# A Survey on an Energy-Efficient and Energy-Balanced Routing Protocol for Wireless Sensor Networks
## 1 Introduction  
The progress in modern technologies has motivated the design of small electronic low-powered sensor devices. Ordinarily, a considerable number of these sensors are deployed in remote areas in the form of a wireless network of nodes to measure different physical values. This kind of network scenarios are referred to as wireless sensor networks (WSNs). WSNs are serviceable in numerous industrial applications. For instance, WSNs find use in environment monitoring and disaster management applications such as forest fire detection, landslide detection, and air pollutiondetection [1; 2; 3; 4]. In intelligent surveillance and defence reconnaissance, WSNs are used in applications such as distributed situation awareness and geographic directed queries [5; 6]. Also, WSNs have been extensively used in health care monitoring activities such as mass-casualty disaster, cancer detection and blood glucose measurement [7; 8; 9]. In these and many other applications, WSNs technology provides different advantages (such as ease of implementation, lower implementation cost, accuracy, scalability) in comparison to the traditional networking solutions [10]. WSNs conventionally consist of hundreds of sensor nodes (SNs) that communicate with each other in order to convey high quality information to the base station (BS) without using pre-existing infrastructure. This means that WSNs are deployed in an ad hoc manner and the SNs are self-organizing. The SNs are randomly placed in a remote area or sensor field whereby they form a connection with each other in order to measure a physical value as shown in Figure 1. Besides, it is very difficult to replace these SNs after complete deployment in many scenarios or applications, especially in harsh environments such as mines, battlefields, etc. In most cases, the larger the number of SNs deployed to monitor a geographical area or an event, the more reliable and accurate is the delivered message [11]. In Figure 1, each SN transmits the sensed information to the BS depending on the routing protocol or algorithm used. The routing protocol states how the SNs communicate with each other in order to circulate the sensed information towards the BS and it allows the SNs to select the most cost-efficient route(s) to the BS. The route(s) selection choice is specified by the routing algorithm which is mostly designed in the form of a clustering routing algorithm [12; 13; 14; 15] or a load-balanced tree routing algorithm [16; 17; 18; 19]. A cost-efficient routing protocol is developed to balance as much as possible some features such as scalability, timeliness, and robustness. Most importantly, the routing protocol must minimise the energy consumption so as to extend the network lifetime for a reasonable period. As a result, routing in WSNs is quite challenging because the routing protocol must guarantee a balance in some or all of these Quality of Service (QoS) requirements. With attention on energy consumption, SNs are primarily battery powered devices. The energy consumption of the SN must therefore be properly managed in order to extend the network lifetime and functionality for a reasonable duration, especially if this is all dependent on energy consumption. Different energy-efficient and energy-balanced routing protocols have been proposed for WSNs. The energy-efficient routing protocols attempt to increase the network lifetime by minimizing the energy consumption in each SN. Energy-efficient routing protocol can easily result in untimely  
Figure 1: Simplified diagram of a wireless sensor network (WSN). partitioning of the sensor network despite there being enough residual energy left in most of the SNs. For example, consider the literal clustering WSN of Figure 2. In this example, the clustering routing algorithm assumes that the cluster head (CH) duty is static, and all non-cluster head (nCH) nodes convey a message to the BS via their CH with single-hop communication.