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- Tim Rogers, Isaac Pérez Castillo, Reimer Kühn, Koujin Takeda
- Physical review. E, Statistical, nonlinear, and…
- 2008

The spectral density of various ensembles of sparse symmetric random matrices is analyzed using the cavity method. We consider two cases: matrices whose associated graphs are locally treelike, and sparse covariance matrices. We derive a closed set of equations from which the density of eigenvalues can be efficiently calculated. Within this approach, the… (More)

- Koujin Takeda, Yoshiyuki Kabashima
- 2010 IEEE International Symposium on Information…
- 2010

We investigate a reconstruction limit of compressed sensing for a reconstruction scheme based on the L<inf>1</inf>-norm minimization utilizing a correlated compression matrix with a statistical mechanics method. We focus on the compression matrix modeled as the Kronecker-type random matrix studied in research on multiple-input multiple-output wireless… (More)

- Koujin Takeda, Shinsuke Uda, Yoshiyuki Kabashima
- ArXiv
- 2006

{ An approach to analyze the performance of the code division multiple access (CDMA) scheme, which is a core technology used in modern wireless communication systems, is provided. The approach characterizes the objective system by the eigenvalue spectrum of a cross-correlation matrix composed of signature sequences used in CDMA communication, which enable… (More)

- Koujin Takeda, Yoshiyuki Kabashima
- ArXiv
- 2010

PACS 89.70.-a – Information and communication theory PACS 75.10.Nr – Spin-glass and other random models PACS 05.70.Fh – Phase transitions: general studies Abstract.-We provide a scheme for exploring the reconstruction limits of compressed sensing by minimizing the general cost function under the random measurement constraints for generic correlated signal… (More)

- Atsushi Hatabu, Koujin Takeda, Yoshiyuki Kabashima
- ArXiv
- 2009

The Kronecker channel model of wireless communication is analyzed using statistical mechanics methods. In the model, spatial proximities among transmission/reception antennas are taken into account as certain correlation matrices, which generally yield non-trivial dependence among symbols to be estimated. This prevents accurate assessment of the… (More)

- Koujin Takeda, Atsushi Hatabu, Yoshiyuki Kabashima
- ArXiv
- 2007

A statistical mechanical framework to analyze linear vector channel models in digital wireless communication is proposed for a large system. The framework is a generalization of that proposed for code-division multiple-access systems in Europhys. Lett., 76 (2006) 1193 and enables the analysis of the system in which the elements of the channel transfer… (More)

- Koujin Takeda
- 2003

We study the four-dimensional Z 2 random-plaquette lattice gauge theory as a model of topological quantum memory, the toric code in particular. In this model, the procedure of quantum error correction works properly in the ordered (Higgs) phase, and phase boundary between the ordered (Higgs) and disordered (confinement) phases gives the accuracy threshold… (More)

This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan, sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will… (More)

- Toshifumi Jittoh, Shigeki Matsumoto, Joe Sato, Yoshio Sato, Koujin Takeda
- 2005

We study the decay process of an unstable quantum system, especially the deviation from the exponential decay law. We show that the exponential period no longer exists in the case of the s-wave decay with small Q value, where the Q value is the difference between the energy of the initially prepared state and the minimum energy of the continuous eigenstates… (More)

- Tomoyuki Obuchi, Kazutaka Takahashi, Koujin Takeda
- ArXiv
- 2010