63,630 research outputs found
Code-timing synchronization in DS-CDMA systems using space-time diversity
The synchronization of a desired user transmitting a known training sequence in a direct-sequence (DS) asynchronous code-division multiple-access (CDMA) sys-tem is addressed. It is assumed that the receiver consists of an arbitrary antenna array and works in a near-far, frequency-nonselective, slowly fading channel. The estimator that we propose is derived by applying the maximum likelihood (ML) principle to a signal model in which the contribution of all the interfering compo-nents (e.g., multiple-access interference, external interference and noise) is modeled as a Gaussian term with an unknown and arbitrary space-time correlation matrix. The main contribution of this paper is the fact that the estimator makes eÆcient use of the structure of the signals in both the space and time domains. Its perfor-mance is compared with the Cramer-Rao Bound, and with the performance of other methods proposed recently that also employ an antenna array but only exploit the structure of the signals in one of the two domains, while using the other simply as a means of path diversity. It is shown that the use of the temporal and spatial structures is necessary to achieve synchronization in heavily loaded systems or in the presence of directional external interference.Peer ReviewedPostprint (published version
An adaptive stereo basis method for convolutive blind audio source separation
NOTICE: this is the author’s version of a work that was accepted for publication in Neurocomputing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in PUBLICATION, [71, 10-12, June 2008] DOI:neucom.2007.08.02
Adaptive Protection and Control in Power System for Wide-Area Blackout Prevention
This paper presents a new approach in adaptive outof-step (OOS) protection settings in power system in real-time. The proposed method uses extended equal area criterion (EEAC) to determine the critical clearing time (CCT) and critical clearing angle (CCA) of the system, which are vital information for OOS protection setting calculation. The dynamic model parameters and the coherency groups of the system for EEAC analysis are determined in real time to ensure that the newly calculated settings suit with the prevalent system operating condition. The effectiveness of the method is demonstrated in a simulated data from 16-machine 68-bus system model
Adaptive Radar Detection of Dim Moving Targets in Presence of Range Migration
This paper addresses adaptive radar detection of dim moving targets. To
circumvent range migration, the detection problem is formulated as a multiple
hypothesis test and solved applying model order selection rules which allow to
estimate the "position" of the target within the CPI and eventually detect it.
The performance analysis proves the effectiveness of the proposed approach also
in comparison to existing alternatives.Comment: 5 pages, 2 figures, submitted to IEEE Signal Processing Letter
Proposal for an Optical Test of the Einstein Equivalence Principle
The Einstein Equivalence Principle (EEP) underpins all metric theories of
gravity. Its key element is the local position invariance of non-gravitational
experiments, which entails the gravitational red-shift. Precision measurements
of the gravitational red-shift tightly bound violations of the EEP only in the
fermionic sector of the Standard Model, however recent developments of
satellite optical technologies allow for its investigation in the
electromagnetic sector. Proposals exploiting light interferometry traditionally
suffer from the first-order Doppler effect, which dominates the weak
gravitational signal necessary to test the EEP, making them unfeasible. Here,
we propose a novel scheme to test the EEP, which is based on a double
large-distance optical interferometric measurement. By manipulating the
phase-shifts detected at two locations at different gravitational potentials it
is possible to cancel-out the first-order Doppler effect and observe the
gravitational red-shift implied by the EEP. We present the detailed analysis of
the proposal within the post-Newtonian framework and the simulations of the
expected signals obtained by using two realistic satellite orbits. Our proposal
to overcome the first-order Doppler effect in optical EEP tests is feasible
with current technology.Comment: manuscript improve
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