Device-to-Device (D2D) communications in this paper refer to autonomous direct communications among end devices without central control. Wireless networks based on autonomous D2D communications are of resiliency feature. We developed a lifelog gathering system using such autonomous D2D communications towards elderly health monitoring in depopulated area, where creating wireless networks with coverage over entire area is costly. The developed system consists of three types of terminals, i.e., sensing terminal (s-terminal), delivering terminal (d-terminal), and gathering terminal (g-terminal). The s-terminal collects lifelog at objective’s house. The d-terminal can be placed in a moving car and it receives lifelog data when running within communication range of the objective’s house. Moreover, the lifelog is forwarded to the g-terminal when the d-terminal enters the communication range of facilities where the g-terminal is in operation. We conducted field experiments in a mountainous village. The measured results show that the developed system can successfully gather lifelog data even under non line-of-sight environments. Examples of observation from the gathered lifelog data are also presented.

This paper describes the sensor network systems developed in cooperation with Shiojiri city. We developed a relay network for sensor networks with high robustness that continues to operate even in the event of a large-scale disaster. By making use of the technology, a relay network composed of more than 600 repeaters was built and is currently operational in Shiojiri city in the Nagano Prefecture. Additionally, by using this relay network as a test bed, we developed various applications, and have been operating them locally as well as in other areas. Based on these experiences, this paper describes the development of the information and communications technology and its outcomes obtained from building the test bed.

In this research, we propose a high-speed simulator for rapidly determining protocol performance of a sensor network comprised of many terminals. We have developed this simulator by using GPGPU technology, in which widely used GPUs (Graphics Processing Units) are applied to general-purpose computing. This simulator executes at high-speed by using the parallelism that is a structural feature of GPUs, and enables simultaneous execution of simulations with various values of the parameters in the protocol. The result is high-speed simulations using inexpensive hardware which previously could only be processed using a supercomputer.

The proliferation of all kinds of devices with different security requirements and constraints, and the arms-race nature of the security problem are increasingly demanding the development of tools to help on the automatic design of Boolean functions with security application. Nowadays, the design of strong cryptographic Boolean functions is a multiobjective problem. However, so far evolutionary multiobjective algorithms have been largely overlooked and not much is known about this problem from a multiobjective optimization perspective. In this work we focus on non-linearity related criteria and explore a multiobjective evolutionary approach aiming to find several balanced functions of similar characteristics satisfying multiple criteria. We show that the multiobjective approach is an efficient alternative to single objective optimization approaches presented so far. We also argue that it is a better framework for automatic design of cryptographic Boolean functions.

The Wireless Ad-Hoc Network for Shiojiri is an urban network being deployed with the objective to serve the community of Shiojiri city. In this work, we use data collected in test experiments on the actual field to find optimal topologies, minimizing the cost given by the number of required transponders for several possible threshold values of strength of the packets sent from the terminals. The results presented here provide valuable information about the reliability of the expected service, give alternatives to the decision maker, and help the designer to set up threshold parameters at the transponders.

In this work, we developed a high speed LSI for encoding and decoding the RSA cryptogram and describe the processing method in this paper. This cryptogram is used not only for encrypting data, but also for such purposes as authentication. However, the RSA encoding and decoding processes take a long time because they require a great deal of calculations. As a result, this cryptogram is not suited for practical use. In order to make a high-speed processing method, we introduce the following ideas: (1) to reduce the number of summation operations, we increase the number of coding bits used to represent a digit; (2) we propose a high-speed addition operation for handling the case in which each digit has a large number of bits; (3) we guarantee the value of modulo operations by determining the possible range and create parallel subtraction circuits as a result. By applying these concepts, we are able to reduce processing times compared to the previous methods. We also developed the LSI to realize our proposed algorithm.

A performance analysis of slotted rings is presented based on a register-insertion method which is proposed for broadband ring topology networks. The analysis is carried out under the assumption that each node contains a finite buffer space. A Markovian model is developed for the ring. The arrival process of packets from upstream nodes is determined from the model. The probability of buffer overflow and the probability distribution of the number of packets in a buffer are calculated using the model. The analytical results are shown to be accurate by comparing them with simulation results.>