# Variants of the Low-Energy Adaptive Clustering Hierarchy Protocol: Survey, Issues and Challenges
###### Abstract  
A wireless sensor network (WSN) is a modern technology in radio communication. A WSN comprises a number of sensors that are randomly spread in a specific area for sensing and monitoring physical attributes that are difficult to monitor by humans, such as temperature, humidity, and pressure. Many problems, including data routing, power consumption, clustering, and selecting cluster heads (CHs), may occur due to the nature of WSNs. Various protocols have been conducted to resolve these issues. One of the important hierarchical protocols that are used to reduce power consumption in WSNs is low-energy adaptive clustering hierarchy (LEACH). This paper presents a comprehensive study of clustering protocols for WSNs that are relevant to LEACH. This paper is the first to emphasis on cluster formation and CHs selection methods and their strengths and weaknesses. A new taxonomy is presented to discuss LEACH variants on the basis of different classes, and the current survey is compared with other existing surveys. A complete comparison of the location, energy, complexity, reliability, multi-hop path, and load balancing characteristics of LEACH variants is conducted. Future research guidelines for CHs selection and cluster formation in WSNs are also discussed. cluster formation; LEACH protocol; energy consumption; wireless sensor networks +
Footnote †: journal: Electronics  
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Owing to the difficulty and inefficiency of replacing the power supply of dead nodes (because the number of nodes can be large and deployment can be arbitrary), meeting application requirements becomes challenging [13; 16]. This survey discusses routing protocols that have been conducted to deal with these challenges to evaluate the efficiency of these protocols and determine their drawbacks. One of the network structure categories is clustering or hierarchical routing protocols [17]. Sensors are self-organized, and clusters are usually formed when the deployment completes in clustering routing protocols. Each cluster contains a private node called the cluster head (CH) that performs extra tasks, such as collecting data from normal nodes in a cluster, compressing the data, and sending them to the base station (BS) for analysis and decision-making [18; 19; 20; 21]. These additional tasks cause the CH to expend the extra amount of energy than other normal nodes do in the cluster. One of the early clustering routing protocols is the low-energy adaptive clustering hierarchy (LEACH), which is proposed by [PERSON] [19] to increase the network lifetime by rotating the CH's tasks among the nodes. However, this protocol has limitations in energy distribution in clusters and in maximizing network lifetime. Thus, many studies have enhanced the LEACH protocol to balance the energy distribution among sensors in clusters [22; 23] and increase network lifetime [24; 25]. LEACH possesses several drawbacks [26; 27], such as CHs being selected randomly without taking into account the residual energy of a node or the distance from a node to the BS [28]. Another problem is the transmission of data from a CH to the BS because the communication is conducted using the single-hop method. This method causes a serious issue when the CH is far from the BS because extra amount of energy is used than when the CH is close to the BS, resulting in energy holes; in which isolated nodes cannot send their data. This situation considerably affects network performance. Therefore, the development of efficient clustering routing protocols is a significant part of research on WSNs to increase network lifetime [29]. Many surveys [30; 31; 32; 33] have examined LEACH enhancement clustering protocols by using different classifications based on different criteria, such as the way of communication in routing protocols, node mobility, and node location awareness.