439 research outputs found
MIMO signal processing in offset-QAM based filter bank multicarrier systems
Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft
On the prospects of imaging Sagittarius A* from space
Very Long Baseline Interferometry (VLBI) at sub-millimeter waves has the
potential to image the shadow of the black hole in the Galactic Center,
Sagittarius A* (Sgr A*), and thereby test basic predictions of the theory of
general relativity. We investigate the imaging prospects of a new Space VLBI
mission concept. The setup consists of two satellites in polar or equatorial
circular Medium-Earth Orbits with slightly different radii, resulting in a
dense spiral-shaped uv-coverage with long baselines, allowing for extremely
high-resolution and high-fidelity imaging of radio sources. We simulate
observations of a general relativistic magnetohydrodynamics model of Sgr A* for
this configuration with noise calculated from model system parameters. After
gridding the -plane and averaging visibilities accumulated over multiple
months of integration, images of Sgr A* with a resolution of up to 4 as
could be reconstructed, allowing for stronger tests of general relativity and
accretion models than with ground-based VLBI.Comment: 4 pages, 4 figures, published in Proceedings IAU Symposium No. 342,
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First spaceborne observation of sea surface height using GPS-reflectometry
An analysis of spaceborne Global Positioning System reflectometry (GPS-R) data from the TechDemoSat-1 (TDS-1) satellite is carried out to image the ocean sea surface height (SSH). An SSH estimation algorithm is applied to GPS-R delay waveforms over two regions in the South Atlantic and the North Pacific. Estimates made from TDS-1 overpasses during a 6 month period are aggregated to produce SSH maps of the two regions. The maps generally agree with the global DTU10 mean sea surface height. The GPS-R instrument is designed to make bistatic measurements of radar cross section for ocean wind observations, and its altimetric performance is not optimized. The differences observed between measured and DTU10 SSH can be attributed to limitations with the GPS-R instrument and the lack of precision orbit determination by the TDS-1 platform. These results represent the first observations of SSH by a spaceborne GPS-R instrument
Diseño de un sistema de gestión de seguridad y salud en el trabajo para reducir la accidentabilidad en una empresa constructora
La presente investigación tiene por objetivo Proponer un sistema de gestión de seguridad y salud en
el trabajo para reducir la accidentabilidad en obra en una constructora, el tipo de investigación utilizada es
aplicativa-descriptiva y el diseño de investigación es no experimental cuantitativa. Para determinar la
situación actual de la organización en cuanto a su SGSST, se realizó la evaluación de la línea base según los
lineamientos, esto nos sirvió para proponer las mejoras de acuerdo a las necesidades y limitaciones de la
empresa. La identificación de las causas de los principales problemas de la SST en la constructora se realizó
mediante el uso de diagrama de Ishikawa, en donde se llegó a la conclusión que implementando un adecuado
SGSST reducirá los accidentes satisfaciendo las necesidades de sus trabajadores, clientes y proveedores. En
la propuesta de implementación del SGSST, se tomaron 3 capítulos de la norma ISO 45001 que son: Liderazgo
y colaboración de los Trabajadores, Operación y Mejora, los cuales también se detallan en la ley de seguridad
29783, estos capítulos se consideran claves para dar inicio al proceso de implementación del SGSST y lograr
el objetivo principal que es la reducción de accidentes. Finalmente, el costo de la propuesta fue de S/ 12,500
soles. Por último, se obtuvo como beneficio-costo de 1.62, indicándose que por cada sol invertido se está
ganando 0.62 céntimos, demostrando que el sistema de seguridad y salud en el trabajo es rentable.TesisInfraestructura, Tecnología y Medio Ambient
Autoeficacia y locus de control en colaboradores de la Gerencia Regional La Libertad
El objetivo general de la presente investigación fue determinar la relación entre la
autoeficacia y locus de control en los colaboradores de la Gerencia Regional La
Libertad, este estudio pertenece a las de tipo descriptivo correlacional, cuya muestra
se conformó por 169 colaboradores de las sub gerencias (transportes y
comunicaciones y trabajo y promoción del empleo), se utilizó dos instrumentos que
permitieron recoger la información de ambas variables: la escala general de
autoeficacia de Baessler y Schwarzer creada en 1996 y la escala de Locus de control
creada por Rotter en 1966 y que cuenta con dos dimensiones: locus de control interno
y externo. Por otro lado, haremos uso de la prueba de Kolmogorov-Smirnov-Lillefors
la cual nos permitirá realizar el contraste de normalidad lo siguiente fue encontrar las
correlaciones mediante Spearman Brow donde los resultados de nuestra investigación
arrojaron que existe una relación significativa aceptable entre ambas variables,
dejando de manifiesto que, a mayor autoeficacia, mayor locus interno poseen y caso
contrario sucede con el locus externo ya que a mayor autoeficacia menor será su
locus externo
Towards a non-error floor multi-stream beamforming design for FBMC/OQAM
This paper investigates the application of filter bank multicarrier modulation based on the OQAM (FBMC/OQAM) to multiple-input-multiple-output (MIMO) systems. Existing solutions guarantee satisfactory performance when the streams multiplexed on each subcarrier (S) and the number of transmit (NT) and receive (NR) antennas are related as S = min (NT, NR). When S <; min (NT, NR), the techniques presented in previous works either exhibit an error floor or perform much worse than orthogonal frequency division multiplexing (OFDM). To make progress towards the combination of FBMC/OQAM with MIMO we propose a two-step approach and a coordinated beamforming algorithm to design the transmit and the receive processing. Numerical results show that the two-step method provides similar bit error rate (BER) as OFDM when S + 1 = NT = NR. Resorting to the coordinated beamforming solution, which is based on an iterative method, the application of FBMC/OQAM is extended to the general case S <; min (NT, NR). Hence, the techniques presented in this paper demonstrate that FBMC/OQAM can achieve practically the same BER as OFDM with an increased spectral efficiency and a significantly decreased out-of-band radiation, which is an important advantage for non-contiguous spectrum allocations.Peer ReviewedPostprint (author's final draft
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