Eiji Okubo

A Cooperative Power-Saving Technique Using DVS and DMS Based on Load Prediction in Sensor Networks

In wireless sensor networks (WSN), energy saving is the main issue of research, and many energy saving techniques have been proposed. Dynamic Voltage Scaling (DVS) and Dynamic Modulation Scaling (DMS) are techniques reduce energy consumption by using the idle time of the sensor node. When we use both techniques at the same time, an appropriate mechanism of cooperation is required because of the limitation of available idle time of the sensor node. Therefore, we propose a cooperative power. saving technique that applies DVS and DMS to sensor nodes for minimizing energy consumption. It uses a prediction mechanism that estimates the load of the processor and the radio communication device based on the log data to realize proper cooperation. We observed that the adaptation of the proposed technique is able to achieve the energy reduction up to 40 percent compared to without any energy saving techniques.

A dynamic synchronization protocol and scheduling method based on Timestamp Ordering for real‐time transactions

In this article, we propose a dynamic synchronization protocol and a scheduling method based on Timestamp Ordering for real-time transactions. First, we describe a synchronization protocol that avoids transaction abort by reserving shared resources accessed by transactions. This protocol does not incur unnecessary wait for resources, so it shows excellent performance under time constraint, compared with the priority ceiling protocol used in static scheduling environment. Next, we describe a dynamic scheduling method that takes into account both Timestamp Ordering and priority of transactions. This method does not incur deadlock unlike two-phase locking, for example, and it can decrease violation of time constraint due to resource waiting. We compare the two proposed methods and other methods by simulation, and discuss the effectiveness of the proposed methods.

Salvia: a privacy-aware operating system for prevention of data leakage

We have developed a privacy-aware operating system that focuses on preventing leakage of sensitive data such as personal information. The existing mandatory access control model is too restrictive for processes required to sustain the operations of user programs such as FTP, e-mail client applications, etc. In order to solve this problem, the proposed approach employs two techniques. First, the operating system kernel limits the execution of system calls only if the process could contribute to data leakage. Second, we implemented contexts; contexts are parameter or hints facilitating the evaluation of the risk of data leakage. These contexts also determine whether the kernel allows or disallows the execution of system calls. These techniques make it possible to realize a more adaptive and flexible data protection mechanism than the existing ones. This study describes the proposed approach.

A scheduling algorithm for multi‐processor real‐time systems with relative timing constraints and resource restrictions

In this paper, a scheduling algorithm for multi-processor real-time systems with relative timing constraints and resource constraints is proposed. The proposed algorithm has the capability to satisfy any timing constraints expressed as inequalities in two variables and a constant. This implies that scheduling problems imposed on various timing constraints such as end-to-end timing constraints and/or relative timing constraints, which are known to be difficult to handle, can be solved. Since the problem addressed in this paper is a generalization of some NP-complete problems, it is difficult to solve efficiently. Thus, the goal of the authors is to derive a heuristic algorithm which performs well on many instances of the problem, although in some cases it will take enormous space and time. Experimental results show that the proposed algorithm achieves a success rate of 80% in 3 minutes of computation time.

A Technique for Construction of Overlay Networks for MANETs with Consideration of Physical Network Topologies

Recent years, the mobile ad hoc networks (MANETs) research community has been very active. Thus, it is of growing importance to build distributed network applications on top of MANETs. DHT is known as a popular technique to build efficient distributed applications in the Internet. However, in MANETs, DHT needs to consider network traffics, moving of nodes and energy efficiency more carefully than the Internet. We propose a technique for construction of overlay networks for MANETs in consideration for topologies of physical networks. Our technique realizes the pure P2P network that does not require special nodes like cluster heads or super peers. It gives a node ID to each node in a network using information from physically neighbor nodes so that the node has a node ID value close to that of neighbor nodes. Thus the neighbor nodes in the physical network will be also close in the logical network. When a node moves, a node ID will be reallocated to meet the above requirement. We evaluate the performance of the proposed technique by the simulations.

Enhancing Network Performance with Adaptive Admission Control

In this paper, we present an approach to enhance the network performance via introduction of adaptive admission control. Control decisions (such as reject, accept, and mark) are generated dynamically with up to per-flow granularity based on the network status feedback which is collected using IPFIX. An implementation which detects and protects multimedia flows in an enhanced DiffServ domain is discussed.

Design and implementation of the Solelc distributed operating system

In order to efficiently use multiple computers on a network, resource management that takes all those computers into account is desirable. However, the resources that each conventional operating system manages are limited to those of the computer on which it works. By making the operating system itself work in a location-transparent fashion, it becomes possible to manage all resources on multiple computers with a single operating system. In this paper, we propose an abstraction method for location-transparent management of computer resources such as memory, CPUs, interrupts, and peripheral devices. The structure and performance evaluations of the Solelc distributed operating system, which is based on this method, are described.

An efficient scheduling algorithm for distributed real‐time systems with end‐to‐end timing constraints

This paper proposes an efficient scheduling algorithm for distributed real-time systems with such timing constraints as jitter and end-to-end timing. Conventionally, backtrack searching and annealing methods have been used for scheduling problems when timing constraints are complicated. These methods, however, need a lot of computation. This paper proposes a heuristic scheduling method which solves the problem without backtrack scheduling. The proposed method has the merit that the constraints applied to processor scheduling can also be applied to network scheduling. Furthermore, the proposed method can be applied to a network system which is not provided with real-time communications functions, because the proposed method arbitrates communications at a scheduling time. Computer simulations in this paper show that the proposed method provides flexible scheduling capability and can achieve efficient scheduling.

When object-oriented operating system is time critical

This paper presents performance results of the object-oriented real-time operating system Theta. There are two current versions of Theta which are written in the object-oriented languages, C++ and COB. In both languages, object-orientation is embedded into the C language. The overhead of the C++ and the COB versions are compared with that of C. Our experiments show that if the classes are carefilly chosen, there is no significant overhead for real-time applications.