A Supervised Learning Framework for Joint Estimation of Angles-of-Arrival and Number of Sources

Machine learning is a promising technique for angle-of-arrival (AOA) estimation of waves impinging a sensor array. However, the majority of the methods proposed so far only consider a known, fixed number of impinging waves, i.e., a fixed number of sources (NOS). This paper proposes a machine-learning-based estimator designed for the case when the NOS is variable and hence unknown a priori. The proposed estimator comprises a framework of single-label classifiers. Each classifier predicts if waves are present within certain randomly selected segments of the array\u27s field of view (FOV), resulting from discretising the FOV with a certain (FOV) resolution. The classifiers\u27 predictions are combined into a probabilistic angle spectrum, whereupon the NOS and the AOAs are estimated jointly by applying a probability threshold whose optimal level is learned from data. The estimator\u27s performance is assessed using a new performance metric: the joint AOA estimation success rate. Numerical simulations show that for low SNR (-10 dB), a low FOV resolution (2\ub0) yields a higher success rate than a high resolution (1\ub0), whereas the opposite applies for mid (0 dB) and high (10 dB) SNRs. In nearly all simulations, except one at low SNR and a high FOV resolution, the proposed estimator outperforms the MUSIC algorithm if the maximum allowed AOA estimation error is approximately equal to (or larger than) the FOV resolution

Mean effective gain of antennas in a wireless channel

The mean effective gain (MEG) is one of the most important parameters for the characterisation of antennas in wireless channels. An analysis of some fundamental properties of the MEG is provided and corresponding physical interpretations are given. Three points are analysed in detail: (i) closed-form expressions for MEG in a mixed environment with both stochastic and deterministic components are provided, showing that the MEG can be written as a sum of gains for the deterministic and stochastic components, (ii) it is shown that under some assumptions, the propagation channel and the antenna are equivalent in the sense that the impact of the channel cross-polarisation ratio (XPR) and the antenna effective cross-polar discrimination on the MEG are symmetrical, (iii) based on the fact that MEG depends on random variables, such as the XPR and antenna rotations because of user's movements, the average, the minimum and maximum MEG of antennas are defined, respectively. Finally, the maximum effective gain of antennas is derived and shown that it is bounded by 4 pi eta(rad), where eta(rad) is the radiation efficiency of the antenna

Interpreting the Total Isotropic Sensitivity and Diversity Gain of LTE-enabled wireless devices from Over The Air Throughput Measurements in Reverberation Chambers

The characterization of the performance of wireless devices is the key to developing new RF products conforming to the latest communications protocols. Traditionally, communication performance tests have focused on the RF performance of the tested devices, e.g., smart phones, pads, laptops, etc. More specifically, the focus has shifted from conducted (i.e., cabled) measurements to more realistic Over-The-Air (OTA) characterization of the RF performance of these devices in transmit or receive mode. For example, the receiver performance of 2G and 3G wireless devices can be measured in terms of the total isotropic sensitivity (TIS) that depends on the antenna and the receiver parts of a wireless device. These measurements can be performed in a reverberation chamber setup. However, standard TIS measurements can be time consuming and do not reflect the actual performance gains of Multiple-Input Multiple- Output (MIMO) antenna systems operating over Orthogonal Frequency Division Multiplexing (OFDM) channels, such as those encountered in 4G Long Term Evolution (LTE) systems. Therefore, in order to meet both time and cost efficiency requirements, we propose here a new method to determine the TIS, as well as the diversity performance, of an LTE device based on throughput measurements. The proposed method shows that the TIS of an LTE device is characterized much faster directly from OTA throughput measurements than from standard TIS measurements and with excellent accuracy

Simulations of a planar array arrangement for automotive Random-LOS OTA testing

We present simulations of near-field plane wave synthesis by a planar array. The focus is on minimization of reference signal errors within the test zone for Random Line-Of-Sight Over-The-Air characterization of wireless devices on cars. The analysis considers the output of the ideal digital threshold receiver model of the device under test as a Probability of Detection curve. The dimensions, the interelement spacings and the number of elements in a planar array comprising Huygens sources are investigated to produce an absolute error less than 0.5 dB

Optimizing Small Wideband Antenna Performance for Both RIMP and Random-LOS

Rich Isotropic Multipath (RIMP) environment like reverberation chamber (RC) has proven to be useful for characterizing mobile LTE devices. The user statistics have larger effect in environments with stronger Line-Of-Sight (LOS), because the angle of arrival (AoA) and the polarization of the LOS contribution become randomized due to the user. Thus, we introduce the term Random-LOS. The present paper elaborates on characterization of an example antenna in both RIMP and random-LOS. We show how to characterize the micro BTS by the probability of detection (PoD) of one and more bitstreams in both RIMP and random-LOS, by considering the user randomly located and oriented within the angular coverage sector. We limit the treatment to a wall-mounted BTS antenna, and assume a desired hemi-spherical coverage

Physical Modeling of MIMO Antennas and Channels by Means of the Spherical Vector Wave Expansion

In this paper we propose a new physically motivated model that allows to study the interaction between the antennas and the propagation channel for Multiple-Input Multiple-Output (MIMO) systems. The key tools employed in the model are the expansion coefficients of the electromagnetic field in spherical vector waves and the scattering matrix representation of the properties of the antenna. We derive the expansion of the MIMO channel matrix, H, in spherical vector wave modes of the electromagnetic field of the antennas as well as the propagation channel. We also introduce the channel scattering dyadic, C, with a corresponding correlation model for co- and cross-polarized elements and introduce the concept of mode-to-mode channel mapping, the M-matrix, between the receive and transmit antenna modes. The M-matrix maps the modes excited by the transmitting antenna to the modes exciting the receive antennas and vice versa. The covariance statistics of this M-matrix are expressed as a function of the double-directional power-angular spectrum (PAS) of co- and cross-polarized components of the electromagnetic field. Our approach aims at gaining insights into the physics governing the interaction between antennas and channels and it is useful for studying the performance of different antenna designs in a specified propagation channel as well as for modeling the propagation channel. It can furthermore be used to quantify the optimal properties of antennas in a given propagation channel. We illustrate the developed methodology by analyzing the interaction of a 2x2 system of slant polarized half-wavelength dipole antennas with some basic propagation channel models

Semi-Analytical Model of the Rician K-Factor

The analysis of the performance of 5G wireless communication systems employing Massive MIMO at millimeter-wave frequencies is of great practical relevance. Of special relevance are the signal fluctuations. In the present paper, we introduce a semi-analytical model for a generic scattering environment by using randomly distributed resonant scatterers to investigate the impact of the size of the scattering environment, the scatterer density, and the number of scatterers on the signal variability in terms of the Rician K-factor as a function of frequency. We further present an investigation of the impact of scattering on the frequency dependence of the signal fading statistics in the 500 MHz–100 GHz band. The simplified model is also verified against full-wave simulation using the Method of Moments (MoM)

Decorrelation Distance Characterization of Long Term Fading of CW MIMO Channels in Urban Multicell Environment

An analysis of long-term fading properties of 4×4 CW MIMO channels is presented in this paper. The main focus has been on the long-term variability of MIMO channels in urban cellular environments, with emphasis on the decorrelation distance over mid range distances along the mobile trajectory for different base station antenna heights. A model that characterizes the decorrelation distance at different probability levels of distribution of the decorrelation distance is proposed. The model predicts that at some probability level all measured decorrelation distances will be within ½Δx0and 2Δx0, where Δx0is the decorrelation distance at the e-1 level of the autocorrelation function

Test Zone Verification Procedures in a Random-LOS Measurement Setup

\ua9 2019 European Association on Antennas and Propagation. In this paper we analyze three different verification procedures of the test zone in the Random Line-of-Sight measurement setup. The goal is to find a way to reduce the number of samples needed to estimate the standard deviation and the mean value within a circular test zone. It was found that more than 50 samples are needed to get reliable performance with the verification procedure using two orthogonal lines. However all three investigated methods work well, but the two other methods need more than 100 samples. This means that the samples can be taken within the test zone along two orthogonal lines, in a spiral shape, as well as a combination of these two methods, depending on the user\u27s preference

An Experimental Study on Indoor Massive 3D-MIMO Channel at 30-40 GHz Band

Three-dimensional (3D) multiple-input multiple-output (MIMO) channel sounder measurements are producposed for a multi-user MIMO channel at the 30-40 GHz mm-wave band. A 3D-MIMO downlink transmissions links withto two users is considered. The measurement campaign employing a vector network analyzer (VNA) washas been performed in an indoor office scenario. Based on the measurement results, weThe characterizeations of mm-wave 3D-MIMO channels are performed in the wavenumber domain and the time domain, which are jointly analyzed via a 3D inverse fast Fourier transform (IFFT). Measurement shows that the massive 3D-MIMO has a significant improvement on resolution of multipathes beyond none-massive 3D-MIMO