An Efficient Tree-Based Power Saving Scheme for Wireless Sensor Networks With Mobile Sink

Wireless sensor networks (WSNs) with mobile sink are expected to increase the flexibility for gathering information in large-scale sensing and detecting environments. Energy saving becomes one of the most important features of the sensor nodes to extend their lifetime in such networks. A novel tree-based power saving scheme is proposed in this paper to reduce the energy consumption in WSNs with mobile sink. We adopt a dynamic sorting algorithm to create a tree-cluster routing structure for the sensor nodes. The main goal of this scheme is to reduce the data transmission distances of the sensor nodes by employing the tree structure and multi-hop concepts. Based on the location of mobile sink, the distances between the sensor nodes, and the residual energy of each sensor node, the proposed scheme makes an efficient decision for creating the routing structure. The energy consumption is reduced and the lifetime is extended for the sensor nodes by balancing the network load. Simulation results demonstrate the superior performance of our proposed scheme and its ability to strike the appropriate performance in the energy consumption, network lifetime, throughput, and transmission overhead. In addition, suitable delay time and number of retransmission messages can be achieved for the WSNs with mobile sink.

I. Introduction

Wireless sensor networks (WSNs) have been widely considered as supplementary technology in the wireless and mobile systems. Powerful, inexpensive, and low-power wireless micro-sensors are designed and used in the various monitoring environments [1]–[5]. A WSN consists of a large number of sensor nodes. Each sensor node has sensing, computing, and wireless communication capability. All of the sensor nodes play the role of an event detector and a data router. The sensor nodes are deployed in the sensing area to monitor specific targets and collect data. Then, the sensor nodes send the data to a sink or a base station (BS) by using the wireless transmission techniques. During the recent years, many energy efficient routing protocols have been proposed for WSNs. Energy efficient routing protocols can be classified into four main schemes: network structure, communication model, topology based, and reliable routing. An analytical survey on energy efficient routing protocols for WSNs is provided in [6]. An energy efficient routing protocol plays a vital role in data transmission and practical applications. To be efficient for WSNs, the most important feature of a routing protocol is the energy consumption and the extension of the network’s lifetime [6]–[8]. The sensor nodes need more transmission power to send data when a sink or a BS is fixed and located far from the sensor nodes. WSNs with mobile sink are expected to increase the flexibility for gathering information in large-scale sensing and detecting environments [8]–[10]. Because a sink can randomly move within the sensing area to collect the sensing data, the data transmission distances of the sensor nodes could be reduced. The sink mobility offers the convenience of data gathering and reduces the energy consumption for the sensor nodes. WSNs have been pervasive in various applications including health care systems, battlefield surveillance systems, environment monitoring systems, various underwater applications, and so on [5]–[12]. Fig. 1 shows the direct communication protocol in WSNs with mobile sink, where each sensor node directly transmits its sensing data to the sink. Energy saving is one of the most important features for the sensor nodes to extend their lifetime. In WSNs, the main power supply of a sensor node is battery and a sensor node consumes most of its energy in transmitting and receiving packets. However, in most application scenarios, users are usually difficult to reach the location of sensor nodes. Due to a large number of sensor nodes, the replacement of batteries might be impossible. Additionally, the battery energy is finite in a sensor node and a sensor node that has its battery drained could make the sensing area uncovered. The energy conservation becomes a critical concern in WSNs. In order to reduce the energy consumption and extend the network lifetime, new and efficient energy saving schemes must be developed. Hence, the performance parameters of interest in this paper are energy consumption and network lifetime. Fig. 1.

Direct communication protocol in WSNs with mobile sink.