Abstract
Machine-to-machine (M2M) communications refer to the autonomous interaction between connected devices without the human intervention. Recently, the Third-Generation Partnership Project (3GPP) introduced the Long-Term Evolution (LTE) and Long-Term Evolution-Advanced (LTE-A) as the improved version of the fourth-generation (4G) cellular networks. LTE/LTE-A networks have been considered an appropriate infrastructure for implementing M2M communications. However, the LTE/LTE-A networks were originally introduced for human-to-human (H2H) communications which have different characteristics from M2M communications. Thus, the LTE/LTE-A networks must be adapted to support the special characteristics of M2M communications. This work provides a comprehensive review of M2M communications over LTE networks, including M2M architectures, LTE structure, deployment challenges, and access control requirements. Moreover, this work introduces a novel classification for the current Random Access (RA) techniques that have been proposed for M2M communications in LTE networks. According to the main targeted objective, the current RA techniques are classified into three categories: massive access control techniques, energy efficiency techniques, and performance improvement techniques. Each category is further divided into two subcategories, and the relevant RA techniques are presented for each category. Furthermore, an analytical comparison has been provided among the different techniques according to the parameters for each approach. This work can be considered a good starting point for those who are interested in RA techniques for M2M communications over LTE/LTE-A networks.