# Energy-Efficient Clustering Scheme for Flying Ad-Hoc Networks Using an Optimized LEACH Protocol
## 3 Related Work  
The selection of the CH based on residual energy is crucial as it affects network performance and lifetime. The network life duration will be extended if the chosen CH is a sensor node with the highest energy leftover among all the cluster members. LEACH-B (LEACH-Balanced) [6; 7] is proposed as an improved variant of LEACH, which keeps the number of CHs practically optimal [8]. LEACH-B is a decentralization technique for the development of clusters that improves the choice of the CHs process, based on the residual energy of the nodes. LEACH-B is initially the same as the LEACH methodology, but in the case of CH selection, it adds a second phase that takes into account the remaining energy and ensures that each round has an equal number of CH. The improved LEACH (I-LEACH) is a clustering routing system [9] in which the selection of CHs is based on residual energy, node location, and neighbors' numbers. The CH selection in the original LEACH algorithm is solely based on the pre-set threshold function, with no consideration for other parameters that affect the network's life duration. The I-LEACH solution solves this problem by incorporating the residual energy, the count of neighbors' nodes, and the distance to the BS factors in the threshold function. LEACH-C is a centralized LEACH clustering method [10] that picks CHs based on the remaining energy of nodes and thus builds clusters in the network. LEACH-C employs a centralized technique to select the most proficient CH from a pool of nominated CHs, thereby addressing the efficiency issue raised by the conventional LEACH protocol [11]. Sensor nodes send information to the sink about their remaining energy and position in the first phase. The sink computes the average energy of nodes grounded on these data and then determines which nodes will be CHs. As a result, in this round, nodes with more leftover energy than the average will be chosen as CHs. The rest become various regular sensor nodes, and the steady phase is the same as LEACH. The mobility element in the standard LEACH algorithm is included in LEACH-M (Mobile LEACH) [12]. During the set-up and steady phases, this mobility affects both CHs and cluster member nodes, although the BS is assessed as stationary in the original LEACH. CHs are selected from the pool of nodes according to the least attenuation and are the nodes with minimum mobility among all nodes. The elected CHs then communicate their choice in the transmission frequency to all nodes. According to LEACH-M authors, all nodes are initially homogeneous, and GPS may be used to search for sensor nodes. LEACH-M elects CHs using the same threshold function as LEACH; however, unlike LEACH, LEACH-M considers node mobility during the data transmission step. In [13], the authors suggested VH-LEACH, an upgraded V-LEACH technique. The main goal of this protocol is to modify the way a CH is elected. The CH is chosen in the VH-LEACH algorithm based on the largest residual energy. First, clusters are formed, and then CHs are selected. Every CH collects information about the cluster members' remaining energy. Following that, the CH selects a VH (Vice Cluster-Head) with the max left-over energy within the cluster. In [14], the authors presented LEACH-T, a unique LEACH-based clustering routing protocol that allows the number of time slots in TDMA of each CH to be fixed based on the count of cluster member nodes. LEACH-T takes into consideration the residual energy of nodes throughout the cluster formation phase, resulting in an optimum number of CHs. T-LEACH incorporates changeable time slots for different CHs in the steady phase. In the LEACH-T approach, a dynamic mechanism to assign time slots (TDMA) depending on the number of cluster members is used instead of on a certain fixed allocation of time slots to CH. This means that if the number of nodes inside the cluster is minimal, the CH should only be allocated a few time slots and major time slots should be allocated if the number of member nodes is enormous.