# RARZ: Ring-Zone Based Routing Protocol for Wireless Sensor Networks
## 2 Related Work
### Centralized Approaches  
In a centralized approach, the base station is responsible for cluster formations and selecting CH for each of the new rounds (e.g., [3, 4, 7, 9]). LEACH-C [5] is built on LEACH and uses the centralized approach for CH selection. It uses direct communication for sending data between CHs and the base station. The authors in [10, 11] present modifications to the LEACH protocol. Both of these approaches distribute the energy dissipation among all the nodes in the network, reducing the average energy depletion in the network and hence extending the overall network lifetime. Both approaches utilize a centralized approach for cluster formation. In these protocols, the data are propagated to the base station in a multi-hop fashion. The routing paths are identified by the base station by connecting all the CHs using the spanning tree algorithm [12], which reduces the energy dissipation for each CH node.  
Another work proposes a new static clustering protocol known as a Low-Energy Static Clustering Scheme (LESCS) [13], which solves the hotspot problem that is common in static clustering schemes. A grid-based cluster formation algorithm is utilized in LESCS. It also utilizes the higher energy sensor nodes for data transmission and hence prolongs the network lifetime. The operation of LESCS is divided into three phases. The first phase is the centralized network clustering calculation phase, the second is the cluster formation phase, and the third is the intra-cluster scheduling phase. One of the drawbacks of this protocol is that, in each cluster, once a CH is selected it cannot be changed. One node doing all the processing will deplete fast and will result in a reduced network lifetime.  
The work presented in [14] is based on a table-less position based routing scheme for low-power, data-centric wireless sensor networks. The algorithm is localized, uses a greedy forwarding approach, and does not rely on the neighborhood information. These characteristics reduce the communication overhead, make the protocol highly scalable (no routing tables are maintained and beacons are not exchanged when a node leaves or enters a network), and perform better in a mobile environment since the next hop is nondeterministic and is computed at runtime.  
An extension of LEACH is called the hierarchical cluster based routing (HCR) [15], which uses a genetic algorithm (GA) to generate energy-efficient clusters. It is the base station that handles the cluster formation, by broadcasting the GA-based cluster configurations. After receiving, each node in the sensing region configures itself accordingly. This protocol is designed for applications where data sampling is done on a continuous basis. The results show that HCR outperforms LEACH in terms of energy efficiency.  
A closely related technique is the static clustering approach, described in [1], wherein the base station is responsible for dividing the network into different clusters. For cluster formation, the base station broadcasts various beacons by incrementally increasing the transmission power in the sensing region. As soon as a node receives the first broadcast message, it sets its ringID to message ID and sends back a join request message to the BS; it belongs to cluster i, where i is the message ID.