15,115 research outputs found
Tiny Graviton Matrix Theory On Time-Dependent Background
In this article we construct a tiny graviton matrix model for type IIB string
theory on a plane-wave background with null dilaton. For the linear null
dilaton case, we analyze its vacuum and the excitation spectrum around the
vacuum, and discuss the time-dependent fuzzy three-sphere solutions and their
evolution. It turns out that at very late time the non-Abelian fuzzy degrees of
freedom disappear, which indicates the appearance of perturbative strings.Comment: 20 pages and 4 figures; published version, with more clarification
D1-D3 (or ) Systems with Fluxes
In this article we study D1-D3 (or ) brane systems with
generic constant electric and magnetic fluxes in IIB string theory. We work out
all possible supersymmetric configurations and find out via T-duality all of
them and corresponding supersymmetry conditions could be related to the
supersymmetric intersecting D1-D1 pairs. And we do D1-D3 (or
) open string quantization for a class of configurations. We
find that there are many near massless states in NS sector for near-BPS
configurations. Furthermore we calculate open string pair creation rate in
generic nonsupersymmetric configurations.Comment: 31 pages. References adde
Simplified Multiuser Detection for SCMA with Sum-Product Algorithm
Sparse code multiple access (SCMA) is a novel non-orthogonal multiple access
technique, which fully exploits the shaping gain of multi-dimensional
codewords. However, the lack of simplified multiuser detection algorithm
prevents further implementation due to the inherently high computation
complexity. In this paper, general SCMA detector algorithms based on
Sum-product algorithm are elaborated. Then two improved algorithms are
proposed, which simplify the detection structure and curtail exponent
operations quantitatively in logarithm domain. Furthermore, to analyze these
detection algorithms fairly, we derive theoretical expression of the average
mutual information (AMI) of SCMA (SCMA-AMI), and employ a statistical method to
calculate SCMA-AMI based specific detection algorithm. Simulation results show
that the performance is almost as well as the based message passing algorithm
in terms of both BER and AMI while the complexity is significantly decreased,
compared to the traditional Max-Log approximation method
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