Wireless sensor networks (WSNs) consist of numerous wireless sensor nodes, each sensor node embedding a tiny communication device enabling the nodes to communicate with each other or the base station. In this paper, we investigate the problem that communication distance must be considered in minimizing the wireless communication energy since the energy consumption is proportional to the 2nd to the 6th power of the distance. Moreover, another problem is that there is a non-uniform energy drain effect in most topologies. Known as the energy hole problem, it can result in premature termination of the entire network. To address these problems, in this paper we first propose a communication routing algorithm that can solve the energy hole problem to the maximum extent possible while minimizing the wireless communication energy by generating an energy efficient spanning tree. This algorithm is beneficial for network lifetimes defined by a high node termination percentage. For the WSNs for which the energy hole problem is critical, we propose two route switching algorithms to solve the energy hole problem; they are beneficial for network lifetimes defined by a low node termination percentage. Simulation results showed that these algorithms avoid the energy hole problem and thereby greatly extend the lifetime of WSNs by more than 3 to 6 times that of ones using direct transmission in a 20-node network and a 50-node network if the lifetime of a WSN is defined by 1% of the number of terminated nodes in the WSN.

In real-time embedded systems, there is requirement for adapting both energy consumption and Quality of Services (QoS) of tasks according to their importance. This paper proposes an adaptive power-aware resource allocation method to resolve a trade-off between the energy consumption and QoS levels according to their importance with guaranteeing fairness. The proposed resource allocator consists of two components: the total resource optimizer to search for the optimal total resource and QoS-fairness-based allocator to allocate resource to tasks guaranteeing the fairness. These components adaptively achieve the optimal resource allocation formulated by a nonlinear optimization problem with the time complexity O(n) for the number of tasks n even if tasks' characteristics cannot be identified precisely. The simulation result shows that the rapidness of the convergence of the resource allocation to the optimal one is suitable for real-time systems with large number of tasks.

The virtual memory functions in real-time operating systems have been used in embedded systems. Recent RISC processors provide virtual memory supports through software-managed Translation Lookaside Buffer (TLB) in software. In real-time aspects of the embedded systems, managing TLB entries is the most important because overhead at TLB miss time gives a great effect to overall performance of the system. In this paper, we propose several TLB management algorithms in MIPS processors. In the algorithms, a replaced TLB entry is randomly chosen or managed. We analyze the algorithms by comparing overheads at task switching times and TLB miss times.

Wireless sensor nodes are becoming more and more common in various settings and require a long battery life for better maintainability. Since most sensor nodes are powered by batteries, energy efficiency is a critical problem. In an experiment, we observed that when peak power consumption is high, battery voltage drops quickly, and the sensor stops working even though some useful charge remains in the battery. We propose three off-line algorithms that extend battery life by scheduling sensors' execution time that is able to reduce peak power consumption as much as possible under a deadline constraint. We also developed a simulator to evaluate the effectiveness of these algorithms. The simulation results showed that one of the three algorithms dramatically can extend battery life approximately three time as long as in simultaneous sensor activation.

SMIL is a markup language which enables us to describe multimedia contents. This paper proposes a design model of SMIL browser functionality for mobile phones whose resources are limited. We introduce SMIL Component, which is based on attachable software architecture to a pre-installed generic web browser and an event-based SMIL scheduler, which is a part of SMIL Component, to provide the multimedia presentation scheduling functionality. These lead to reducing the memory amount that SMIL Component consumes and brings high portabilty of SMIL Component for various web browsers. We implement SMIL Component and evaluate RAM sizes and presentation delays. As a result, we conclude that SMIL Component is practical for MMS presentations on a mobile phone.

Role-based access control (RBAC) is widely used as an access control mechanism in various computer systems. Since an organization's lines of authority influence the authorized privileges of jobs, roles also form a hierarchical structure. A role graph is a model that represents role hierarchies and is suitable for the runtime phase of RBAC deployment. Since a role graph cannot take various forms for given roles and cannot handle abstraction of roles well, however, it is not suitable for the design phase of RBAC deployment. Hence, an extended role graph, which can take a more flexible form than that of a role graph, is proposed. The extended role graph improves diversity and clarifies abstraction of roles, making it suitable for the design phase. An equivalent transformation algorithm (ETA), for transforming an extended role graph into an equivalent role graph, is also proposed. Using the ETA, system administrators can deploy efficiently RBAC by using an extended role graph in the design phase and a standard role graph in the runtime phase.