## 1 Introduction and Related Works  
Wireless sensor networks (WSNs) are a large number of small devices capable of executing sensing, data processing and communication tasks. As sensor nodes may be placed everywhere, this type of network can be applied to multiple scenarios [1]. e.g., in healthcare [2], where they are used to monitor and assist disabled patients, habitat monitoring [3], disaster management [4], and even for commercial applications such as managing an inventory, monitoring product quality, surveillance, and target tracking [5]. In cluster based architectures, mobile nodes are divided into virtual groups. Each cluster has adjacencies with other clusters. All the clusters have the same rules. A cluster can be made up of a Cluster Head node, Cluster Gateways and Cluster Members [6]. The Cluster Head node is the parent node of the cluster, which manages and checks the status of the links in the cluster, and routes the information to the right clusters. Inter cluster data transfer takes place through the cluster gateways [7]. Cluster members are the rest of the nodes in a cluster. In this kind of network, Cluster Head nodes are used to control the cluster and the size of the cluster is usually about one or two hops from the Cluster Head node. A cluster member does not have inter-cluster links, only cluster gateways. There are many cluster based architectures [8]. Sensor networks clustering schemes can be classified according to several criteria. For example, they can be classified according to whether the architectures are based on Cluster Head [9] or on Non Cluster Head [10]. The first architecture needs a Cluster Head to control and manage the group, and the second one does not have a specific node to perform this task. Another way to differentiate the cluster-based architectures is observing the hop distance between node pairs in a cluster. The schedules can be divided into 1-hop clustering [11], multi-hop clustering [12] or multilevel clustering [13]. The maintenance of the hierarchical multilevel requires heavy communication overheads due to random change of multilevel topology. By contrast, the cluster head of single level clustering is simple, since it only tracks local topology changes due to host mobility. In addition to these classification criteria, reference [8] presents another classification based on the objectives of the clustering protocols. There are six clustering schemes: dominating-set-based (DS-based) clustering [14], low-maintenance clustering [9], mobility-aware clustering [15], energy-efficient clustering [10, 16], load-balancing clustering [17] and combined-metrics based clustering [11]. The clustering architectures provide many benefits. Reference [18] shows the most important features of cluster-based architectures over _ad hoc_ and sensor networks. The last feature is strongly linked with energy conservation, given that clustered wireless sensor networks offer two major advantages over their non-clustered counterparts; firstly, clustered wireless sensor networks are capable of reducing the volume of inter-node communication by localizing data transmission within the formed clusters and decreasing the number of transmissions to the sink node; secondly, clustered wireless sensor networks are capable of extending the nodes' sleep times by allowing cluster heads to coordinate and optimize the activities. In the literature several cluster deployments and proposals can be found. One of them is the one presented in [19], which proposes a cluster-based system to overcome problems of bottleneck and poor scalability. In [20], [PERSON] and [PERSON] proposed a cluster-based distributed sensor network deployment and target localization to enhance the coverage after an initial random placement of sensors. All these works use a routing protocol inside the cluster [21, 22] or they use the cluster to build a unique protocol for the entire network (such as the one presented by [PERSON] _et al_.