3,701 research outputs found
On Interference Cancellation and Iterative Techniques
Recent research activities in the area of mobile radio communications have moved to third generation (3G) cellular systems to achieve higher quality with variable transmission rate of multimedia information. In this paper, an overview is presented of various interference cancellation and iterative detection techniques that are believed to be suitable for 3G wireless communications systems. Key concepts are space-time processing and space-division multiple access (or SDMA) techniques. SDMA techniques are possible with software antennas. Furthermore, to reduce receiver implementation complexity, iterative detection techniques are considered. A particularly attractive method uses tentative hard decisions, made on the received positions with the highest reliability, according to some criterion, and can potentially yield an important reduction in the computational requirements of an iterative receiver, with minimum penalty in error performance. A study of the tradeoffs between complexity and performance loss of iterative multiuser detection techniques is a good research topic
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
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
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
Spectral Properties near the Mott Transition in the One-Dimensional Hubbard Model
Single-particle spectral properties near the Mott transition in the
one-dimensional Hubbard model are investigated by using the dynamical
density-matrix renormalization group method and the Bethe ansatz. The
pseudogap, hole-pocket behavior, spectral-weight transfer, and upper Hubbard
band are explained in terms of spinons, holons, antiholons, and doublons. The
Mott transition is characterized by the emergence of a gapless mode whose
dispersion relation extends up to the order of hopping t (spin exchange J) in
the weak (strong) interaction regime caused by infinitesimal doping.Comment: 4 pages, 2 figure
Tracing star formation in galaxies with molecular line and continuum observations
We report our recent progress on extragalactic spectroscopic and continuum
observations, including HCN(J=1-0), HCO(J=1-0), and CN(N=1-0) imaging
surveys of local Seyfert and starburst galaxies using the Nobeyama Millimeter
Array, high-J CO observations (J=3-2 observations using the Atacama
Submillimeter Telescope Experiment (ASTE) and J=2-1 observations with the
Submillimeter Array) of galaxies, and 1.1 mm continuum observations
of high-z violent starburst galaxies using the bolometer camera AzTEC mounted
on ASTE.Comment: 6 pages, 5 figures, To appear in proceedings of "Far-Infrared and
Submillimeter Emission of the Interstellar Medium", EAS Publication Series,
Bad Honnef, November 2007, Eds. C. Kramer, S. Aalto, R. Simon. See
http://www.nro.nao.ac.jp/~f0212kk/FIR07/kk-ver20.pdf for a version with high
resolution figure
Three-Cluster Equation Using Two-Cluster RGM Kernel
We propose a new type of three-cluster equation which uses two-cluster
resonating-group-method (RGM) kernels. In this equation, the orthogonality of
the total wave-function to two-cluster Pauli-forbidden states is essential to
eliminate redundant components admixed in the three-cluster systems. The
explicit energy-dependence inherent in the exchange RGM kernel is
self-consistently determined. For bound-state problems, this equation is
straightforwardly transformed to the Faddeev equation which uses a modified
singularity-free T-matrix constructed from the two-cluster RGM kernel. The
approximation of the present three-cluster formalism can be examined with more
complete calculation using the three-cluster RGM. As a simple example, we
discuss three di-neutron (3d') and 3 alpha systems in the harmonic-oscillator
variational calculation. The result of the Faddeev calculation is also
presented for the 3' system.Comment: 12 pages, no figur
Superconductive Phonon Anomalies in High- Cuprates
We consider the effects on phonon dynamics of spin-lattice coupling within
the slave-boson mean-field treatment of the extended - model. With no
additional assumptions the theory is found to give a semi-quantitative account
of the frequency and linewidth anomalies observed by Raman and neutron
scattering for the 340 phonon mode in at the
superconducting transition. We discuss the applicability of the model to phonon
modes of different symmetries, and report a connection to spin-gap features
observed in underdoped YBCO. The results suggest the possibility of a unified
understanding of the anomalies in transport, magnetic and lattice properties.Comment: heavily revised version of previous paper, including systematic
treatment of effect of term, coupling constant derivation and calculation
of phonon linewidth broadening. Revised Figs. 3 and 4 still only available by
sending fax # to [email protected]
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