9,861 research outputs found
VLSI implementation of an energy-aware wake-up detector for an acoustic surveillance sensor network
We present a low-power VLSI wake-up detector for a sensor network that uses acoustic signals to localize ground-base vehicles. The detection criterion is the degree of low-frequency periodicity in the acoustic signal, and the periodicity is computed from the "bumpiness" of the autocorrelation of a one-bit version of the signal. We then describe a CMOS ASIC that implements the periodicity estimation algorithm. The ASIC is functional and its core consumes 835 nanowatts. It was integrated into an acoustic enclosure and deployed in field tests with synthesized sounds and ground-based vehicles.Fil: Goldberg, David H.. Johns Hopkins University; Estados UnidosFil: Andreou, Andreas. Johns Hopkins University; Estados UnidosFil: Julian, Pedro Marcelo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional del Sur. Departamento de IngenierĂa ElĂ©ctrica y de Computadoras; ArgentinaFil: Pouliquen, Philippe O.. Johns Hopkins University; Estados UnidosFil: Riddle, Laurence. Signal Systems Corporation; Estados UnidosFil: Rosasco, Rich. Signal Systems Corporation; Estados Unido
Software correlators as testbeds for RFI algorithms
In-correlator techniques offer the possibility of identifying and/or excising
radio frequency interference (RFI) from interferometric observations at much
higher time and/or frequency resolution than is generally possible with the
final visibility dataset. Due to the considerable computational requirements of
the correlation procedure, cross-correlators have most commonly been
implemented using high-speed digital signal processing boards, which typically
require long development times and are difficult to alter once complete.
"Software" correlators, on the other hand, make use of commodity server
machines and a correlation algorithm coded in a high-level language. They are
inherently much more flexible and can be developed - and modified - much more
rapidly than purpose-built "hardware" correlators. Software correlators are
thus a natural choice for testing new RFI detection and mitigation techniques
for interferometers. The ease with which software correlators can be adapted to
test RFI detection algorithms is demonstrated by the addition of kurtosis
detection and plotting to the widely used DiFX software correlator, which
highlights previously unknown short -duration RFI at the Hancock VLBA station.Comment: 6 pages, 1 figure, accepted for publication in Proceedings of Science
[PoS(RFI2010)035]. Presented at RFI2010, the Third Workshop on RFI Mitigation
in Radio Astronomy, 29-31 March 2010, Groningen, The Netherland
Performance Analysis of Channel Extrapolation in FDD Massive MIMO Systems
Channel estimation for the downlink of frequency division duplex (FDD)
massive MIMO systems is well known to generate a large overhead as the amount
of training generally scales with the number of transmit antennas in a MIMO
system. In this paper, we consider the solution of extrapolating the channel
frequency response from uplink pilot estimates to the downlink frequency band,
which completely removes the training overhead. We first show that conventional
estimators fail to achieve reasonable accuracy. We propose instead to use
high-resolution channel estimation. We derive theoretical lower bounds (LB) for
the mean squared error (MSE) of the extrapolated channel. Assuming that the
paths are well separated, the LB is simplified in an expression that gives
considerable physical insight. It is then shown that the MSE is inversely
proportional to the number of receive antennas while the extrapolation
performance penalty scales with the square of the ratio of the frequency offset
and the training bandwidth. The channel extrapolation performance is validated
through numeric simulations and experimental measurements taken in an anechoic
chamber. Our main conclusion is that channel extrapolation is a viable solution
for FDD massive MIMO systems if accurate system calibration is performed and
favorable propagation conditions are present.Comment: arXiv admin note: substantial text overlap with arXiv:1902.0684
Toward single particle reconstruction without particle picking: Breaking the detection limit
Single-particle cryo-electron microscopy (cryo-EM) has recently joined X-ray
crystallography and NMR spectroscopy as a high-resolution structural method for
biological macromolecules. In a cryo-EM experiment, the microscope produces
images called micrographs. Projections of the molecule of interest are embedded
in the micrographs at unknown locations, and under unknown viewing directions.
Standard imaging techniques first locate these projections (detection) and then
reconstruct the 3-D structure from them. Unfortunately, high noise levels
hinder detection. When reliable detection is rendered impossible, the standard
techniques fail. This is a problem especially for small molecules, which can be
particularly hard to detect. In this paper, we propose a radically different
approach: we contend that the structure could, in principle, be reconstructed
directly from the micrographs, without intermediate detection. As a result,
even small molecules should be within reach for cryo-EM. To support this claim,
we setup a simplified mathematical model and demonstrate how our
autocorrelation analysis technique allows to go directly from the micrographs
to the sought signals. This involves only one pass over the micrographs, which
is desirable for large experiments. We show numerical results and discuss
challenges that lay ahead to turn this proof-of-concept into a competitive
alternative to state-of-the-art algorithms
Oscillator Phase Noise and Small-Scale Channel Fading in Higher Frequency Bands
This paper investigates the effect of oscillator phase noise and channel
variations due to fading on the performance of communication systems at
frequency bands higher than 10GHz. Phase noise and channel models are reviewed
and technology-dependent bounds on the phase noise quality of radio oscillators
are presented. Our study shows that, in general, both channel variations and
phase noise can have severe effects on the system performance at high
frequencies. Importantly, their relative severity depends on the application
scenario and system parameters such as center frequency and bandwidth. Channel
variations are seen to be more severe than phase noise when the relative
velocity between the transmitter and receiver is high. On the other hand,
performance degradation due to phase noise can be more severe when the center
frequency is increased and the bandwidth is kept a constant, or when
oscillators based on low power CMOS technology are used, as opposed to high
power GaN HEMT based oscillators.Comment: IEEE Global Telecommun. Conf. (GLOBECOM), Austin, TX, Dec. 201
Inflight estimation of gyro noise
A method is described and demonstrated for estimating single-axis gyro noise levels in terms of the Farrenkopf model parameters. This is accomplished for the Cosmic Background Explorer (COBE) by comparing gyro-propagated attitudes with less accurate single-frame solutions and fitting the squared differences to a third-order polynomial in time. Initial results are consistent with the gyro specifications, and these results are used to determine limits on the duration of batches used to determine attitude. Sources of error are discussed, and guidelines for a more elegant implementation, as part of a batch estimator or filter, are included for future work
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