Indoor small-scale spatiotemporal propagation characteristics across multiple 5G millimeter-wave (mmWave) candidate bands are investigated. First, using a custom-designed channel sounder, channel ...measurement campaigns are conducted in indoor environments to capture the delay and angles of departure and arrival of the paths. Measurement results exhibit excellent agreements with physical scatterers and radio propagation environments. Next, the layout-related multipath propagation analyses are utilized to model frequency-dependent channel parameters for different polarimetric combinations, including root-mean-square delay and angular spread. Modeling results not only complete the 3GPP channel model above 6 GHz, but also help to understand the impacts of frequency and polarization on the radio wave propagation at the mmWave bands.
This work establishes and validates a Grid Graph Signal Processing (G-GSP) framework for estimating the state vector of a radial distribution feeder. One of the key insights from GSP is the ...generalization of Shannon's sampling theorem for signals defined over the irregular support of a graph, such as the power grid. Using a GSP interpretation of Ohm's law, we show that the system state can be well approximated with relatively few components that correspond to low-pass Graph Fourier Transform (GFT) frequencies. The target application of this theory is the formulation of a three-phase unbalanced Distribution System State Estimation (DSSE) formulation that recovers the GFT approximation of the system state vector from sparse Advanced Metering Infrastructure (AMI) measurements. To ensure convergence of G-GSP for DSSE, the proposed solution relies on a convex relaxation technique. Furthermore, we propose an optimal sensor placement algorithm for AMI measurements. Numerical results demonstrate the efficacy of the proposed method.
This paper reports on the impact of soft- and hard-switching conditions on the dynamic ON-resistance of AlGaN/GaN high-electron mobility transistors. For this study, we used a special double pulse ...setup, which controls the overlapping of the drain and gate waveforms (thus inducing soft and hard switching), while measuring the corresponding impact on the ON-resistance, drain current, and electroluminescence (EL). The results demonstrate that the analyzed devices do not suffer from dynamic R ON increase when they are submitted to soft switching up to V DS = 600 V. On the contrary, hard-switching conditions lead to a measurable increase in the dynamic ON-resistance (dynamic-R ON ). The increase in dynamic R ON induced by hard switching is ascribed to hot-electrons effects: during each switching event, the electrons in the channel are accelerated by the high electric field and subsequently trapped in the AlGaN/GaN heterostructure or at the surface. This hypothesis is supported by the following results: 1) the increase in R ON is correlated with the EL signal measured under hard-switching conditions and 2) the impact of hard switching on dynamic R ON becomes weaker at high-temperature levels, as the average energy of hot electrons decreases due to the increase scattering with the lattice.
When a fault occurs on the tie line of ac/dc hybrid system, the change rule of electrical quantity on the inverter side is different from that of infinite ac power source. Sensitivity and reliability ...of the traditional relay protection methods will be affected. A longitudinal protection method for ac/dc hybrid system based on voltage wave similarity comparison is proposed. The protection compares the similarity of the measuring voltage wave and the calculated reference voltage wave, and determines the fault location roughly. By comparing the judgment results of voltage similarity between both ends of line, a reliable judgment can be made to distinguish between internal and external faults. In order to improve the reliability of voltage wave similarity comparison, dynamic time warping method is used to overcome the influence caused by phase error, and Pearson correlation coefficient method is used to judge the similarity of voltage wave. The simulation results of real time digital simulation system (RTDS) show that the proposed method can identify the fault which occurs on the tie line of ac/dc hybrid system accurately which has high reliability and good applicability.
Phase retrieval is in general a non-convex and non-linear task and the corresponding algorithms struggle with the issue of local minima. We consider the case where the measurement samples within ...typically very small and disconnected subsets are coherently linked to each other - which is a reasonable assumption for our objective of antenna measurements. Two classes of measurement setups are discussed which can provide this kind of extra information: multi-probe systems and holographic measurements with multiple reference signals. We propose several formulations of the corresponding phase retrieval problem. The simplest of these formulations poses a linear system of equations similar to an eigenvalue problem where a unique non-trivial null-space vector needs to be found. Accurate phase reconstruction for partially coherent observations is, thus, possible by a reliable solution process and with judgment of the solution quality. Under ideal, noise-free conditions, the required sampling density is less than two times the number of unknowns. Noise and other observation errors increase this value slightly. Simulations for Gaussian random matrices and for antenna measurement scenarios demonstrate that reliable phase reconstruction is possible with the presented approach.
This paper addresses the multistatic sonar localization problem using time measurements only or with bearings in the presence of Gaussian transmitter positions, receiver positions, and propagation ...speed variations. We develop efficient algebraic solutions to this nonlinear estimation problem through parameter transformation and multistage processing. Both situations of known and unknown statistical distribution of the propagation speed are considered. Analysis supports their performance in reaching the hybrid Cramer-Rao lower bound (CRLB) over the small error region.
We propose a Bayesian method for distributed sequential localization of mobile networks composed of both cooperative agents and noncooperative objects. Our method provides a consistent combination of ...cooperative self-localization (CS) and distributed tracking (DT). Multiple mobile agents and objects are localized and tracked using measurements between agents and objects and between agents. For a distributed operation and low complexity, we combine particle-based belief propagation with a consensus or gossip scheme. High localization accuracy is achieved through a probabilistic information transfer between the CS and DT parts of the underlying factor graph. Simulation results demonstrate significant improvements in both agent self-localization and object localization performance compared to separate CS and DT, and very good scaling properties with respect to the numbers of agents and objects.
This paper studies the problem of bearing-based network localization, which aims to estimate the absolute positions of the nodes in a network by using the inter-node bearings measured in each node's ...local reference frame and the absolute positions of a small number of nodes called anchors. In the first part of the paper, we propose a continuous-time localization algorithm, which consists of coupled orientation and position estimation procedures. Compared to the existing works, the proposed algorithm has a concise form and guarantees global estimation convergence. In the second part of the paper, we study the discrete-time case which is still an open problem till now. We fill this gap by proposing a discrete-time localization algorithm to globally localize three-dimensional networks using locally measured bearings. The discrete-time algorithm does not require designing sufficiently small step sizes to ensure convergence. Numerical simulation is presented to verify the proposed algorithms.
The wireless local area network (WLAN), particularly the wireless fidelity (WiFi) communication technology, has greatly facilitated human productivity and entertainment in recent decades. Accurate ...channel models are identified as a key point for the optimization of transceivers and network deployment in WiFi system. In this paper, we conduct a passive measurement for indoor WiFi channels at 2.4GHz and 5.8GHz bands. Three scenarios are investigated including 1) small office; 2) office-to-corridor; 3) office-to-office. The large-scale and small-scale channel characteristics, including path loss (PL), shadowing, power delay porfiles (PDPs), Rician K-factor and RMS delay spread (RMS-DS), as well as interband correlation are analyzed and compared with the current standard channel model as well as other existing works. Elaborated physical interpretations are provided for the modeling results, revealing that the channels at 2.4GHz and 5.8GHz cannot be accurately described by a uniform model. The obtained results are essential for the accurate understanding of the WiFi propagation mechanisms and can greatly contribute to the optimization of WiFi deployments.
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