# FTUC: A Flooding Tree Uneven Clustering Protocol for a Wireless Sensor Network
## 1 Introduction  
With the rapid development of wireless communications, integration of sensors, and embedded technology, the development of wireless sensor networks (WSNs) has become more and more attractive. A WSN [1; 2; 3] consists of a large number of sensor nodes (SNs) with wireless transmitter and data processing elements to perform monitoring of a, potentially large, sensed area. The increasing number of application domains for WSNs [4; 5; 6] has aroused great attention in academia and industry. As the network nodes are spread across a large area, they are mainly battery operated, leading to energy, computation, and resource limitations. It is then important to build energy efficient WSNs. Topology control provides an effective way to cope with this challenge. In general, topology control refers to a set of technologies that can transform the underlying network topology to improve the system performances or reduce its costs [7]. Among all these methods, clustering [8] is an efficient and extensively used scheme to manage WSNs. In these networks, SNs are divided into several clusters, including a leader node named cluster head (CH) [9]. The CH is a bridge and creates the link between the nodes in its cluster and the rest of the network. Clustering has various significantsuperiorities over the classical scheme. Firstly, the SNs monitoring the environment send their data to their corresponding CH, which avoids the need for nodes to transmit large sets of data directly to the base station (BS) [3]. The CHs consume less energy for gathering data (referenced as intra-cluster communications) since they are close to the SNs [10]. Secondly, the CHs can be arranged in a multi-hop sub-network to forward data and save energy by avoiding long distance communications, named inter-cluster communications. However, due to the large forwarding data task, the CHs near the BS will see their battery depleted quicker. The zones including such CHs are called hot zones [11]. Unequal cluster-based routing (UCR) [12] introduces a competition radius to reduce the cluster sizes near the BS. Smaller clusters, with less SN members, decrease the CH energy consumption by lowering intra-cluster communications. Therefore, UCR reduces the hot zone problem to a certain extent. The UCR algorithm elects cluster heads depending on the competition radius, which depends on the relative node position in the network, leading to a possibly large number of CHs elected in the same area with similar position values. This is the unevenly distributed CH phenomenon. Due to this phenomenon, a new hot zones problem can be created in the network, and can also lead to uncovered nodes if they are too far from the BS. Also, UCR needs to calculate the competition radius; therefore, the global minimum and maximum distances between each node and the BS are needed. This is not realistic for large networks due to the amount of data required, and also for long distance transmissions that might be impossible for all nodes. To solve these problems, we propose the flooding tree uneven clustering algorithm (FTUC). The main contributions presented in this paper are:  
* A clustering algorithm enabling the CH election in large WSNs by building a tree network to convey the global minimum and maximum distance data to the BS. * A way to balance the uneven distribution of CH by introducing referenced positions to elect CH, which balance the network load and prolong the network lifetime. * The construction of unequal clusters to optimize the energy consumption of the overall network. * A set of simulations to show the effectiveness of our approach, and to compare to state-of-art algorithms. The remainder of this paper is organized as follows. We give a brief discussion on the related literature in Section 2. In Section 3, definitions, and models used in this work are introduced. In Section 4, the problems of current statements are introduced. The FTUC algorithm is presented in detail in Section 5.