This paper proposes a general channel estimation framework for movable antenna (MA) communication systems. In this framework, the channel state information between the entire transmitter (Tx) and ...receive (Rx) regions can be re-constructed, so as to find the optimal positions of the MAs for reaping performance gains. Specifically, the field-response channel structure is utilized to represent the channel response in terms of the angles of departure (AoDs), angles of arrival (AoAs), and complex coefficients of the multi-path components (MPCs). Then, the compressed sensing method is employed to jointly estimate the MPC information, i.e., the AoDs, AoAs, and complex coefficients of the paths, with a limited number of channel measurements. Notably, the measurement matrix under the proposed framework is fundamentally determined by the Tx-MA and Rx-MA measurement positions, which further affects the channel estimation performance. In this regard, four MA measurement position setups are proposed, and the channel estimation performance of each setup is further compared. Finally, simulation results show that the complete CSI between the entire Tx and Rx regions can be reconstructed by our proposed channel estimation framework with a high accuracy.
A novel measurement setup is proposed for the contactless characterization of on-chip antennas. A D-band patch antenna is fabricated on a 100 μm-thick GaAs substrate and is monolithically integrated ...with a reflective load switch to allow for fast electronic control of the antenna port termination. The antenna under test is illuminated by a reference antenna in the anechoic chamber after which the impedance and gain of the patch antenna are reconstructed from the change in backscattered field due to different port terminations. In our experiment, the over-the-air reconstructed antenna input impedance exhibits a frequency shift of less than 1% with respect to the (nonideal) on-wafer probe measurement in the 115-130 GHz frequency range. Furthermore, the measured realized gain of <inline-formula><tex-math notation="LaTeX">\mathbf {{\text {0.9}}\pm {\text {0.5}}}</tex-math></inline-formula> dBi is close to the simulated one of 1.1 dBi.
Tactile perception plays an important role in activities of daily living, and it can be impaired in individuals with certain medical conditions. The most common tools used to assess tactile ...sensation, the Semmes-Weinstein monofilaments and the 128 Hz tuning fork, have poor repeatability and resolution. Long term, we aim to provide a repeatable, high-resolution testing platform that can be used to assess vibrotactile perception through smartphones without the need for an experimenter to be present to conduct the test. We present a smartphone-based vibration perception measurement platform and compare its performance to measurements from standard monofilament and tuning fork tests. We conducted a user study with 36 healthy adults in which we tested each tool on the hand, wrist, and foot, to assess how well our smartphone-based vibration perception thresholds (VPTs) detect known trends obtained from standard tests. The smartphone platform detected statistically significant changes in VPT between the index finger and foot and also between the feet of younger adults and older adults. Our smartphone-based VPT had a moderate correlation to tuning fork-based VPT. Our overarching objective is to develop an accessible smartphone-based platform that can eventually be used to measure disease progression and regression.
The Two‐Column Aerosol Project (TCAP), conducted from June 2012 through June 2013, was a unique study designed to provide a comprehensive data set that can be used to investigate a number of ...important climate science questions, including those related to aerosol mixing state and aerosol radiative forcing. The study was designed to sample the atmosphere between and within two atmospheric columns; one fixed near the coast of North America (over Cape Cod, MA) and a second moveable column over the Atlantic Ocean several hundred kilometers from the coast. The U.S. Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) was deployed at the base of the Cape Cod column, and the ARM Aerial Facility was utilized for the summer and winter intensive observation periods. One important finding from TCAP is that four of six nearly cloud‐free flight days had aerosol layers aloft in both the Cape Cod and maritime columns that were detected using the nadir pointing second‐generation NASA high‐spectral resolution lidar (HSRL‐2). These layers contributed up to 60% of the total observed aerosol optical depth (AOD). Many of these layers were also intercepted by the aircraft configured for in situ sampling, and the aerosol in the layers was found to have increased amounts of biomass burning material and nitrate compared to aerosol found near the surface. In addition, while there was a great deal of spatial and day‐to‐day variability in the aerosol chemical composition and optical properties, no systematic differences between the two columns were observed.
Key Points
TCAP provides a data set to investigate science questions and evaluate model performance
There is a large amount of variability in aerosol properties near northeast coast of North America
Aerosol layers aloft have a large impact on aerosol optical depth
This paper presents the PIX instrument based on a raspberry Pi and a MiniPIX device dedicated to make measurements of ionizing particles onboard stratospheric balloons. The hardware part and the ...software part of the PIX instrument are described. All the characteristics of the instrument are given in this paper. The three flight opportunities are also presented, with the associated measurements. The methodology to calculate fluxes based on measurements is explained. In particular, the calculation of response functions of protons, electrons, and photons by using Monte-Carlo simulations, the identification algorithm based on a neural network trained with simulated data, and the calculation of fluxes from count rates are described. Some measurements performed in different facilities are presented. A part of these experimental tracks have been used to challenge the neural network previously trained with simulated date, to check the robustness of the algorithm. Proton, electron, and photon fluxes are presented and compared to the MAIRE model.
Measurement of pupil size (pupillometry) has recently gained renewed interest from psychologists, but there is little agreement on how pupil-size data is best analyzed. Here we focus on one aspect of ...pupillometric analyses: baseline correction, i.e., analyzing changes in pupil size relative to a baseline period. Baseline correction is useful in experiments that investigate the effect of some experimental manipulation on pupil size. In such experiments, baseline correction improves statistical power by taking into account random fluctuations in pupil size over time. However, we show that baseline correction can also distort data if unrealistically small pupil sizes are recorded during the baseline period, which can easily occur due to eye blinks, data loss, or other distortions. Divisive baseline correction (corrected pupil size = pupil size/baseline) is affected more strongly by such distortions than subtractive baseline correction (corrected pupil size = pupil size − baseline). We discuss the role of baseline correction as a part of preprocessing of pupillometric data, and make five recommendations: (1) before baseline correction, perform data preprocessing to mark missing and invalid data, but assume that some distortions will remain in the data; (2) use subtractive baseline correction; (3) visually compare your corrected and uncorrected data; (4) be wary of pupil-size effects that emerge faster than the latency of the pupillary response allows (within ±220 ms after the manipulation that induces the effect); and (5) remove trials on which baseline pupil size is unrealistically small (indicative of blinks and other distortions).
Two models describing properties of the thermal noise power emerging from an antenna mounted in a reverberation chamber are described. The first compares the reverberation chamber to an over-molded ...cavity acting as a black-body source; the second describes the noise in terms of the antenna noise temperature. Measurements based on the antenna noise temperature model show the noise power to be dependent on the position of the rotating mechanical stirrer. The correlation of the antenna noise temperature with the stirrer position-dependent antenna mismatch factor is shown. When a signal is injected into the chamber measurements of the signal to noise power ratio show that this ratio is dependent on the stirrer position and also the position of the signal source within the chamber. These results have significant consequences for the detection of weak signals from radiating sources in a reverberation chamber.
In this study, we were interested in the question whether vibrotactile thresholds on the back, in terms of the Just Noticeable Difference (JND), scale with back length. Although there exists only ...indirect physiological evidence, it could be assumed that the density of mechanoreceptors is lower if back size is larger. As a consequence, the JND would increase with back length. We measured psychophysical curves for 40 male participants with back lengths in the range of 36 to 55 cm. Nine equally spaced vibration motors were placed in vertical direction on their back, 2 cm left of the spine. For each stimulus pair, participants had to decide whether the second vibration was above or below the first vibration. It was found that the slope of the fit of the JND as a function of back length was not significantly different from zero, so contrary to our expectation, we did not find an influence of back length on JND. This means that when customizing a wearable haptic device for the back, measuring back length is not the way to go.
To date, the most proficient instrument type for rapid measurements of broadband terahertz (THz) spectra is the time-domain spectrometer, which acquires the RF signal either transmitted through or ...reflected by a sample without following a standardized method for calibration. Simultaneously, application-oriented research drives a strong need for fast and precise instrumentation capable of capturing well-established characteristics, such as scattering parameters. In this letter, a robust THz instrument capable of synchronously measuring transmission and reflection from 150 GHz to 3 THz is implemented and evaluated. The main sources of error in the system are characterized, and an adapted network analysis calibration scheme for magnitude- and phase-correct wideband scattering parameter measurements is proposed. Finally, the method is validated in a comparison of simulation and measurement of a known sample.
This work considers a collocated radar scenario where a probing signal is emitted toward the targets of interest and records the received echoes. Estimating the relative delay-Doppler shifts of the ...targets allows determining their relative locations and velocities. However, the received radar measurements are often affected by impulsive non-Gaussian noise which makes a few measurements partially corrupted. While demixing radar signal and impulsive noise is challenging in general by traditional subspace-based methods, atomic norm minimization (ANM) has been recently developed to perform this task in a much more efficient manner. Nonetheless, the ANM cannot identify close delay-Doppler pairs and also requires many measurements. Here, we propose a smoothed <inline-formula> <tex-math notation="LaTeX">\ell _{0} </tex-math></inline-formula> atomic optimization problem encouraging both the sparse features of the targets and the impulsive noise. We design a majorization-minimization algorithm that converges to the solution of the proposed non-convex problem using alternating direction method of multipliers (ADMM). Simulations results verify the superior accuracy of our proposed algorithm even for very close delay-Doppler pairs in comparison to ANM with around 40 dB improvement.
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