7,202 research outputs found
On compact splitting complex submanifolds of quotients of bounded symmetric domains
In the current article our primary objects of study are compact complex
submanifolds of quotient manifolds of irreducible bounded symmetric domains by
torsion free discrete lattices of automorphisms. We are interested in the
characterization of the totally geodesic submanifolds among compact splitting
complex submanifolds, i.e. under the assumption that the tangent sequence
splits holomorphically over the submanifold.Comment: Accepted for publication in SCIENCE CHINA Mathematic
Integrated Wireless Multimedia Turbo-Transceiver Design Approaching the Rayleigh Channel's Capacity: Interpreting Shannon's Lessons in the Turbo-Era
Claude Shannon's pioneering work quantified the performance limits of communications systems operating over classic wireline Gaussian channels. However, his source and channel coding theorems were derived for a range of idealistic conditions, which may not hold in low-delay, interactive wireless multimedia communications. Firstly, Shannon's ideal lossless source encoder, namely the entropy encoder may have an excessive codeword length, hence exhibiting a high delay and a high error sensitivity. However, in practice most multimedia source signals are capable of tolerating lossy, rather than lossless delivery to the human eye, ear and other human sensors. The corresponding lossy and preferably low-delay multimedia source codecs however exhibit unequal error sensitivity, which is not the case for Shannon's ideal entropy codec. There are further numerous differences between the Shannonian lessons originally outlined for Gaussian channels and their ramifications for routinely encountered dispersive wireless channels, where typically bursty, rather than random errors are encountered. This paper elaborates on these intriguiging lessons in the context of a few turbo-transceiver design examples, using a jointly optimised turbo transceiver capable of providing unequal error protection in the context of MPEG-4 aided wireless video telephony. The transceiver investigated consists of Space-Time Trellis Coding (STTC) invoked for the sake of mitigating the effects of fading, Trellis Coded Modulation (TCM) or Bit-Interleaved Coded Modulation (BICM) as well as two different-rate Non-Systematic Convolutional codes (NSCs) or Recursive Systematic Convolutional codes (RSCs). A single-class protection based benchmarker scheme combining STTC and NSC is used for comparison with the unequal-protection scheme advocated. The video performance of the various schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the achievable performance of the proposed scheme is within 0.99~dB of the corresponding capacity of the Rayleigh fading channel
Turbo-Detected Unequal Protection MPEG-4 Wireless Video Telephony using Multi-Level Coding, Trellis Coded Modulation and Space-Time Trellis Coding
Most multimedia source signals are capable of tolerating lossy, rather than lossless delivery to the human eye, ear and other human sensors. The corresponding lossy and preferably low-delay multimedia source codecs however exhibit unequal error sensitivity, which is not the case for Shannon’s ideal entropy codec. This paper proposes a jointly optimised turbo transceiver design capable of providing unequal error protection for MPEG-4 coding aided wireless video telephony. The transceiver investigated consists of space-time trellis coding (STTC) invoked for the sake of mitigating the effects of fading, in addition to bandwidth efficient trellis coded modulation or bit-interleaved coded modulation, combined with a multi-level coding scheme employing either two different-rate non-systematic convolutional codes (NSCs) or two recursive systematic convolutional codes for yielding a twin-class unequal-protection. A single-class protection based benchmark scheme combining STTC and NSC is used for comparison with the unequal-protection scheme advocated. The video performance of the various schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the proposed scheme requires about 2.8 dBs lower transmit power than the benchmark scheme in the context of the MPEG-4 videophone transceiver at a similar decoding complexity
Quantum phase transitions in attractive extended Bose-Hubbard Model with three-body constraint
The effect of nearest-neighbor repulsion on the ground-state phase diagrams
of three-body constrained attractive Bose lattice gases is explored
numerically. When the repulsion is turned on, in addition to the uniform Mott
insulating state and two superfluid phases (the atomic and the dimer
superfluids), a dimer checkerboard solid state appears at unit filling, where
boson pairs form a solid with checkerboard structure. We find also that the
first-order transitions between the uniform Mott insulating state and the
atomic superfluid state can be turned into the continuous ones as the repulsion
is increased. Moreover, the stability regions of the dimer superfluid phase can
be extended to modest values of the hopping parameter by tuning the strength of
the repulsion. Our conclusions hence shed light on the search of the dimer
superfluid phase in real ultracold Bose gases in optical lattices.Comment: 4 + epsilon pages, 5 figures. Rewritten to emphasize the effect of
nonzero nearest-neighbor repulsion. Conclusions unchanged. Accepted for
publication in Phys. Rev.
Supersolid phases in the extended boson hubbard model
We present a comprehensive numerical study on the ground state phase diagram
of the two-dimensional hardcore boson extended Hubbard model with nearest
() and next nearest neighbor () repulsions. In addition to the
quantum solid and superfluid phases, we report the existence of striped
supersolid and three-quarter (quarter) filled supersolid at commensurate
density (0.25) due to the interplay of and
interactions. The nature of three-quarter filled supersolid and the associated
quantum solid will be discussed. Quantum phase transition between the two
supersolids of different symmetries is observed and is clearly of first order.Comment: 4 pages, 6 figure
Robust Beamforming for Amplify-and-Forward MIMO Relay Systems Based on Quadratic Matrix Programming
In this paper, robust transceiver design based on minimum-mean-square-error
(MMSE) criterion for dual-hop amplify-and-forward MIMO relay systems is
investigated. The channel estimation errors are modeled as Gaussian random
variables, and then the effect are incorporated into the robust transceiver
based on the Bayesian framework. An iterative algorithm is proposed to jointly
design the precoder at the source, the forward matrix at the relay and the
equalizer at the destination, and the joint design problem can be efficiently
solved by quadratic matrix programming (QMP).Comment: Proceedings of IEEE International Conference on Acoustics, Speech,
and Signal Processing (ICASSP'2010), U.S.
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