Proposal of data intensive sensor networks with forwarder nodes Katsuhiro Naito, Kazuo Mori, and Hideo Kobayashi Department of Electrical and Electronic Engineering, Mie University, 1577 Kurimamachiya, Tsu, 514-8507, Japan Email: {naito, kmori, koba}@elec.mie-u.ac.jp Abstract— Reducing power consumption and increasing battery life of sensor nodes are important challenges for sensor net- works. In this paper, we propose a simple routing protocol that constructs routes depending on a remaining battery capacity. Then, we explore a new type of sensor network with forwarder nodes and a data aggregation scheme. The forwarder node is a special node that has a large size of battery and supports the route construction to the sink node from sensor nodes. Finally, we evaluate the advantage of the data aggregation scheme for this sensor network. In numerical results, we show that our protocol can extend the lifetime of the sensor networks and improve the event delivery ratio at the sink node. Keywords— Sensor networks, Forwarder nodes, Data aggre- gation scheme, Routing protocol I. I NTRODUCTION The availability of micro-sensors and low-power wireless communications will enable the deployment of distributed sensor networks. In the sensor networks, each node transmits the detected information to the sink node that is a special node to collect the information. Since sensor nodes are deployed in wide sensing area and the transmission range of the sensor node is limited, multi-hop communication is used to convey the information between the sensor node and the sink node. Hence, routing protocol is the important factor to achieve scalable, robust, and long-lived networks. In this paper, we will propose a simple routing protocol for wireless sensor networks and propose a new type of sensor networks, which employs the special forwarder nodes. The sensor networks lead interesting challenges for network research. Foremost purpose among these researches is the development of long-lived sensor networks in spite of energy constraints of sensor nodes[1], [2]. Researches about power saving mechanisms are classified broadly into two categories. The first is at the Media Access Control (MAC) layer, where sensor nodes turn off some circuits when they are not required for communication[3], [4]. The sensor nodes periodically wake up to communicate with neighbor nodes in almost all researches. The MAC layer approach is the effective scheme to reduce the power consumption for several sizes of sensor networks. The second is at the network layer, where sensor nodes find the optimum route for low power consumption[5]-[7]. However, various types of control information should be transferred for finding the lowest power consumption route. Moreover, the complexity for route construction process will be increased according to the increasing of the network size. Generally, the device for sensor nodes has a small battery and small computational resources. For these reasons, a complex computational procedure will be difficult for real sensor net- works. In recent researches, it is known that the sensor nodes near the sink node will suffer from battery exhaustion at an early time since these nodes are required to forward the packets from another node to the sink node[8]. Hence, some researchers have proposed another type of protocols, which construct the route for extending the lifetime of sensor networks[9], [10]. In sensor networks, a lot of sensor nodes are located densely. Therefore, the sensing areas of neighbor sensor nodes are overlapped. As a result, some sensor nodes can detect the same information at the same time. It is known that the data aggregation is effective to extend the life time of sensor networks[11]. In this situation, the data aggregation scheme is an important function for achieving the effective communication[12]-[14]. In this paper, we propose the simple routing protocol for data intensive sensor networks with forwarder nodes. In this protocol, each sensor node checks the status of the battery capacity. If the remaining battery capacity is small, the sensor node waits to contribute to the route construction process. If the remaining battery capacity is large, the sensor node contributes aggressively to the route construction process. As a result, sensor nodes with large remaining battery capacity construct the route to the sink node. Then, the lifetime of sensor networks can be extended. In the proposed protocol, the same route is selected from some neighbor sensor nodes if the status of remaining battery capacity does not change greatly. Therefore, same information packets are transmitted from some sensor nodes to the sensor node that constructs the route. Then, more power saving can be achieved if the data aggregation scheme is employed at this sensor node. In addition, some data aggregation schemes are considered in some researches[15], [16]. But, almost all researchers consider a general sensor network consisting of only sensor nodes. The feature of this study is considering a special sensor network consisting of sensor nodes and forwarder nodes. In the numerical results, we show that the data aggregation scheme is effective if the forwarder nodes are located optimally. II. DATA INTENSIVE SENSOR NETWORKS WITH FORWARDER NODES In this paper, we consider the data aggregation scheme for sensor networks. The conceptual diagram of this paper 2009 Eighth International Conference on Networks 978-0-7695-3552-4/09 $25.00 © 2009 IEEE DOI 10.1109/ICN.2009.29 82