67 research outputs found
Spherical Wavefront Near-Field DoA Estimation in THz Automotive Radar
Automotive radar at terahertz (THz) band has the potential to provide compact
design. The availability of wide bandwidth at THz-band leads to high range
resolution. Further, very narrow beamwidth arising from large arrays yields
high angular resolution up to milli-degree level direction-of-arrival (DoA)
estimation. At THz frequencies and extremely large arrays, the signal wavefront
is spherical in the near-field that renders traditional far-field DoA
estimation techniques unusable. In this work, we examine near-field DoA
estimation for THz automotive radar. We propose an algorithm using multiple
signal classification (MUSIC) to estimate target DoAs and ranges while also
taking beam-squint in near-field into account. Using an array transformation
approach, we compensate for near-field beam-squint in noise subspace
computations to construct the beam-squint-free MUSIC spectra. Numerical
experiments show the effectiveness of the proposed method to accurately
estimate the target parameters
Signal Subspace Processing in the Beam Space of a True Time Delay Beamformer Bank
A number of techniques for Radio Frequency (RF) source location for wide bandwidth signals have been described that utilize coherent signal subspace processing, but often suffer from limitations such as the requirement for preliminary source location estimation, the need to apply the technique iteratively, computational expense or others. This dissertation examines a method that performs subspace processing of the data from a bank of true time delay beamformers. The spatial diversity of the beamformer bank alleviates the need for a preliminary estimate while simultaneously reducing the dimensionality of subsequent signal subspace processing resulting in computational efficiency. The pointing direction of the true time delay beams is independent of frequency, which results in a mapping from element space to beam space that is wide bandwidth in nature. This dissertation reviews previous methods, introduces the present method, presents simulation results that demonstrate the assertions, discusses an analysis of performance in relation to the Cramer-Rao Lower Bound (CRLB) with various levels of noise in the system, and discusses computational efficiency. One limitation of the method is that in practice it may be appropriate for systems that can tolerate a limited field of view. The application of Electronic Intelligence is one such application. This application is discussed as one that is appropriate for a method exhibiting high resolution of very wide bandwidth closely spaced sources and often does not require a wide field of view. In relation to system applications, this dissertation also discusses practical employment of the novel method in terms of antenna elements, arrays, platforms, engagement geometries, and other parameters. The true time delay beam space method is shown through modeling and simulation to be capable of resolving closely spaced very wideband sources over a relevant field of view in a single algorithmic pass, requiring no course preliminary estimation, and exhibiting low computational expense superior to many previous wideband coherent integration techniques
Communication Networks in CubeSat Constellations: Analysis, Design and Implementation
CubeSat constellations are redefining the way we approach to space missions, from
the particular impact on scientific mission possibilities, constellations potential is
growing with the increasing accessibility in terms of low development and launch
costs and higher performances of the available technologies for CubeSats.
In this thesis we focus on communication networks in CubeSat constellations: the
project consist of developing a clustering algorithm able to group small satellites
in order to create an optimized communication network by considering problems
related to mutual access time and communication capabilities we reduce the typical
negative effects of clustering algorithms such as ripple effect of re-clustering and
optimizing the cluster-head formation number.
The network creation is exploited by our proposed hardware system, composed
by a phased array with up to 10dB gain, managed by a beamforming algorithm,
to increase the total data volume transferable from a CubeSat constellation to the
ground station. The total data volume earned vary from 40% to a peak of 99% more,
depending on the constellation topology analyzed
Analytical evaluation of uncertainty on active antenna arrays
An analytical method for evaluating the uncertainty of the performance of active antenna arrays in the whole spatial spectrum is presented. Since array processing algorithms based on spatial reference are widely used to track moving targets, it is essential to be aware of the impact of the uncertainty sources on the antenna response. Furthermore, the estimation of the direction of arrival (DOA) depends on the array uncertainty. The aim of the uncertainties analysis is to provide an exhaustive characterization of the behavior of the active antenna array associated with its main uncertainty sources. The result of this analysis helps to select the proper calibration technique to be implemented. An illustrative example for a triangular antenna array used for satellite tracking is presented showing the suitability of the proposed method to carry out an efficient characterization of an active antenna array
Terahertz-Band Direction Finding With Beam-Split and Mutual Coupling Calibration
peer reviewedTerahertz (THz) band is currently envisioned as the
key building block to achieving the future sixth generation (6G)
wireless systems. The ultra-wide bandwidth and very narrow
beamwidth of THz systems offer the next order of magnitude
in user densities and multi-functional behavior. However, wide
bandwidth results in a frequency-dependent beampattern causing
the beams generated at different subcarriers split and point
to different directions. Furthermore, mutual coupling degrades
the system’s performance. This paper studies the compensation
of both beam-split and mutual coupling for direction-of-arrival
(DoA) estimation by modeling the beam-split and mutual coupling
as an array imperfection. We propose a subspace-based
approach using multiple signal classification with CalibRated for
bEAam-split and Mutual coupling (CREAM-MUSIC) algorithm
for this purpose. Via numerical simulations, we show the proposed
CREAM-MUSIC approach accurately estimates the DoAs
in the presence of beam-split and mutual coupling
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