671 research outputs found
An all-lag rotating-reference correlator and its efficient implementation
This paper proposes an all-lag correlator that employs a rotating reference code sequence. The proposed correlator has an advantage over the previously proposed all-lag correlator, which employs a fixed reference code, in that correlation peaks remain at the same output positions regardless of update from newly arrived data samples. Therefore, the correlation information can be more conveniently manipulated in certain applications, and the posterior signal processing requirement can be reduced. Low-complexity implementation of the correlator using a recursive form is also presented. The degree of implementation complexity is of the order N, the reference-code length.published_or_final_versio
The S2 VLBI Correlator: A Correlator for Space VLBI and Geodetic Signal Processing
We describe the design of a correlator system for ground and space-based
VLBI. The correlator contains unique signal processing functions: flexible LO
frequency switching for bandwidth synthesis; 1 ms dump intervals, multi-rate
digital signal-processing techniques to allow correlation of signals at
different sample rates; and a digital filter for very high resolution
cross-power spectra. It also includes autocorrelation, tone extraction, pulsar
gating, signal-statistics accumulation.Comment: 44 pages, 13 figure
The UTMOST: A hybrid digital signal processor transforms the MOST
The Molonglo Observatory Synthesis Telescope (MOST) is an 18,000 square meter
radio telescope situated some 40 km from the city of Canberra, Australia. Its
operating band (820-850 MHz) is now partly allocated to mobile phone
communications, making radio astronomy challenging. We describe how the
deployment of new digital receivers (RX boxes), Field Programmable Gate Array
(FPGA) based filterbanks and server-class computers equipped with 43 GPUs
(Graphics Processing Units) has transformed MOST into a versatile new
instrument (the UTMOST) for studying the dynamic radio sky on millisecond
timescales, ideal for work on pulsars and Fast Radio Bursts (FRBs). The
filterbanks, servers and their high-speed, low-latency network form part of a
hybrid solution to the observatory's signal processing requirements. The
emphasis on software and commodity off-the-shelf hardware has enabled rapid
deployment through the re-use of proven 'software backends' for its signal
processing. The new receivers have ten times the bandwidth of the original MOST
and double the sampling of the line feed, which doubles the field of view. The
UTMOST can simultaneously excise interference, make maps, coherently dedisperse
pulsars, and perform real-time searches of coherent fan beams for dispersed
single pulses. Although system performance is still sub-optimal, a pulsar
timing and FRB search programme has commenced and the first UTMOST maps have
been made. The telescope operates as a robotic facility, deciding how to
efficiently target pulsars and how long to stay on source, via feedback from
real-time pulsar folding. The regular timing of over 300 pulsars has resulted
in the discovery of 7 pulsar glitches and 3 FRBs. The UTMOST demonstrates that
if sufficient signal processing can be applied to the voltage streams it is
possible to perform innovative radio science in hostile radio frequency
environments.Comment: 12 pages, 6 figure
The Expanded Very Large Array
In almost 30 years of operation, the Very Large Array (VLA) has proved to be
a remarkably flexible and productive radio telescope. However, the basic
capabilities of the VLA have changed little since it was designed. A major
expansion utilizing modern technology is currently underway to improve the
capabilities of the VLA by at least an order of magnitude in both sensitivity
and in frequency coverage. The primary elements of the Expanded Very Large
Array (EVLA) project include new or upgraded receivers for continuous frequency
coverage from 1 to 50 GHz, new local oscillator, intermediate frequency, and
wide bandwidth data transmission systems to carry signals with 16 GHz total
bandwidth from each antenna, and a new digital correlator with the capability
to process this bandwidth with an unprecedented number of frequency channels
for an imaging array. Also included are a new monitor and control system and
new software that will provide telescope ease of use. Scheduled for completion
in 2012, the EVLA will provide the world research community with a flexible,
powerful, general-purpose telescope to address current and future astronomical
issues.Comment: Added journal reference: published in Proceedings of the IEEE,
Special Issue on Advances in Radio Astronomy, August 2009, vol. 97, No. 8,
1448-1462 Six figures, one tabl
Detection of gravitational wave bursts by interferometric detectors
We study in this paper some filters for the detection of burst-like signals
in the data of interferometric gravitational-wave detectors. We present first
two general (non-linear) filters with no {\it a priori} assumption on the
waveforms to detect. A third filter, a peak correlator, is also introduced and
permits to estimate the gain, when some prior information is known about the
waveforms. We use the catalogue of supernova gravitational-wave signals built
by Zwerger and M\"uller in order to have a benchmark of the performance of each
filter and to compare to the performance of the optimal filter. The three
filters could be a part of an on-line triggering in interferometric
gravitational-wave detectors, specialised in the selection of burst events.Comment: 15 pages, 8 figure
Real-time software receiver
A real-time software receiver that executes on a general purpose processor. The software receiver includes data acquisition and correlator modules that perform, in place of hardware correlation, baseband mixing and PRN code correlation using bit-wise parallelism
Real-Time Wavelet-transform spectrum analyzer for the investigation of 1/f^\alpha noise
A wavelet transform spectrum analyzer operating in real time within the
frequency range 3X10^(-5) - 1.3X10^5 Hz has been implemented on a low-cost
Digital Signal Processing board operating at 150MHz. The wavelet decomposition
of the signal allows to efficiently process non-stationary signals dominated by
large amplitude events fairly well localized in time, thus providing the
natural tool to analyze processes characterized by 1/f^alpha power spectrum.
The parallel architecture of the DSP allows the real-time processing of the
wavelet transform of the signal sampled at 0.3MHz. The bandwidth is about
220dB, almost ten decades. The power spectrum of the scattered intensity is
processed in real time from the mean square value of the wavelet coefficients
within each frequency band. The performances of the spectrum analyzer have been
investigated by performing Dynamic Light Scattering experiments on colloidal
suspensions and by comparing the measured spectra with the correlation
functions data obtained with a traditional multi tau correlator. In order to
asses the potentialities of the spectrum analyzer in the investigation of
processes involving a wide range of timescales, we have performed measurements
on a model system where fluctuations in the scattered intensities are generated
by the number fluctuations in a dilute colloidal suspension illuminated by a
wide beam. This system is characterized by a power-law spectrum with exponent
-3/2 in the scattered intensity fluctuations. The spectrum analyzer allows to
recover the power spectrum with a dynamic range spanning about 8 decades. The
advantages of wavelet analysis versus correlation analysis in the investigation
of processes characterized by a wide distribution of time scales and
non-stationary processes are briefly discussed.Comment: 12 pages, 6 figure
Techniques and errors in measuring cross- correlation and cross-spectral density functions
Techniques and errors in measuring cross spectral density and cross correlation functions of stationary dynamic pressure dat
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