16,085 research outputs found
Linear Paul trap design for an optical clock with Coulomb crystals
We report on the design of a segmented linear Paul trap for optical clock
applications using trapped ion Coulomb crystals. For an optical clock with an
improved short-term stability and a fractional frequency uncertainty of 10^-18,
we propose 115In+ ions sympathetically cooled by 172Yb+. We discuss the
systematic frequency shifts of such a frequency standard. In particular, we
elaborate on high precision calculations of the electric radiofrequency field
of the ion trap using the finite element method. These calculations are used to
find a scalable design with minimized excess micromotion of the ions at a level
at which the corresponding second- order Doppler shift contributes less than
10^-18 to the relative uncertainty of the frequency standard
Design of a Low-Cost Microstrip Directional Coupler with High Coupling for a Motion Detection Sensor
A coupled-line coupler based on the asymmetric cascade connection of two coupled line sections is used to achieve a high coupling factor using low-cost material and technology in the X frequency band, and its performance is compared with a standard quarter-wave, coupled-line coupler, showing an increase in the coupling factor of about 3 dB. The proposed coupler can be effectively used in a Doppler motion detection sensor, due to its strong coupling and relatively high isolation. The coupler is designed through a simple, yet rigorous, equivalent circuital model. Then,anoptimizationprocedurewasperformedusingthecommercialsoftwareAnsysHFSSinorder to compensate for losses and second order effects. A prototype of the designed coupler was realized, and the measured data show very good agreement with simulations
Advanced Algorithms for Satellite Communication Signal Processing
DizertaÄŤnĂ práce je zaměřena na softwarovÄ› definovanĂ© pĹ™ijĂmaÄŤe urÄŤenĂ© k ĂşzkopásmovĂ© druĹľicovĂ© komunikaci. KomunikaÄŤnĂ kanály druĹľicovĂ˝ch spojĹŻ zahrnujĂcĂch komunikaci s hlubokĂ˝m vesmĂrem jsou zatĂĹľeny vysokĂ˝mi ĂşrovnÄ›mi šumu, typicky modelovanĂ©ho AWGN, a silnĂ˝m DopplerovĂ˝m posuvem signálu zpĹŻsobenĂ˝m mimořádnou rychlostĂ pohybu objektu. DizertaÄŤnĂ práce pĹ™edstavuje moĹľnĂ© postupy Ĺ™ešenĂ vĂ˝poÄŤetnÄ› efektivnĂ digitálnĂ downkonverze ĂşzkopásmovĂ˝ch signálĹŻ a systĂ©mu odhadu kmitoÄŤtu nosnĂ© ĂşzkopásmovĂ˝ch signálĹŻ zatĂĹľenĂ˝ch DopplerovĂ˝m posuvem v řádu násobkĹŻ šĂĹ™ky pásma signálu. Popis navrhovanĂ˝ch algoritmĹŻ zahrnuje analytickĂ˝ postup jejich vĂ˝voje a tam, kde je to moĹľnĂ©, i analytickĂ© hodnocenĂ jejich chovánĂ. Algoritmy jsou modelovány v prostĹ™edĂ MATLAB Simulink a tyto modely jsou vyuĹľity pro ověřenĂ vlastnostĂ simulacemi. Modely byly takĂ© vyuĹľity k experimentálnĂm testĹŻm na reálnĂ©m signálu pĹ™ijatĂ©m z druĹľice PSAT v laboratoĹ™i experimentálnĂch druĹľic na Ăşstavu radioelektroniky.The dissertation is focused on software defined receivers intended for narrowband satellite communication. The satellite communication channel including deep space communication suffers from a high level of noise, typically modeled by AWGN, and from a strong Doppler shift of a signal caused by the unprecedented speed of an object in motion. The dissertation shows possible approaches to the issues of computationally efficient digital downconversion of narrowband signals and the carrier frequency estimation of narrowband signals distorted by the Doppler shift in the order of multiples of the signal bandwidth. The description of the proposed algorithms includes an analytical approach of its development and, if possible, the analytical performance assessment. The algorithms are modeled in MATLAB Simulink and the models are used for validating the performance by the simulation. The models were also used for experimental tests on the real signal received from the PSAT satellite at the laboratory of experimental satellites at the department of radio electronics.
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
Acoustical Ranging Techniques in Embedded Wireless Sensor Networked Devices
Location sensing provides endless opportunities for a wide range of applications in GPS-obstructed environments;
where, typically, there is a need for higher degree of accuracy. In this article, we focus on robust range
estimation, an important prerequisite for fine-grained localization. Motivated by the promise of acoustic in
delivering high ranging accuracy, we present the design, implementation and evaluation of acoustic (both
ultrasound and audible) ranging systems.We distill the limitations of acoustic ranging; and present efficient
signal designs and detection algorithms to overcome the challenges of coverage, range, accuracy/resolution,
tolerance to Doppler’s effect, and audible intensity. We evaluate our proposed techniques experimentally on
TWEET, a low-power platform purpose-built for acoustic ranging applications. Our experiments demonstrate
an operational range of 20 m (outdoor) and an average accuracy 2 cm in the ultrasound domain. Finally,
we present the design of an audible-range acoustic tracking service that encompasses the benefits of a near-inaudible
acoustic broadband chirp and approximately two times increase in Doppler tolerance to achieve better performance
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