Signal Power Distribution Research Articles

60-GHz Millimeter-Wave over Visible Light Communications for Downlink Wireless Networks

Background and Objective: In this paper, we address potential solution for downlink wireless communications by integrating visible light communications (VLC) with the broadband radio frequency (RF) networks operating at 60 GHz-millimeter wave (mmWave) band. For this hybrid design, the outdoor 60 GHz-mmWave based RF link is utilized to ensure backhaul connectivity for VLC indoor system, while the VLC exploiting the lighting infrastructure that essentially used LEDs as optical source to provide low-cost and high-speed data access. Methods: The hybrid 60 GHz-mmWave/VLC system is analyzed by using 16-QAM OFDM signal, and its performance is investigated by evaluating the signal to noise ratio (SNR) and the received signal power distributions, for regular placement of LEDs and random location of receivers within the room. The impact of the transmitter-receiver parameters, and their orientations and directivities are also considered. Results: Numerical results show the efficiency of the proposed system, which can retransmit RF signals at 60 GHz-mmWave band using visible optical carriers in the indoor environment. Conclusion: The results suggest that the hybrid 60 GHz-mmWave/VLC system is able to provide reliable wireless data transmission, making it an attractive solution for downlink indoor communications.

Bistatic radar cross section estimation by using DDM for better spatial resolution of ocean surface wind speed

The delay-Doppler map (DDM) is the signal power distribution of the Coarse/Acquisition code (C/A code) of the received Global Navigation Satellite System (GNSS) signal in different code phase delay and Doppler frequency. When the received signal is reflected from ocean surface, the DDM can be used to retrieve the ocean surface wind speed, which is the GNSS-reflectometry (GNSS-R) technique. Due to the signal power distribution in DDM is the correlation results of received and artificial C/A code from receiver in different code phase delay and Doppler frequency, the Woodward ambiguity function (WAF) occurs in the DDM. In the case of DDM, the WAF is the correlation results of two square waves in different code phase delay and Doppler frequency, and is approximated a triangular function and a sinc function in code phase delay and Doppler frequency axes, respectively. It means the correlation results not only show the code phase delay and Doppler frequency of the received signal but also influence the surrounding code phase delay and Doppler frequency values and cause the structure of DDM more complex. Using more bins in DDM in the wind speed retrieval process can reduce the influence of WAF but cause the spatial resolution to worsen. In order to use as less bins as possible in the retrieval process and not reduce the retrieval efficiency too much, a simple method to estimate bistatic radar cross section (BRCS) from DDM is developed in this study. Furthermore, a retrieval process is also developed for ocean surface wind speed retrieving by using less bins in the DDM from Cyclone Global Navigation Satellite System (CYGNSS) mission.

Comparison of power probability density functions for vertical sound propagation

When sound travels through the atmosphere, fluctuations in the wind velocity and temperature generate fluctuations in the sound amplitude and phase, which makes source detection, localization, and identification more difficult. While there are several parametric probability density functions for the signal power, the previous literature has not shown which model performs best in a wide variety of environments. This paper compares the noncentral Erlang, gamma, compound gamma, generalized gamma, and log exponentially modified Gaussian distributions' ability to approximate the signal power distributions collected at the National Wind Technology Center (Colorado, United States) in 2018. This weeklong experimental campaign measured the vertical and slanted sound propagation of a non-moving, sinusoidal source (600-3500 Hz) on the ground using microphones mounted to a meteorological tower up to 130 m high. The dataset included several different atmospheric conditions, which were recorded by the meteorological tower and resulted in a wide range of scattering regimes in the measured acoustic data. When evaluated using the Kullback-Leibler divergence, the gamma distribution was the best two-parameter model, and the log exponentially modified Gaussian distribution was the best three-parameter model.

Performance Analysis of RIS-Assisted Large-Scale Wireless Networks Using Stochastic Geometry

In this paper, we investigate the performance of a reconfigurable intelligent surface (RIS) assisted large-scale network by characterizing the coverage probability and the average achievable rate using stochastic geometry. Considering the spatial correlation between transmitters (TXs) and RISs, their locations are jointly modelled by a Gauss-Poisson process (GPP). Two association strategies, i.e., nearest association and fixed association, are both discussed. For the RIS-aided transmission, the signal power distribution with a direct link is approximated by a gamma random variable using a moment matching method, and the Laplace transform of the aggregate interference power is derived in closed form. Based on these expressions, we analyze the channel hardening effect in the RIS-assisted transmission, the coverage probability, and the average achievable rate of the typical user. We derive the coverage probability expressions for the fixed association strategy and the nearest association strategy in an interference-limited scenario in closed form. Numerical results are provided to validate the analysis and illustrate the effectiveness of RIS-assisted transmission with passive beamforming in improving the system performance. Furthermore, it is also unveiled that the system performance is independent of the density of TXs with the nearest association strategy in the interference-limited scenario.

Guaranteeing wireless communication reliability via an extended hybrid carrier system

In this paper, we propose an extended hybrid carrier system based on the weighted fractional Fourier transform to ensure the reliability of wireless communication. The proposed scheme improves the dispersion and compensation capabilities of the hybrid carrier system for channel fading through the design of the signal power distribution, which has greatly reduced the probability of high-power distortion of the signal and improved the bit error rate performance as a result. Theoretical analysis has shown the superiority of the extended hybrid carrier system. With a lower cost of computational complexity increment, the proposed scheme obtains a performance improvement without occupying additional time-frequency physical resources. Compared with the existing hybrid carrier scheme, numerical simulation results have shown that the proposed extended hybrid carrier scheme has better anti-fading performance under the doubly-selective channel and improves the reliability of the wireless communication system effectively.

IRS-Assisted RF-Powered IoT Networks: System Modeling and Performance Analysis

Emerged as a promising solution for future wireless communication systems, intelligent reflecting surface (IRS) is capable of reconfiguring the wireless propagation environment by adjusting the phase-shift of a large number of reflecting elements. To quantify the gain achieved by IRSs in the radio frequency (RF) powered Internet of Things (IoT) networks, in this work, we consider an IRS-assisted cellular-based RFpowered IoT network, where the cellular base stations (BSs) broadcast energy signal to IoT devices for energy harvesting (EH) in the charging stage, which is utilized to support the uplink (UL) transmissions in the subsequent UL stage. With tools from stochastic geometry, we first derive the distributions of the average signal power and interference power which are then used to obtain the energy coverage probability, UL coverage probability, overall coverage probability, spatial throughput and power efficiency, respectively. With the proposed analytical framework, we finally evaluate the effect on network performance of key system parameters, such as IRS density, IRS reflecting element number, charging stage ratio, etc. Compared with the conventional RF-powered IoT network, IRS passive beamforming brings the same level of enhancement in both energy coverage and UL coverage, leading to the unchanged optimal charging stage ratio when maximizing spatial throughput.

Constant Power Psychoacoustic Spectrum Optimization for Loudness and Sharpness with Application to Vehicle Interiors

<div>Sound quality assessments are an integral part of vehicle design. Especially now, as manufacturers move towards electrification, vehicle sounds are fundamentally changing. By improving the quality of the interior sounds of a vehicle, consumers’ subjective evaluation of it can be increased. Therefore, the field of psychoacoustics, which is the study of human perception of sound, is broadly applicable here. In fact, the perceived quality of a sound signal is influenced by several psychoacoustic indicators, including loudness, sharpness, and roughness. Of particular utility is identifying in advance how to distribute audible frequency content in a way that optimizes psychoacoustic metrics as this can help automotive engineers obtain specific design targets that optimize vehicle noise, vibration, and harshness (NVH).</div> <div>In this article, a novel modified gradient-based optimization technique (MGOT) is developed to optimize psychoacoustic loudness and sharpness. The new technique is applied to identify targeted adjustments to a measured vehicle interior sound signal that keep the signal energy constant but reduce loudness and/or sharpness. The MGOT numerically approximates the objective function gradient for small changes in the signal power distribution for which constant overall signal power is maintained. These gradient calculations identify power spectrum one-third octave band trades that minimize a sound signal metric that is a weighted sum of loudness and sharpness while conserving the total signal power. A trade consists of a reduction of power content from a one-third octave band designated as a source together with a simultaneous addition of that power to another receiver one-third octave band. In the MGOT, a one-third octave band that is at any time identified as a source can never later become a receiver of power. The MGOT results and execution times are compared with two widely available general-purpose optimization routines (a standard gradient-based optimizer and a “genetic,” non-gradient optimizer) are used to achieve identical optimization objectives. In comparison to existing optimization techniques, MGOT is found to identify spectrum modifications that produce a superior minimization of the objective function for comparable or even reduced execution times. The resultant sound spectrum modifications can guide vehicle structural or calibration design recommendations that realize a preferred frequency distribution for enhancing the vehicle driving experience.</div>

C-band 120-Gb/s PAM-4 transmissions over a 100-km dispersion-uncompensated SSMF using joint combined pulse shaping and low-complexity nonlinear equalization.

In C-band intensity modulation and direct detection (IM/DD) systems, the frequency-dependent power fading induced by chromatic dispersion (CD) and square-law detection limits the transmission capacity and distance, especially for beyond 100-Gb/s transmissions over a 100-km dispersion-uncompensated link. To reach this goal, we propose a scheme of nonlinear pre-distortion, novel, to the best of our knowledge, combined pulse shaping, and post nonlinear equalization for four-level pulse amplitude modulation (PAM-4)-based IM/DD systems. At the transmitter, the nonlinear pre-distortion is used to generate unequally spaced PAM-4 symbols for pre-compensating the nonlinearities. While the novel pulse shaping, simply shaped by the linear combination of two inter-symbol interference (ISI)-free pulses, alters the frequency-domain power distribution of the PAM-4 signal and results in performance improvement. At the receiver, low-complexity post nonlinear equalization using an absolute-term based nonlinear equalizer with weight sharing (AT-NLE-WS) is performed to eliminate CD-induced power fading and residual nonlinear impairments. With the cooperation of these techniques, record 120-Gb/s PAM-4 signals are successfully transmitted over a 100-km standard single-mode fiber (SSMF) with the measured bit error ratio (BER) below 3.8 × 10-3, achieving >9% improvement of system capacity in comparison with the conventional pulse shaping schemes.

Integrated signal dynamic power distribution method for inter-satellite ranging and communication links in navigation constellation

By utilizing inter-satellite ranging and communication links, the navigation system can operate autonomously. The unbalanced QPSK (UQPSK) signal can transmit two types of data with different rates simultaneously, by leveraging different power configurations for the orthogonal signal. Therefore, the ranging and communication functions can be both considered to improve the application of UQPSK in the navigation inter-satellite links. Based on the analysis of users' demand for communication and ranging performance, and given the transmission characteristics of inter-satellite links, this paper proposes an integrated dynamic signal power distribution method for inter-satellite ranging and communication links in navigation constellation. The parameters that affect the frequency spectrum efficacy are discussed in detail. The numerical results show that the proposed method can greatly improve the utilization efficacy of the spectrum. Moreover, the proposed method is validated by using the global navigation satellite system, which has certain guidance for the multifunctional design of the navigation inter-satellite links.

Signal power distributions for simulated outdoor sound propagation in varying refractive conditions.

Probability distributions of acoustic signals propagating through the near-ground atmosphere are simulated by the parabolic equation method. The simulations involve propagation at four angles relative to the mean wind, with frequencies of 100, 200, 400, and 800 Hz. The environmental representation includes realistic atmospheric refractive profiles, turbulence, and ground interactions; cases are considered with and without parametric uncertainties in the wind velocity and surface heat flux. The simulated signals are found to span a broad range of scintillation indices, from near zero to exceeding ten. In the absence of uncertainties, the signal power (or intensity) is fit well by a two-parameter gamma distribution, regardless of the frequency and refractive conditions. When the uncertainties are included, three-parameter distributions, namely, the compound gamma or generalized gamma, are needed for a good fit to the simulation data. The compound gamma distribution appears preferable because its parameters have a straight forward interpretation related to the saturation and modulation of the signal by uncertainties.

Vibroartrografi Kullanılarak Diz Eklemi Sağlığı Değerlendirmesi için Kontak Mikrofon Tabanlı Giyilebilir Cihazın Kurum İçi Geliştirilmesi

Nowadays, bone joint disorders are very common in humans. The knee joint abnormality often comes with the increasing age of people. Cartilage degradation and rubbing action of the femoral condyle to the tibial condyle generates the knee joint sounds and this stage turns into osteoarthritis. There are pre-existing diagnosis methods available like X-ray, MRI, etc. but they have their limitations. Some treatment methods are invasive and some are semi-invasive. Early diagnosis of osteoarthritis is possible using vibroarthrography which is a purely non-invasive method and sensor signal output can be featured as an informative tool for next-level treatment. In this study, a contact microphone-based wearable device has been fabricated for knee joint health monitoring and joint angle-based sensor voltage output is characterized. The result of fast Fourier transformation from healthy subjects is observed to be from 0 Hz-100 Hz and short-term Fourier transformation is performed for the obtained decibel value from 40-45 dB. The result of a pathological knee is studied in spectral density analysis and observed a continuous emission of joint sound and signal power distribution is observed over the frequency range of 0 Hz - 500 Hz.

Silicon nonlinear switch as a conditional circulator for monostatic LiDAR systems

All-optical silicon-photonics-based LiDAR systems allow for desirable features in scanning resolution and speed, as well as leverage other advantages such as size, weight, and cost. Implementing optical circulators in silicon photonics enables bidirectional use of the light path for both transmitters and receivers, which simplifies the system configuration and thereby promises low system cost. In this work, to the best of our knowledge, we present the first experimental verification of all-passive silicon photonics conditional circulators for monostatic LiDAR systems using a nonlinear switch. The proposed silicon nonlinear interferometer is realized by controlling signal power distribution with power-splitting circuits, allowing the LiDAR transmitter and receiver to share the same optical path. Unlike the traditional concept requiring a permanent magnet, the present device is implemented by using common silicon photonic waveguides and a standard foundry-compatible fabrication process. With several additional phase shifters, the demonstrated device exhibits considerable flexibility using a single chip, which can be more attractive for integration with photodetector arrays in LiDAR systems.

Physics-based modeling of sea clutter phenomenon by a full-wave numerical solver

The sea clutter phenomenon is investigated from a different perspective by using the finite element domain decomposition (FEDD) method, which is a full-wave numerical method based on the decomposition of the problem into sub-problems with the help of the locally-conformal perfectly matched layer (LC-PML) approach. The numerical model developed in this work provides the means to investigate the sea clutter phenomenon by a full-wave Maxwell solver, although the electrical size of computational domain is formidably large. Monte Carlo simulations are performed to obtain some statistical properties of reflectivity. The results are compared with those obtained from existing empirical models and measured data for different polarizations, frequencies, grazing angles and wind speeds (or sea states). It is numerically shown that the probability distribution of the clutter signal power appears to follow the gamma distribution. Furthermore, the concept of ergodicity, which means that the statistical results obtained by ensemble averaging in a single cell are equivalent to those obtained by spatial averaging over a set of consecutive range cells in a radar system, is examined. It is observed from the numerical results that the behavior of the sea clutter random field is consistent with the ergodicity hypothesis. Some conclusions are drawn about the statistical behavior of the sea surface reflectivity.

Characterization of Mayer-wave oscillations in functional near-infrared spectroscopy using a physiologically informed model of the neural power spectra.

.Significance: Mayer waves are spontaneous oscillations in arterial blood pressure that can mask cortical hemodynamic responses associated with neural activity of interest.Aim: We aim to characterize the properties of oscillations in the functional near-infrared spectroscopy (fNIRS) signal generated by Mayer waves in a large sample of fNIRS recordings. Further, we aim to determine the impact of short-channel correction for the attenuation of these unwanted signal components.Approach: Mayer-wave oscillation parameters were extracted from 310 fNIRS measurements using the fitting oscillations and one-over-f method to compute normative values. The effect of short-channel correction on Mayer-wave oscillation power was quantified on 222 measurements. The practical benefit of the short-channel correction approach for reducing Mayer waves and improving response detection was also evaluated on a subgroup of 17 fNIRS measurements collected during a passive auditory speech detection experiment.Results: Mayer-wave oscillations had a mean frequency of 0.108 Hz, bandwidth of 0.04 Hz, and power of . The distribution of oscillation signal power was positively skewed, with some measurements containing large Mayer waves. Short-channel correction significantly reduced the amplitude of these undesired signals; greater attenuation was observed for measurements containing larger Mayer-wave oscillations.Conclusions: A robust method for quantifying Mayer-wave oscillations in the fNIRS signal spectrum was presented and used to provide normative parameterization. Short-channel correction is recommended as an approach for attenuating Mayer waves, particularly in participants with large oscillations.

Base Station Coordination Scheme for Multi-Tier Ultra-Dense Networks

In this paper, we consider a relative received link power (RRLP)-based coordinated multi-point (CoMP) joint transmission (JT) in the multi-tier ultra-dense networks (UDN). In this CoMP scheme, we identify the cooperating base stations (BSs) by comparing the average received link power (ARLP) of the neighbouring BSs with respect to the BS having the strongest ARLP (i.e., the main link BS) to a user. To analyze the performance of this CoMP scheme in the downlink multi-tier UDN, we first approximate the received signal power distribution, and derive the coverage probability using stochastic geometry. After revisiting the area spectral efficiency (ASE) to make it more suitable for CoMP transmission in UDN, we also analyze the ASE and the network energy efficiency (NEE). Using simulations, we validate the derived coverage probability, and investigate the CoMP performance in multi-tier UDN. Our simulations show that the RRLP-based CoMP scheme can outperform the fixed number of strongest BS-based CoMP scheme in the high BS density regime. Our study of the NEE performance reveals that not only the RRLP-based CoMP scheme is more efficient than conventional non-CoMP transmission scenario, but also its NEE performance improves with the average number of cooperating BSs.

Brief segments of neurophysiological activity enable individual differentiation

Large, openly available datasets and current analytic tools promise the emergence of population neuroscience. The considerable diversity in personality traits and behaviour between individuals is reflected in the statistical variability of neural data collected in such repositories. Recent studies with functional magnetic resonance imaging (fMRI) have concluded that patterns of resting-state functional connectivity can both successfully distinguish individual participants within a cohort and predict some individual traits, yielding the notion of an individual’s neural fingerprint. Here, we aim to clarify the neurophysiological foundations of individual differentiation from features of the rich and complex dynamics of resting-state brain activity using magnetoencephalography (MEG) in 158 participants. We show that akin to fMRI approaches, neurophysiological functional connectomes enable the differentiation of individuals, with rates similar to those seen with fMRI. We also show that individual differentiation is equally successful from simpler measures of the spatial distribution of neurophysiological spectral signal power. Our data further indicate that differentiation can be achieved from brain recordings as short as 30 seconds, and that it is robust over time: the neural fingerprint is present in recordings performed weeks after their baseline reference data was collected. This work, thus, extends the notion of a neural or brain fingerprint to fast and large-scale resting-state electrophysiological dynamics.

An efficient cylindrical coordinate subgrid parabolic equation model for predicting the power distribution and coverage of radar signals in a complex multi‐scale marine environment

An efficient cylindrical coordinate subgrid parabolic equation model is proposed to predict the power distribution and coverage of radar signals in a complex multi-scale marine environment. The model adopts different grid systems for the multi-scale marine environment including flat sea surface, islands, ships and other elements, and realizes the transformation between grids through spatial mesh refinement technology. For the prediction of radio wave propagation in a large area complex environment, the model can balance the calculation efficiency and accuracy, thus effectively reducing the memory requirement and CPU computing time. In addition, combined with digital map and radar equation, the power distribution and coverage of radar signal in complex multi-scale marine environment are calculated. Numerical results verify the correctness and efficiency of the proposed model.

Millimeter-Wave Dielectric Slab-Based Chip-to-Chip Interconnect Network Allowing for Relaxed Assembly Tolerances

An on-chip, low-loss, and wideband transition to dielectric slab waveguide is proposed in this article, for millimeter-wave interchip communication network applications. The transition design features a three-terminal circuit with one on-chip planar microstrip line and two off-chip dielectric slab-waveguide ports. It presents an add-drop attribute, which can be employed to realize the traditional bus and backbone network topologies. Prototypes presented operate on a thin-film layer imitating the back-end-of-line layers of a chip. Measurements are performed for an end-to-end connection and a hexagonal ring interconnect network at 170 and 100 GHz, respectively. In addition, the proposed transition is shown to enable an equal signal power distribution scheme in a linear array of receivers. To provide much needed relaxation against mechanical tolerances and thermal expansion effects in multiport circuits based on the ceramic dielectric waveguide, a novel low-loss and mechanically flexible connection between two dielectric slab waveguides is presented. The design of this connection, operating from 80 to 100 GHz, is verified by measurements. Technical merits, packaging attributes, and limitations of the proposed single hierarchy interchip interconnect network are discussed.

Integrated Optical Power Splitter With Continuously Adjustable Power Splitting Ratio

Optical power splitter (OPS) as one of the basic elements in photonic integrated circuits (PIC) is widely used in many fields. The OPS with continuously adjustable power splitting ratio (PSR) can improve the flexibility of PIC and also simplify the PIC system. We propose and demonstrate an integrated OPS based on silicon-on-insulator. Our scheme combines several common structures such as 2 × 2 multimode interference coupler, waveguide grating and slot. The PSR of the OPS can be continuously adjustable by tuning the wavelength of the input signal or the voltages applied to the electrodes on the chip. The maximum tunable range of the PSR is from 28.2 dB to -1.7 dB when no voltages are applied to the electrodes and the wavelength of the input signal varies from 1542.62 nm to 1547.94 nm. And the maximum and minimum tunable ranges of the PSR are 35 dB and 0.4 dB, respectively, when the power consumption of the micro-heaters varies from 0 to 27 mW. So, our OPS can be both temperature-sensitive and temperature-insensitive. Our scheme has the advantages of compact structure and high flexibility, and it can be widely used in optical switching, signal channel division and power distribution.

Supply-Power-Constrained Cable Capacity Maximization Using Multi-Layer Neural Networks

We experimentally solve the problem of maximizing capacity under a total supply power constraint in a massively parallel submarine cable context, i.e., for a spatially uncoupled system in which fiber Kerr nonlinearity is not a dominant limitation. By using multi-layer neural networks trained with extensive measurement data acquired from a 12-span 744-km optical fiber link as an accurate digital twin of the true optical system, we experimentally maximize fiber capacity with respect to the transmit signal's spectral power distribution based on a gradient-descent algorithm. By observing convergence to approximately the same maximum capacity and power distribution for almost arbitrary initial conditions, we conjecture that the capacity surface is a concave function of the transmit signal power distribution. We then demonstrate that eliminating gain flattening filters (GFFs) from the optical amplifiers results in substantial capacity gains per Watt of electrical supply power compared to a conventional system that contains GFFs.