# A Hybrid Unequal Clustering Based on Density with Energy Conservation in Wireless Nodes
## 2 Literature Review
Other solutions, such as energy-based clustering for WSNs lifetime optimization and balancing energy consumption in clustered WSNs (BLAC), were proposed by [PERSON] et al. [23]. BLAC used the energy level and the degree of nodes or the density of nodes for clustering. The protocol performs as distributed and dynamic. BLAC balanced the energy consumption between nodes and improved the network lifetime and stability. In order to balance the energy, the CH rotates between nodes. These methods involve overload. Energy and coverage-aware distributed clustering (ECDC) protocol [24] was proposed in 2014. The protocol was based on two components: energy and coverage. In this protocol, nodes share their information with their neighbors for calculating a delay time. According to the calculated delay time, CH is elected to the network. ECDC protocol was able to improve the coverage. Thus, the aforementioned protocol contributed to decreased energy consumption and increased the lifespan of the network. However, this method is carried out dynamically and it involves higher overload. Hybrid unequal clustering with layering protocol (HUCL) was presented in 2015 [15]. HUCL is a hybrid of dynamic and static clustering methods. Clusters closer to the BS were smaller. In this method, CHs are selected based on the energy status of the node, the distance to a BS and the number of neighbors. Also, data is transferred to the BS as multihops. Each node shared its own information with the size of its cluster reduces for neighbors. In the HUCL method, each node computes its own delay time and CH are selected according to the computed delay times and, therefore, the nodes join to the nearest CH. In this algorithm the CH that has no member node changes its own state to a member node and finally, it joins to the nearest CH. Data transmission step is divided into time periods. Member nodes send their own data clusters to CH and CH use multihop routing to transmit data to the BS. Simulation results show that compared to other available protocols, HUCL is able to reduce the network overhead, optimize energy consumption, and increase the network lifetime. In this algorithm, in order to compute the cluster radius, energy consumption of nodes, and also for calculation delay time, a distance of a node to BS is not taken into account. An improved energy aware distributed unequal clustering protocol (EADUC-II) was proposed in 2016 [25]. In this method, clusters are formed with unequal sizes and thus, clusters near to a BS have a smaller size. To determine the competition radius of cluster nodes, other parameters have been considered including node energy and to determine routing, the criterion of node energy to select the next step is taken into account for routing between CH. In this method, in order to compute the node delay time and node density, its distance to the BS is not considered. Although this method is performed in hybrid form, the improvement of overload reduction is less. Another algorithm is an unequal multi-hop balanced immune clustering protocol (UMBIC) which was proposed in 2016 [26]. In multi-hop routing, the CH which is near to the BS loses its energy due to the relay data of the further CH. This protocol provided the WSNs with the nodes of various sizes and with a variety of homogeneous and heterogeneous nodes with distinctive densities; therefore, this method resulted in an improved network lifetime. UMBIC used an unequal clustering method to optimize the energy consumption in intra- and intercluster routing, forming the unequal clusters based on the distance of a node to BS and the energy level of the node. Also, UMBIC used the multi-objective immune algorithm to provide the routing tree with the aim of minimizing the cost of the nodes' relationship. Hence, this method could effectively reduce the network overhead and improve network lifetime. A grid-based reliable routing protocol (GBRR) was proposed in 2016 [27].