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Yasutada Oohama

Publications and source records attributed to Yasutada Oohama.

At least 37 records · Page 2Linked to original sources

A New Inequality Related to Proofs of Strong Converse Theorems for Source or Channel Networks

In this paper we provide a new inequality useful for the proofs of strong converse theorems in the multiterminal information theory. We apply this inequality to the recent work by Tyagi and Watanabe on the strong converse theorem for the Wyner-Ziv source coding problem to obtain a new strong converse outer bound. This outer bound deviates from the Wyner-Ziv rate distortion region with the order $O\left(\frac{1}{\sqrt{n}}\right)$ on the length $n$ of source outputs.

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Secrecy Amplification for Distributed Encrypted Sources with Correlated Keys using Affine Encoders

This paper proposed the application of post-encryption-compression (PEC) to strengthen the secrecy in the case of distributed encryption where the encryption keys are correlated to each other. We derive the universal code construction for the compression and the rate region where codes with achievability and secrecy are obtainable. Our main technique is to use affine encoders which are constructed from certain linear encoders to encode the ciphertexts before sending them to public communication channels. We show that if the rates of linear codes are within a certain rate region:(1) information leakage on the original sources from the encoded ciphertexts without the keys is negligible, while (2) one who has legitimate keys is able to retrieve the original source data with negligible error probability.

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On a Relationship between the Correct Probability of Estimation from Correlated Data and Mutual Information

Let $X$, $Y$ be two correlated discrete random variables. We consider an estimation of $X$ from encoded data $φ(Y)$ of $Y$ by some encoder function $φ(Y)$. We derive an inequality describing a relation of the correct probability of estimation and the mutual information between $X$ and $φ(Y)$. This inequality may be useful for the secure analysis of crypto system when we use the success probability of estimating secret data as a security criterion. It also provides an intuitive meaning of the secrecy exponent in the strong secrecy criterion.

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An Iterative Algorithm for Computing the Optimal Exponent of Correct Decoding Probability for Rates below the Rate Distortion Function

The form of Dueck and Körner's exponent function for correct decoding probability for discrete memoryless channels at rates above the capacity is similar to the form of Csiszár and Körner's exponent function for correct decoding probability in lossy source coding for discrete memoryless sources at rates below the rate distortion function. We recently gave a new algorithm for computing Dueck and Körner's exponent. In this paper, we give an algorithm for computing Csiszár and Körner's exponent. The proposed algorithm can be also used to compute cutoff rate and the rate distortion function.

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Exponent Function for Source Coding with Side Information at the Decoder at Rates below the Rate Distortion Function

We consider the rate distortion problem with side information at the decoder posed and investigated by Wyner and Ziv. The rate distortion function indicating the trade-off between the rate on the data compression and the quality of data obtained at the decoder was determined by Wyner and Ziv. In this paper, we study the error probability of decoding at rates below the rate distortion function. We evaluate the probability of decoding such that the estimation of source outputs by the decoder has a distortion not exceeding a prescribed distortion level. We prove that when the rate of the data compression is below the rate distortion function this probability goes to zero exponentially and derive an explicit lower bound of this exponent function. On the Wyner-Ziv source coding problem the strong converse coding theorem has not been established yet. We prove this as a simple corollary of our result.

cs.IT↗

Strong Converse Theorems for Degraded Broadcast Channels with Feedback

We consider the discrete memoryless degraded broadcast channels with feedback. We prove that the error probability of decoding tends to one exponentially for rates outside the capacity region and derive an explicit lower bound of this exponent function. We shall demonstrate that the information spectrum approach is quite useful for investigating this problem.

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Outer Bound of the Capacity Region for Identification via Multiple Access Channels

In this paper we consider the identification (ID) via multiple access channels (MACs). In the general MAC the ID capacity region includes the ordinary transmission (TR) capacity region. In this paper we discuss the converse coding theorem. We estimate two types of error probabilities of identification for rates outside capacity region, deriving some function which serves as a lower bound of the sum of two error probabilities of identification. This function has a property that it tends to zero as $n\to \infty$ for noisy channels satisfying the strong converse property. Using this property, we establish that the transmission capacity region is equal to the ID capacity for the MAC satisfying the strong converse property. To derive the result we introduce a new resolvability problem on the output from the MAC. We further develop a new method of converting the direct coding theorem for the above MAC resolvability problem into the converse coding theorem for the ID via MACs.

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Broadcast Channels with Confidential Messages by Randomness Constrained Stochastic Encoder

In coding schemes for the wire-tap channel or the broadcast channels with confidential messages, it is well known that the sender needs to use a stochastic encoding to avoid the information about the transmitted confidential message to be leaked to an eavesdropper. In this paper, it is investigated that the trade-off between the rate of the random number to realize the stochastic encoding and the rates of the common, private, and confidential messages. For the direct theorem, the superposition coding scheme for the wire-tap channel recently proposed by Chia and El Gamal is employed, and its strong security is proved. The matching converse theorem is also established. Our result clarifies that a combination of the ordinary stochastic encoding and the channel prefixing by the channel simulation is suboptimal.

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On Two Strong Converse Theorems for Stationary Discrete Memoryless Channels

In 1973, Arimoto proved the strong converse theorem for the discrete memoryless channels stating that when transmission rate $R$ is above channel capacity $C$, the error probability of decoding goes to one as the block length $n$ of code word tends to infinity. He proved the theorem by deriving the exponent function of error probability of correct decoding that is positive if and only if $R>C$. Subsequently, in 1979, Dueck and Körner determined the optimal exponent of correct decoding. Arimoto's bound has been said to be equal to the bound of Dueck and Körner. However its rigorous proof has not been presented so far. In this paper we give a rigorous proof of the equivalence of Arimoto's bound to that of Dueck and Körner.

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Cognitive Interference Channels with Confidential Messages under Randomness Constraint

The cognitive interference channel with confidential messages (CICC) proposed by Liang et. al. is investigated. When the security is considered in coding systems, it is well known that the sender needs to use a stochastic encoding to avoid the information about the transmitted confidential message to be leaked to an eavesdropper. For the CICC, the trade-off between the rate of the random number to realize the stochastic encoding and the communication rates is investigated, and the optimal trade-off is completely characterized.

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Secret Key Agreement from Correlated Gaussian Sources by Rate Limited Public Communication

We investigate the secret key agreement from correlated Gaussian sources in which the legitimate parties can use the public communication with limited rate. For the class of protocols with the one-way public communication, we show a closed form expression of the optimal trade-off between the rate of key generation and the rate of the public communication. Our results clarify an essential difference between the key agreement from discrete sources and that from continuous sources.

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Distributed Source Coding of Correlated Gaussian Sources

We consider the distributed source coding system of $L$ correlated Gaussian sources $Y_i,i=1,2,...,L$ which are noisy observations of correlated Gaussian remote sources $X_k, k=1,2,...,K$. We assume that $Y^{L}={}^{\rm t}(Y_1,Y_2,$ $..., Y_L)$ is an observation of the source vector $X^K={}^{\rm t}(X_1,X_2,..., X_K)$, having the form $Y^L=AX^K+N^L$, where $A$ is a $L\times K$ matrix and $N^L={}^{\rm t}(N_1,N_2,...,N_L)$ is a vector of $L$ independent Gaussian random variables also independent of $X^K$. In this system $L$ correlated Gaussian observations are separately compressed by $L$ encoders and sent to the information processing center. We study the remote source coding problem where the decoder at the center attempts to reconstruct the remote source $X^K$. We consider three distortion criteria based on the covariance matrix of the estimation error on $X^K$. For each of those three criteria we derive explicit inner and outer bounds of the rate distortion region. Next, in the case of $K=L$ and $A=I_L$, we study the multiterminal source coding problem where the decoder wishes to reconstruct the observation $Y^L=X^L+N^L$. To investigate this problem we shall establish a result which provides a strong connection between the remote source coding problem and the multiterminal source coding problem. Using this result, we drive several new partial solutions to the multiterminal source coding problem.

cs.IT↗

Secret Key Agreement from Vector Gaussian Sources by Rate Limited Public Communication

We investigate the secret key agreement from correlated vector Gaussian sources in which the legitimate parties can use the public communication with limited rate. For the class of protocols with the one-way public communication, we show that the optimal trade-off between the rate of key generation and the rate of the public communication is characterized as an optimization problem of a Gaussian random variable. The characterization is derived by using the enhancement technique introduced by Weingarten et.al. for MIMO Gaussian broadcast channel.

cs.IT↗

Capacity Results for Relay Channels with Confidential Messages

We consider a communication system where a relay helps transmission of messages from {a} sender to {a} receiver. The relay is considered not only as a helper but as a wire-tapper who can obtain some knowledge about transmitted messages. In this paper we study a relay channel with confidential messages(RCC), where a sender attempts to transmit common information to both a receiver and a relay and also has private information intended for the receiver and confidential to the relay. The level of secrecy of private information confidential to the relay is measured by the equivocation rate, i.e., the entropy rate of private information conditioned on channel outputs at the relay. The performance measure of interest for the RCC is the rate triple that includes the common rate, the private rate, and the equivocation rate as components. The rate-equivocation region is defined by the set that consists of all these achievable rate triples. In this paper we give two definitions of the rate-equivocation region. We first define the rate-equivocation region in the case of deterministic encoder and call it the deterministic rate-equivocation region. Next, we define the rate-equivocation region in the case of stochastic encoder and call it the stochastic rate-equivocation region. We derive explicit inner and outer bounds for the above two regions. On the deterministic/stochastic rate-equivocation region we present two classes of relay channels where inner and outer bounds match. We also evaluate the deterministic and stochastic rate-equivocation regions of the Gaussian RCC.

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Distributed Source Coding for Correlated Memoryless Gaussian Sources

We consider a distributed source coding problem of $L$ correlated Gaussian observations $Y_i, i=1,2,...,L$. We assume that the random vector $Y^{L}={}^{\rm t} (Y_1,Y_2,$ $...,Y_L)$ is an observation of the Gaussian random vector $X^K={}^{\rm t}(X_1,X_2,...,X_K)$, having the form $Y^L=AX^K+N^L ,$ where $A$ is a $L\times K$ matrix and $N^L={}^{\rm t}(N_1,N_2,...,N_L)$ is a vector of $L$ independent Gaussian random variables also independent of $X^K$. The estimation error on $X^K$ is measured by the distortion covariance matrix. The rate distortion region is defined by a set of all rate vectors for which the estimation error is upper bounded by an arbitrary prescribed covariance matrix in the meaning of positive semi definite. In this paper we derive explicit outer and inner bounds of the rate distortion region. This result provides a useful tool to study the direct and indirect source coding problems on this Gaussian distributed source coding system, which remain open in general.

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Distributed Source Coding of Correlated Gaussian Remote Sources

We consider the distributed source coding system for $L$ correlated Gaussian observations $Y_i, i=1,2, ..., L$. Let $X_i,i=1,2, ..., L$ be $L$ correlated Gaussian random variables and $N_i,$ $i=1,2,... L$ be independent additive Gaussian noises also independent of $X_i, i=1,2,..., L$. We consider the case where for each $i=1,2,..., L$, $Y_i$ is a noisy observation of $X_i$, that is, $Y_i=X_i+N_i$. On this coding system the determination problem of the rate distortion region remains open. In this paper, we derive explicit outer and inner bounds of the rate distortion region. We further find an explicit sufficient condition for those two to match. We also study the sum rate part of the rate distortion region when the correlation has some symmetrical property and derive a new lower bound of the sum rate part. We derive a sufficient condition for this lower bound to be tight. The derived sufficient condition depends only on the correlation property of the sources and their observations.

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