AUTHOR]

This study presents preliminary results about the multi-sensory recognition of indoor daily activities and fall detection, to monitor the well-being of older people at risk of physical and cognitive chronic health conditions. Five different sensors, continuous wave (CW) radar, frequency-modulated CW (FMCW) radar, and inertial measurement unit comprising an accelerometer, gyroscope, and magnetometer were used to simultaneously collect data from 20 subjects performing 10 activities. Rather than using all of the available sensors, it is more efficient and economical to select part of them to maximise the classification accuracy and avoid unnecessary computation to process information if it is not salient. Each individual sensor and several sensor combinations are trained with a quadratic-kernel support vector machine classifier. In addition, they are validated with an improved statistical approach, which uses data from unknown participants to test model rather than random cross-validation to verify if the model generalises well for unknown subjects. Furthermore, the most suitable sensor combinations are derived for each specific group of tested subjects selected (e.g. the oldest, youngest, tallest, and shortest sub-groups of participants out of the entire group). [ABSTRACT FROM AUTHOR]

The authors construct the piecewise vibrational resonance (VR) method by introducing the piecewise idea and combine the re-scaled and twice sampling methods for the linear frequency modulated (LFM) signal. Importantly, they put forward a new spectral amplification factor to quantify the VR. The new spectral amplification factor has some advantages as compared with the cross-correlated coefficient, which can also be used to quantify the aperiodic VR. The top value of the spectrum amplification factor is the necessary and sufficient condition for the occurrence of the optimal VR phenomenon. Here, they discuss the effects of different parameters on VR by using some numerical examples. The method described in this study provides an effective way to improve the LFM signal, and even other kinds of frequency modulated signals. [ABSTRACT FROM AUTHOR]

A broadband beam‐forming antenna is designed for intelligent emergency detection and rescue systems. Recognizing emergencies hinges on identifying and analyzing the motion of humans. Combined with deep learning, the radio frequency signal of an antenna can capture the motion of humans behind a wall and in closed rooms using frequency‐modulated carrier wave (FMCW) signals operating in broadband from 5.56 GHz to 7.25 GHz (26%). The beam‐forming antenna is composed of four slot‐coupled patch antennas. The proposed array antenna satisfies a broad FMCW bandwidth and sufficient gain over 15.8 dBi in the overall bandwidth. To extend the focusing capability, we specifically design a 4 × 1 array structure and optimize the distance of antenna to 32.9 mm (0.7 λ0). The antenna is compact enough to realize a handheld motion‐tracking device. The array antenna forms a fan beam with a wide beam coverage and low side lobe level. The motion of a human body is tracked as a beam scanning by the antenna array. To accomplish this goal with adaptive array architectures, we implement beam‐forming techniques with a phase shifter, an amplifier, and a power divider. [ABSTRACT FROM AUTHOR]

Multistage reducer vibration signals have complicated spectral structures owing to the amplitude and frequency modulations of gear damage-induced vibrations and the multiplicative amplitude modulation effect caused by time-varying vibration transfer paths (in the case of local gear damage) when the multistage reducer contains both planetary and spur gears. Moreover, the difference between the vibration energies of these gears increases the difficulty of fault feature extraction when multiple failures occur in the reducer. As the meshing frequency of each gear group often varies significantly, variational mode decomposition can be performed to decompose the vibration signal according to frequency, enabling separation of the vibration signals of the spur and planetary gears. The common fault features of these gears can be extracted from the spectrum of the amplitude demodulation envelope. To verify the effectiveness of this method, we first analyzed a simulation signal, and then utilized the experimental signals from a laboratory multistage reducer for verification. In the multistage reducer simulation, we considered the amplitude and frequency modulation of the gear damage and transfer paths. In the experimental verification, we processed local faults (broken teeth) and uniform faults (uniform wear) on the sun gear and the spur gear of the planetary gear separately. [ABSTRACT FROM AUTHOR]

The vibration signals are usually characterized by nonstationary, nonlinearity, and high frequency shocks, and the redundant features degrade the performance of fault diagnosis methods. To deal with the problem, a novel fault diagnosis approach for rotating machinery is presented by combining improved local mean decomposition (LMD) with support vector machine–recursive feature elimination with minimum redundancy maximum relevance (SVM-RFE-MRMR). Firstly, an improved LMD method is developed to decompose vibration signals into a subset of amplitude modulation/frequency modulation (AM-FM) product functions (PFs). Then, time and frequency domain features are extracted from the selected PFs, and the complicated faults can be thus identified efficiently. Due to degradation of fault diagnosis methods resulting from redundant features, a novel feature selection method combining SVM-RFE with MRMR is proposed to select salient features, improving the performance of fault diagnosis approach. Experimental results on reducer platform demonstrate that the proposed method is capable of revealing the relations between the features and faults and providing insights into fault mechanism. [ABSTRACT FROM AUTHOR]

In this study, results of wideband dual polarised measurements conducted in indoor environments including office, factory, corridor and computer foyer, using state-of-the-art 2×2 multiple-input-multiple-output frequency modulated continuous wave-based channel sounder, are presented. The measurements were performed in two frequency bands with 6 GHz bandwidth, centred at 54 and 70 GHz, with directional steerable ~20 dBi (18° beamwidth) horn antennas. Using twists at the transmitter and at the receiver simultaneous co-polar and cross-polar measurements were performed to quantify the polarisation effects on channel parameters such as angular spread, delay spread and path loss. The results show that the co-polarised radio links experienced lower angular spread and delay spread compared with the cross-polarised links. For co-polarised links, the estimated synthesised omnidirectional path loss exponent was found to be in the range of 1.5-2 (close-in model) and 0.9-1.9 (log-distance model) in the respective environments. In individual scenarios, the median cross-polarisation ratio was found to be within 11.7-14.4 and 7.5-17.6 dB at 54 and 70 GHz, respectively. [ABSTRACT FROM AUTHOR]

In the state of oil-film instability coupled with rub-impact, the vibration signal of rotor-bearing system generally presents the weak non-linear frequency modulation (FM) features. In order to get a deep insight into the complicated FM phenomenon, the mechanism analysis is carried out on the motion model of non-linear Jeffcott rotor in oil-film instability coupled with rub-impact fault. The method of directional cyclic demodulation is proposed to extract the weak FM information embodied in the strong oil-film instability vibration. In this method, the directional cyclic autocorrelation density (DCRD) is adopted to infuse the information of two-directional vibration signals, and then is sliced along the cyclic frequency axis. The FM features and rotor motion direction are extracted from the slice of DCRD. Then the experimental research on the rotor-bearing system demonstrates the validity of the proposed method. [ABSTRACT FROM AUTHOR]

This article presents a simple and efficient method for the design of a self-diplexed antenna based on loading asymmetric grounding-vias. The structure consists of two antenna elements loaded with two asymmetric grounding-vias, specifying the uplink and downlink operation frequencies. By choosing the appropriate positions of the two grounding-vias, high isolation between the two antennas can be achieved. To validate the feasibility of the proposed structure, two self-diplexed antennas with different operational frequencies have been fabricated and tested. Experimental results verify the multi-functionalities of the proposed compact structure in terms of high isolation and low cross-polarization discrimination. [ABSTRACT FROM AUTHOR]

Signal demodulation method of a frequency output resonant gyroscope is studied in this study. It has been a major problem of frequency micro gyroscopes. The detection elements of frequency gyroscopes are two double-ended tuning forks (DETF). The vibratory response of DETF is a periodic signal modulated by both amplitude and frequency. According to the characteristic that the amplitude and frequency of the gyro signal vary continuously with time, the signal demodulation algorithm is designed based on instantaneous frequency analysis. Hilbert transform is used to solve the instantaneous frequency. The algorithm is programmed in digital signal processor (DSP) and a test circuit board is made. Experimental test demonstrates that the demodulation circuit has a high precision and linearity, and the correlation coefficient between input signals and demodulation results achieves as much as 0.99999998. The demodulation method is proved to be feasible. This study provides a new train of thought for the study of the signal demodulation method of frequency micro gyroscopes and brings a new direction for the signal analysis of resonant sensors. [ABSTRACT FROM AUTHOR]

A cascaded intensity modulator (IM) and phase modulator (PM) are used to modulate a continuous-wave (CW) laser and generate an optical frequency comb (OFC). Thus, the generated comb is utilized as an initial seed and combined with another CW-laser to generate four-wave mixing (FWM) in photonic crystal fiber (PCF). Results show that an initial flat 30 GHz OFC of 29, 55 lines within power fluctuation of 0.8 dB and 2 dB, respectively, can be achieved by setting the ratio of the DC bias to amplitude of sinusoidal signal at 0.1 and setting the modulation indices of both IM and PM at 10. Moreover, the 1st order of FWM created through 14 m of PCF has over 68 and 94 lines with fluctuation of 0.8 dB and 2 dB, respectively. Hence, the generated wavelengths of 1st left and right order of FWM can be tuned in a range from ~1500 nm to ~1525 nm and ~1590 nm to ~1604 nm, respectively. [ABSTRACT FROM AUTHOR]

This letter presents a reduced reference spur multiplying delay-locked loop (MDLL). The static phase offset (SPO) between the reference edge and its counterpart of MDLL output is the dominant mechanism causing reference spur in the spectrum of MDLL output. SPO is mainly caused by the non-idealities on charge pump (e.g., sink and source current mismatch) and control line (e.g., gate leakage of loop filter and voltage-controlled delay line control circuit). With a high-gain stage inserting between phase detector/phase frequency detector and charge pump, the equivalent SPO has been decreased by a factor equal to the gain of the gain stage. To validate the effectiveness of the proposed technique, an MDLL is implemented in TSMC CMOS 0.18 µm process. The simulation result shows that −60.1 dBc reference spur was achieved at center frequency of 1.8 GHz. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this study, an enhanced short-time Fourier transform (STFT)-based jamming mitigation system which employs several windows to increase time--frequency (t-f) plane resolution is proposed. A technique for employing near-optimum windows is also proposed. It is observed that selection of these windows leads to increasing the resolution of the t-f representation. An infinite impulse-response notch filter is employed for jamming removal process. Performance of the proposed method is evaluated by a set of measured global positioning system data. It is compared with conventional STFT-based algorithms reported in literature. [ABSTRACT FROM AUTHOR]

In monostatic continuous wave (CW) radar the dominant waveform is periodic linear frequency modulation, mostly because its stretch processing requires sampling rate much lower than the bandwidth. In a bistatic scene a clean copy of the transmitted signal, required in stretch processing, is not available to the receiver. That opens the competition for other periodic waveforms. The authors study describes and demonstrates, through bistatic field trials, the good performances of bi-phase and tri-phase CW waveforms. Among their advantages are sidelobe-free range response, availability at all prime lengths and ease of synchronisation. Successful bistatic operation is a prerequisite for multistatic systems. [ABSTRACT FROM AUTHOR]

In power electronics, the switching elements are controlled by pulse width modulated (PWM) signals making their currents on and off repeatedly. This might cause electromagnetic interference (EMI) problems especially in switched mode power supplies. One method for mitigating the EMI is to use the frequency modulation technique in the control signal of the switching metal-oxide-semiconductor field-effect transistor. According to this approach, frequency of the PWM signal is modulated in order to spread its spectrum and hence reduce the EMI levels. This paper presents the theoretical analysis for the spectrum of a frequency modulated PWM signal. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY It is important in maintenance to detect rubbing of sliding bearings in the early stage. An experiment on mild rubbing conditions was conducted, and the changes in vibration were examined. Importantly, a newly found fact is that peaks in the spectral domain with respect to the rotational period occur as a result of rubbing. Consequently, cepstrum analysis was shown to be effective for the detection of rubbing in the early stage. A device that can follow the level of the quefrency was developed based upon this idea. Utilizing the device is a highly efficient way to monitor the condition of a sliding bearing. [ABSTRACT FROM AUTHOR]

A new multilevel DC-link three-phase five-level voltage source inverter topology is introduced here. A multilevel DC-link formed from single DC voltage supply and two cascaded half-bridge (CHB) power cells is connected to 12-switch three-phase bridge in such a way that the proposed inverter produces five levels in the output voltage waveform. Compared to comparable inverters, such as symmetrical CHB and hybrid multilevel inverters, the proposed topology maximises the number of voltage levels and reduces the number of utilised DC voltage supplies, switches, gate driver circuits and installation area. A modified fundamental frequency modulation technique based on determination of switching states of inverter is developed, to generate the appropriate switching gate signals. Furthermore, to validate the proposed topology, a low power prototype inverter has been built. The obtained simulation and experimental results ensure the feasibility of the suggested topology and also the compatibility of the used modulation technique. [ABSTRACT FROM AUTHOR]

SUMMARY This paper describes the implementation of the first enhanced spread spectrum aloha demodulator, based on an innovative architecture which combines software-defined radio with processing via commercial graphics processing units. The validation tests performed both in laboratory conditions and directly on the satellite EUTELSAT 10A are presented. The performance assessment results obtained via satellite validate the theoretical results to a sufficient degree to make enhanced spread spectrum aloha technology a viable option for low-power mobile and fixed terminals, thus encouraging the growth of satellite mass market applications. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

LLC resonant converters, generally adopting frequency modulation control, can hardly achieve high efficiency under both heavy and light load conditions. Especially under light load conditions, the high-switching frequency seriously degrades converter's efficiency. This study propose a new pulse-width modulation (PWM) control strategy for LLC resonant converters under light load applications on the premise of no change in the main circuit structure. The voltage gain of the converter is regulated by varying duty ratio instead of increasing switching frequency and therefore zero-current switching for rectifier diodes can be realised under light load conditions. With the proposed PWM control strategy, the gain is not affected by the load variations and an optimal design of the magnetic components is possible, therefore the efficiency is further improved by reducing both the switching losses and the losses in magnetic components. Experimental results demonstrate the effectiveness of the proposed PWM strategy by increasing the efficiency of LCC resonant converter, especially under light load conditions. [ABSTRACT FROM AUTHOR]

In high-resolution radar systems, stretch processing technique is generally used to process the returned signals of a range-spread target. Consequently, this results in mixer outputs that consist of several linear frequency modulation components with a small frequency rate (FR). The authors define an FR function to transform a signal from the time domain into the FR domain and discuss the FR range of a discrete signal. Then an interesting phenomenon is found in the FR domain, that is, the mixer output is concentrated in a low FR region, while the Gaussian noise spreads over the entire FR region. Therefore, a range-spread target detector has been proposed that regards the integration of the values in a vicinity of zero FR as the test statistic. This detector uses a single mixer output and thus has the ability to detect the target with a high velocity. Finally, the proposed detector is evaluated by recorded radar data. Experimental results show that the proposed detector outperforms the detectors using the high-resolution range profile. [ABSTRACT FROM AUTHOR]

Birdsong often contains large amounts of rapid frequency modulation (FM). It is believed that the use or otherwise of FM is adaptive to the acoustic environment and also that there are specific social uses of FM such as trills in aggressive territorial encounters. Yet temporal fine detail of FM is often absent or obscured in standard audio signal analysis methods such as Fourier analysis or linear prediction. Hence, it is important to consider high-resolution signal processing techniques for analysis of FM in bird vocalizations. If such methods can be applied at big data scales, this offers a further advantage as large data sets become available., We introduce methods from the signal processing literature which can go beyond spectrogram representations to analyse the fine modulations present in a signal at very short time-scales. Focusing primarily on the genus Phylloscopus, we investigate which of a set of four analysis methods most strongly captures the species signal encoded in birdsong. We evaluate this through a feature selection technique and an automatic classification experiment. In order to find tools useful in practical analysis of large data bases, we also study the computational time taken by the methods, and their robustness to additive noise and MP3 compression., We find three methods which can robustly represent species-correlated FM attributes and can be applied to large data sets, and that the simplest method tested also appears to perform the best. We find that features representing the extremes of FM encode species identity supplementary to that captured in frequency features, whereas bandwidth features do not encode additional information., FM analysis can extract information useful for bioacoustic studies, in addition to measures more commonly used to characterize vocalizations. Further, it can be applied efficiently across very large data sets and archives. [ABSTRACT FROM AUTHOR]

ABSTRACT A fast and adjustable spectrum sensing method is proposed using a phase frequency detector for cognitive radio applications. Using this method, spectral sensing can be done in a very short time by a low-cost, low-power circuit, compared with available implemented methods. Different aspects of sensing procedure in different situations are investigated including frequency sweep time and system errors. Accurate operation of this method is verified through simulations, and comparison with other methods shows faster sweep rates. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a wide band linearly polarized beam squinted radial line slot array (RLSA) antenna at 5.8-GHz band. The open ended air gap technique was used to broader the bandwidth, reduce the antenna size but maintain the high-performance characteristic. The antenna implemented radiating slot design with diameter of 200 and 1.6 mm hybrid FR4 and 8-mm open ended air gap for dielectric height. The antenna also successfully fabricated and performed a good result. The measured results show a wide 38% of bandwidth with 16 dBi gain at 5.8-GHz frequency. The beamwidth obtained below 15° for E and H plane. The research found a wide band RLSA antenna can be achieved using air gap technique and will be a potential candidate for future point to point application for fixed broadband wireless access. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:938-944, 2014 [ABSTRACT FROM AUTHOR]

Fast encoding of frequency modulated ( FM) sweeps is crucial for communication. In humans, FM sweeps deviating from the acoustic regularity elicit the mismatch negativity ( MMN) evoked potential. Yet, direction sensitivity to FM sweeps is found in animals' primary auditory cortex, upstream of MMN sources found in humans. Here, we were interested in whether direction deviants of complex FM sweeps modulated brain responses earlier than MMN. We used a controlled oddball paradigm, and measured the middle latency responses ( MLRs) and the MMN. Our results showed a repetition enhancement to the standards at the Pa component of the MLR and a genuine MMN in the later response range. These results show that, early in the cortical hierarchy, the system is sensitive to the physical characteristics of the repetitive stimuli, but a higher-order mechanism is needed to detect violations of the acoustic regularity. [ABSTRACT FROM AUTHOR]

This study presents a very important feature of the technique of pulse width modulation (PWM) with injection of harmonic and triangular frequency carrier modulated in frequency. This technique is used to improve the quality of the output voltage signal of the power inverters controlled PWM. The purpose of this study is to show a new feature of controllability by the selection of different parameters. This allows multiple responses, from the point of view of the spectrum and the properties of the signal quality, with the same number of pulses per second, allowing the controllability of the modulated output signal. With this ability to control, it is possible to choose, for example, the total harmonic distortion of the signal output from the inverter, or the value of the fundamental term of voltage. It is also possible to select the low order harmonic, of interest for the selective reduction of harmonics. To show this feature, some examples have been developed with different number of pulses per period and with their corresponding parameter selection. [ABSTRACT FROM AUTHOR]

Cognitive dysfunction is suggested to be the best predictor of functional outcome in schizophrenia. Therefore, new diagnostic and treatment strategies are needed to both ascertain the biological underpinning of cognitive deficits and to restore them. Modulation of gamma oscillations (30-50 Hz) has been associated with cognitive performance, particularly in the dorsolateral prefrontal cortex (DLPFC). In this manuscript, we review evidence for gamma modulation deficits during cognitive performance in schizophrenia. We demonstrate that transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG) is a reliable method that permits systematic quantification of gamma modulation in the cortex. Using TMS-EEG, we show that patients with schizophrenia have selective gamma inhibition deficits in the DLPFC. Finally, we demonstrate that repetitive TMS therapy over the DLPFC can normalize excessive gamma oscillations and ultimately cognitive performance in patients. We suggest that restoring gamma impairments in the DLPFC may be a potential strategy for improving cognitive deficits in schizophrenia. [ABSTRACT FROM AUTHOR]

Gearboxes usually run under fluctuating load conditions during service, however most of papers available in the literature describe models of gearboxes under stationary load conditions. Main task of published papers is fault modeling for their detection. Considering real situation from industry, the assumption of stationarity of load conditions cannot be longer kept. Vibration signals issued from monitoring in maintenance operations differ from mentioned models (due to load non-stationarity) and may be difficult to analyze which lead to erroneous diagnosis of the system. The objective of this paper is to study the influence of time varying load conditions on a gearbox dynamic behavior. To investigate this, a simple spur gear system without defects is modeled. It is subjected to a time varying load. The speed-torque characteristic of the driving motor is considered. The load variation induces speed variation, which causes a variation in the gearmesh stiffness period. Computer simulation shows deep amplitude modulations with sidebands that don't differ from those obtained when there is a defective tooth. In order to put in evidence the time varying load effects, Short Time Fourier Transform and then Smoothed Wigner-Ville distribution are used. Results show that the last one is well suited for the studied case. The experimental validation presented at the end of the paper confirms the obtained results. Such results offer useful information when diagnosing gear transmissions by avoiding confusing conclusions from vibration signals. [ABSTRACT FROM AUTHOR]

The article presents a study which describes the first recordings of narwhals in winter in West Greenland. The study used an Offshore Acoustics hydrophone to collect data and a Sony TCD-D7 Digital Audio Tape (DAT) recorder. Results show that each sound produced by narwhals were classified as either tonal frequency modulated (FM) or pulsed (amplitude modulated).

The linear canonical transform is shown to be one of the most powerful tools for nonstationary signal processing. Based on the properties of the linear canonical transform and the classical Wigner-Ville transform, this paper investigates the Wigner-Ville distribution in the linear canonical transform domain. Firstly, unlike the classical Wigner-Ville transform, a new definition of Wigner- Ville distribution associated with the linear canonical transform is given. Then, the main properties of the newly defined Wigner-Ville transform are investigated in detail. Finally, the applications of the newly defined Wigner-Ville transform in the linear-frequency-modulated signal detection are proposed, and the simulation results are also given to verify the derived theory. [ABSTRACT FROM AUTHOR]

We propose a novel intercarrier interference (ICI) self-cancellation scheme for orthogonal frequency division multiplexing (OFDM) systems. The symmetric scheme is the best among all ICI self-cancellation scheme in the literature. Its coefficient pair is (1, − 1), and the loading subcarriers are the kth and N− k − 1th subcarriers, where N is the number of subcarriers. We propose to modify the symmetric scheme and change the coefficient pair from (1, − 1) to (1, −µ) where µis between 0 and 1. The proposed modified symmetric scheme has better carrier-to-interference-ratio (CIR) than all previous ICI self-cancellation schemes by at least 1.7 dB when the normalized frequency offset is 0.5. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper deals with an FPGA implementation of a high performance FM modulator and demodulator for software defined radio (SDR) system. The individual component of proposed FM modulator and demodulator has been optimized in such a way that the overall design consists of a high-speed, area optimized and low-power features. The modulator and demodulator contain an optimized direct digital frequency synthesizer (DDFS) based on quarter-wave symmetry technique for generating the carrier frequency with spurious free dynamic range (SFDR) of more than 64 dB. The FM modulator uses pipelined version of the DDFS to support the up conversion in the digital domain. The proposed FM modulator and demodulator has been implemented and tested using XC2VP30-7ff896 FPGA as a target device and can operate at a maximum frequency of 334.5MHz and 131MHz involving around 1.93 K and 6.4 K equivalent gates for FM modulator and FM demodulator respectively. After applying a 10 KHz triangular wave input and by setting the systemclock frequency to 100MHz using Xpower the power has been calculated. The FM modulator consumes 107.67mW power while FM demodulator consumes 108.67mW power for the same input running at same data rate [ABSTRACT FROM AUTHOR]

Dense deployments of hybrid WLANs result in high levels of interference and low end-user throughput. Many frequency allocation mechanisms for WLANs have been proposed by a large body of previous studies. However, none of these mechanisms considers the load that is carried by APs in terms of channel conditions, number of affiliated users as well as communication-load, in conjunction. In this paper, we propose LAC, a load-aware channel allocation scheme for WLANs, which considers all the above performance determinant factors. LAC incorporates an airtime cost metric into its channel scanning process, in order to capture the effects of these factors and select the channel that will provide approximately maximum long-term throughput. We evaluate LAC through extensive OPNET simulations, for many different traffic scenarios. Our simulations demonstrate that LAC outperforms other frequency allocation policies for WLANs in terms of total network throughput by up to 135%. [ABSTRACT FROM AUTHOR]

This paper describes the responses of brainstem lateral line units in goldfish, Carassius auratus, to constant-amplitude and to amplitude-modulated sinusoidal water motions. If stimulated with constant amplitude sinusoidal water motions, units responded with phasic (50%) or with sustained (50%) increases in dicharge rate. Based on isodisplacement curves, units preferred low (33 Hz, 12.5%), mid (50 Hz, 10% and 100 Hz, 30%) or high (200 Hz, 47.5%) frequencies. In most units, responses were weakly phase locked to the carrier frequency. However, at a carrier frequency of 50Hz or 100 Hz, a substantial proportion of the units exhibited strong phase locking. If stimulated with amplitude-modulated water motions, units responded with a burst of discharge to each modulation cycle, that is, units phase locked to the amplitude modulation frequency. Response properties of brainstem units were in many respects comparable to those of midbrain units, suggesting that they emerge first in the lateral line brainstem. [ABSTRACT FROM AUTHOR]

In this article, we discuss the accuracy of behavioral models in simulating the intermodulation distortion (IMD) of microwave GaN-based high-power amplifiers in the presence of strong electrothermal (ET) feedback. Exploiting an accurate self-consistent ET model derived from measurements and thermal finite-element method simulations, we show that behavioral models are able to yield accurate results, provided that the model identification is carried out with signals with wide bandwidth and large dynamics. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2789–2792, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24732 [ABSTRACT FROM AUTHOR]

Male concave-eared torrent frogs ( Odorrana tormota) have an unusually large call repertoire and have been shown to communicate ultrasonically. We investigated the individual specificity of male advertisement calls in order to explore the acoustic bases of individual recognition, which was demonstrated in an accompanying study. Vocalizations of 15 marked males were recorded in the field. A quantitative analysis of the signals revealed eight basic call-types. Two of them (the single- and multi-note long-calls) were investigated in more detail. Long-calls were characterized by pronounced and varying frequency modulation patterns, and abundant occurrence of nonlinear phenomena (NLP), i.e., frequency jumps, subharmonics, biphonations and deterministic chaos. The occurrence of NLP was predictable from the contour of the fundamental frequency in the harmonic segment preceding the onset of the NLP, and this prediction showed individual-specific patterns. Fifteen acoustic variables of the long calls were measured, all of which were significantly different among individuals, except biphonic segment duration. Discriminant function analysis (DFA) showed that 54.6% of the calls could be correctly assigned to individual frogs. The correct classification was above chance level, suggesting that individual specificity of calls underlie the ability of males to behaviorally discriminate the vocal signals of their neighbors from those of strangers, a remarkable feat for a frog species with a diverse vocal repertoire. The DFA classification results were lower than those for other anurans, however. We hypothesize that there is a tradeoff between an increase in the fundamental frequency of vocalizations to avoid masking by low-frequency ambient background noise, and a decrease in individual-specific vocal tract information extractable from the signal. [ABSTRACT FROM AUTHOR]

Electric power systems in Japan are composed of remote and distributed location of generators and loads mainly concentrated in large-demand areas. The structures having long-distance transmission tend to produce heavy power flow with increasing electric power demand. In addition, some independent power producers (IPP) and power producer and suppliers (PPS) are participating in the power generation business, which makes power system dynamics more complex. However, there was little observation as a whole power system. In this paper the authors present a global monitoring system of power system dynamics by using the synchronized phasor measurement of demand-side outlets. Phasor Measurement Units (PMU) are synchronized based on the global positioning system (GPS). The purpose of this paper is to show oscillation characteristics and methods for processing original data obtained from PMU after certain power system disturbances triggered by accidents. This analysis resulted in the observation of the lowest and the second lowest frequency mode. The derivation of eigenvalue with the two-degree-of-freedom model brings a monitoring of two oscillation modes. Signal processing based on wavelet analysis and simulation studies to illustrate the obtained phenomena are presented in detail. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(3): 10– 18, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20316 [ABSTRACT FROM AUTHOR]

The article expands the characterization of sea clutter as nonlinear dynamic process and the role of the z-parameter or Mann-Whitney rank-sum statistic with the use of a principled theoretical approach. The author states that degree of nonlinearity is governed by the extent of frequency modulation (FM). Moreover, the study suggests that radar sea clutter is nonlinear over appreciable timescales such that the temporal variation in the radar cross-section (RCS) is significant.. Furthermore, the nonlinearity is also determined by the extent of frequency modulation

Pulse‐compression techniques have been used for many years to increase sensitivity and range resolution in military and air traffic control radar systems. However, their application to ground‐based weather radar has, so far, been very limited and restricted to research applications. This article describes the practical implementation of pulse compression using non‐linear frequency modulation (NLFM) in a commercial digital processor/receiver and demonstrates its application to operational weather radars.Three case studies are presented, including the first application of pulse compression to ground‐based travelling wave tube (TWT) weather radars. TWT radars use coherent transmitters with relatively low peak power compared to traditional magnetron or klystron systems, so in this case the sensitivity gain is crucial. The cases are from two different operational radars and illustrate the improved range resolution and sensitivity gain obtained using NLFM pulses compared to traditional simple pulses. Observations obtained using NLFM 40 µs pulses were nearly 15 dB more sensitive than those recorded with lower resolution using 1 µs simple pulses. A comparison of concurrent precipitation observations obtained with a TWT radar using pulse compression and low peak power (NLFM 40 µs and 8 kW) and a nearby traditional magnetron weather radar (2 µs and 250 kW) is also presented. The higher power system was more sensitive by less than 4 dB, but the improved resolution in the pulse compression allowed for enhanced Doppler filtering of ground clutter. Copyright © 2007 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Formulations to determine the resonance frequencies of hexagonal and half hexagonal microstrip antennas have been proposed based on their equivalence with circular and semicircular microstrip antennas, respectively. The new configuration of half hexagonal patch formed by bisecting the full hexagon along its resonant length, has the same resonance frequency as that of the full hexagonal patch, with half the size. Simulations and experiments have been performed to validate the proposed method. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2876–2879, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22843 [ABSTRACT FROM AUTHOR]

This article discusses the determination of snow water equivalent by acoustic impulse of snowpacks in Saskatchewan and British Columbia, Canada. Depth and density of snow layers was estimated by seismological techniques and frequency-modulated continuous wave radar. This method also estimates the tortuosity of snow. The authors compared the acoustic sounding method with gravimetric sampling to determine snow water equivalent. According to the authors, correlation variations were primarily found with higher water contents and in areas where multiple layers were found.

This paper defines the issues required for the development of successful visualization sensors for use in open cut and underground mines. It examines the mine environment and considers both the reflectivity of the rock and attenuation effects of dust and water droplets. Millimeter wave technology, as an alternative to the more commonly used laser and sonar implementations, is selected due to its superior penetration through adverse atmospheric conditions. Of the available radar techniques, frequency modulated continuous wave (FMCW) is selected as being the most robust. The theoretical performance of a number of 77 and 94 GHz FMCW millimeter wave radar systems is determined and these confirm the capability of these sensors in the mining environment. Implementations of FMCW radar sensors for simple ranging and three-dimensional surface profiling are discussed before data obtained during field trials in mines is presented to justify the selection of this technology. © 2007 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Objective: Analyse the difference in school careers and secondary school qualification levels between unilateral hearing aid users and bilateral hearing aid users. Study design: Retrospective questionnaire study. Setting: Postal-based questionnaire. Participants: Names of adults known to have been fitted with unilateral or bilateral hearing aids during childhood were retrieved. This resulted in 292 names. Participants were selected using the following criteria: availability of the medical record, presence of bilateral hearing loss, completed secondary school education, normal IQ and a minimum aided word-recognition score of 70% at 10 years of age. The questionnaire was sent to 50 potential participants of whom 40 responded, resulting in two groups comprising 19 unilateral and 21 bilateral hearing aid users. Methods: A questionnaire was developed to obtain data on secondary school levels and aspects of the school careers, such as type of schools attended (mainstream versus special), repeating a school year and additional assistance (speech and language therapy, personal frequency modulation systems). Main outcome measures: Comparison of the benefit of bilateral hearing aid fitting versus unilateral hearing aid fitting on secondary school qualification level, type of school the children attended, class failure and additional assistance used. Results: The group of bilaterally fitted hearing aid users eventually completed secondary school at a superior level than the unilaterally fitted users. 33% of binaural hearing aid users achieved qualifications giving access to a bachelors degree compared with 21% of unilateral users. There were no differences between those fitted with unilateral and bilateral hearing aids in the type of schools attended, repeating a school year and additional assistance. Conclusions: The bilateral hearing aid users obtained superior secondary school qualifications than the unilateral users but their school careers were comparable. [ABSTRACT FROM AUTHOR]

An SCM optical FM method can obtain an FM gain, so it is effective on employing an RoF link which transfers a broad-band or multicarrier RF signal. However, the RF signal quality is degraded by intermodulation distortions due to the nonlinearity of LDs and optical frequency discriminator. The nonlinear compensation technique in the RoF link has been investigated in order to obtain a higher RF signal quality. This paper proposes an insertion-type distortion nonlinear compensation. In the proposed scheme, a nonlinear device is inserted between transmitter and receiver and we propose an optical chirp controller as the nonlinear device. The proposed scheme suppresses the higher order intermodulation distortion which degrades RF signal quality in the adaptive transmittance control method. In this paper we theoretically analyze the SFDR of the optical FM method using the optical chirp controller and show that improvement in the SFDR at 9 and 5 dB compared to methods without nonlinear compensation and the adaptive transmittance control method, respectively, can be obtained. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(12): 1–11, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20322 [ABSTRACT FROM AUTHOR]

Islanding protection is one of the most important sources of discrepancy in grid‐connected photovoltaic systems. Even when islanding is not very likely to happen, regulations demand the photovoltaic inverters to implement effective protection methods. Due to its several advantages, the frequency shift method of islanding prevention, commonly known as Sandia Frequency Shift, is one of the most important active methods. This method implements a positive feedback of the frequency that tends to move it outside the trip limits in case of islanding. The method shows a very high detection capability, which depends on both the values of the method parameters and the characteristics of the load that remains in the same power section after islanding.This paper develops a mathematical analysis of the Sandia Frequency Shift method and proposes a new methodology to design its parameters as a trade‐off between the detection capability, which is evaluated as a function of the load characteristics, and the distortion that the method could introduce in the grid as a consequence of transitory frequency disturbances. The ability of this methodology to design the method parameters and achieve the highest detection capability is satisfactorily proved by means of both simulation and experimental results on a commercial photovoltaic inverter that implements the method once its parameters have been designed with the proposed methodology. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We describe a method to determine a material's complex permittivity and permeability over a range of temperatures. Input impedances are calculated from scattering parameters measured with the sample terminated by two offset shorts. These are manipulated to solve for complex permittivity and permeability over the frequency band of the waveguide. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 449–453, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11086 [ABSTRACT FROM AUTHOR]

Birth and death rates, as so many other biological processes, are usually not linearly related to environmental variation. Common examples of non-linear response forms include unimodal “optimum-type” responses and various saturating responses. These responses filter the signal coming from the environment to a corresponding biological process. We explored how different types of environmental signal may be transformed to a biological process. We were interested in the effect of the filter on modulation of (1) the variance of the signal, on (2) the variance-covariance structure between the signal and the filtered signal, and on (3) the match between the power spectra of the signal and the filtered signal. We found that the filters will change the frequency distribution (mean, variance, modality) of the signal. Especially symmetric filters that have a single peak of optimum will change signal structure so that there either exists or does not exist a correlation between the signal and the filtered signal. When the correlation exists it may be either positive or negative depending on the signal's mode relative to the filter structure. Also, the power spectrum properties of the signal may be dramatically transformed after passing the filter, e.g., blue noise can turn into red noise. Our results strongly suggest that studies on the influence of external signals on biological processes, such as population dynamics, should explicitly consider how the signal is transferred to biological processes. [ABSTRACT FROM AUTHOR]

The oscillation line from a two-mode stabilized inner-mirror-type 633-nm He-Ne laser was locked to the iodine saturated absorption line. FM spectroscopy was used to detect the saturated absorption signal. An iodine cell was placed within the ring cavity to multiply the excited light. When the oscillation line on the red side (long-wavelength side) of the two-mode stabilized laser was locked to the 6-3 band P(33) transition a-component of 127I2/ the degree of frequency stabilization measured from the Allan variance σ(2, τ) was 2.3 × 10-11 × τ-1/2 on either the red or blue side. Under this condition, the nonmodulated optical power on the blue side was 1.3 mW. In addition, the dependence of the frequency shift of the P(33) transition a-component on iodine vapor pressure and the frequency separations of oscillations for a to j components were measured. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(3): 1–9, 2000 [ABSTRACT FROM AUTHOR]

In this paper, a four-port digital millimetric receiver (FP/DMR) is studied in detail. The FP/DMR is achieved by eliminating one of the output ports and the reference port of an ordinary six-port junction in the digital millimetric receiver proposed earlier. This paper provides the principle of operation of FP/DMR, its real time or “on-line” calibration methods, and a comparison with a traditional quadrature I/Q receiver. The principle of operation of the FP/DMR can also be used at lower frequencies (e.g., in the L-band) whenever mass-market applications demand the lowest possible receiver costs. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 350–355, 1999 [ABSTRACT FROM AUTHOR]