Yasunori Owada

On the Energy-Efficient of Throughput-Based Scheme Using Renewable Energy for Wireless Mesh Networks in Disaster Area

We study the emergency communication problem in the post-disaster scenario. The emergence of Renewable Energy-enabled Based Station (REBS), which has pre-equipped energy harvesting devices, provides a new perspective to solve this problem, since the post-disaster communication scenario happens to be a Wireless Mesh Network (WMN) constituted by REBSs. However, one needs to address the unstable and inadequate power supply, insufficient capacities of the communication links, and the time-varying traffic demands accordingly during a period of time. In this paper, we deal with these problems and focus on optimizing data traffic throughput with the lowest weighted energy consumption based on the expectation of traffic demands. We firstly analyze the post-disaster communication issue and formulate this problem into a Mixed Integer Linear Programming (MILP) problem, and propose an off-line energy efficient scheme using the expectation of traffic demands. Furthermore, an on-line scheme is put forward which dynamically adjusts the off-line result with the knowledge of the current real data traffic demands. The efficiency of our proposal is demonstrated by theoretical analyses and numerical results.

Fast Recovery from Link Failures and Blackout of a Managed Wireless Mesh for NerveNet

A managed wireless mesh for infrastructure-level, stable regional mesh network has been studied. NerveNet, which we have been proposing, is a concept of future regional platform network that covers local regions and provides various context-aware services with the shared use of sensors and actuators. The managed wireless mesh developed for materializing NerveNet features auto-configuration of multiple, different routes between any two base stations for high capacity and reliability. The managed wireless mesh of ten base stations was implemented on PCs and commercial L2 switches. Performance evaluation showed that route switching after one or two link failures had been detected was completed in no later than 70 milliseconds while it takes a few to tens of seconds with existing adhoc routing-based mesh networks. It was also shown that the restart of the network took only about three minutes, enabling urgent recovery of communication in emergency situations.

Field measurement of an implemented solar powered BS-based wireless mesh network

Developing effective communications infrastructure, that is, a BS-based communication system, in “off-grid” locations without electricity (rural areas without power grid, areas affected by disasters, etc.) is a challenging research area in the information and communication technology sector. Since users in such areas usually exhibit demands for stable communication (e.g., mail service with constant delivery delay, voice call service with consistent quality), the BSs need to operate utilizing available resources under an energy-constricted environment. With the absence of power grid in rural regions and the occurrence of power outage in disaster-stricken areas, ambient energy sources such as solar and wind energy have become viable alternatives to power BSs. These energy harvesting BSs, however, have to confront the variable behavior of the ambient energy sources, which lead to variable amounts and rates of energy available over time. In this article, we present our considered wireless mesh network exploiting solar energy harvesting BSs, and conduct a study based on field experiments to estimate the factors that influence their energy harvesting capability. Particularly, the results of our conducted experiments demonstrate that the ON/OFF states of the radio links have a direct impact on the power consumption of the BSs. Also, the manner in which the amount of solar radiation during different weather conditions over different days affects the array voltage in an energy harvesting BS is investigated.

On Energy Efficient Scheduling and Load Distribution Based on Renewable Energy for Wireless Mesh Network in Disaster Area

In recent years, disasters happened in many places, and resulted in power shortage and communication interruption. The Wireless Mesh Networks (WMNs) constituted by Renewable Energy-enabled Base Station (REBS) is regarded as a powerful solution in post-disaster recovery, for its energy harvesting ability and the ready-made facilities. However, this solution needs to address several challenges such as unstable power supply, limited bandwidth and long-term optimization. In this paper, we focus on the issue of energy efficiency when realizing the maximal network throughput in a period of time, by the combination of energy usage and network data distribution. To this end, we firstly analyze the unique features of REBS and its associated network in disaster area. Then a throughput-maximization problem is proposed in order to figure out the maximal network throughput. Based on the maximal value, we count out the most energy-efficiency result while guaranteeing the maximal network throughput. We formulate the proposed model into a two-stage Mixed-Integer Linear Programming (MILP) problem and solve it by branch-and-bound algorithm. Simulation results demonstrate our considered two-stage energy efficient scheme strikes a balance between network throughput and its associated energy consumption, and outperforms the existing schemes.

Multiple-gateway deployment for wired/wireless converged access networks

Wired/wireless converged networks offer a promising solution to broadband access. The performance of a wired/wireless converged network largely depends on the locations of gateways that interconnect the two parts. We study multiple-gateway deployment in a wired/wireless converged scenario, and formulate the problem of minimizing average distance between wireless access points and gateways, wherein distance measure can be hop count, expected transmission count, etc. An efficient scheme is proposed to globally optimize gateway locations, and meanwhile assign each access point to a gateway. Performance studies show that our approach for gateway deployment effectively improves the throughput of a wired/wireless converged network.

Deployment of wireless mesh network using RSSI-based swarm robots

This paper proposes a novel method for deploying a wireless mesh network (WMN) using a group of swarm robots equipped with wireless transceivers. The proposed method uses the rough relative positions of the robots estimated by their Radio Signal Strength Indicators (RSSIs) to deploy the WMN. The employed algorithm consists of three parts, namely, (1) a fully distributed and dynamic role decision method among the robots, (2) an adaptive direction control using the time difference of the RSSIs, and (3) a narrow corridor for the robots to pass by movement function along walls. In our study, we evaluated the performances of the proposed deployment method and a conventional method in a real environment using 12 real robots for simple deployment, and 10 real robots for passing the narrow corridor. The results of the performed experiments showed that (1) the proposed method outperformed the conventional method with regard to the deployment time, power consumption, and the distances traveled by the robots, and (2) the movement function along the walls is effective while passing a narrow corridor unlike any other function.

An implementation of multichannel multi-interface MANET for fire engines and experiments with WINDS satellite mobile earth station

We propose a novel communication system for an emergency fire response team, which provides Internet service on the way to and in the disaster area. The system is composed of a multi-interface mobile ad-hoc network (MANET) router, a Global Positioning System (GPS) receiver, and two Wi-Fi interfaces with directional antennas, which can be easily attached to the roof of a vehicle. The front-side Wi-Fi interface of the vehicle is operated in the infrastructure mode, and the rear-side interface is operated in the access point mode. Different channels are assigned to each AP interface of the vehicles. Infrastructure-mode Wi-Fi interfaces automatically scan and connect to an appropriate AP interface and create MANET links. Some experiments using this wireless system with the WINDS satellite mobile earth station and nine fire engines were conducted in Ebetsu, Hokkaido. We measured the TCP throughput and confirmed that a throughput of more than 10 Mbps was able to be obtained by most of the node pairs. In addition, high-vision video streaming was able to be successfully transmitted to the streaming server on the Internet through MANET and satellite communication links while they were platooning.

Urban Disaster Simulation Incorporating Human Psychological Models in Evacuation Behaviors

Building evacuation simulation provides us with various knowledge and suggestion before a real disaster happens. To date, however, evacuees were often modeled as homogeneous without individual motivation in a large-scale urban simulation model, which is rather different from real human behavior. In this paper, an evacuation simulation model with human psychological models is developed for urban disaster situation. Three psychological models are actually incorporated: normalcy bias, emotional contagion bias, and sympathy behavior bias. Normalcy bias is the initial evacuation delay caused by a belief that abnormal events rarely happen. Emotional contagion is the effect of one person’s emotional state on the emotional state of people around him/her both explicitly and implicitly. Simulated experimental results show that the proposed model provides accurate evacuation behaviors than the normal behavior model without psychological consideration.

Ubiquitous monitoring of infrasound for early detection of events relevant to disaster

A terrestrial event resulting in natural disaster often radiates infrasound when it occurs. Similar phenomenon can be observed in extreme weathers as well. Infrasound travels through the air approximately at the speed of sound and it is faster than traveling of physical kinetic energy which may sometimes bring about a disastrous impact on human lives. Therefore, early detection and source localization of such events are promising for hazard prevention and damage mitigation. To achieve this purpose, coverage of the land is important in terms of celerity and spatial precision, but facilities suitable for monitoring infrasound are not common. In Japan, one monitoring station, IS30, is in operation under Comprehensive Nuclear-Test-Ban Treaty (CTBT) and a few microbalrometer arrays are experimentally set up by Japan Weather Association (JWA) on some parts of Japanese coast. A group of University of Hawaii developed an app for capturing infrasound on iOS devices, and the captured data can be utilized for furthe...

Energy-efficient construction algorithm for mobile mesh networks

In this paper, we propose an autonomous control method for the movement of distributed nodes in a mobile wireless mesh network. Our approach estimates the mutual position of nodes from the received signal strength indicator (RSSI), and constructs a network using a number of autonomous moving nodes to enable wireless communication. The proposed method controls the direction of node movement using two features: (1) the dynamic allocation of reference and moving nodes, and (2) the temporal variation of RSSI. To evaluate the effectiveness of our method, we employ three criteria. First, the area coverage ratio represents the degree of coverage of the target area with nodes such as sensors or communication devices. Second, the communication stability represents the latency and connectivity in the communication between nodes. Third, the energy consumption represents travel distance between nodes. Experimental results using a network simulator demonstrate that the proposed method achieves full area coverage using less than 3.8% of the energy required by the conventional method.