Error-correcting codes, which are fundamental methods for correcting errors occurring in digital information, realize reliable information systems. Erasure-correcting codes are a class of error-correcting codes and correct erasures in digital information. Fountain codes are erasure-correcting codes providing reliable multicasting, which sends the same message to multiple destinations. In this paper, we briefly review existing erasure-correcting and fountain codes. Then, we introduce the zigzag decodable fountain codes proposed by the author. Moreover, we compare their performance with an existhing fountain code called Raptor code.

Petri nets are one of the modeling languages of discrete event systems and concurrent systems. They were introduced by Dr. Carl Adam Petri in his Ph.D. thesis in 1962 and sice then, an enormous amount of theoretical and practical research has been carried our on them. The reachability problem is one of the fundamental problems in Petri nets. Although this problem is decidable, its computational complexity is exponential to the size of the Petri nets, making the analysis of various problems on Petri nets difficult. However, recent advances in computational capabilities and the development of various methods have enabled us to solve problems on Petri nets of a certain scale. This paper outlines the following recent methods used for the reachability problem: the symbolic state-space method, the unfolding method, the modular state-space method, and the method using model-checking tools.

With the rising importance of information security, the necessity of implementing better security measures in physical as well as upper layers is becoming increasingly apparent. Given the development of high-accuracy, low-cost measurement devices, high-performance computers, and large storage devices, the threat of advanced attacks at the physical level has expanded from the military and government sectors to the commercial sector. In this paper, we introduce the problem of information security degradation through electromagnetic (EM)-based compromising of security measures in the physical layer (i.e., EM information security). Owing to the invisibility of EM radiation, such attacks can lead to serious threats. Moreover, we explain the mechanisms of EM information leakage and introduce countermeasures that make it difficult for information to leak. In particular, this study is focused on the countermeasures applicable to conventional information devices that do not depend on upper-layer protocols and applications.

Orthogonal frequency division multiplexing (OFDM) is a key technology in radio communication. The application of OFDM to optical wireless communication using intensity modulation has also been actively studied in recent years. When we use intensity modulation, the transmitted signal must be real and non-negative. Thus, it is required to generate an OFDM signal taking such restrictions into consideration. In this article, we mainly deal with direct current biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), and layered ACO-OFDM systems as basic OFDM systems that are applicable to optical wireless communication, and explain the signal structure and communication performance of those systems.

In recent years, high intensity ultrasound has been widely used in medical and the industrial applications, However, the sound field could not be measured because the electrode or piezoelectric vibrator of the hydrophone was damaged by acoustic cavitation. Therefore, we have developed a tough hydrophone that can be used for measurement without damage even in high intensity ultrasound fields with the occurrence of acoustic cavitation. In this paper, the tough hydrophone for measuring high intensity ultrasound with the occurrence of acoustic cavitation is reported. This hydrophone is fabricated by hydrothermally deposition of a PZT polycrystalline film on the back surface of a titanium front plate and the use of titanium backing.