# BITS: Bits of Information, Transmitted and Stored

クルカスキー研究室　KURKOSKI Laboratory

E-mail：kurkoskijaist.ac.jp
［研究分野］
Information theory, coding theory, communications theory
［キーワード］
reliable communications, wireless communications, data storage

## 研究を始めるのに必要な知識・能力

We welcome students with motivation and ability in three areas.
（1） Mathematical skills of basic probability theory, such as Bayes rule, and linear algebra, such as basic matrix operations.
（2） Computer programming skills, such as C/C++, Java, or Matlab.
（3） Passion to use English as a technical language.

## この研究で身につく能力

Graduating students will have knowledge of fundamental methods for understanding and designing state-of-the-art communication and data storage systems. These systems are implemented as algorithms, and so students will gain understanding of mathematical techniques underlying these algorithms. Students will be able to read a paper, understand the contents, implement the algorithm in a program, and evaluate by computer simulations. Most students study and gain deep knowledge of error-correcting codes for reliable communications.

【就職先企業・職種】 communications, data storage

### 研究内容

#### Information, Transmitted and Stored

Information transmission is sending data from one point to another point, for example, from the mobile phone in your hand, to a base station on the top of a building. Information storage is the sending of data from one point in time, to another point in time, for example files saved to your hard drive or SSD today can be recovered next week. Noise in the environment and unreliable storage media can corrupt signals and cause errors in data.

#### Information Theory and Coding Theory

The BITS Lab studies information theory and coding theory, to provide reliable communications and reliable storage of information. Information theory deals with the fundamental limits of reliable information transmission and compression. Remarkably, information can be transmitted reliably over a communications channel, even if the channel is unreliable. A central result states that the information rate R of transmission can be no greater than the channel capacity:

R <1/2 log （1 + SNR）

An error-correcting code.

for a channel with signal-to-noise ratio SNR.

Coding theory deals with error-correcting codes, a concrete method to correct some errors, and even achieve the channel capacity. One such code can be represented using three circles, as shown in the figure. The number of 1’s inside each circle must be even. The code consists of seven bits, each either a 0 or a 1. But some bits have been erased to an unknown “?”. Can you recover the original bits?

#### Codes for Data Storage

Data storage is at the core of the information technology revolution, from the smartphones in our hands to data centers in the cloud. Flash memory, hard disk drives and distributed storage networks combine to provide ubiquitous access to data. But these exciting new systems pose new problems of storage density, reliability and efficiency. Coding theory provides an answer.

#### Cooperative Wireless Communications

With the arrival of the smartphone, the demand for wireless network communications has exploded. But new electromagnetic spectrum is scarce. To increase future data rates, cooperative wireless communications is the new way forward. In cooperative wireless communications, users, relays and base stations work together to increase data rates, as shown in the figure.

A cooperative wireless network.
Lattices are codes which use the same real-number algebra for both the code and the channel, where electromagnetic signals are superimposed. Lattice codes correct errors introduced by channel noise, satisfy transmission power constraints, and possess properties needed for network coding. We are developing lattice coding theory to enable next-generation cooperative wireless communications.

### 主な研究業績

1. R. Sekiya, B. M. Kurkoski, “Applying Write-Once Memory Codes to Binary Symmetric Asymmetric Multiple Access Channels,” IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 99-A, vol. 12, pp. 2202-2210, 2016.
2. B. M. Kurkoski and H. Yagi, “Quantization of binary-input discrete memoryless channels,” IEEE Transactions on Information Theory, vol. 60, pp. 4544-4552, August 2014.
3. H. Uchikawa, B. M. Kurkoski, K. Kasai, and K. Sakaniwa, “Iterative encoding with Gauss-Seidel method for spatially-coupled low-density lattice codes,” in Proceedings of IEEE International Symposium on Information Theory, pp. 1747-1751, July 2012.

### 研究室の指導方針

Our lab is a dynamic and interactive environment. Students are primarily advised in one-on-one meetings between the advisor and student. More senior students are encouraged to participate in the advising of newer students. Conversely, even Masters students are given research projects that can lead to presentations at international conferences and publications in English-language journals.

［研究室HP］ URL：http://bits.kurkoski.org/

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