# A Survey on an Energy-Efficient and Energy-Balanced Routing Protocol for Wireless Sensor Networks
## 1 Introduction
Also, the \"\(x\)\" J (J-Joules) in the circles of Figure 2 represents the the energy level (residual energy) of the SNs. As depicted in the figure, the nCH nodes in cluster 3 (C3) still have enough energy to perform another data transmission round or phase but the CH battery energy has been depleted. Hence, all SNs in that cluster are segregated from the whole network and cannot transmit information to the BS. In turn, this debilitates the network functionality. The energy-balanced routing protocols, on the other hand, protract the network lifetime by uniformly balancing the energy consumption among the SNs in the network. Energy-balanced routing protocols may offer better performance in terms of energy efficiency because their load balances the energy usage among SNs. Therefore, it prolongs the network lifetime and functionality. Although an energy-balanced routing protocol is desirable, designing an optimal energy-balanced routing protocol for WSNs can be a NP-hard problem because of the network structure and formulations. Some of the \"energy-balanced routing protocols\" in literature may be energy-efficient but do not--in the actual sense--offer an optimal load-balanced feature during the network data transmission phase. As such, using these routing protocols in a large-scale WSN scenario often result in untimely partitioning of the network. The energy-efficient and energy-balanced routing protocols in the literature have been proposed using different solution types or algorithms such as heuristic, meta-heuristic, linear programming (LP), evolutionary approach, game theory, and swarm intelligence. The focus of most of these routing protocols has been to optimize the energy consumption during the network data transmission activities. Although, a lot of energy is gobbled by the SN components, even while in inactive mode, this survey emphasised only on the routing protocols developed to optimize the energy consumption during the network data transmission phase. Also, this survey only considers routing towards the BS. Consequently, we present a systematic investigation of the different state-of-the-art energy-efficient and energy-balanced routing protocols. The advantages and disadvantages of these energy-efficient and energy-balanced routing protocols are analysed. A taxonomy is introduced to classify the energy-efficient and energy-balanced routing protocols surveyed in this paper based on their proposed  
Figure 2: Simplified diagram of a clustered WSN. mode of communication towards the BS. Moreover, there are factors or parameters to be considered when designing an energy-efficient or energy-balanced routing protocol for WSNs. As such, this paper classifies these routing protocols based on the input decision variables, stating the advantages and disadvantages of using these design decision variables. Besides, we classified the surveyed energy-efficient and energy-balanced routing protocols based on the solution types or algorithms. The contribution and relevance of this paper is as follows. We note that there have been various survey papers put forward by researchers to review the performance and classify the different energy-efficient routing protocols for WSNs as discussed in Section 2. However, there seems to be no clear survey emphasizing the importance, concepts, and principles of load-balanced energy routing protocols for WSNs. This survey paper provides a clear picture of both the energy-efficient and energy-balanced routing protocols for WSNs. Hence, we present an extensive survey of the different state-of-the-art energy-efficient and energy-balanced routing protocols that attempt to optimize the energy consumption in SNs so as to prolong the network lifetime. With this in mind, the paper introduces a taxonomy to classify the surveyed routing protocols based on their mode of communication towards the BS and the technique(s) used in their implementation. Moreover, we grouped these surveyed routing protocols based on the solution types or algorithms, and the decision variables used in the routing algorithm.