5,886 research outputs found
TS-MUWSN: Time synchronization for mobile underwater sensor networks
Time synchronization is an important, yet challenging, problem in underwater sensor networks (UWSNs). This challenge can be attributed to: 1) messaging timestamping; 2) node mobility; and 3) Doppler scale effect. To mitigate these problems, we present an acoustic-based time-synchronization algorithm for UWSN, where we compare several message time-stamping algorithms in addition to different Doppler scale estimators. A synchronization system is based on a bidirectional message exchange between a reference node and a slave one, which has to be synchronized. Therefore, we take as reference the DA-Sync-like protocol (Liu et al., 2014), which takes into account node's movement by using first-order kinematic equations, which refine Doppler scale factor estimation accuracy, and result in better synchronization performance. In our study, we propose to modify both time-stamping and Doppler scale estimation procedures. Besides simulation, we also perform real tests in controlled underwater communication in a water test tank and a shallow-water test in the Mediterranean Sea.Peer ReviewedPostprint (author's final draft
The Chrono-Geometrical Structure of General Relativity and Clock Synchronization
After a review of the chrono-geometrical structure of special relativity,
where the definition of the instantaneous 3-space is based on the
observer-dependent convention for the synchronization of distant clocks, it is
shown that in a class of models of general relativity the instantaneous 3-space
and the associated clock synchronization convention are dynamically determined
by Einstein's equations. This theoretical framework is necessary to understand
the relativistic effects around the Earth, to be tested with the ACES mission
of ESA, and the implications for metrology induced by the accuracy of the new
generation of atomic clocks.Comment: 13 pages, Talk at the First Colloquium Scientific and Fundamental
Aspects of the Galileo Programme, Toulouse 1-4 October 200
Quantum clock synchronization and quantum error correction
I consider quantum protocols for clock synchronization, and investigate in
particular whether entanglement distillation or quantum error-correcting codes
can improve the robustness of these protocols. I also draw attention to some
unanswered questions about the relativistic theory of quantum measurement. This
paper is based on a talk given at the NASA-DoD Workshop on Quantum Information
and Clock Synchronization for Space Applications (QuICSSA), September 25-26,
2000.Comment: 8 pages, 5 figures, REVTeX and eps
Recommended from our members
Review of Unbiased FIR Filters, Smoothers, and Predictors for Polynomial Signals
Extracting an estimate of a slowly varying signal corrupted by noise is a common task. Examples can be found in industrial, scientific and biomedical instrumentation. Depending on the nature of the application the signal estimate is allowed to be a delayed estimate of the original signal or, in the other extreme, no delay is tolerated. These cases are commonly referred to as filtering, prediction, and smoothing depending on the amount of advance or lag between the input data set and the output data set. In this review paper we provide a comprehensive set of design and analysis tools for designing unbiased FIR filters, predictors, and smoothers for slowly varying signals, i.e. signals that can be modeled by low order polynomials. Explicit expressions of parameters needed in practical implementations are given. Real life examples are provided including cases where the method is extended to signals that are piecewise slowly varying. A critical view on recursive implementations of the algorithms is provided
Software Defined Radio Implementation of Carrier and Timing Synchronization for Distributed Arrays
The communication range of wireless networks can be greatly improved by using
distributed beamforming from a set of independent radio nodes. One of the key
challenges in establishing a beamformed communication link from separate radios
is achieving carrier frequency and sample timing synchronization. This paper
describes an implementation that addresses both carrier frequency and sample
timing synchronization simultaneously using RF signaling between designated
master and slave nodes. By using a pilot signal transmitted by the master node,
each slave estimates and tracks the frequency and timing offset and digitally
compensates for them. A real-time implementation of the proposed system was
developed in GNU Radio and tested with Ettus USRP N210 software defined radios.
The measurements show that the distributed array can reach a residual frequency
error of 5 Hz and a residual timing offset of 1/16 the sample duration for 70
percent of the time. This performance enables distributed beamforming for range
extension applications.Comment: Submitted to 2019 IEEE Aerospace Conferenc
Interval-based clock synchronization with optimal precision
AbstractWe present description and analysis of a novel optimal precision clock synchronization algorithm (OP), which takes care of both precision and accuracy with respect to external time. It relies upon the generic interval-based algorithm of Schmid and Schossmaier [Real-Time Syst. 12 (2) (1997) 173] and utilizes a convergence function based on the orthogonal accuracy algorithm of Schmid [Chicago J. Theor. Comput. Sci. 3 (2000) 3]. As far as precision is concerned, we show that OP achieves optimal worst case precision, optimal maximum clock adjustment, and optimal rate, as does the algorithm of Fetzer and Cristian [Proceedings 10th Annual IEEE Conference on Computer Assurance, Gaithersburg, MD, 1995]. However, relying upon a perception-based hybrid fault model and a fairly realistic system model, our results are valid for a wide variety of node and link faults and apply to very high-precision applications as well: Impairments due to clock granularity and discrete rate adjustment cannot be ignored here anymore. Our accuracy analysis focuses on the nodes’ local accuracy interval, which provides the atop running application with an on-line bound on the current deviation from external time. We show that this bound could get larger than twice the necessary lower bound (“traditional accuracy”), hence OP is considerably suboptimal in this respect
Attack-Aware Data Timestamping in Low-Power Synchronization-Free LoRaWAN
Low-power wide-area network technologies such as LoRaWAN are promising for
collecting low-rate monitoring data from geographically distributed sensors, in
which timestamping the sensor data is a critical system function. This paper
considers a synchronization-free approach to timestamping LoRaWAN uplink data
based on signal arrival time at the gateway, which well matches LoRaWAN's
one-hop star topology and releases bandwidth from transmitting timestamps and
synchronizing end devices' clocks at all times. However, we show that this
approach is susceptible to a {\em frame delay attack} consisting of malicious
frame collision and delayed replay. Real experiments show that the attack can
affect the end devices in large areas up to about . In a
broader sense, the attack threatens any system functions requiring timely
deliveries of LoRaWAN frames. To address this threat, we propose a
gateway design that integrates a commodity LoRaWAN gateway
and a low-power software-defined radio receiver to track the inherent frequency
biases of the end devices. Based on an analytic model of LoRa's chirp spread
spectrum modulation, we develop signal processing algorithms to estimate the
frequency biases with high accuracy beyond that achieved by LoRa's default
demodulation. The accurate frequency bias tracking capability enables the
detection of the attack that introduces additional frequency biases. Extensive
experiments show the effectiveness of our approach.Comment: 40th IEEE International Conference on Distributed Computing Systems
(ICDCS
Influence of relativistic effects on satellite-based clock synchronization
Clock synchronization between the ground and satellites is a fundamental
issue in future quantum telecommunication, navigation, and global positioning
systems. Here, we propose a scheme of near-Earth orbit satellite-based quantum
clock synchronization with atmospheric dispersion cancellation by taking into
account the spacetime background of the Earth. Two frequency entangled pulses
are employed to synchronize two clocks, one at a ground station and the other
at a satellite. The time discrepancy of the two clocks is introduced into the
pulses by moving mirrors and is extracted by measuring the coincidence rate of
the pulses in the interferometer. We find that the pulses are distorted due to
effects of gravity when they propagate between the Earth and the satellite,
resulting in remarkably affected coincidence rates. We also find that the
precision of the clock synchronization is sensitive to the source parameters
and the altitude of the satellite. The scheme provides a solution for
satellite-based quantum clock synchronization with high precision, which can be
realized, in principle, with current technology.Comment: 7 pages, 3 figures, to appear in Phys. Rev.
On the "barcode" functionality of the DNA, or The phenomenon of Life in the physical Universe
The information contained in the genome is insufficient for the control of
organism development. Thus, the whereabouts of actual operational directives
and workings of the genome remain obscure. In this work, it is suggested that
the genome information plays a role of a "barcode". The DNA structure presents
a pseudo-random number(PRN)with classification tags, so organisms are
characterized by DNA as library books are characterized by catalogue numbers.
Elaboration of the "barcode" interpretation of DNA implicates the
infrastructure of the physical Universe as a seat of biological information
processing. Thanks to the PRNs provided by DNA, biological objects can share
these facilities in the Code Division Multiple Access (CDMA) mode, similarly to
cellular phone communications. Figuratively speaking, populations of biological
objects in the physical Universe can be seen as a community of users on the
Internet with a wireless CDMA connection. The phenomenon of Life as a
collective information processing activity has little to do with physics and is
to be treated with the methodology of engineering design. The concept of the
"barcode" functionality of DNA confronts the descriptive scientific doctrines
with a unique operational scheme of biological information control. Recognition
of this concept would require sacrificing the worldview of contemporary
cosmology.Comment: 52 pages, 2 textual figures, 1 bitmap figur
KPI/KQI-Driven Coordinated Multi-Point in 5G: Measurements, Field Trials, and Technical Solutions
The fifth generation (5G) systems are expected to be able to support massive
number of wireless devices and intense demands for high data rates while
maintaining low latency. Coordinated multipoint (CoMP) is advocated by recent
advances and is envisioned to continue its adoption in 5G to meet these
requirements by alleviating inter-cell interference and improving spectral
efficiency. The higher requirements in 5G have raised the stakes on developing
a new CoMP architecture. To understand the merits and limitations of CoMP in
5G, this article systematically investigates evaluation criteria including key
performance indicators (KPIs) and key quality indicators (KQIs) in 5G, conducts
empirical measurements and field tests, and then proposes a KPI/KQI-driven CoMP
architecture that fulfills KPI requirements and provides KQI guarantee for each
user
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