Rotating Energy Efficient Clustering for Heterogeneous Devices (REECHD) Matteo Micheletti Computer Science Department University of Camerino Camerino, IT matteo.micheletti@unicam.it Leonardo Mostarda Computer Science Department University of Camerino Camerino, IT leonardo.mostarda@unicam.it Andrea Piermarteri Computer Science Department University of Camerino Camerino, IT andrea.piermarteri@unicam.it Abstract—Wireless sensor networks (WSNs) are an essential part of the Internet of Things (IoT). They provide a virtual layer where is possible to collect information about the physical world. WSN devices can be battery powered, produce a large volume of data and have heterogeneous hardware such as computational power, memory, and communication capabilities. Gathering data from battery powered heterogeneous devices in an energy efficient way is a challenging research area. Clustering is one of the solutions which has been proposed by researchers. In this paper we propose a novel Rotating Energy Efficient Clustering for Heterogeneous Devices (REECHD). Our experiments show that REECHD improves the network lifetime when compared to the state of art clustering protocols for heterogeneous WSNs. Index Terms—Wireless Sensor and Actuator Networks; Inter- net of Things; Clustering Protocols; Routing; Energy Efficiency. I. I NTRODUCTION The Internet of Things (IoT) is a makeup of interre- lated smart objects, wireless devices and people that have autonomous capabilities to communicate data over the net- work [9]. The term IoT was first coined by Kevin Ashton in 2002 and in Forbes Magazine saying as, “We need an internet for things, a standardised way for computers to understand the real world” [12]. Various studies predict that more than 20 billion devices will be connected to the internet by 2020 [9] generating a market size of 267 Billion dollars. IoT main applications [2] include transportation, smart homes, smart supply chain, smart cities, connected cars, smart industry, and smart retails. Wireless sensor networks (WSNs) provide a virtual layer which can collect information about the physical world. WSN devices can produce a large volume of data and can have heterogeneous features such as computational power, memory, and communication capabilities. When devices are battery powered, gathering data from them in an energy efficient way is a challenging research area [10]. Clustering is a possible solution proposed by the researchers. This organises the de- vices into sets (clusters). Each cluster has a cluster head (CH) that gathers data from its nodes (intra-cluster communication) and communicates with other CHs in order to report data to a centralised base station (BS) (inter-cluster communication). Quite a few clustering protocols have been proposed [11] [8]. Some protocols are based on equal-sized clusters while others use clusters of unequal size. Some others make use of rotation techniques to reduce the amount of cluster head elections. Most of the clustering approaches have their roots on the homogeneous WSN field which assumes devices with homogeneous capabilities [13] [10]. Cluster head selection is usually based on the node residual energy. Few approaches may consider the node transmission rate for cluster formation. In this paper, we propose a Rotating Energy Efficient Clustering for Heterogeneous Devices (REECHD). We assume heterogeneous WSNs that are composed of nodes with differ- ent transmission rates and different energy levels. REECHD introduces a novel leader election protocol which, not only considers the node residual energy, but also the node induced work. This is estimated by using the node transmission rate. REECHD also introduces the concept of intra-traffic limit rate (ITLR). This defines a limit on the intra-traffic communication that all WSN clusters must comply with. ITLR can be used to improve energy efficiency. Our experiments compare REECHD with well-known pro- tocols for homogeneous WSNs such as Low-Energy Adaptive Clustering Hierarchy (LEACH) [5], Hybrid Energy-Efficient Distributed Clustering (HEED) [17], Unequal clustering al- gorithm based on HEED (UHEED) [4], HEED with rotations (ER-HEED) [15]. We also consider protocols from the hetero- geneous WSN field such as FMUC [8]. Our simulation results show that REECHD performs better under various network conditions. The rest of the article is organised as follows: Section II reviews the state of art of clustering for homogeneous and heterogeneous WSNs; Section III details the REECHD election and its novel contribution as well as the algorithm for cluster formation; Section IV describes the network model and the simulation results; finally, Section V concludes the article and outlines future work. II. RELATED WORKS A great deal of literature and research articles are available on clustering protocols. In this section, we focus on existing prominent clustering protocols for homogeneous and heteroge- neous WSNs. We consider clustering approaches having equal and unequal size clustering, rotation and non rotation, single hop and multi-hop.