# Robust Clustering Routing Method for Wireless Sensor Networks Considering the Locust Search Scheme
## 2 Related Work  
Multiple applications of WSNs, such as those represented by the Internet of Things and monitoring dangerous geographical spaces, have motivated the enhancement of different aspects of WSNs, namely, topology optimization [18], distributed and decentralized detection [19; 20; 21], multipath routing protocols [22], and communication failures [23; 24]. From the wide range of enhancements, routing protocols have attracted the attention of several scientific communities due to their applications in energy savings. From all routing protocols, clustering schemes represent the most popular approaches to manage energy consumption. A clustering scheme allows the efficient administration of the energy consumption for the working cycle of WSNs [25; 26]. The Low Energy Adaptive Clustering Hierarchy Protocol (LEACH) [27] corresponds to the most well-known clustering protocol scheme in the case of homogeneous WSNs. In its operation, the LEACH method considers a set of cluster heads (CHs) which are randomly identified while the rest of the sensor nodes are frequently interchanged as CHs or generic nodes. Therefore, the energy consumption is uniformly distributed in each node with the objective to extend the network operation. Multiple other protocols that use the LEACH method as a part of their structure have been proposed in the literature producing distinct levels of performance [28; 29; 30; 31; 32]. Another popular routing protocol represents the Vice-CH-enabled (VCH) scheme [33]. It reduces energy consumption by the use of a two-step process. In the mechanism of VCH, the CH nodes are selected, considering only the nodes that currently maintain power possibilities. The numerical results produced by VCH indicate that its operative properties are better than those included in the LEACH protocol [34]. The LEACH and VCH schemes are designed to work with homogeneous WSNs. In spite of interesting characteristics, they present a low performance when they are used in Heterogeneous Wireless Sensor Networks (HWSNs). For this reason, elements of both approaches have been incorporated to design other new routing protocols [35; 36] that can operate appropriately with HWSNs. From these schemes, the Stable Election Protocol (SEP) [37] protocol is one of the most popular. Under the operation of SEP, it is considered two-node prototypes: advanced elements and normal nodes. Advanced elements have a higher probability than normal nodes to present a CHs behavior. Therefore, the SEP approach considers distinct threshold patterns according to the node behavior. With this mechanism, SEP manages the energy of advanced elements efficiently and eliminates the consumption of normal nodes to extend the lifetime of the network. The mechanisms of the SEP protocols have been used to produce several other approaches. Some interesting methods involve the Modified Stable Election Protocol (M-SEP) [38]. Under the operation of the M-SEP, the consumed energy of each node is evaluated with regard to the complete network to identify the nodes that have a high potential to become CHs. Therefore, nodes with a better energy level have a higher probability of being CHs than those that present low energy levels. The incorporation of this process by M-SEP considerably enhanced the life cycle of the network and its transmission rate. The P-SEP [39] protocol is another method based on the original SEP approach. The P-SEP determines probabilistically the uncertainty of the energy contained in each node through the modeling of this level according to its behavior. With this information, it is avoided the selection of a node with a lower energy that is lower than a threshold value. Therefore, only the elements that surpass this threshold have a possibility to become CHs nodes. With a similar mechanism as P-SEP, the clustering protocol Distributed Energy-Efficient Clustering Algorithm (DEEC) [40] has been designed as an effective method to operate HWSNs. In DEEC, it is also employed a threshold limit to identify the CHs.