537 research outputs found
Modulation Identification and Carrier Recovery System for Adaptive Modulation in Satellite Communications
We introduce the modulation identification technique implementing the multimode phase locked loop (PLL) in the satellite communication using adaptive modulation scheme which is a countermeasure against the rain attenuation. In the multimode PLL, phase lock detectors (PLDs) are used for not only phase lock, but also modulation identification. We present the sub-optimized design of the PLDs for modulation identification with respect to the throughput and show the validity of sub-optimization. In addition, by the comparison between the multimode PLL and conventional scheme in ISDB-S, we present the effectivity of the multimode PLL
Method of Non-Data-Aided Carrier Recovery with Modulation Identification
A non-data aided carrier recovery technique using digital modulation format identification called multi-mode PLL (Phase Locked Loop) is proposed. This technique can be interpreted as a modulation identification method that is robust against static phase and frequency offsets. The performance of the proposed technique is studied and the analytical expressions are derived for the probability of lock detection, acquisition time over AWGN channel in the cases of M-PSK and M-QAM modulations with respect to frequency offset and signal-to-noise ratio
A Method of Non-Data-Aided Carrier Recovery with Modulation Identification
A non-data aided carrier recovery technique using modulation format identification is proposed. This technique can also be interpreted as a modulation identification method that is robust against static phase and frequency offsets. The performance of the proposed technique is studied and analytical expressions derived for the mean acquisition time to detect lock in the cases of M-PSK, M=2,4,8, and 16-QAM modulation, with respect to frequency offset and signal-to-noise ratio. The results are verified with Monte Carlo simulations. The main advantage of the proposed method lies in its simpler implementation and faster lock detection, when compared to conventional methods
Gas pressure sintering of Beta-Sialon with Z=3
An experiment conducted on beta-sialon in atmospheric pressure, using a temperature of 2000 C and 4 MPa nitrogen atmosphere, is described. Thermal decomposition was inhibited by the increase of the nitrogen gas pressure
Magnetorotational Instability in Protoplanetary Disks. II. Ionization State and Unstable Regions
We investigate where in protoplanetary disks magnetorotational instability
operates, which can cause angular momentum transport in the disks. We
investigate the spatial distribution of various charged particles and the
unstable regions for a variety of models for protoplanetary disks taking into
account the recombination of ions and electrons at grain surfaces, which is an
important process in most parts of the disks. We find that for all the models
there is an inner region which is magnetorotationally stable due to ohmic
dissipation. This must make the accretion onto the central star non-steady. For
the model of the minimum-mass solar nebula, the critical radius, inside of
which the disk is stable, is about 20 AU, and the mass accretion rate just
outside the critical radius is 10^{-7} - 10^{-6} M_{\odot} yr^{-1}. The stable
region is smaller in a disk of lower column density. Dust grains in
protoplanetary disks may grow by mutual sticking and may sediment toward the
midplane of the disks. We find that the stable region shrinks as the grain size
increases or the sedimentation proceeds. Therefore in the late evolutionary
stages, protoplanetary disks can be magnetorotationally unstable even in the
inner regions.Comment: 23 pages + 16 figures + 3 tables, accepted for publication in Ap
Primary Channel Duty Cycle Estimation Under Imperfect Spectrum Sensing Based on Mean Channel Periods
The Origin of Jovian Planets in Protostellar Disks: The Role of Dead Zones
The final masses of Jovian planets are attained when the tidal torques that
they exert on their surrounding protostellar disks are sufficient to open gaps
in the face of disk viscosity, thereby shutting off any further accretion. In
sufficiently well-ionized disks, the predominant form of disk viscosity
originates from the Magneto-Rotational Instability (MRI) that drives
hydromagnetic disk turbulence. In the region of sufficiently low ionization
rate -- the so-called dead zone -- turbulence is damped and we show that lower
mass planets will be formed. We considered three ionization sources (X-rays,
cosmic rays, and radioactive elements) and determined the size of a dead zone
for the total ionization rate by using a radiative, hydrostatic equilibrium
disk model developed by Chiang et al. (2001). We studied a range of surface
mass density (Sigma_{0}=10^3 - 10^5 g cm^{-2}) and X-ray energy (kT_{x}=1 - 10
keV). We also compared the ionization rate of such a disk by X-rays with cosmic
rays and find that the latter dominate X-rays in ionizing protostellar disks
unless the X-ray energy is very high (5 - 10 keV). Among our major conclusions
are that for typical conditions, dead zones encompass a region extending out to
several AU -- the region in which terrestrial planets are found in our solar
system. Our results suggest that the division between low and high mass planets
in exosolar planetary systems is a consequence of the presence of a dead zone
in their natal protoplanetary disks. We also find that the extent of a dead
zone is mainly dependent on the disk's surface mass density. Our results
provide further support for the idea that Jovian planets in exosolar systems
must have migrated substantially inwards from their points of origin.Comment: 28 pages, 10 figures, accepted by Ap
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