Relay Nodes in Wireless Sensor Networks: A Survey

A sensor network is a network of low-powered, energy-constrained nodes equipped with sensor(s) and wireless communication devices that are intended to sense some physical phenomena from the area of deployment. Recent technological advances in the field of micro-electromechanical systems (MEMS) have made the development of multi-functional sensor nodes technically and economically feasible. The sensor nodes in a sensor network are usually resource constrained, which means they have limited energy, limited processing and memory capability as well as limited transmission range. Sensor nodes are expected to operate in an unattended manner with the help of lightweight batteries, which cannot be replaced or recharged. Therefore, the life of a sensor network is usually defined by the time interval between which a certain amount of critical nodes run out of their battery power. A great deal of research have focused on the energy conservation in sensor networks so that the lifetime of the network is maximized. A major factor for the power consumption in a sensor node is due to the its transmit electronics, which increases with the increment of (1) the amount of data to be transmitted and (2) the distance between the transmitter and the receiver. In the past few years, many researches have proposed various schemes for minimizing such power consumption in sensor networks. One of them is to introduce some special nodes, known as relay nodes, in sensor networks. The idea is to take some burden from the sensor nodes by the relay nodes. The deployment of relay nodes in sensor networks has been proposed for maximizing the network lifetime, energy-efficient data gathering, load-balanced data gathering as well as making the network fault tolerant. This paper has focused on the literature that has proposed the use of relay nodes in sensor networks.