Kiyohito Yoshihara

DAG based in-network aggregation for sensor network monitoring

Wireless sensor network monitoring is important for network maintenance, since it keeps the observer aware of node failures, resource depletion etc. Since communication overheads increase if the sink collects data individually from all sensor nodes, in-network data aggregation methods have been proposed which reduce the overheads. They form a routing tree and data follows up from the edge of the tree to the sink. However, in the event of heavy packet loss, the error margin of the collected data received by the sink grows. Furthermore, when the assumed hop count of the edge of the tree is smaller than the actual count, data can not be followed up from the edge. For the reasons mentioned above, observers find it problematic to assess the state of the network, since the error margin increases as the accuracy of the collected data falls. In this paper, we propose a new in-network aggregation method for sensor network monitoring. The method provides fault tolerance for packet loss by forming a directed acyclic graph (DAG), which allows a node to have multiple parent nodes. In addition, the method can ensure correct data transmission timing, according to the actual hop count of the edge of the DAG. Furthermore, we evaluated the proposed method in comparison with the existing methods, from the perspective of the error margin of the collected data

ECO-friendly distributed routing protocol for reducing network energy consumption

The growth of Internet traffic has led to an increase in energy consumption by network equipment such as routers and switches. Consequently, energy consumption is becoming a key environmental, social, political and cost issue. Focusing on energy consumption by Internet Service Provider networks, the energy bottleneck is routers. Thus, it is imperative for us to reduce the energy consumption of routers. In this paper, we propose a new ECO-friendly distributed routing protocol (ECO-RP) based on OSPF. In our proposal, an ECO-RP entity periodically checks the amount of traffic forwarded by the ECO-RP entity. Moreover, an ECO-RP entity floods information on the amount of traffic to other entities such as the OSPF Link State Advertisement. This allows each ECO-RP entity to obtain information on traffic in the network, and to dynamically change OSPF link weights based on the information. For example, when the amount of overall network traffic is small, the entity changes link weights so that the traffic can be routed only through a subset of routers, and unneeded routers can shift into sleep mode. Several simulation studies, which assume two ECO-RP enabled networks, are conducted. The result shows that the proposed protocol is able to reduce energy consumption by about 18.5% at maximum without network congestion.

Implementation and evaluation of on-demand address allocation for event-driven sensor network

In this paper, we propose an energy-efficient address allocation method for the event-driven sensor network, and implement and evaluate the proposed method. The proposed method allocates a temporary address only to a sensor node which detects an event, on an on-demand basis. By performing simulation studies, we evaluated the proposed method and compared it with one of the existing methods from the perspective of the number of control messages for the address allocation. The results show that the number of control messages of the proposed method is small compared to that of the existing methods. We also evaluated the processing time overhead of the proposed method using the implemented system. Although the proposed method has little extra overhead, the results show the processing time is short enough for practical use.

Dynamic polling scheme based on time variation of network management information values

Network monitoring is one of the most significant functions in network management to understand the state of a network in real-time. In network management, such as SNMP (simple network management protocol), polling is used for this purpose. If the time interval for two consecutive polling requests is too long, then we cannot understand the state of the network in real-time. Conversely, if it is too short, then the polling message traffic increases and imposes a heavy load on the network although we can understand the state of the network in real-time. Many schemes have been proposed for controlling the overheads of dynamic polling by throttling polling rates. Unfortunately, by only considering overheads, these schemes fail to take into account the rate at which information must be obtained in order to achieve management tasks. Examples of these tasks include checking for threshold violations and determining if additional capacity should be allocated dynamically. This paper proposes a new scheme for dynamic polling that considers both the overhead of polling traffic and the message rates required for management tasks. Our scheme examines polling traffic, applying the discrete Fourier transformation to extract the desired polling rate. We demonstrate the availability of this approach through simulations in which polling requests are varied dynamically. Our scheme adjusts polling rates to make them more consistent and to reduce resource overheads.

Dynamic load balancing for distributed network management

The scalability limitations of centralized management models have motivated distributed management models, in which management programs describing some management tasks are distributed and executed on managed systems. In the models, management program distribution that considers dynamic network resource utilization is one of the most important challenges, in striking a load balance between management and managed systems for an entire managed network. Some methods for load balancing have been studied; however, they cannot adequately be achieved throughout an entire managed network. This arises from criteria for load balancing that lacks dynamic network resource utilization, or from a localized subnetwork in which the performance is limited, although it does include processing loads for dynamic network resource utilization. To solve this, a new dynamic load balancing method is proposed for distributed network management. Thus, systems that execute management programs are decided dynamically on the basis of CPU utilization for each system and the bandwidth required for executing all management programs. Two typical algorithms derived from the proposed method, each having different criteria in the form of mean deviation and range types with respect to CPU utilization, are introduced. They were evaluated analytically. according to capability, i.e., how well they perform as close to load balancing as possible, as well as time complexity. The results show that the mean deviation type algorithm performs better at almost the same computational cost. A prototype system is also implemented based on the proposed method, and evaluated empirically by applying it to an operational LAN. The proposed method performs well in trials with a trivial overhead.

Deployment adviser tool for wireless sensor networks

This paper presents a system for the purpose of field deployment of nodes in wireless sensor networks. We propose a mobile phone based deployment adviser tool which is robust as well as practically implementable. The tool advises a layman deployer to create a optimized wireless sensor network by placing of the nodes according to application requirements. The tool is presented here as logically linked sub-modules. Each sub-modules are described in detail. Also we propose an algorithm which helps in distributing the power consumption among the nodes in the network, thus, increasing the network lifetime. The adviser tool has been verified by implementing it in IITH mote. The tool we propose has significant implication since it greatly eases, but more importantly extracts the best performance possible while deploying the wireless sensor networks.

A power-saving standby method to extend battery life in dual-mode cellular phones

Dual-mode cellular phones, including smartphones, are recently attracting much attention from both users and telecom operators throughout many countries. To avoid traffic concentration generated by these devices on 3G networks, it is important to lead users to connect with fixed networks via WLAN. However, keeping both 3G and WLAN interfaces on consumes a great deal of power, which considerably shortens the standby time. To achieve longer battery life, we propose a power-saving standby method (PSSM) whose features are: (1) constant deactivation of the WLAN interface except for when required; (2) no additional functions in a mobile operators network; and (3) avoidance of a WLAN AP search distant from a cellular phone. We implemented PSSM as a BREW application and measured the electrical current in a cellular phone as well as the delay in email retrieval transaction. Experimental results using the prototype system show that PSSM achieves about 73%-134% longer battery life than a conventional dual-mode cellular phone, while PSSM keeps the application transaction delay short by reducing unproductive WLAN AP searches.

Address Autoconfiguration for Event-Driven Sensor Network

An event-driven sensor network composed of a large number of sensor nodes has been widely studied. A sensor node sends packets to a sink when the node detects an event. For the sink to receive packets it fails to acquire, the sink must send re-transmission requests to the sensor node. To send the requests to the sensor node using unicast, the network address of the sensor node is required to distinguish the sensor node from others. Since it is difficult to allocate the address manually to a number of nodes, a reasonable option is to use existing address autoconfiguration methods. However, the methods waste the limited energy of the sensor nodes due to using a number of control messages to allocate a permanent address to every node. In this paper, we propose an energy-efficient address autoconfiguration method for the event-driven sensor network. The proposed method allocates a temporary address only to a sensor node which detects an event, on an on-demand basis. By performing simulation studies, we evaluated the proposed method and compared it with one of the existing methods based on the number of control messages for the address allocation. The results show that the number of control messages of the proposed method is small compared to that of the existing method. We also evaluated the process time overhead of the proposed method using the implemented system. Although the proposed method has little extra overhead, the results show the processing time is short enough for practical use.

Mobile phone based acoustic localization for wireless sensor networks

In wireless sensor networks, localization techniques are required for finding physical location of the sensor nodes. Most of the existing 2D and 3D localization schemes are reference based. Finding physical locations of sensor nodes in an application field with only 2D or 3D physical topology map or logical topology map is arduous and tedious. This paper refers to mobile phone based acoustic localization technique for wireless sensor networks, which can be used along with physical topology map or logical topology map. In our proposed method, deployer searches the sensor node by using Doppler effect of acoustic wave, which is generated by his mobility. The proposed method helps in quick localizing of the sensor nodes without consuming much time and it has been implemented, tested by using mobile phone and IITH motes, the in-house developed sensor nodes.

Centroid based 3D localization technique using RSSI with a mobile robot

Knowledge of sensor node 3D location in a sensor network is more important, because many practical applications needs to know the location of sensor data source. This paper presents a new technique for finding indoor 3D location of a sensor node by using Received Signal Strength Indication (RSSI). Proposed localization algorithm is derived from centroid algorithm with composition of empirical path loss model. It gives less error in estimating 3D location of sensor node in a sensor network when compared to its actual location. Algorithm has been implemented and analysed by using IITH motes and a Mobile Robot.