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Generalized spatial modulations (GSM) represent a novel multiple input multiple output (MIMO) scheme, which can be regarded as a compromise between spatial multiplexing MIMO and conventional spatial modulations, achieving both spectral efficiency and energy efficiency. Due to the high computational complexity of the maximum likelihood detector in large antenna settings and symbol constellations, in this correspondence paper we propose a lower complexity iterative suboptimal detector. The derived algorithm comprises a sequence of simple processing steps, namely, an unconstrained Euclidean distance minimization problem, an element-wise projection over the signal constellation, and a projection over the set of valid active antenna combinations. To deal with scenarios where the number of possible active antenna combinations is large, an alternative version of the algorithm, which adopts a simpler cardinality projection, is also presented. Simulation results show that, compared with other existing approaches, both versions of the proposed algorithm are effective in challenging underdetermined scenarios where the number of receiver antennas is lower than the number of transmitter antennas. [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]

Purpose -- This paper aims to demonstrate the practicability of the liquid metal printer, developed in the authors' laboratory, in the direct manufacture and assembly of circuit boards at the end customer side using GaIn24.5 alloy as printing ink at room temperature. Design/methodology/approach -- A practical procedure for printing a real designed frequency modulation (FM) radio circuit on flexible and transparent substrate using liquid metal printer was established. Necessary electronic components are then assembled on this circuit board. To enhance the mechanical stability of the FM radio circuit board, we further package the circuit board using room temperature vulcanizing silicone rubber. Finally, an efficient way to recycle the liquid metal ink and electronic components is presented at the end of circuit board's life cycle. Findings -- Methods of designing the circuit patterns that are applicable to liquid metal printer are similar to the conventional printed circuit board (PCB) designing strategies. The procedure of applying liquid metal printer for printing the circuits is entirely automatic, cost-effective and highly time-saving, which allows the user to print out desired device in a moment. Through appropriate packaging, the FM radio circuit board can be flexibly used. These PCBs own many outstanding merits including easy modification and stretchability. Nearly all liquid metal ink and components can be recycled. Originality/value -- The present end-customer-oriented liquid metal printing opens the way for large-scale personal electronics manufacture which is expected to initiate many emerging applications in education, design, industry, entertainment and more maker targets. [ABSTRACT FROM AUTHOR]

Recent advances in the Micro Electro-Mechanical System (MEMS) technology have made wireless MEMS accelerometers an attractive tool for Structural Health Monitoring (SHM) of civil engineering structures. To date, sensors' low sensitivity and accuracy--especially at very low frequencies--have imposed serious limitations for their application in monitoring large-sized structures. Conventionally, the MEMS sensor's analog signals are converted to digital signals before radio-frequency (RF) wireless transmission. The conversion can cause a low sensitivity to the important low-frequency and low-amplitude signals. To overcome this difficulty, the authors have developed a MEMS accelerometer system, which converts the sensor output voltage to a frequency-modulated signal before RF transmission. This is achieved by using a Voltage to Frequency Conversion (V/F) instead of the conventional Analog to Digital Conversion (ADC). In this paper, a prototype MEMS accelerometer system is presented, which consists of a transmitter and receiver circuit boards. The former is equipped with a MEMS accelerometer, a V/F converter and a wireless RF transmitter, while the latter contains an RF receiver and a F/V converter for demodulating the signal. The efficacy of the MEMS accelerometer system in measuring low-frequency and low-amplitude dynamic responses is demonstrated through extensive laboratory tests and experiments on a flow-loop pipeline. [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]

Energy detection is a widely used method for spectrum sensing in cognitive radios due to its simplicity and accuracy. However, it is severely affected by the noise uncertainty. To solve this problem, a blind multiband spectrum sensing scheme which is robust to noise uncertainty is proposed in this paper. The proposed scheme performs spectrum sensing over the total frequency channels simultaneously rather than a single channel each time. To improve the detection performance, the proposal jointly utilizes the likelihood function combined with Gerschgorin radii of unitary transformed covariance matrix. Unlike the conventional sensing methods, our scheme does not need any prior knowledge of noise power or PU signals, and thus is suitable for blind spectrum sensing. In addition, no subjective decision threshold setting is required in our scheme, making it robust to noise uncertainty. Finally, numerical results based on the probability of detection and false alarm versus SNR or the number of samples are presented to validate the performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

As a ranging sensor, a continuous transmission frequency modulation (CTFM) sonar with its ability for range finding and range profile formation works effectively under stationary conditions. When a relative velocity exists between the target and the sonar, the echo signal is Doppler-shifted. This situation causes the output of the sensor to deviate from the actual target range, thus limiting its applications to stationary conditions only. This work presents an approach for correcting such a deviation. By analyzing the Doppler effect during the propagation process, the sensor output can be corrected by a Doppler factor. To obtain this factor, a conventional CTFM system is slightly modified by adding a single tone signal with a frequency that locates out-of-sweep range of the transmitted signal. The Doppler factor can be extracted from the echo. Both verification experiments and performance tests are carried out. Results indicate the validity of the proposed approach. Moreover, ranging precision under different processing setups is discussed. For adjacent multiple targets, the discrimination ability is influenced by displacement and velocity. A discrimination boundary is provided through an analysis. [ABSTRACT FROM AUTHOR]

We present an extensive atomic resolution frequency modulation dynamic force microscopy study of ultrathin aluminium oxide on a single crystalline NiAl(110) surface. One-dimensional surface defects produced by domain boundaries have been resolved. Images are presented for reflection domain boundaries (RDBs), four different types of antiphase domain boundaries, a nucleation-related translation domain boundary and also domain boundary junctions. New structures and aspects of the boundaries and their network are revealed and merged into a comprehensive picture of the defect arrangements. The alumina film also covers the substrate completely at the boundaries and their junctions and follows the structural building principles found in its unit cell. This encompasses square and rectangular groups of surface oxygen sites. The observed structural elements can be related to the electronic signature of the boundaries and therefore to the electronic defects associated with the boundaries. A coincidence site lattice predicted for the RDBs is in good agreement with experimental data. With Σ = 19 it can be considered to be of low-sigma type, which frequently coincides with special boundary properties. Images of asymmetric RDBs show points of good contact alternating with regions of nearly amorphous disorder in the oxygen sublattice. [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]

Frequency modulation detection limens (FMDLs) were measured for carrier frequencies (fc) of 1000, 4000, and 6000 Hz, using modulation frequencies (fm) of 2 and 10 Hz and levels of 20 and 60 dB sensation level (SL), both with and without random amplitude modulation (AM), applied in all intervals of a forced-choice trial. The AM was intended to disrupt excitation-pattern cues. At 60 dB SL, the deleterious effect of the AM was smaller for fm = 2 than for fm = 10 Hz for fc = 1000 and 4000 Hz, respectively, while for fc = 6000 Hz the deleterious effect was large and similar for the two values of fm. This is consistent with the idea that, for fc below about 5000 Hz and fm = 2 Hz, frequency modulation can be detected via changes in phase locking over time. However, at 20 dB SL, the deleterious effect of the added AM for fc = 1000 and 4000 Hz was similar for the two values of fm, while for fc = 6000 Hz, the deleterious effect of the AM was greater for fm = 10 than for fm = 2 Hz. It is suggested that, at low SLs, the auditory filters become relatively sharp and phase locking weakens, so that excitation-pattern cues influence FMDLs even for low fc and low fm. [ABSTRACT FROM AUTHOR]

We present new frequency allocation schemes for wireless networks and show that they outperform all other published work. Two categories of schemes are presented: 1) those purely based on measurements and 2) those that use site-specific knowledge, which refers to knowledge of building layouts, the locations and electrical properties of access points (APs), users, and physical objects. In our site-specific knowledge-based algorithms, a central network controller communicates with all APs and has site-specific knowledge so that it can a priori predict the received power from any transmitter to any receiver. Optimal frequency assignments are based on predicted powers to minimize interference and maximize throughput. In our measurement-based algorithms, clients periodically report in situ interference measurements to their associated APs; then, the APs' frequency allocations are adjusted based on the reported measurements. Unlike other work, we minimize interference seen by both users and APs, use a physical model rather than a binary model for interference, and mitigate the impact of rogue interference. Our algorithms consistently yield high throughput gains, irrespective of the network topology, AP activity level, number of APs, rogue interferers, and available channels. Our algorithms outperform the best published work by 18.5%, 97.6%, and 1180% for median, 25th percentile, and 15th percentile user throughputs, respectively. [ABSTRACT FROM AUTHOR]

The framework of digital frequency modulation (FM) exciter is proposed, and the realization scheme of stereo signal composition and frequency modulation is studied. Combined with analysis and algorithm simulation, the design of hardware platform based on FPGA + DDS structure is accomplished. The performance of the signal after demodulation is analyzed by modulation analyzer and stereo decoder. Test results indicated that, compared with the conventional analog realization scheme, the signal synthesis method in digital FM exciter had simple structure and less error, and each parameter can satisfy the requirement of synchronization in broadcasting system, demanding exat unison in frequency, phase and modulation degree. [ABSTRACT FROM AUTHOR]

In this paper, a novel trellis source encoding scheme based on punctured ring convolutional codes is presented. Joint Source and Channel Coding (JSCC) using trellis coded Continuous Phase Modulation (CPM) with punctured convolutional codes over rings is investigated. The channels considered are the Additive White Gaussian Noise (AWGN) channel and the Rayleigh fading channel. Optimal soft decoding for the proposed JSCC scheme is studied. The soft decoder is based on the A Posteriori Probability (APP) algorithm for trellis coded CPM with punctured ring convolutional codes. It is shown that these systems with soft decoding outperform the same systems with hard decoding especially when the systems operate at low to medium Signal-to-Noise Ratio (SNR). Furthermore, adaptive JSCC approaches based on the proposed source coding scheme are investigated. Compared with JSCC schemes with fixed source coding rates, the proposed adaptive approaches can achieve much better performance in the high SNR region. The novelties of this work are the development of a trellis source encoding method based on punctured ring convolutional codes, the use of a soft decoder, the APP algorithm for the combined systems and the adaptive approaches to the JSCC problem. [ABSTRACT FROM AUTHOR]

High frequency field expressions are derived around feed point of a two dimensional Gregorian system using the Maslov's method. Maslov's method is a systematic procedure for predicting the field in the caustic region combining the simplicity of ray and generality of the transform method. Numerical computations are made for the computation of field pattern around the caustic of a Gregorian system. [ABSTRACT FROM AUTHOR]

In this paper, we propose a cognitive radio based multi-user resource allocation framework for mobile ad hoc networks using multi-carrier DS CDMA modulation over a frequency-selective fading channel. In particular, given preexisting communications in the spectrum where the system is operating, in addition to potential narrow-band interference, a channel sensing and estimation mechanism is provided to obtain information such as subcarrier availability, noise power and channel gain. Given this information, both frequency spectrum and power are allocated to emerging new users (i.e., cognitive radio users), based on a distributed multi-user resource allocation framework, in order to satisfy a target data rate and a power constraint of each cognitive radio user, while attempting to avoid interference to the existing communications as well as to minimize total power consumption of the cognitive radio users. [ABSTRACT FROM AUTHOR]

In this paper, a method for precise rms measurement of periodic signals based on signal reconstruction is presented. Reconstruction is performed in two steps. In the first step, the Fourier coefficients are estimated from integrative samples, and in the second step, using the method of least squares and precision measurement of rectified-signal average, the estimators are corrected. It is shown that this approach considerably increases accuracy of the rms measurements of low-frequency signals. [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]

The performance characteristics of a frequency-selective Josephson detector based on a symmetrical [001]-tilt YBa2Cu3O7− x bicrystal junction have been studied in the terahertz frequency range. At an external radiation frequency of 0.692 THz and a detector temperature of 55 K, the volt-watt responsivity reaches (7 ± 2) × 104 V/W, which corresponds to theoretical estimates calculated with allowance for thermal fluctuations in the junction. The noise equivalent power (2.9 ± 0.9) × 10–13 W/Hz1/2 and the power dynamic range D = 47 ± 3 dB of the detector are determined by the excess 1/ f type noise in the junction. It is shown that NEP values up to 5 × 10−15 W/Hz1/2 and D above 60 dB can be reached with high-frequency modulators or pulsed sources of terahertz radiation. [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]

Presents information on a study that examined a nonlinear-controlled strategy for soft-switched series-resonant DC/AC inverter without auxiliary switches. Principles of the full-bridge series-resonant DC/AC inverter; System control and synthesized sinusoidal waveforms; Conclusion of the study.

A low-threshold amplifier–discriminator (AD) is intended for reading information from resistive-plate chambers (RPCs) and consists of a preamplifier and discriminator. The minimum operation threshold of the device is 60 μV at an input impedance of 25 Ω, which corresponds to a charge of 0.12 pC induced on a strip. The AD time jitter is below 0.6 ns over an input signals range of (2–20)Uthr. The preamplifier noise referred to the input is <25 μV (rms). The AD was developed for testing RPCs for the ATLAS (CERN) experiment. [ABSTRACT FROM AUTHOR]

Doppler-free absorption spectrum from 5P56S to 5P56P transitions of Xe in a hollow cathode discharge was measured in the wavelength region from 810 to 910 nm. The saturated dip signals detected by a frequency modulated probe beam were doubly AM-modulated by a pump beam chopped using a conventional mechanical chopper. The Doppler background was greatly reduced by detection using a second lock in amplifier synchronous to the chopping signal. The isotope shifts of even mass 136−128Xe in natural abundance were resolved for the five transitions from the metastable states of J=2 and 0, while in the transitions from the J=1 states were partially resolved. The nuclear magnetic and quadrupole hyperfine coupling constants of 131Xe and 129Xe determined are listed with those reported previously. The specific mass shifts and the field shifts were estimated using the relation given by King''s diagram and compared with those obtained from the changes in the mean square-radii of the nuclear charge distribution. [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]

Describes a high-frequency modulation and detection system capable of measuring absorbance changes on the order of 10[sup-6] in optical pump-probe experiments using submilliwatt laser powers from a mode-locked ultrafast laser. Use of two base oscillators to realize a single modulation scheme; Shot-noise-limited performance offered by the system.

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]

Nanoscale plasmonic switch based on graphene at far infrared frequencies are proposed and designed. Mode-guiding switching/mode-cutoff analyses are given for the modulation function. High modulation depth and bandwidth can be obtained. This plasmonic graphene-based switch can be used to promote the performance of current switches in the integrated optical field, providing another method for interconnect in ultrahighly integrated photonic circuits. [ABSTRACT FROM AUTHOR]

In this letter, we propose a high speed and ultralow driving voltage traveling wave electro-optic (EO) modulator based on a dual horizontal slot waveguide. The proposed design harnesses the unique properties of ferroelectric materials such as LiNBO3 and exotic, organic EO polymers to tightly confine both the optical and rf modes in a nanoscale slot maximizing the nonlinear interaction with the electric field. Larger electrode separation allows for significant reduction in rf propagation loss. Simulations of the half-wavelength voltage-length product and electro-optic response of the proposed device reveal ultrabroadband operation, up to 250 GHz, and subvolt driving voltage for a 1 cm long modulator. [ABSTRACT FROM AUTHOR]

In this letter, we propose a high speed and ultralow driving voltage traveling wave electro-optic (EO) modulator based on a dual horizontal slot waveguide. The proposed design harnesses the unique properties of ferroelectric materials such as LiNBO3 and exotic, organic EO polymers to tightly confine both the optical and rf modes in a nanoscale slot maximizing the nonlinear interaction with the electric field. Larger electrode separation allows for significant reduction in rf propagation loss. Simulations of the half-wavelength voltage-length product and electro-optic response of the proposed device reveal ultrabroadband operation, up to 250 GHz, and subvolt driving voltage for a 1 cm long modulator. [ABSTRACT FROM AUTHOR]

A bilayer magnetostrictive sensor is inserted into a cylindrical tube where air flows at a controlled rate. A circuit connected to the sensor conveys a signal that arises from changes in frequency as a function of displacement using the frequency modulation principle. The performance of the sensor was tested at air stream speeds up to 25 m/s and at a range of distances from the center of the tube. The acquired response of the sensor was compared against a displacement simulation model designed using the Comsol Structural Mechanics package. The results demonstrate that this system provides a robust solution to the problem of monitoring variable airflows as needed by the automotive and biomedical industry. [ABSTRACT FROM AUTHOR]

The use of channelled waves in tunable 2-D anisotropic L-C meshes as a means for frequency identification has been investigated. For such structures it is shown that under resonant conditions signal propagation is restricted to a narrow well-defined channel. Using this type of grid, a single matched detector is required from which the frequency of an unknown applied signal can be directly determined from the value of voltage used to tune the grid. Experimental characterisation of a tunable grid operating from 2.2 to 3.4 GHz is given. [ABSTRACT FROM AUTHOR]

Using a 1 MHz length-extension type of quartz resonator as a force sensor for frequency-modulation atomic force microscopy (AFM), atomically resolved images of the Si(111)-(7×7) surface was obtained. Fabrications of a tip attached at the front end of the resonator by focused ion beam, and removal of the native oxide layer on the tip by in-situ field ion microscopy are found effective for achieving the highly-resolved AFM imaging. [ABSTRACT FROM AUTHOR]

Considers the application of max-log-ML symbol estimation postprocessing for intermediate frequency limiter-discriminator-integrator (LDI) detectors, which can be used in Bluetooth or DECT receivers. Demonstration that this postprocessing considerably improves the error performance obtained with regular limiter-discriminator-integrator based receivers.