# A Survey on an Energy-Efficient and Energy-Balanced Routing Protocol for Wireless Sensor Networks
## 2 Related Work  
The importance of developing energy-efficient and energy-balanced routing protocols for WSNs cannot be overemphasised. There are numerous ongoing works on the design of energy-efficient and energy-balanced routing protocols for WSNs. Some of these routing protocols may be designed based on the application requirements and the formulation of the network. In addition, the techniques and design requirements of these routing protocols may differ but the ultimate goal is to optimize the energy consumption during the network activities. There are different survey papers on routing protocols in WSNs, and WSNs in general. Nevertheless, we strive to discuss some of the existing survey literature on WSNs and provided the differences between this paper and the existing survey papers. An extensive survey on the concept of WSNs is presented in [30; 31]. The authors discussed in detail the potential applications and factors affecting the design of WSNs. They defined the communication architecture for WSNs, where they surveyed the routing protocols developed for each communication layer. The authors summarise their survey with general possible research directions for WSNs. Quite the contrary, we focus our attention on energy consumption issues with WSNs. This paper provides a taxonomy to classify the energy-efficient and energy-balanced routing protocols for WSNs based on their mode of communication towards the BS. Moreover, the surveyed energy-efficient and energy-balanced routing protocols are classified based on the solution types or algorithms, and the decision variable defined in the routing algorithms. A general survey on routing techniques in WSNs is provided in [11]. The authors analysed the difficulties in designing a routing protocol for WSNs. Afterwards, the authors classify routing strategies into flat, hierarchical, and location-based routing. This classification is based on the network formulations. They also classified these routing protocols based on other metrics such as negotiation-based, QoS-based, multipath-based, etc. They presented a detailed comparison of these routing algorithms, stating their strengths and weaknesses in terms of the energy and communication overhead savings. Nonetheless, we focus our attention on energy consumption optimization problems. An extensive review of the different state-of-the-art energy-efficient and energy-balanced routing protocols is presented in this paper. More importantly, the taxonomy introduced in this paper is based on the mode of communication used in the energy-efficient and energy-balanced routing technique to convey the sensed message from the source node to the BS, and the decision variables deployed in the design of these studied routing algorithms. The authors in [32] presented a survey on routing protocols in WSNs. The work in [32] classifies the surveyed routing protocols into three categories: data-centric, hierarchical, and location-based. Their survey work entails routing generally in WSNs, whereby some other QoS requirements are considered. We focus our attention on minimising the energy consumption by SNs in a WSN so as to prolong the network lifetime. In this regard, we surveyed different energy-efficient and energy-balanced routing protocols, discussing their pros and cons. Moreover, this paper classifies these routing protocols based on the solution types or algorithms, and the decision variables defined in the routing algorithm. This paper further discussed possible research directions in order to extend the network lifetime and functionality of WSNs. In [33], the authors provided a general survey on WSNs. Following a stepwise approach, the authors gave a general overview of numerous WSN applications and review literature on different aspect of WSNs. They described the challenges with WSNs and classified these challenges into three categories, namely: (1) Internal platform and underlying operating system; (2) Communication protocol stack; and (3) Network services, provisioning, and deployment.