# Variants of the Low-Energy Adaptive Clustering Hierarchy Protocol: Survey, Issues and Challenges
###### Abstract
This survey presents an organized and comprehensive review of LEACH enhancement clustering routing protocols by using a new taxonomy depends on different parameters, such as distance, routing path, and network coverage, with emphasis on clustering technology and challenges. The classification in this survey depends on CH selection and cluster formation methods, which are new classifications of LEACH enhancement protocols for WSNs in term of distance, energy efficiency, residual energy, and network coverage. The rationale behind focusing on the CH selection and the cluster formation categories in this survey is due to their importance in the hierarchical-based protocols because the CH selection and the cluster formation play a significant role in prolonging the network lifetime. The difference between these categories is that the CHs are firstly selected based on some criteria such as the energy and the distance to the BS. After that, the clusters will be formed by joining each normal node to its suitable CH based on different methods. This classification is expected to provide researchers a clear view of such protocols and guide them in proposing new efficient cluster formation and CH selection methods. Recent LEACH enhancement clustering routing protocols for WSNs will be discussed based on CH selection and cluster formation methods. Each clustering routing protocol is examined in detail, and each CH selection method and its specifications and obstacles are emphasized. Summarization and comparisons of clustering routing protocols for WSNs are performed based on the parameters that are used to select CHs and the parameters that are used to form clusters. The comparison of different protocols has been done using different performance elements, like distance, reliability, and complexity. The last part of the paper presents several important matters that are necessary to be considered when proposing new clustering routing protocols or CH selection methods for WSNs. The contributions of this survey are as follows:* Hierarchical routing protocols based on LEACH are classified based on cluster formation and CH selection methods by using a new taxonomy based on new parameters, such as residual energy, distance, and network coverage. * A large number of LEACH-based protocols based on the new taxonomy are discussed. * A comprehensive survey is performed to discuss LEACH enhancements in detail. * Qualitative comparisons with other existing surveys are conducted. * A comparison among protocols is performed in terms of several parameters (e.g., energy, overhead, and complexity) to help researchers select the most efficient protocol based on their needs. This survey is organized as follows: Section 2 provides a background of WSNs and an overview of the LEACH protocol. In addition, LEACH-based routing techniques and their classification into two main categories, namely, CH selection-based and cluster formation-based protocols are analyzed and discussed. Routing protocols that belong to each category are also discussed in detail. In Section 3, a comparative analysis of different protocols is described in detail. The future issues in designing routing protocols are discussed in Section 4. The survey is presented in Section 5.