# Optimized Clustering Algorithms for Large Wireless Sensor Networks: A Review
## 4 Comparison of the Optimized Clustering Approaches  
In this section, we present a summary of some optimized clustering algorithms. They are compared and classified according to the ML/CI used, the data delivery rate, the energy consumption which takes in account the network lifetime, the scalability of the algorithms, the type of the approach which can be centralized or distributed, the integration or not of a data aggregation technique, and the homogeneity of nodes. * The data delivery rate concerns the amount of data received by the BS or a receiver node according to the number of sent data by another node. This metric is very important because it helps to have an overview of the data loss during transfers and reliability during communication. * The energy consumption metric here is the most important parameter to take into account to evaluate a clustering algorithm. The energy consumed by a sensor node across the time is strongly related to its lifetime that can affect to the lifetime of the whole network. Then a node with a lower energy consumption would have a longer lifetime than another node consuming more energy. * Since our study is focused on large scale WSNs, we examine the scalability of the presented algorithm. The scalability here aims to classify the proposed solutions by the number of nodes present in the sensor field. Algorithms with more than 500 nodes are more interesting for our study because they manage more efficiently the amount of communication between nodes than other with less than 100 or 200 nodes within the sensor field. * Approaches used to implement clustering algorithm can be either centralized or distributed. On centralized clustering approaches, important decision making and most of the operations are done at the BS, which is not usually limited by its resources. On these approaches, the MI/CI is implemented by the BS, each node has to send their necessary information (its location,remaining energy, etc.) for computations by the BS. In distributed approaches, the decision and the computation are made by the nodes themselves. The BS receive results of computations or decisions, in some case the BS is replaced by the sink node. * Another metric considered in this study is the homogeneity of nodes within the field. The network is said to be homogeneous when all the nodes have the same characteristics (performance of the microcontroller, available memory, communication range, energy level, etc. ); however, it is heterogeneous when the algorithm considers one or more special nodes with extended performance compared to other normal nodes. In this last case, these special nodes are mostly set as CHs due to their performance and the number of clusters mostly depend of the number of these special nodes. * In order to evaluate the amount of energy consume by each node within the field, clustering approach integrate a radio model which has to be as accurate as possible to real behavior. This parameter is important because most of the energy dissipated by a sensor is caused by transmitting and receiving data through the transceiver. The type of radio model also allows you to know whether or not the implementation in real environment can be similar to the simulation context. * For our analysis, we evaluate if the presented algorithms are based or not on multihop communication between nodes. The multihop ability assumes that a node can send a data to another far node out of reach but helps by an intermediate node within its communication range. * To consider the fault tolerance of the presented algorithms, we set the multipath metric. Algorithms that implement multipath are more fault tolerance than others that do not use it, if a route to a BS is not available anymore, it is possible to access the BS by a secondary path. This parameter allows an algorithm to avoid the entire network failure caused by nodes crash. Table 1 presents the crosstalk between the ML/CI and the energy consumption. We observe that the approaches which consume the most the energy are based on FL or GA.