Jun Muramatsu

Low density parity check matrices for coding of correlated sources

Linear codes for a coding problem of correlated sources are considered. It is proved that we can construct codes by using low-density parity-check (LDPC) matrices with maximum-likelihood (or typical set) decoding. As applications of the above coding problem, a construction of codes is presented for multiple-access channel with correlated additive noises and a coding theorem of parity-check codes for general channels is proved.

Secret Key Agreement from Correlated Source Outputs Using Low Density Parity Check Matrices

This paper deals with a secret key agreement problem from correlated random numbers. It is proved that there is a pair of linear matrices that yields a secret key agreement in the situation wherein a sender, a legitimate receiver, and an eavesdropper have access to correlated random numbers. A relation between the coding problem of correlated sources and a secret key agreement problem from correlated random numbers are also discussed.

Common-chaotic-signal induced synchronization in semiconductor lasers

We experimentally and numerically observe synchronization of two semiconductor lasers commonly driven by a chaotic semiconductor laser subject to optical feedback. Under condition that the relaxation oscillation frequency is matched between the two response lasers, but mismatched between the drive and the two response lasers, we show that it is possible to observe strongly correlated synchronization between the two response lasers even when the correlation between the drive and response lasers is low. We also show that the cross correlation between the two responses is larger than that between drive and responses over a wide parameter region.

Information-theoretic secure key distribution based on common random-signal induced synchronization in unidirectionally-coupled cascades of semiconductor lasers

It has been proposed that a secure key distribution scheme using correlated random bit sequences can be implemented using common random-signal induced synchronization of semiconductor laser systems. In this scheme it is necessary to use laser systems consisting of multiple cascaded lasers to be secure against a powerful eavesdropper. In this paper, we report the results of an experimental study that demonstrate that the common random-signal induced synchronization is possible in cascaded semiconductor laser systems. We also show that the correlated random bit sequences generated in the synchronized cascaded laser systems can be used to create an information-theoretically secure key between two legitimate users.

Channel Coding and Lossy Source Coding Using a Generator of Constrained Random Numbers

Stochastic encoders for channel coding and lossy source coding are introduced with a rate close to the fundamental limits, where the only restriction is that the channel input alphabet and the reproduction alphabet of the lossy source code are finite. Random numbers, which satisfy a condition specified by a function and its value, are used to construct stochastic encoders. The proof of the theorems is based on the hash property of an ensemble of functions, where the results are extended to general channels/sources and alternative formulas are introduced for channel capacity and the rate-distortion region. Since an ensemble of sparse matrices has a hash property, we can construct a code by using sparse matrices.

A Construction of Lossy Source Code Using LDPC Matrices

Research into applying LDPC code theory, which is used for channel coding, to source coding has received a lot of attention in several research fields such as Distributed Source Coding. In this paper a source coding problem with a fidelity criterion is considered. Matsunaga et al. [6] constructed a lossy code under the conditions of a binary alphabet, a uniform distribution, and a Hamming measure of fidelity criterion. We extend their results and construct a lossy code under the extended conditions of a binary alphabet, a distribution that is not necessarily uniform, and a fidelity measure that is bounded and additive and show that the code can achieve the optimal rate, rate-distortion function.

Construction of strongly secure wiretap channel code based on hash property

A strongly secure wiretap channel code is proposed. The construction is based on the strong hash property introduced in Proc. ISIT2010, pp. 575–579. Since an ensemble of sparse matrices satisfies the conditions for the strong hash property, the rate of the proposed code using sparse matrices can achieve the secrecy capacity.

Information theoretic security based on bounded observability

Under the condition that all users can observe a common object, each using an observation function independently chosen from the same limited set of observation functions, we show necessary and sufficient conditions for users to be able to generate secret keys by public discussion.

Construction of Codes for the Wiretap Channel and the Secret Key Agreement From Correlated Source Outputs Based on the Hash Property

The aim of this paper is to prove coding theorems for the wiretap channel and the secret key agreement based on the the notion of a hash property for an ensemble of functions. These theorems imply that codes using sparse matrices can achieve the optimal rate. Furthermore, fixed-rate universal coding theorems for a wiretap channel and a secret key agreement are also proved.

Hash Property and Fixed-Rate Universal Coding Theorems

The aim of this paper is to prove the fixed-rate universal coding theorems by using the notion of the hash property. These theorems are the fixed-rate lossless universal source coding theorem and the fixed-rate universal channel coding theorem. Since an ensemble of sparse matrices (with logarithmic column degree) satisfies the hash property requirement, it is proved that we can construct universal codes by using sparse matrices.