2,222 research outputs found
Coherent versus non-coherent decode-and-forward relaying aided cooperative space-time shift keying
Motivated by the recent concept of Space-Time Shift Keying (STSK), we propose a novel cooperative STSK family, which is capable of achieving a flexible rate-diversity tradeoff, in the context of cooperative space-time transmissions. More specifically, we first propose a Coherent cooperative STSK (CSTSK) scheme, where each Relay Node (RN) activates Decode-and-Forward (DF) transmissions, depending on the success or failure of Cyclic Redundancy Checking (CRC). We invoke a bitto- STSK mapping rule, where according to the input bits, one of the Q pre-assigned dispersion vectors is activated to implicitly convey log2(Q) bits, which are transmitted in combination with the classic log2(L)-bit modulated symbol. Additionally, we introduce a beneficial dispersion vector design, which enables us to dispense with symbol-level Inter-Relay Synchronization (IRS). Furthermore, the Destination Node (DN) is capable of jointly detecting the signals received from the source-destination and relay-destination links, using a low-complexity single-stream-based Maximum Likelihood (ML) detector, which is an explicit benefit of our Inter-Element Interference (IEI)-free system model. More importantly, as a benefit of its design flexibility, our cooperative CSTSK arrangement enables us to adapt the number of the RNs, the transmission rate as well as the achievable diversity order. Moreover, we also propose a Differentially-encoded cooperative STSK (DSTSK) arrangement, which dispenses with CSI estimation at any of the nodes, while retaining the fundamental benefits of the cooperative CSTSK scheme
Conclusion: Epistemic communities, world order, and the creation of a reflective research program
Este artĂculo se extrae de la revista International Organization, vol. 46, nÂș 1, Knowledge, Power and International Policy Coordination, invierno 1992, ps. 367-390 y ha sido traducido con
permiso de la editorial MIT PressLas Relaciones Internacionales carecen de una teorĂa y un juego de explicaciones creĂble sobre el origen de las instituciones internacionales, los intereses estatales y el comportamiento de los estados en condiciones de incertidumbre. En este volumen no sĂłlo desarrollamos âestudios particulares que (âŠ) pueden iluminar asuntos importantes en la polĂtica internacional,â sino que tambiĂ©n ofrecemos un programa de investigaciĂłn mediante el cual los estudiantes de polĂtica internacional pueden estudiar de modo empĂrico el papel de las ideas en las relaciones internacionalesAccording to this research program, international relations can be seen as an evolutionary process in which epistemic communities play meaningful roles as sources of policy innovation, channels by which these innovations diffuse internationally, and catalysts in the political and institutional processes leading to the selection of their shared goals. International cooperation and, indeed, the development of new world orders based on common meanings and understandings may thus depend on the extent to which nation-states apply their power on behalf of practices that epistemic communities may have helped create, diffuse, and perpetuat
Governing Complexity in World Politics
Complexity is the new global ontology for world politics. This article summarizes the characteristics of complexity and its implications for informed US state policy making. We conclude with some suggestions about administrative reforms to improve US policy making to address global complexity
Performance of Spatial Modulation using Measured Real-World Channels
In this paper, for the first time real-world channel measurements are used to
analyse the performance of spatial modulation (SM), where a full analysis of
the average bit error rate performance (ABER) of SM using measured urban
correlated and uncorrelated Rayleigh fading channels is provided. The channel
measurements are taken from an outdoor urban multiple input multiple output
(MIMO) measurement campaign. Moreover, ABER performance results using simulated
Rayleigh fading channels are provided and compared with a derived analytical
bound for the ABER of SM, and the ABER results for SM using the measured urban
channels. The ABER results using the measured urban channels validate the
derived analytical bound and the ABER results using the simulated channels.
Finally, the ABER of SM is compared with the performance of spatial
multiplexing (SMX) using the measured urban channels for small and large scale
MIMO. It is shown that SM offers nearly the same or a slightly better
performance than SMX for small scale MIMO. However, SM offers large reduction
in ABER for large scale MIMO.Comment: IEEE Vehicular Technology Conference Fall 2013 (VTC-Fall 2013),
Accepte
Experimental investigation of Hall thruster interal magnetic field topography
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76207/1/AIAA-2001-3890-254.pd
An experimental investigation of the internal magnetic field topography of an operating Hall thruster
Magnetic field measurements were made in the discharge channel of the 5 kW-class P5 laboratory-model Hall thruster to investigate what effect the Hall current has on the static, applied magnetic field topography. The P5 was operated at 1.6 and 3.0 kW with a discharge voltage of 300 V. A miniature inductive loop probe (B-Dot probe) was employed to measure the radial magnetic field profile inside the discharge channel of the P5 with and without the plasma discharge. These measurements are accomplished with minimal disturbance to thruster operation with the High-speed Axial Reciprocating Probe system. The results of the B-Dot probe measurements indicate a change in the magnetic field topography from that of the vacuum field measurements. The measured magnetic field profiles are then examined to determine the possible nature and source of the difference between the vacuum and plasma magnetic field profiles. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70249/2/PHPAEN-9-10-4354-1.pd
Increasing Spatial Fidelity and SNR of 4D-STEM using Multi-frame Data Fusion
4D-STEM, in which the 2D diffraction plane is captured for each 2D scan
position in the scanning transmission electron microscope (STEM) using a
pixelated detector, is complementing and increasingly replacing existing
imaging approaches. However, at present the speed of those detectors, although
having drastically improved in the recent years, is still 100 to 1,000 times
slower than the current PMT technology operators are used to. Regrettably, this
means environmental scanning-distortion often limits the overall performance of
the recorded 4D data. Here we present an extension of existing STEM distortion
correction techniques for the treatment of 4D-data series. Although applicable
to 4D-data in general, we use electron ptychography and electric-field mapping
as model cases and demonstrate an improvement in spatial-fidelity,
signal-to-noise ratio (SNR), phase-precision and spatial-resolution
The Kepler Pixel Response Function
Kepler seeks to detect sequences of transits of Earth-size exoplanets
orbiting Solar-like stars. Such transit signals are on the order of 100 ppm.
The high photometric precision demanded by Kepler requires detailed knowledge
of how the Kepler pixels respond to starlight during a nominal observation.
This information is provided by the Kepler pixel response function (PRF),
defined as the composite of Kepler's optical point spread function, integrated
spacecraft pointing jitter during a nominal cadence and other systematic
effects. To provide sub-pixel resolution, the PRF is represented as a
piecewise-continuous polynomial on a sub-pixel mesh. This continuous
representation allows the prediction of a star's flux value on any pixel given
the star's pixel position. The advantages and difficulties of this polynomial
representation are discussed, including characterization of spatial variation
in the PRF and the smoothing of discontinuities between sub-pixel polynomial
patches. On-orbit super-resolution measurements of the PRF across the Kepler
field of view are described. Two uses of the PRF are presented: the selection
of pixels for each star that maximizes the photometric signal to noise ratio
for that star, and PRF-fitted centroids which provide robust and accurate
stellar positions on the CCD, primarily used for attitude and plate scale
tracking. Good knowledge of the PRF has been a critical component for the
successful collection of high-precision photometry by Kepler.Comment: 10 pages, 5 figures, accepted by ApJ Letters. Version accepted for
publication
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