3,219 research outputs found
Cost-effective aperture arrays for SKA Phase 1: single or dual-band?
An important design decision for the first phase of the Square Kilometre
Array is whether the low frequency component (SKA1-low) should be implemented
as a single or dual-band aperture array; that is, using one or two antenna
element designs to observe the 70-450 MHz frequency band. This memo uses an
elementary parametric analysis to make a quantitative, first-order cost
comparison of representative implementations of a single and dual-band system,
chosen for comparable performance characteristics. A direct comparison of the
SKA1-low station costs reveals that those costs are similar, although the
uncertainties are high. The cost impact on the broader telescope system varies:
the deployment and site preparation costs are higher for the dual-band array,
but the digital signal processing costs are higher for the single-band array.
This parametric analysis also shows that a first stage of analogue tile
beamforming, as opposed to only station-level, all-digital beamforming, has the
potential to significantly reduce the cost of the SKA1-low stations. However,
tile beamforming can limit flexibility and performance, principally in terms of
reducing accessible field of view. We examine the cost impacts in the context
of scientific performance, for which the spacing and intra-station layout of
the antenna elements are important derived parameters. We discuss the
implications of the many possible intra-station signal transport and processing
architectures and consider areas where future work could improve the accuracy
of SKA1-low costing.Comment: 64 pages, 23 figures, submitted to the SKA Memo serie
A Generalized Spatial Correlation Model for 3D MIMO Channels based on the Fourier Coefficients of Power Spectrums
Previous studies have confirmed the adverse impact of fading correlation on
the mutual information (MI) of two-dimensional (2D) multiple-input
multiple-output (MIMO) systems. More recently, the trend is to enhance the
system performance by exploiting the channel's degrees of freedom in the
elevation, which necessitates the derivation and characterization of
three-dimensional (3D) channels in the presence of spatial correlation. In this
paper, an exact closed-form expression for the Spatial Correlation Function
(SCF) is derived for 3D MIMO channels. This novel SCF is developed for a
uniform linear array of antennas with nonisotropic antenna patterns. The
proposed method resorts to the spherical harmonic expansion (SHE) of plane
waves and the trigonometric expansion of Legendre and associated Legendre
polynomials. The resulting expression depends on the underlying arbitrary
angular distributions and antenna patterns through the Fourier Series (FS)
coefficients of power azimuth and elevation spectrums. The novelty of the
proposed method lies in the SCF being valid for any 3D propagation environment.
The developed SCF determines the covariance matrices at the transmitter and the
receiver that form the Kronecker channel model. In order to quantify the
effects of correlation on the system performance, the information-theoretic
deterministic equivalents of the MI for the Kronecker model are utilized in
both mono-user and multi-user cases. Numerical results validate the proposed
analytical expressions and elucidate the dependence of the system performance
on azimuth and elevation angular spreads and antenna patterns. Some useful
insights into the behaviour of MI as a function of downtilt angles are
provided. The derived model will help evaluate the performance of correlated 3D
MIMO channels in the future.Comment: Accepted in IEEE Transactions on signal processin
Multi-beam 4 GHz Microwave Apertures Using Current-Mode DFT Approximation on 65 nm CMOS
A current-mode CMOS design is proposed for realizing receive mode multi-beams
in the analog domain using a novel DFT approximation. High-bandwidth CMOS RF
transistors are employed in low-voltage current mirrors to achieve bandwidths
exceeding 4 GHz with good beam fidelity. Current mirrors realize the
coefficients of the considered DFT approximation, which take simple values in
only. This allows high bandwidths realizations using simple
circuitry without needing phase-shifters or delays. The proposed design is used
as a method to efficiently achieve spatial discrete Fourier transform operation
across a ULA to obtain multiple simultaneous RF beams. An example using 1.2 V
current-mode approximate DFT on 65 nm CMOS, with BSIM4 models from the RF kit,
show potential operation up to 4 GHz with eight independent aperture beams.Comment: 7 pages, 4 figures, In: IEEE International Microwave Symposium 201
Image formation in synthetic aperture radio telescopes
Next generation radio telescopes will be much larger, more sensitive, have
much larger observation bandwidth and will be capable of pointing multiple
beams simultaneously. Obtaining the sensitivity, resolution and dynamic range
supported by the receivers requires the development of new signal processing
techniques for array and atmospheric calibration as well as new imaging
techniques that are both more accurate and computationally efficient since data
volumes will be much larger. This paper provides a tutorial overview of
existing image formation techniques and outlines some of the future directions
needed for information extraction from future radio telescopes. We describe the
imaging process from measurement equation until deconvolution, both as a
Fourier inversion problem and as an array processing estimation problem. The
latter formulation enables the development of more advanced techniques based on
state of the art array processing. We demonstrate the techniques on simulated
and measured radio telescope data.Comment: 12 page
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