26 research outputs found
On the choice of reference in sensor offset calibration
Sensor calibration is an indispensable feature in any networked cyberphysical
system. In this paper we consider a sensor network plagued with offset errors
measuring a rank-1 signal subspace where each sensor collects measurements
under additive zero-mean Gaussian noise. Under varying assumptions on the
underlying noise covariance, we investigate the effect of using an arbitrary
reference for estimating the sensor offsets in contrast to the mean of all the
unknown sensor offsets as a reference. We show that the mean reference yields
an efficient estimator in the mean square error sense. If the underlying noise
is homoscedastic in nature then the mean reference yields a factor 2
improvement on the variance as compared any arbitrarily chosen reference within
the network. Furthermore when the underlying noise is independent, but not
identical, we derive an expression for the improvement offered by the mean
reference. We demonstrate our results using the problem of clock
synchronization in sensor networks, and present directions for future work.Comment: In submissio
Multi-FEAT: Multi-Feature Edge AlignmenT for Targetless Camera-LiDAR Calibration
The accurate environment perception of automobiles and UAVs (Unmanned Ariel
Vehicles) relies on the precision of onboard sensors, which require reliable
in-field calibration. This paper introduces a novel approach for targetless
camera-LiDAR extrinsic calibration called Multi-FEAT (Multi-Feature Edge
AlignmenT). Multi-FEAT uses the cylindrical projection model to transform the
2D(Camera)-3D(LiDAR) calibration problem into a 2D-2D calibration problem, and
exploits various LiDAR feature information to supplement the sparse LiDAR point
cloud boundaries. In addition, a feature matching function with a precision
factor is designed to improve the smoothness of the solution space. The
performance of the proposed Multi-FEAT algorithm is evaluated using the KITTI
dataset, and our approach shows more reliable results, as compared with several
existing targetless calibration methods. We summarize our results and present
potential directions for future work
Joint Ranging and Phase Offset Estimation for Multiple Drones using ADS-B Signatures
A new method for joint ranging and Phase Offset (PO) estimation of multiple
drones/aircrafts is proposed in this paper. The proposed method employs the
superimposed uncoordinated Automatic Dependent Surveillance Broadcast (ADS-B)
packets broadcasted by drones/aircrafts for joint range and PO estimation. It
jointly estimates range and PO prior to ADS-B packet decoding; thus, it can
improve air safety when packet decoding is infeasible due to packet collision.
Moreover, it enables coherent detection of ADS-B packets, which can result in
more reliable multiple target tracking in aviation systems using cooperative
sensors for detect and avoid (DAA). By minimizing the Kullback Leibler
Divergence (KLD) statistical distance measure, we show that the received
complex baseband signal coming from K uncoordinated drones corrupted by
Additive White Gaussian Noise (AWGN) at a single antenna receiver can be
approximated by an independent and identically distributed Gaussian Mixture
(GM) with 2 power K mixture components in the two dimensional (2D) plane. While
direct joint Maximum Likelihood Estimation (MLE) of range and PO from the
derived GM Probability Density Function (PDF) leads to an intractable
maximization, our proposed method employs the Expectation Maximization (EM)
algorithm to estimate the modes of the 2D Gaussian mixture followed by a
reordering estimation technique through combinatorial optimization to estimate
range and PO. An extension to a multiple antenna receiver is also investigated
in this paper. While the proposed estimator can estimate the range of multiple
drones with a single receive antenna, a larger number of drones can be
supported with higher accuracy by the use of multiple antennas at the receiver.
The effectiveness of the proposed estimator is supported by simulation results.
We show that the proposed estimator can jointly estimate the range of three
drones accurately
DARIS, a fleet of passive formation flying small satellites for low frequency radio astronomy
DARIS (Distributed Aperture Array for Radio Astronomy In Space) is a mission to conduct radio astronomy in the low frequency region from 1-10MHz. This region has not yet been explored, as the Earth's ionosphere is opaque to those frequencies, and so a space based observatory is the only solution. DARIS will undertake an extragalactic survey of the low frequency sky, and can also detect some transient radio events such as solar or planetary bursts. To achieve these scientific objectives, DARIS comprises a space-based array, forming a very large effective aperture, as required for such a long wavelength survey. Each station in the array (each required to be a small satellite to ensure several nodes can be flown) carries three orthogonal dipole antennas, each 5m in length. The more station nodes in the array, the more sensitive the antenna. The entire fleet remains within a 100km diameter cloud. \ud
A very large data volume is generated by each node, as the antennas have to capture all radio signals, after which the data can be correlated to find the astronomical signal in the noise. As the astronomical signals also have a noise-like nature, no compression is possible on the data captured by the nodes. The data volume is too high to transfer directly to Earth, and will need to be correlated in space. Distributed correlation between the nodes is technically challenging, and therefore a mothership acts as the central correlator and then downlinks the correlated data (lower volume) to Earth. \u
Space-based Aperture Array For Ultra-Long Wavelength Radio Astronomy
The past decade has seen the rise of various radio astronomy arrays,
particularly for low-frequency observations below 100MHz. These developments
have been primarily driven by interesting and fundamental scientific questions,
such as studying the dark ages and epoch of re-ionization, by detecting the
highly red-shifted 21cm line emission. However, Earth-based radio astronomy
below frequencies of 30MHz is severely restricted due to man-made interference,
ionospheric distortion and almost complete non-transparency of the ionosphere
below 10MHz. Therefore, this narrow spectral band remains possibly the last
unexplored frequency range in radio astronomy. A straightforward solution to
study the universe at these frequencies is to deploy a space-based antenna
array far away from Earths' ionosphere. Various studies in the past were
principally limited by technology and computing resources, however current
processing and communication trends indicate otherwise. We briefly present the
achievable science cases, and discuss the system design for selected scenarios,
such as extra-galactic surveys. An extensive discussion is presented on various
sub-systems of the potential satellite array, such as radio astronomical
antenna design, the on-board signal processing, communication architectures and
joint space-time estimation of the satellite network. In light of a scalable
array and to avert single point of failure, we propose both centralized and
distributed solutions for the ULW space-based array. We highlight the benefits
of various deployment locations and summarize the technological challenges for
future space-based radio arrays.Comment: Submitte