# Multi-Gateway-Based Energy Holes Avoidance Routing Protocol for WSN
## 2 Related Work
### Gateway Based Approaches  
In the clustering techniques, cluster heads are selected from the normal sensors which may expire rapidly due to fast energy diminution for such an additional workload. Therefore, some researchers [PERSON] _et al._ (2015); [PERSON] _et al._ (2015); [PERSON] _et al._ (2015) have suggested the use of some extraordinary nodes called gateways or relay nodes, which are equipped with superfluous energy and larger communication range than the normal sensor nodes. Authors in [PERSON] _et al._ (2015) have proposed a fault tolerance and gateway-based energy-efficient method. In their method, gateway nodes perform the work of cluster heads. Hence, they have considered that the gateways are also energy constrained and can fail during network operation. They have considered the problem of failure of cluster head (CH)/gateway. In clustering-based methods, if a CH node fails, all member nodes will not be able to transmit data. Authors have used a heterogeneous network in which a CH is equipped with more battery power than non-CH nodes and it acts as a gateway node. They have proposed a distributed algorithm for fault tolerance routing (DFTR) which is based on the distance and residual energy parameters. The DFTR selects the next hop gateway in such a manner that energy utilization of the gateways is balanced. It also considers those gateways which have no next hop gateway towards the sink. In our model, gateway nodes are not energy constrained; therefore, there is no need to search the availability of next hop gateway node in each round of the algorithm. There is no possibility of a gateway node's failure. Authors in [PERSON] _et al._ (2015) have introduced a gateway node-based load balancing scheme which assigns the sensor nodes to gateways in such a way that load of all gateways is minimized. However, in our method, there is no fixed number of nodes assigned to a gateway node. In our model, there is a region-wise distribution of nodes. A gateway node can handle the data of any number of nodes, within its region. [PERSON] _et al._[PERSON] et al. (2016) have proposed the gateway based distributed cluster head scheduling (DCHS) algorithm. The authors have partitioned the network into primary and secondary tiers by using the received signal strength indicator (RSSI) of the sensors from the base station. Cluster heads are present in the primary tier while cluster nodes are present in the secondary tier. This two tier approach decreases the communication distance between cluster heads and their member nodes. Therefore, similar to our method, this approach also reduces the consumption of transmission energy by reducing the transmission distance. The DCHS reduces the distance between the cluster head and cluster node, while our method reduces the transmission distance between the cluster head and the sink node. In the DCHS, the base station calculates the aggregate RSSI value of all nodes and decides the tier of the nodes. Nodes which have higher RSSI values belong to the primary tier while others belong to the secondary tier. Next, the base station elects three types of nodes in the primary tier, such as CHs (cluster heads) which communicate with cluster nodes, G1 (gateway nodes) which send the data between the primary tier and the base station, and G2 (gateway nodes) which operate as the relay nodes between primary and secondary tiers. [PERSON] _et al._[PERSON] et al. (2016) have proposed a gateway node and multi-hop cluster-based routing protocol. They have assumed unlimited battery power in the gateway nodes. The cluster heads and the gateway nodes form a multi-level hierarchy in the network. This hierarchy is used for data transmission between the sensors and the base station. However, this model restricts the number of cluster heads in a network. If the size of the area increases, the number of cluster heads cannot cover the entire area. Moreover, the number of gateway nodes and their position are fixed. It can create unbalanced energy consumption in the area.