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Differential amplitude phase shift keying (DAPSK) is a promising modulation technique for use in high-mobility environments, as it does not require channel estimation. In this paper, a novel reduced complexity soft demodulator for high-order DAPSK constellations is proposed. The main idea relies on a two-step approximation of the sum-log demapper. In the first step, a parallel factor analysis (PARAFAC) decomposition is used to approximate log-likelihood ratios. Next, the basis functions obtained through the first step are approximated by piecewise-linear curves. Numerical optimization techniques are employed for the PARAFAC decomposition and its piecewise-linear approximation whose parameters are then stored in a lookup table. It has been verified through computer simulations that the proposed scheme clearly outperforms the scheme proposed in the paper “Reduced-complexity noncoherent soft-decision-aided DAPSK dispensing with channel estimation,” (IEEE Trans. Veh. Technol., vol. 62, pp. 2633–2643, 2013.), while also having lower computational cost. Moreover, it is shown that the performance of the exact sum-log demapper and the proposed demapper is very close for \text2\times \text4 and \text4\times \text16 DAPSK constellations. [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]

Demodulation is a necessary step in the field of diagnostics to reveal faults whose signatures appear as an amplitude and/or frequency modulation. The Hilbert transform has conventionally been used for the calculation of the analytic signal required in the demodulation process. However, the carrier and modulation frequencies must meet the conditions set by the Bedrosian identity for the Hilbert transform to be applicable for demodulation. This condition, basically requiring the carrier frequency to be sufficiently higher than the frequency of the modulation harmonics, is usually satisfied in many traditional diagnostic applications (e.g. vibration analysis of gear and bearing faults) due to the order-of-magnitude ratio between the carrier and modulation frequency. However, the diversification of the diagnostic approaches and applications shows cases (e.g. electrical signature analysis-based diagnostics) where the carrier frequency is in close proximity to the modulation frequency, thus challenging the applicability of the Bedrosian theorem. This work presents an analytic study to quantify the error introduced by the Hilbert transform-based demodulation when the Bedrosian identity is not satisfied and proposes a mitigation strategy to combat the error. An experimental study is also carried out to verify the analytical results. The outcome of the error analysis sets a confidence limit on the estimated modulation (both shape and magnitude) achieved through the Hilbert transform-based demodulation in case of violated Bedrosian theorem. However, the proposed mitigation strategy is found effective in combating the demodulation error aroused in this scenario, thus extending applicability of the Hilbert transform-based demodulation. [ABSTRACT FROM AUTHOR]

Features of propagation of low-frequency electromagnetic waves in the low-latitude ionosphere are considered in the case when such waves are generated by means of demodulation of the radiation of a high-power short-wave ground transmitter in the lower ionosphere. Calculations are performed in the ray approximation based on a simplified model (developed specially for the case under study) of the anomaly of the low-latitude equatorial electron density. It is demonstrated that latitude gradients of the equatorial anomaly may result in both additional focusing and defocusing of the beam of demodulated low-frequency waves. [ABSTRACT FROM AUTHOR]

Electric power system instantaneous frequency, also referred to as electrical network frequency (ENF), pollutes digital recordings due to a variety of factors (e.g., transformer hum). This unwanted interference has been used as a forensic tool in conjunction with a database of ground truth ENF measurements to determine the time at which a recording was made, as well as to detect tampering. Recent work has suggested that that ENF could be used to geolocate a digital recording under the assumption that the low-energy location-unique power system dynamics are observable, which is not always the case in the presence of noise and interference. This letter aims to take advantage of the intrinsic nature of power system instantaneous frequency in order to frame the ENF extraction problem as one of FM demodulation. By considering the ENF as a sinusoid of nominal power system frequency that is frequency modulated by a weak stochastic signal, a 0-Hz Intermediate Frequency (IF) signal can be created and analyzed rather than direct measurements. In doing so, significant data reduction can be achieved through extensive downsampling, FM demodulation algorithms can be applied to extract the ENF, and the spectrum of the IF signal provides a straightforward way of estimating the maximum observable frequency content of the ENF buried in a digital recording. These findings are supported through the analysis of audio recordings made in the presence of ENF interference in the U.S. Eastern Interconnection power system. [ABSTRACT FROM AUTHOR]

We present a novel method for demodulating multiple frequency components of an ac magnetic field for use in electromagnetic tracking systems. Our undersampling method allows for a low sampling rate to acquire signals of interest in a range of 20–30 kHz without significant loss of precision. Lower sample rates give additional computation time between each sample, allowing for real-time demodulation without expensive high speed data acquisition and processing hardware. This also allows the use of low speed high precision analog-to-digital converters (ADCs) for sampling high frequency signals. The presented system demodulates 16 frequency components from two signals using an Arduino Due microcontroller and a two channel 16-bit ADC. The demodulated signals are then used to accurately determine the position of a magnetic sensor to within 1 mm in a volume 25 cm \times 25~cm \times 25 cm. The system accuracy compares well with both commercial and research systems in terms of accuracy, but at a dramatically lower cost. [ABSTRACT FROM PUBLISHER]

When an optical chopper is used to modulate the light source, the rotating speed of the wheel may vary with time and subsequently cause jitter of the modulation frequency. The amplitude calculated from the modulated signal would be distorted when the frequency fluctuations occur. To precisely calculate the amplitude of the modulated light flux, we proposed a method to estimate the range of the frequency fluctuation in the measurement of the spectrum and then extract the amplitude based on the sum of power of the signal in the selected frequency range. Experiments were designed to test the feasibility of the proposed method and the results showed lower root means square error than the conventional way. [ABSTRACT FROM AUTHOR]

This work is devoted to the problems of information transmission with frequency shift keying and fast frequency hopping in special channels where the signal/noise ratio is low, and a high energy interfering signal is present. We propose a demodulation algorithm that is significantly more stable to the influence of a powerful interfering signal as compared to other known algorithms. Under these conditions, we show a statistical criterion that lets one significantly reduce error probability on the demodulator's output. For the chosen criterion we prove several lemmas that let us speed up the demodulation algorithm. Computer modeling results show that the proposed demodulation algorithm has better correcting ability under a powerful interfering signal than previously known ones. [ABSTRACT FROM AUTHOR]

This paper presents a zero-IF Gaussian frequency-shift keying (GFSK) demodulator based on a phase-domain analog-to-digital converter (Ph-ADC) which directly quantizes the phase information of the received complex baseband signal. The Ph-ADC linearly combines the in-phase and quadrature parts of the incoming signal, and the generated phase-shifted versions are fed to comparators to detect the zero-crossings and build a 4-b digital representation of the signal phase. Seeking for a low-area and low-power consumption realization, our proposal employs a resistor-less scheme which performs phase rotations in current domain. Together with the Ph-ADC, the fully integrated GFSK demodulator also includes a channel-filtering programmable gain amplifier and a symbol decision block. Altogether, the demodulator occupies 0.14 \mm^2 in a 0.13-\mu\m CMOS technology with a total power consumption of 190 \mu\W from a 1-V supply. For a data rate of 1 Mbps and 0.5 modulation depth, the GFSK demodulator requires an EB/N0 of 14.8 dB for a bit error rate of 0.1% considering a flicker noise corner of 150 kHz, obtains a dynamic range of 74 dB, and is able to tolerate carrier frequency offsets of \pm170 kHz. This performance safely complies with the requirements of the Bluetooth Low Energy (BLE) standard. [ABSTRACT FROM PUBLISHER]

The random demodulator (RD) and the modulated wideband converter (MWC) are two recently proposed compressed sensing (CS) techniques for the acquisition of continuous-time spectrally sparse signals. They extend the standard CS paradigm from sampling discrete, finite dimensional signals to sampling continuous and possibly infinite dimensional ones, and thus establish the ability to capture these signals at sub-Nyquist sampling rates. The RD and the MWC have remarkably similar structures (similar block diagrams), but their reconstruction algorithms and signal models strongly differ. To date, few results exist that compare these systems, and owing to the potential impacts they could have on spectral estimation in applications like electromagnetic scanning and cognitive radio, we more fully investigate their relationship in this paper. We show that the RD and the MWC are both based on the general concept of random filtering, but employ significantly different sampling functions. We also investigate system sensitivities (or robustness) to sparse signal model assumptions. Last, we show that “block convolution” is a fundamental aspect of the MWC, allowing it to successfully sample and reconstruct block-sparse (multiband) signals. Based on this concept, we propose a new acquisition system for continuous-time signals whose amplitudes are block sparse. The paper includes detailed time and frequency domain analyses of the RD and the MWC that differ, sometimes substantially, from published results. [ABSTRACT FROM PUBLISHER]

A new broadband frequency discriminator is introduced for demodulating the frequency modulated signals in the microwave frequency range. Direct demodulation with no need for tuning the center frequency of the resonance circuits is the most important advantage of the proposed technique. This technique uses the in-phase/quadrature demodulation, in some manner, without using any additional local oscillator for down conversion. Simulation of the proposed demodulator has been done with Advanced Design System software to evaluate and predict the system behavior. A setup based on the proposed method was designed and implemented in order to verify the accuracy of the theory. We tested the proposed frequency discriminator for FM signals at different microwave frequencies with various waveforms of the modulating signal. We also measured the bit error rate of the demodulator when the modulating signal is pseudorandom binary sequences for some data rates. To the best of our knowledge, this structure demonstrates the widest bandwidth direct demodulator without any tuning circuits among published FM demodulators to date. [ABSTRACT FROM AUTHOR]

We report on the design of a current-assisted photonic demodulator (CAPD) using standard 0.18- \mu\m complementary metal–oxide–semiconductor technology and its electrooptical characterization. The device can perform both light detection and demodulation in the charge domain, owing to a drift field generated in the silicon substrate by a majority carrier flow. Minimum-sized \10 \times \10\ \mu\m^2 CAPDs exhibit a direct-current charge–transfer efficiency larger than 80% (corresponding to demodulation contrast larger than 40% under sine-wave modulation) at the modest power consumption of 10 \mu\W and a 3-dB bandwidth of > 45 MHz. An excellent linearity value with an error lower than 0.11% is obtained in phase measurements. CAPDs with optimized modulation electrode geometries are finally designed, aiming at an improved contrast-versus-power tradeoff. [ABSTRACT FROM PUBLISHER]

Detection of modulated light signals transmitted by active image markers can be used in object localization tasks and machine vision applications. The asynchronous demodulation pixel is able to detect the signal transmitted by these modulated markers. The modulated marker position in a two-dimensional pixel array can be used to identify the marker location in the field. In this paper the asynchronous demodulation pixel is analyzed and its operation is investigated in the presence of non-ideal effects such as parasitic elements, device mismatches and process variations. The effect of demodulator bias conditions and different switch pulsing techniques are examined and a modified demodulator controlling method is presented to increase the dynamic range and sensitivity of the pixel compared with the common operation schemes. The different demodulator structures are also simulated as 64 × 64 pixel array sensors using a 0.18 μm standard CMOS process and their operation is compared regarding sensitivity, filter transfer function, pixel size and power consumption. [ABSTRACT FROM AUTHOR]

In this paper, a sensorless controller for an interior permanent-magnet synchronous motor is presented based on well-known high-frequency signal injection techniques. The issue of the demodulation process is the key point of this paper. A novel approach based on discrete Fourier transform and nonconventional reference frame transformation is presented, allowing a simple and robust noncoherent demodulation, i.e., in which no information about the carrier phase is needed. In the classically adopted coherent approaches, in fact, uncertainty about carrier phase reflects in uncertainty in the demodulated signal amplitude, affecting observer gains and signal-to-noise ratio and definitively providing a degradation of the performance of the estimator. Analytical development of the sensorless algorithm, including the demodulation technique, is provided. A complete investigation by simulation is carried out aiming at showing the performance of the proposed method. Finally, experimental results are presented based on a prototype motor drive for city scooters. [ABSTRACT FROM AUTHOR]

To acquire images of dynamic scenes from multiple points of view simultaneously, the acquisition time of vision sensors should be synchronized. This paper describes an illumination-based synchronization method derived from the phase-locked loop (PLL) algorithm. Incident light to a vision sensor from an intensity-modulated illumination source serves as the reference signal for synchronization. Analog and digital computation within the vision sensor forms a PLL to regulate the output signal, which corresponds to the vision frame timing, to be synchronized with the reference. Simulated and experimental results show that a 1,000 Hz frame rate vision sensor was successfully synchronized with 32 μs jitters. [ABSTRACT FROM AUTHOR]

This paper reports a fully integrated disposable labon- a-chip with acoustic microagitation based on a piezoelectric β-poly(vinylidene fluoride) (β-PVDF) polymer. The device can be used for the measurement, by optical absorption spectroscopy, of biochemical parameters in physiological fluids. It comprises two dies: the fluidic die that contains the reaction chambers fabricated in SU-8 and the β-PVDF polymer deposited underneath them; and the detection die that contains the photodetectors, its readout electronics, and the piezoelectric actuation electronics, all fabricated in a CMOS microelectronic process. The microagitation technique improves mixing and shortens reaction time. Further, it generates heating, which also improves the reaction time of the fluids. In this paper, the efficiency of the microagitation system is evaluated as a function of the amplitude and the frequency of the signal actuation. The relative contribution of the generated heating is also discussed. The system is tested for the measurement of the uric acid concentration in urine. [ABSTRACT FROM AUTHOR]

We describe a new method for high-frequency precision sensing. The method combines synchronous detection with chopping in a fully differential architecture that includes an instrumentation amplifier. An integrated circuit implementation of the proposed synchronous chopping demodulator front end was designed and fabricated in a 0.35-μm CMOS process technology and tested with high-frequency inductive position sensors. The measured results show that the new technique offers considerable advantages in terms of offset reduction compared to traditional techniques for these sensors, which rely on a microcontroller to measure the offset before each position measurement is taken. The measured average input-referred offset for the 20 fabricated chip samples is 87 μV at a chopping frequency of 500 kHz when the resonant target is off and synchronous demodulation and transmitter excitation are both applied at 1 MHz. The technique, in addition to improving system resolution and immunity to common-mode interference, allows these high-frequency position sensors to work with multiple targets, thus increasing speed and functionality. [ABSTRACT FROM AUTHOR]

The envelope order spectrum based on the generalized demodulation time-frequency analysis is proposed and applied to the processing of the gear instantaneous signal in this paper. The generalized demodulation time-frequency analysis approach that is a new signal processing method can decompose a multi-component signal into some single-component signals whose instantaneous frequencies possess physics sense. While each single-component signal can be amplitude and frequency modulated signal, the generalized demodulation time-frequency analysis approach is very applicable for processing the multi-component amplitude and frequency modulated signals. When fault occurs in gear, the gear vibration signal in the start-stop process shows the multi-component amplitude and frequency modulated characteristics. In the method of envelope order spectrum based on the generalized demodulation time-frequency analysis, firstly the multi-component signal is decomposed into some single-component signals by using the generalized demodulation time-frequency analysis method; secondly the envelope analysis is applied to each single-component signal; thirdly each envelope signal is resampled in angle-domain; finally the spectrum analysis is applied to each resampled signal and the envelope order spectrum can be obtained. Furthermore, the gear work state can be identified according to the envelope order spectrum. The analysis results from the simulated and experimental signals show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The partial maximum a posteriori probability (PMAP) principle can be applied to reduce the complexity of the multiple- input-multiple-output (MIMO) detection through the successive interference cancellation (SIC). In this paper, we apply the PMAP principle to the list detection method for MIMO detection, where the SIC is performed with a list of candidates. The PMAP principle helps to choose candidate symbol vectors in the list detection. It is shown that the proposed method outperforms the conventional list detection method with a reasonable complexity. [ABSTRACT FROM AUTHOR]

A novel design idea for frequency-locked-loop (FLL) discriminator is proposed, under the premise of changing rate of frequency-rate in returned signal is rather small, the signal after quadrature-demodulation can be regarded as a linear frequency-modulated (LFM) signal, by using estimations of its initial frequency and frequency rate as error control quantities of FLL, FLL's toleration ability to high dynamic signals is greatly enhanced. FFT discriminator and dot-product cross-product discriminator are exploited by FLL discriminator at different phase of frequencytracking, thus wide discriminate range and high discriminate precision are acquired. An effective and simple abnormal value elimination method is presented especially for the abnormal discriminate value under extremely-low-SNR. Simulation results applying the discriminator to a FLL showed that FLL can tolerate rather high dynamics and tracking accuracy of frequency achieved 0.2 Hz even under a SNR as low as --40 dB, which verified the validity of above ideas. [ABSTRACT FROM AUTHOR]

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Abstract  This paper presents a 0.35 μm CMOS AM demodulator circuit. Design details, simulations and measurements results of the monolithic implementation of a highly accurate synchronous rectifier are shown. The circuit implements an envelope detector with a ±1.5 V output swing on a 15 pF load. It dissipates 15 mW from a ±2.5 V voltage supply, and presents SNR = 81 dB measured at a THD = −40 dB for an input signal having 100% modulation index. [ABSTRACT FROM AUTHOR]

In this paper, we propose an original detection scheme for high rate short-range impulse radio ultra-wideband systems. The proposed receiver relies on both the introduction of the cyclic prefix at the transmitter and the use of a frequency domain multiuser detector at the receiver. Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) detection strategies have been investigated and compared with the classical RAKE, considering a scenario where several mobile terminals communicate with a base station in an indoor environment characterized by severe multipath propagation. The results show that the MMSE receiver achieves the best performance, irrespective of the number of active terminals, both in the uplink and in the downlink communications. Hence, the proposed approach is well suited in indoor wireless environments where the multipath propagation tends to increase the effects of both the inter-path and the inter-user interference. [ABSTRACT FROM AUTHOR]

An integrated quadrature demodulator with an on-chip frequency divider is reported. The mixer consists of a transconductance stage, a passive current switching stage, and an operational amplifier output stage. A complementary input architecture has been used to increase the transconductance for a given bias current. The circuit is inductorless and is capable of operating over a broad frequency range. The chip was implemented in a 0.13-µm CMOS technology. From 700 MHz to 2.5 GHz, the demodulator achieves 35 dB of conversion voltage gain with 250-kHz IF bandwidth, a double-sideband NF of 10 dB with 9-33 kHz 1/f-noise corner. The measured IIP3 is +4 dBm for a 0.1-MHz IF frequency and +10 dBm for a 1-MHz IF frequency. The total chip draws 20 to 24 mA from a single 1.5-V supply. [ABSTRACT FROM AUTHOR]

In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level discrimination performance and (2) lower tone-in-noise detection thresholds using a modulated masker compared to those using an unmodulated masker. In the current study, translations of these two experiments were carried out to test the hypothesis that analogous cues might be used in the envelope-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (ms=0.25) and a range of AM frequencies (4–64 Hz). In a second experiment, masked sinusoidal AM detection thresholds were compared in conditions with and without slow and regular fluctuations imposed on the instantaneous masker AM depth. Release from masking was obtained only for very slow masker fluctuations (less than 2 Hz). A physiologically motivated model that effectively acts as a first-order envelope change detector accounted for several, but not all, of the key aspects of the data. [ABSTRACT FROM AUTHOR]

A method for the accurate spectral analysis of signals containing components that do not require synchronism either with each other or with the sampling clock is presented. The method employs an algorithm based on the quadrature amplitude demodulation which is applied in a number of stages to achieve an accurate decomposition of a given time domain signal into frequency components. Using the simulated signal examples, the suitability of the method for the analysis of noisy quantized nonrepetitive signals is considered. When compared to the discrete Fourier transform, the benefits of using the method for the accurate detection of nonsynchronous tones in a signal are demonstrated. [ABSTRACT FROM AUTHOR]

We present a class of suboptimal multiple-symbol differential detectors (MSDDs) for differential unitary space-time (ST) codes in a time-selective Rayleigh flat-fading channel. These noncoherent detectors, termed Fano ST-MSDDs, employ the well-known Fano algorithm as their decoding engines. Their bit-error rate (BER) performance is excellent, as there is no irreducible error floor, even at very high fade rates. Compared with the sphere decoder, which is optimal, our best detector, termed an on-demand bi-Fano ST-MSDD, suffers only a 0.3 dB degradation in power efficiency. However, its computational complexity, as a function of the signal-to-noise ratio (SNR), is consistently lower than that of the sphere decoder and does not experience the exponential growth in complexity in the latter when the SNR decreases. It can thus be concluded that the Fano algorithm is a powerful detection strategy for differential ST codes in fading channels. Our main contribution is in making the modifications and improvements to the Fano algorithm that enables this realization. The innovations include the bi-Fano, edge-bi-Fano, and on-demand bi-Fano search strategies, as well as a new dynamic threshold adjustment scheme for avoiding unnecessary back-and-forth node evaluations during backtracking. [ABSTRACT FROM AUTHOR]

We investigate the performance degradation of basic modulation schemes in a rapidly time-varying channel using a first-order autoregressive channel model. Various performance metrics are used to indicate the relative advantages of each modulation scheme. We find that noncoherent frequency-shift keying (FSK) is suitable for operating at very high mobility and high signal-to-noise ratio, ideal for some military applications. We then propose a partially coherent detector for FSK and differential phase-shift keying that exploits partial channel knowledge to enable the receiver to operate effectively in both fast and slow fading. The maximum-likelihood rule obtained for the partially coherent FSK turns out to be a linear combination of coherent and noncoherent detection rules. Results demonstrate that significant performance improvement can be achieved over the best of coherent and noncoherent FSK detection. The detector is robust to estimation errors present in the channel statistics. We also propose a few adaptive schemes that employ various combinations of modulation schemes to increase the robustness of the system in fast fading. [ABSTRACT FROM AUTHOR]

Purpose ? This paper presents a prediction on the impact of technology scaling on phase-locked loop (PLL) performance behaviour. Power and maximum operating frequency of an Analogue PLL and a Type II phase-frequency detector (PFD)-based PLL from which the behaviours of other PLLs derived from the two architectures can be estimated, are analysed and their future behaviours as a function of technology are predicted. Design/methodology/approach ? Analogue models were developed and Mentor Graphics VHDL-AMS mixed-signal simulations were performed on the two PLL architectures. Behavioural power and frequency equations as a function of technology were derived based on thorough data and graphical analyses. Findings ? A prediction of PLL frequency and power dissipation as a function of technology for two main PLL architectures. Research limitations/implications ? The parameters in each equation derived should include other contributing factors as well as other design approaches such as multi-VDD, multi-Vth, etc. future work should also include prediction of jitter and phase noise for the two main PLL topologies. Originality/value ? This paper is of high significance in PLL design. The predicted equations could be used to reduce a major portion of a PLL designers' design time when choosing a PLL topology, and help them predict the impact of technology on the performance of the chosen architecture. [ABSTRACT FROM AUTHOR]

Abstract: The possibility of realizing femtogram mass detection using a piezoresistive microcantilever has been studied for bioscience applications. The mass detection was undertaken by employing the resonance frequency shift of a cantilever. In the experiments, we measured the change in the mass of adsorbed water molecules and the reaction between an antigen and an antibody on the cantilever from the resonance frequency shift. We used a prototype and a commercially available piezoresistive cantilever. The sensor was formed by using Wheatstone bridge circuits, a positive feedback controller, a piezoactuator and a phase-locked loop (PLL) demodulator. A mass sensitivity of around 200fg/Hz and a noise level of about 12fg were estimated experimentally from the water molecules adsorbed on the cantilever. We also confirmed that the sensor could detect an antigen and antibody reaction in an egg allergy test. [Copyright &y& Elsevier]

Islanding detection is a mandatory feature for grid- connected inverters. The effectiveness of passive islanding detection methods (IDMs) is usually demonstrated by means of nondetection zones (NDZ5) represented in a power mismatch space (ΔP versus SQ). Active frequency drifting IDMs have been shown to provide improved performance but their theoretical NDZ cannot be described in the ΔP versus ΔQ space for a general RLC load. This paper shows that a load parameter space based on the values of the quality factor and resonant frequency of the local load (Qf versus fo) can be used in these cases. It employs a single curve to represent the NDZ of frequency drifting IDMs for any RLC loads. Equations that represent NDZs of three common active IDMs in the Qf versus fo load parameter space are derived and it is shown that the slip mode frequency shift and the Sandia frequency shift IDMs can be designed to guarantee islanding detection for equivalent RLC loads with a quality factor smaller than a design value. The accuracy of the NDZs is verified with simulation and experimental results. [ABSTRACT FROM AUTHOR]

This letter introduces a generalized version of Kay's estimator for the frequency of a single complex sinusoid in complex additive white Gaussian noise. The Kay estimator is a maximum-likelihood (ML) estimator at high signal-to-noise ratio (SNR) based on differential phase measurements with a delay of one symbol interval. In this letter, the corresponding ML estimator with an arbitrary delay in the differential phase measurements is derived. The proposed estimator reduces the variance at low SNR, compared with Kay's original estimator. For certain delay values, explicit expressions for the window function and the corresponding high SNR variance of the proposed generalized Kay (GK) estimator are presented. Furthermore, for some delay values, the window function is nearly uniform and the implementation complexity is reduced, compared with the original Kay estimator. For a delay value of two, we show that the variance at asymptotically high SNR approaches the Cramer-Rao bound as the sequence length tends to infinity. We also explore the effect of exchanging the order of summation and phase extraction for reduced-complexity reasons. The resulting generalized weighted linear predictor estimator and the GK estimator are compared with both autocorrelation-based and periodogram-based estimators in terms of computational complexity, estimation range, and performance at both low and high SNRs. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel criterion for the detection of weak m-ary signals. In the sense of minimizing the error probability, the proposed criterion is optimal when the signal strength approaches zero. Based on the proposed criterion, a detection scheme for ultrawideband multiple access systems is proposed and analyzed in the presence of impulsive interference. Numerical results show that the proposed detector requires less complexity than, and possesses almost the same performance as, the maximum likelihood detector. In impulsive interference, the proposed detector also offers significant performance improvement over the detector optimized for a Gaussian environment. [ABSTRACT FROM AUTHOR]

Abstract: There are many phase measuring experimental setups in which the rate of temporal phase variation cannot be easily determined. In the case of phase stepping techniques, asynchronous phase measuring techniques were developed to solve this problem. However, there are situations for which the standard asynchronous techniques are not appropriated, like experiments with a sensitivity variation in the phase. In this work, we present an asynchronous demodulation technique for which the only requirement is the monotonicity of the phase in time. The proposed method is based in the computation of the quadrature sign (QS) of the fringe pattern and afterwards the demodulation is performed by a simple arccos calculation, that thanks to the QS extends its range from half fringe to a modulo 2π calculation. The presented demodulation method is asynchronous, direct, fast and can be applied to a general n-dimensional case. We have applied the proposed method to a load stepping experimental fringe pattern obtaining good results. [Copyright &y& Elsevier]

In this letter, we consider iterative decision-feedback differential demodulation (iterative DFDM), which was proposed previously as a low-complexity solution for power-efficient transmission over flat fading channels without channel state information at the receiver. We devise a modified demodulator (inner decoder), which improves both the achievable bit-error rate performance and the convergence of iterative UFOM without increasing complexity. We also establish an equivalent decoder model for iterative DFDM which enables a convergence analysis by means of extrinsic information transfer charts. [ABSTRACT FROM AUTHOR]

In this paper, we present a RAKE receiver design with adaptive antenna arrays for the wide-band code-division multiple- access (WCDMA) frequency-division duplexing (FDD) uplink. The RLS-based adaptive beamforming scheme is proposed and can be built with the existing one-dimensional RAKE receiver. We adaptively calculate the beamforming weight vector for each multipath of the desired user, and use maximum ratio combining (MRC) to combine each multipath signal in the demodulation process. Two matched filters based on the spreading waveforms are designed in our scheme for WCDMA FDD uplink application. The proposed scheme has the ability of suppressing strong multiuser access interference and the other types of interferers through spatial nulling. The tracking capability of the proposed algorithm is demonstrated in the simulation results. [ABSTRACT FROM AUTHOR]

It is shown that a non-square (NS) 22n+1-ary quadrature amplitude modulation (QAM) can be decomposed into a single parity-check (SPC) block encoder and a memoryless modulator in such a way that the inherent block encoder has a recursive nature. When concatenated with a forward-error-correcting (FEC) code, iterative demodulation, demapping, and decoding of the FEC code and the inherent SPC code of NS-22n+1-QAM is then possible. Simulation results show that coded NS-SQAM performs nearly 2 dB better than standard SQAM and star-8QAM, and nearly 1 dB better than 8-ary phase-shift keying when the FEC code is a rate-1/2, 16-state convolutional code, while coded NS-32QAM performs 0.75 dB better than standard 32QAM. [ABSTRACT FROM AUTHOR]

qIn this letter, we present a modification of Vertical Bell Laboratories Layered Space-Time (V-BLAST), and propose an effective transmit power allocation (TPA) scheme for the modified system. The proposed TPA scheme minimizes the uncoded bit-error rate (BER) averaged over all detection stages, and requires small feedback overhead. Simulation results show that the modified V-BLAST system with the proposed TPA scheme provides a significant reduction in the uncoded BER compared with the conventional V-BLAST system. When the minimum mean-square error nulling is adopted, the modified V-BLAST system is found to achieve the uncoded BER performance comparable to that of the maximum-likelihood detection for the conventional V-BLAST architecture. [ABSTRACT FROM AUTHOR]

In this paper, we show some preliminary numerical results in order to increase the multiplexing capability of a multipoint fiber Bragg grating (FBG) sensor network without increase the system complexity. We base the new approach on the possibility of exploiting the chirped-pulsed frequency modulation technique (C-PFM). This technique, extensively used in radar applications, is based on the amplitude modulation of the emitted signal (pulsed) by a chirped frequency signal and on the demodulation of the reflected signal by means of adaptive filter. FBG sensors are instrumental to obtain cheap and easy handling multipoint sensing arrays. [Copyright &y& Elsevier]

This paper presents a method for evaluating the performance of demodulation-based frequency measurement algorithms in the presence of additive interfering sinusoids. Determination of the performance of amplitude measurement schemes under such conditions is straightforward once the frequency responses of the filters involved in the process are known, since the error induced by a single interfering tone is easily computed using the cascade algorithm's frequency response magnitude. This paper presents a similar method for predicting the worst error of frequency measurement schemes with respect to sinusoidal interference. Once acquainted with the proposed error prediction formula, the only difficulty in designing effective frequency measurement algorithms is the appropriate selection of output filters to achieve the specified performance. The method has been used successfully in designing frequency measurement algorithms currently used in Hydro-Québec's special protection schemes. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) is a technique used for terrestrial digital video broadcasting (DVB-T) and many other modern applications. The longer OFDM symbol duration provides an advantage in a presence of weak impulsive noise, because impulsive noise energy is spread among simultaneously transmitted OFDM sub-carriers. However, it has been recently recognized that this advantage turns into a disadvantage of the impulsive noise energy exceeds certain threshold. In this paper the algorithm for impulsive noise suppression in OFDM receivers is proposed and investigated. Whereas traditional methods for impulsive noise suppression are implemented in a time domain before OEDM demodulation, proposed algorithm compensates impulsive noise in a frequency domain after OFDM demodulation and channel equalization. The method is applied to DVB- T and its performance is studied by means of simulation. [ABSTRACT FROM AUTHOR]

Presents an efficient method for evaluating the carrier frequency error in Gaussian minimum shift-keying (GMSK) communication systems. Frequency error measurement; GMSK neural network based demodulator; Method validation; Conclusion.

Presents information on a study which investigated the performance of asynchronous slow frequency-hop spread-spectrum multiple-access networks using M-ary frequency-shift keying (MFSK) modulation with noncoherent demodulation. Description of the system and channel model; Decision variables for a given multiple FSK symbol; Analytic approximation for the error probability; Numerical results; Conclusions.

Performance of a DSP demodulator for FM broadcasting receiver is examined by computer simulation and system parameters suitable for obtaining demodulated signal quality (SNR) are clarified. The DSP demodulator is preceded by an m-digit linear A-D converter operating at the IF stage of the receiver. A relation between required values of n, the register length of the processor, and m is investigated under the condition that a demodulated signal SNR of 60 dB and 55 dB for monophonic and stereophonic signals, respectively, is ensured. Moreover, only a slight increment of C/Ni (C is input carrier power; Ni is thermal noise power at the receiver input) is necessary to recover degradation due to quantization noise and mathematical rounding-off errors. Simulation results show that demodulation can be performed with a margin by using parameters n = 16 with m = 7 and 10 under the condition of C/Ni = 23.5 dB and 40.5 dB for monophonic and stereophonic signals, respectively. However, an ideal analog receiver requires C/Ni of 23.2 and 0,0.0 dB to obtain the previously mentioned demodulated SNRs. [ABSTRACT FROM AUTHOR]

FM demodulators using DSP techniques include the DPLL type, the quadrature type, the tangent type, etc. Compared to their analog counterparts, they are more useful with respect to stability, reliability and convenience of adjustment. However, since the detection characteristics for DPLL or quadrature-type demodulators are sinusoidal, the introduction of distortion cannot be avoided. In particular, if the input signal is wideband FM, there marked deterioration in the characteristics caused by distortion. This paper investigates the tangent-type FM demodulator whose circuit construction only has in the past been shown and whose characteristics have not been studied at all. It is made clear that the parameter-setting condition is strictly limited. Next, the detection condition is described and an improved tangent-type FM demodulator, whose detection characteristics are largely elevated, is represented and its better characteristics are shown. Moreover, comparison is made between this and other types of demodulators by means simulation, and the effectiveness of this type is shown. [ABSTRACT FROM AUTHOR]