9,324 research outputs found
Cdma blind channel equalization: a weighted subsface a proach
This paper considers the problem of blind demodulation of multiuser information symbols in a direct-sequence code-division multiple access (DS-CDMA) environment. Channel estimation and symbol detection in the presence of both multiple access interference (MAI) and intersymbol interference (ISI) is carried out with second order statistics methods from the received data. This problem is similar to direction of arrival (DOA) estimation, where many solutions like the MUSIC algorithm orPeer ReviewedPostprint (published version
Symbol decoding based on signal subspace decomposition in msk
The availability of fast processors with architectures tailored to meet the computational demand of digital signal processing algorithms is widely applied to demodulation and decodification of CPM signals in some scenes: Mobiles, AWGN channels,… In this application the number of floating point operations executed by each processed symbol is a critical parameter to be designed, this is to be minimized. In this paper a method that reduces significantly the number of operations (until 80%) by symbol for CPM signals is presented. The decodification stage is performed from the rank reduced signal subspace obtained by means of an orthogonal decomposition of the signal [1].Peer ReviewedPostprint (published version
Blind channel equalization using weighted subspace methods
This paper addresses the problems of blind channel estimation and symbol detection with second order statistics methods from the received data. It can be shown that this problem is similar to direction of arrival (DOA) estimation, where many solutions like the MUSIC algorithm orPeer ReviewedPostprint (published version
Pulsating strings with mixed three-form flux
Circular strings pulsating in with mixed R-R
and NS-NS three-form fluxes can be described by an integrable deformation of
the one-dimensional Neumann-Rosochatius mechanical model. In this article we
find a general class of pulsating solutions to this integrable system that can
be expressed in terms of elliptic functions. In the limit of strings moving in
with pure NS-NS three-form flux, where the action reduces to the
WZW model, we find agreement with the analysis of the
classical solutions of the system performed using spectral flow by Maldacena
and Ooguri. We use our elliptic solutions in to extend the dispersion
relation beyond the limit of pure NS-NS flux.Comment: 10 pages. Late
Minimal surfaces with mixed three-form flux
We study minimal area world sheets ending on two concentric circumferences on
the boundary of Euclidean with mixed R-R and NS-NS three-form fluxes.
We solve the problem by reducing the system to a one-dimensional integrable
model. We find that the NS-NS flux term either brings the surface near to the
boundary or separates the circumferences. In the limit of pure NS-NS flux the
solution adheres to the boundary in the former case and the outer radius
diverges in the latter. We further construct the underlying elliptic spectral
curve, which allows us to analyze the deformation of other related minimal
surfaces. We show that in the regime of pure NS-NS flux the elliptic curve
degenerates.Comment: 15 pages. Latex. v2: Title changed together with minor updates to
emphasize that minimal area surfaces in the presence of mixed fluxes are
found. v3: Published versio
The Wess-Zumino-Witten spin chain sigma model
Classical strings propagating in supported
with Neveu-Schwarz-Neveu-Schwarz flux are described by a Wess-Zumino-Witten
model. In this note, we study the emergence of their semiclassical
spectrally flowed sectors as the Landau-Lifshitz limit of the underlying
quantum spin chain. We consider the propagator in the coherent state picture,
and find that the time interval is discretized proportionally to the lattice
spacing. In the Landau-Lifshitz limit, where both time and space become
continuous, we derive a path integral representation of the propagator for each
spectrally flowed sector. We prove that the arbitrariness of the global phase
of coherent states is mapped to the gauge freedom of the -field in the
classical action. We show that higher order corrections in the Landau-Lifshitz
limit are suppressed by inverse powers of the 't Hooft coupling.Comment: 10 pages, Latex. v2: Published version. v3: Acknowledgement adde
Enhancing scarce-resource language translation through pivot combinations
Chinese and Spanish are the most spoken languages in the world. However, there is not much research done in machine translation for this language pair. We experiment with the parallel Chinese-Spanish corpus (United Nations) to explore alternatives of SMT strategies which consist on using a pivot language. Particularly, two well-known alternatives are shown for pivoting: the cascade system and the pseudo-corpus. As Pivot language we use English, Arabic and French. Results show that English is the best pivot language between Chinese and Spanish. As a new strategy, we propose to perform a combination of the pivot strategies which is capable to highly outperform the direct translation strategy.Postprint (published version
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