# Multi-Gateway-Based Energy Holes Avoidance Routing Protocol for WSN
## 1 Introduction  
A wireless sensor network (WSN) contains a large number of densely-deployed sensor nodes that have limited energy and data processing capability. Sensor nodes monitor regions, gather data and transfer data towards the sink [1]. Sensors are being used in many applications, e.g., military area, habitat, and smart home monitoring [2]. Energy efficiency is one of the main concerns in designing of a routing protocol for a WSN. The sensory data is forwarded to the sink node, by using one-hop or multi-hop routing. In the case of multi-hop communication, some nodes transmit only their data while others transmit their own data plus data of other nodes. Therefore, energy depletion of one node varies from another, _i.e._, nodes nearby the sink node have more energy depletion than other nodes. This gives rise to the creation of energy holes near the sink [3,4]. Due to the energy holes problem further data transmission towards the sink is not possible. If nodes use direct communication or single-hop routing, nodes which are at a far distance from the sink will deplete energy faster than other nodes in the network. It will create energy holes in the outer area of the network and the area will remain uncovered at this place. Therefore, the network lifespan ends shortly and energy of the nodes would be unexploited [5,6]. There are several existing techniques which can improve network lifetime by balancing energy consumption, like clustering [7], data fusion [8], an optimal node deployment [9], and using the assistance of the gateway nodes [10]. We propose a multi-gateway-based energy holes avoidance (MGBEHA) routing protocol for a WSN. In this work we have achieved balanced energy depletion by reducing the transmission distance between the transmitter and the receiver. The network is divided into multiple regions. One gateway node is placed between two regions. Nodes in different regions use different types of communication. Nodes near the sink communicate directly with the sink, nodes near gateways communicate directly with the gateway, and in other regions communicate with cluster heads (CHs). We have compared our protocol with the LEACH [7], the M-GEAR [11], and the gateway-based stable election multi-hop routing protocol for wireless sensor networks (GSEP) [12] protocols. The MGBEHA protocol is novel, as it provides the solution of the energy holes problem by using gateway nodes. The existing research mainly uses the gateway nodes to improve lifetime of the network, but the use of gateway nodes for energy holes problem is not available until now. Moreover, the MGBEHA protocol deploys the gateway nodes in an optimal way with respect to the size of the area. If the size of the area is large, an additional number of gateways can be deployed in the network. There is no constraint on the number of gateways which can be deployed in the area. The MGBEHA protocol supports scalable networks, whereas the existing related research has fixed the number of gateways and does not provide scalability. We have also computed the throughput improvement ratio per round for all protocols, and it was never provided in the existing related literature. [PERSON] _et al._, in [11] have proposed a gateway-based model to improve the lifetime of the network. They have deployed sensor nodes in the logical regions on the basis of their location in the sensing field. They have placed the gateway node at the middle of the sensing field. The gateway node collects data from the other nodes in the field and transmits it to the base station (BS). This approach improves the network's lifetime, but fails when the size of the area increases as there is a single centralized gateway node to assist entire nodes in the area. While, in our approach, the number of gateway nodes increases as the size of the area increases. Moreover, there is no constraint on the number of gateway nodes, which can be deployed in the network area. Authors in [12] have proposed a gateway-based model in heterogeneous sensor networks (nodes with unequal initial energy).