# RARZ: Ring-Zone Based Routing Protocol for Wireless Sensor Networks
## 2 Related Work
### Distributed Approaches  
In a distributed approach, the constituent nodes collaboratively make a decision about the new CH based on local information [5]. One of the earliest hierarchical clustering protocols is the Low Energy Adaptive Clustering Hierarchy (LEACH) [5]. In LEACH, cluster heads are selected in a distributed fashion, where nodes elect a CH among themselves based on probability calculation of the current energy level nodes for each round of communication. The working of LEACH is divided into different rounds. Each round begins with a setup phase followed by a steady state phase. The data are transported from nodes to the CH and then to the base station.  
The research described in [16] presents a routing protocol that is inspired by both LEACH and PEGASIS and emphasizes node computation rather than communication. The authors also define a new cost metric for balancing energy amongst the nodes. In [17], the authors put forward a distributed online sensor network clustering algorithm that does not need any global information about the network, for achieving energy efficiency. The authors claim to have achieved higher performance against well-known clustering protocols. There is an effort to extend the network lifetime by deploying an energy efficient routing scheme with adaptive energy slope control (AESC) [18] method to keep all the nodes alive for a required period of time. In this technique, the network has the ability to cope with worst-case environment-dependent connectivity issues while maintaining energy-efficient connectivity among the nodes in normal situations.  
In [19], a neural-network-based clustering scheme with energy-efficient routing is used with the objective of increasing the network lifetime. In the proposed scheme, the issue is addressed by formulating a linear programming problem with some specified limitations. The CHs are selected using a neural network scheme with adaptive learning followed by routing and data communication.  
Enhanced low-energy clustering protocol (ELECP) has been developed for routing in WSN with the aim of increasing the network lifetime [20]. The ELECP relies on a distributed clustering algorithm that can better be used over poorly correlated sensed data of a specific area. There have been efforts to reduce the average path length in the WSNs in order to conserve the energy. One such effort is the small world routing protocol (SWRP) [21], which, by adding a few shortcut links amounting to a fraction of the network diameter, constructs what is termed a small world network. Following this, the routing protocol finds the path through regular propagations of weak and strong links. SWRP shows a significant reduction in the energy consumption and end-to-end data delay but at the cost of increasing the overall network lifetime. A link-based routing scheme has been presented in [22], based on passive clustering to increase the network lifetime in WSN. This technique selects cluster heads and gateway nodes based on their location and their energy level. Thus it provides persistent, energy-efficient, and reliable routing paths.  
An ant colony path optimization-based clustering energy-efficient transmission protocol (CEETP-ACPO) is proposed [23]. In this protocol, the cluster heads are selected using a distributed algorithm and the optimized path is based on ant colony optimization algorithm. To reduce the message exchange overhead, an optimal technique has been developed in [24], which acquired the neighborhood information for finding the optimal routing paths. It optimized the total number of hops in the network and hence increased the network lifetime.  
The work described in [25] presented a protocol called EADV (energy-aware distance vector) for ultra-low-powered WSNs. With the EADV protocol it is very simple to handle the low memory space and low energy availability on part of the sensor nodes. In EADV, BS is assumed to be power-efficient and keeps the prolonged network lifetime as its key design parameter.