2,193 research outputs found
Theory and design of uniform concentric spherical arrays with frequency invariant characteristics
IEEE International Conference on Acoustics, Speech and Signal Processing, Toulouse, France, 14-19 May 2006This paper proposes a new digital beamformer for uniform concentric spherical array (UCSA) having nearly frequency invariant (FI) characteristics. The basic principle is to transform the received signals to the phase mode and remove the frequency dependency of the individual phase mode through the use of a digital beamforming network. It is shown that the far field pattern of the array is determined by a set of weights and it is approximately invariant over a wide range of frequencies. FI UCSAs are electronic steerable in both the azimuth angle and elevation angle, unlike their concentric circular array counterpart. A design example is given to demonstrate the design and performance of the proposed FI UCSA. © 2006 IEEE.published_or_final_versio
Frequency invariant uniform concentric circular arrays with directional elements
A new approach for designing frequency invariant (FI) uniform concentric circular arrays (UCCAs) with directional elements is proposed, and their applications to direction-of-arrival (DOA) estimation and adaptive beamforming are studied. By treating the sensors along the radial direction of the UCCA as linear subarrays and using appropriately designed beamformers, each subarray is transformed to a virtual element with appropriate directivity. Consequently, the whole UCCA can be viewed as a virtual uniform circular array (UCA) with desired element directivity for broadband processing. By extending the approach for designing FI-UCAs, the frequency dependency of the phase modes of the virtual UCA is compensated to facilitate broadband DOA and adaptive beamforming. Both the linear array beamformers (LABFs) and compensation filters can be designed separately using second- order cone programming (SOCP). Moreover, a new method to tackle the possible noise amplification problem in such large arrays by imposing additional norm constraints on the design of the compensation filters is proposed. The advantages of this decoupled approach are 1) the complicated design problem of large UCCAs can be decoupled into simpler problems of designing the LABFs and compensation filters, and 2) directional elements, which are frequently encountered, can be treated readily under the proposed framework. Numerical examples are provided to demonstrate the effectiveness and improvement of the proposed methods in DOA estimation, adaptive beamforming, and elevation control over the conventional FI-UCCA design method.published_or_final_versio
Enabling More Users to Benefit from Near-Field Communications: From Linear to Circular Array
Massive multiple-input multiple-output (MIMO) for 5G is evolving into the
extremely large-scale antenna array (ELAA) to increase the spectrum efficiency
by orders of magnitude for 6G communications. ELAA introduces
spherical-wave-based near-field communications, where channel capacity can be
significantly improved for single-user and multi-user scenarios. Unfortunately,
the near-field region at large incidence/emergence angles is greatly reduced
with the widely studied uniform linear array (ULA). Thus, many randomly
distributed users may fail to benefit from near-field communications. In this
paper, we leverage the rotational symmetry of uniform circular array (UCA) to
provide uniform and enlarged near-field regions at all angles, enabling more
users to benefit from near-field communications. Specifically, by exploiting
the geometrical relationship between UCA and users, the near-field beamforming
technique for UCA is developed. Based on the analysis of near-field
beamforming, we reveal that UCA is able to provide a larger near-field region
than ULA in terms of the effective Rayleigh distance. Moreover, a
concentric-ring codebook is designed to realize efficient codebook-based
beamforming in the near-field region. In addition, we find out that UCA could
generate orthogonal near-field beams along the same direction when the focal
point of the near-field beam is exactly the zeros of other beams, which has the
potential to further improve spectrum efficiency in multi-user communications
compared with ULA. Simulation results are provided to verify the effectiveness
of theoretical analysis and feasibility of UCA to enable more users to benefit
from near-field communications by broadening the near-field region.Comment: Accepted by IEEE TWC. In this paper, the rotational symmetry of UCA
is leveraged to provide uniform and enlarged near-field regions, enabling
more users to benefit from near-field communications. Simulation codes will
be provided to reproduce the results in this paper:
http://oa.ee.tsinghua.edu.cn/dailinglong/publications/publications.htm
Joint Direction-of-Arrival and Time-of-Arrival Estimation with Ultra-wideband Elliptical Arrays
This paper presents a general technique for the joint Direction-of-Arrival
(DoA) and Time-of-Arrival (ToA) estimation in multipath environments. The
proposed ultra-wideband technique is based on phase-mode expansions and the use
of nearly frequency-invariant elliptical arrays. New possibilities open with
the present approach, as not only elliptical, but also circular and linear
(highly flattened) arrays can be considered with the same implementation.
Systematic selection/rejection of signals-of-interest/signals-not-of-interest
in smart wireless environments is possible, unlike with previous approaches
based on circular arrays. Concentric elliptical arrays of many sizes and
eccentricities can be jointly considered, with the subsequent improvement that
entails in DoA and ToA detection. This leads to the realization of
pseudo-random array patterns; namely, quasi-arbitrary geometries created from
the superposition of multiple elliptical arrays. Some simulation and
experimental tests (measurements in an anechoic chamber) are carried out for
several frequency bands to check the correct performance of the method. The
method is proven to give accurate estimations in all tested scenarios, and to
be robust against noise and position uncertainty in sensor placement.Comment: Published in IEEE Transactions on Wireless Communication
A Review of Metamaterial Invisibility Cloaks
The exciting features of metamaterial in conjunction with transformation optics leads to various applications in the microwave regime with such examples as invisible cloak, frequency selective surfaces (FSS), radomes, etc. The concept of electromagnetic invisibility is very much important in aerospace platform. Hence to study the feasibility of implementation of this concept for stealth, an extensive literature survey of metamaterial cloaks has been carried out and reported in this paper along with the basic concept of cloaking. To make the review more effective, the technical papers are classified into three broad sections viz. mathematical modeling, design and simulations, and fabrications and experimental demonstration. Further the design and simulation is focused on different techniques implemented such as finite difference time domain (FDTD), finite element method (FEM), finite integration technique (FIT), inductor-capacitor representation of metamaterial (LC MTM) etc. The review also reports the methods implemented for analysis of metamaterial cloaks with possibility of application to the specific frequency rang
A Complexity-Efficient High Resolution Propagation Parameter Estimation Algorithm for Ultra-Wideband Large-Scale Uniform Circular Array
Millimeter wave (mm-wave) communication with large-scale antenna array
configuration is seen as the key enabler of the next generation communication
systems. Accurate knowledge of the mm-wave propagation channels is fundamental
and essential. In this contribution, a novel complexity-efficient high
resolution parameter estimation (HRPE) algorithm is proposed for the mm-wave
channel with large-scale uniform circular array (UCA) applied. The proposed
algorithm is able to obtain the high-resolution estimation results of the
spherical channel propagation parameters. The prior channel information in the
delay domain, i.e., the delay trajectories of individual propagation paths
observed across the array elements, is exploited, by combining the
high-resolution estimation principle and the phase mode excitation technique.
Fast initializations, effective interference cancellations and reduced
searching spaces achieved by the proposed schemes significantly decrease the
algorithm complexity. Furthermore, the channel spatial non-stationarity in path
gain across the array elements is considered for the first time in the
literature for propagation parameter estimation, which is beneficial to obtain
more realistic results as well as to decrease the complexity. A mm-wave
measurement campaign at the frequency band of 28-30 GHz using a large-scale UCA
is exploited to demonstrate and validate the proposed HRPE algorithm.Comment: Single column, 28 pages. In review process with IEEE Transactions on
Communication
Spatial dissection of a soundfield using spherical harmonic decomposition
A real-world soundfield is often contributed by multiple desired and undesired sound sources. The performance of many acoustic systems such as automatic speech recognition, audio surveillance, and teleconference relies on its ability to extract the desired sound components in such a mixed environment. The existing solutions to the above problem are constrained by various fundamental limitations and require to enforce different priors depending on the acoustic condition such as reverberation and spatial distribution of sound sources. With the growing emphasis and integration of audio applications in diverse technologies such as smart home and virtual reality appliances, it is imperative to advance the source separation technology in order to overcome the limitations of the traditional approaches.
To that end, we exploit the harmonic decomposition model to dissect a mixed soundfield into its underlying desired and undesired components based on source and signal characteristics. By analysing the spatial projection of a soundfield, we achieve multiple outcomes such as (i) soundfield separation with respect to distinct source regions, (ii) source separation in a mixed soundfield using modal coherence model, and (iii) direction of arrival (DOA) estimation of multiple overlapping sound sources through pattern recognition of the modal coherence of a soundfield.
We first employ an array of higher order microphones for soundfield separation in order to reduce hardware requirement and implementation complexity. Subsequently, we develop novel mathematical models for modal coherence of noisy and reverberant soundfields that facilitate convenient ways for estimating DOA and power spectral densities leading to robust source separation algorithms. The modal domain approach to the soundfield/source separation allows us to circumvent several practical limitations of the existing techniques and enhance the performance and robustness of the system. The proposed methods are presented with several practical applications and performance evaluations using simulated and real-life dataset
Joint Ultra-wideband Characterization of Azimuth, Elevation and Time of Arrival with Toric Arrays
In this paper, we present an analytical framework for the joint
characterization of the 3D direction of arrival (DoA), i.e., azimuth and
elevation components, and time of arrival (ToA) in multipath environments. The
analytical framework is based on the use of nearly frequency-invariant
beamformers (FIB) formed by toric arrays. The frequency response of the toric
array is expanded as a series of phase modes, which leads to azimuth-time and
elevation-time diagrams from which the 3D DoA and the ToA of the incoming waves
can be extracted over a wide bandwidth. Firstly, we discuss some practical
considerations, advantages and limitations of using the analytical method.
Subsequently, we perform a parametric study to analyze the influence of the
method parameters on the quality of the estimation. The method is tested in
single-path and multipath mm-wave environments over a large bandwidth. The
results show that the proposed method improves the quality of the estimation,
i.e., decreases the level of the artifacts, compared to other state-of-art FIB
approaches based on the use of single/concentric circular and elliptical
arrays.Comment: 10 pages, 8 figure
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