471 research outputs found
On the Capacity-Achieving Input of Channels with Phase Quantization
Several information-theoretic studies on channels with output quantization
have identified the capacity-achieving input distributions for different fading
channels with 1-bit in-phase and quadrature (I/Q) output quantization. But can
analytical results on the capacity-achieving input also be obtained for
multi-bit quantization? We answer the question in the affirmative by
considering multi-bit phase quantization. We first consider a complex Gaussian
channel with -bit phase-quantized output and prove that the
capacity-achieving distribution is a rotated -phase shift keying (PSK).
The analysis is then extended to multiple fading scenarios. We show that the
optimality of rotated -PSK continues to hold under noncoherent fast fading
Rician channels with -bit phase quantization when line-of-sight (LoS) is
present. When channel state information (CSI) is available at the receiver, we
identify -symmetry and constant amplitude as the necessary
and sufficient conditions for the ergodic capacity-achieving input
distribution; which a -PSK satisfies. Finally, an optimum power control
scheme is presented which achieves ergodic capacity when CSI is also available
at the transmitter.Comment: Submitted to IEEE Transactions on Information Theor
On the potential of the EChO mission to characterise gas giant atmospheres
Space telescopes such as EChO (Exoplanet Characterisation Observatory) and
JWST (James Webb Space Telescope) will be important for the future study of
extrasolar planet atmospheres. Both of these missions are capable of performing
high sensitivity spectroscopic measurements at moderate resolutions in the
visible and infrared, which will allow the characterisation of atmospheric
properties using primary and secondary transit spectroscopy. We use the NEMESIS
radiative transfer and retrieval tool (Irwin et al. 2008, Lee et al. 2012) to
explore the potential of the proposed EChO mission to solve the retrieval
problem for a range of H2-He planets orbiting different stars. We find that
EChO should be capable of retrieving temperature structure to ~200 K precision
and detecting H2O, CO2 and CH4 from a single eclipse measurement for a hot
Jupiter orbiting a Sun-like star and a hot Neptune orbiting an M star, also
providing upper limits on CO and NH3. We provide a table of retrieval
precisions for these quantities in each test case. We expect around 30
Jupiter-sized planets to be observable by EChO; hot Neptunes orbiting M dwarfs
are rarer, but we anticipate observations of at least one similar planet.Comment: 22 pages, 30 figures, 4 tables. Accepted for publication in MNRA
THE CONTROL OF ROTATION DURING RUGBY UNION GOAL KICKING
INTRODUCTION: While the basic kicking technique in ball sports is well understood, there has been limited research conducted on the biomechanics of rugby union goal kicking. Specifically, the movement characteristics which contribute to kicking accuracy have not been well defined. It is probable that the control of body rotation plays an important role in determining kicking accuracy. The quantity of rotation is characterised by the extent of angular momentum but surprisingly this quantity has seldom been used in analysis of kicking technique. This study aims to investigate how rugby players control rotation during execution of. the kicking action and to determine the relationship between segmental angular
momentum contributions and kicking accuracy
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