# RARZ: Ring-Zone Based Routing Protocol for Wireless Sensor Networks
## 1 Introduction  
Wireless sensor networks (WSN) are used to monitor and gather data from accessible as well as inaccessible environments [1]. Generally, each of the constituent nodes senses the data from its surrounding and sends them to the base station [2]. WSNs have applications in many domains including the military, environment, health, and industry. Of special importance in this context is the growth potential of these networks for the distributed monitoring of terrains that are physically isolated, hostile, and/or inaccessible. The rapid growth of sensor networks is resulting in increased functionality and decreased implementation costs [3]. The downside is the limited available energy possessed by the sensor nodes, since it is usually infeasible to replace or recharge the node battery [1] due to the cost and/or geographic reasons. Besides energy, there are challenges like restricted memory and processing power, short range communication, scalability, and deployment in hostile environments. In this paper, we focus on the energy issue, which is restricting widespread deployment of sensor networks. Major culprits in the consumption of energy are the processor and radio at the node. Different layers of the protocol stack may contribute variably to energy consumption, but we believe the primary focus should be the network layer, as efficient routing can minimize processor as well as radio energy consumption. For instance, reducing the number of messages should economize the energy consumed in processing on the one hand and the energy consumed in transmission and reception on the other. An overwhelming majority of the current research focuses on the development of energy-efficient routing protocols, which are low-cost, secure, and fault-tolerant. Routing protocols in wirelesssensor networks can be classified into three broad categories: direct, flat, and hierarchical. Indirect communication sensor nodes send their data directly to the base station. Such protocols are not scalable and consume more energy [4]. In flat routing, a node sends the data to the base station in a multi-hop fashion. In cluster-based routing protocols, each cluster has a cluster head (CH) and all the nodes in the cluster send their data to the CH. Each CH performs data aggregation and sends data to the base station [5; 6]. Hierarchical protocols, also called clustering protocols, are proven to be energy-efficient and more scalable in WSN because the nodes in a specific region or cluster will send their sensed information to their corresponding CH in one hop and then the cluster head may send directly or CH to CH the aggregated information to BS (Base Station). In this way, the information is routed to the ultimate destination (i.e., BS) in just a few hops, and the number of transmissions is greatly reduced. If we have fewer transmissions in the network, ultimately we have enhanced the network lifetime. In Figure 1, the whole sensing region is divided into different clusters. Cluster C1 has 10 nodes including CH. All the nodes in C1 will send their data to CH according to their TDMA slot. As there are nine nodes in C1, there will be nine transmissions in C1 and then three transmissions are carried out to route the aggregated data of C1 to BS. So there are only 12 transmissions carried out to route the aggregated information from cluster C1 to BS. On the other hand, if all those nodes send their information individually, and the average number of hops between senders to BS is four, then to send the same information of the same area nodes to BS, 40 transmissions are required. So it is clear from the statistics above that hierarchical routing (12 transmissions) is more energy-efficient than flat multihop routing (40 transmissions). The hierarchical scheme reduces the number of transmissions in the network to enhance the overall network lifetime. Computation of node positions is, however, a complex and energy-consuming task--a fact that reinforces our basic motivation.