# Energy-Efficient Hybrid Routing Protocol for IoT Communication Systems in 5G and Beyond
## 2 Related Works  
Several clustering protocols [6; 7; 12; 13; 14] and unequal clustering protocols [8; 11; 15; 16; 17; 18; 19; 20] have been proposed to lessen the energy depletion. The authors in [6] proposed LEACH, a protocol that uses control mechanism and local coordination to establish cluster activities. LEACH is a distributed cluster formation in which nodes randomly select themselves as cluster heads without the control of central station or providing frameworks for data aggregation. Every sensor node picks an arbitrary value between 0 and 1 to become a Cluster Head. LEACH follows a randomized Cluster Head rotation to share the burden of energy between the sensor nodes. Another enhanced version of the LEACH scheme, LEACH-Centralized (LEACH-C), is suggested by [12]. As compared to LEACH, in LEACH-C a central station performs cluster formation and decides the cluster heads by using a simulated annealing technique. However, LEACH and LEACH-C have drawbacks including variable set of cluster formation, randomized and unequal cluster heads deployment resulting in a short-lived network. This is due to the inefficient consumption of energy. Various types of LEACH protocols have been proposed to address these issues. [PERSON] and [PERSON] [7] propose PEGASIS as a means to reduce issues of overhead in WSNs. PEGASIS uses greedy algorithm to form chains by neighboring nodes. The Cluster Head of the chain is assigned to forward data to the central station instead of several nodes. Sensors in the chain rotate among each other to forward data to central station. Yet, one of the disadvantages of PEGASIS is that whole data transmission to the central station takes longer due to the greedy chain forming process, which results in a higher latency. An energy-efficient Cluster Head selection scheme EECHS [13] protocol is suggested to lessen the energy depletion caused by Cluster Head selection. In EECHS there are three types of nodes within a cluster: Cluster Head, Member node, and scheduling node. The scheduling node is intended to track and store real-time information about the remaining energy of all nodes within cluster. In the Cluster Head selection phase, the scheduling node specifies a corresponding Member node as the new cluster head based on the monitored results. EEUC [8] has been developed to address the problems associated with WSN hotspots. EEUC organize the network into unequal radius cluster, where clusters adjacent to the central station have smaller radius than those far from the central station. Therefore, Cluster Head adjacent to the central station saves power for data routing in multi-hop route. EAUCF [16] is an unequal clustering mechanism which employs the fuzzy techniques, and considers the position of the central station when a cluster group has been created. According to the remaining energy level and range to the central station, EAUCF changes the radius of the Cluster Head. A particle swarm optimization-based unequal and fault tolerant clustering protocol (PSO-UFC) [19] protocol is suggested. PSO-UFC employs the unequal clustering method to balance intra and inter-cluster energy depletion among the master cluster head. In addition, in PSO-UFC protocol the network connectivity is recovered by selecting an additional Cluster Head called surrogate Cluster Head in case of unexpected failure of master Cluster Head. A flooding tree uneven clustering FTUC [20] protocol is suggested. FTUC developed for large-scale networks. FTUC first determines minimum and maximum distances values of the network by constructing sub-network style tree and then apply the unequal cluster mechanism. Referenced position circles is defined to equally elect cluster heads. Cluster heads are therefore selected based on the remaining energy of the node and their distance to the referenced circle. A gradient-based routing (EBCAG) protocol [15] is suggested to address constraints resulting from unequaled energy depletion among cluster heads.