# Novel Reliable and Energy-Efficient Routing Protocols for Wireless Sensor Networks
## 2 Related Work  
Previous works were done in the field, classify energy-efficient routing protocols into homogeneous WSN protocols (where all the nodes are identical) and heterogeneous WSN protocols, where both are subdivided into static and mobile [9]. Other researchers classify them based on network structure (flat and hierarchical); communication model (negotiation-based, query-based, and coherent-based); topology (location-based and mobile agent-based); and reliability (QoS-based and multipath-based) [10]. Some researchers improved the energy efficiency of WSN by using hierarchical packet forwarding protocols. Low Energy Adaptive Clustering Hierarchy (LEACH) is a hierarchical cluster-based protocol. The network is divided into several clusters; a cluster head (CH) is selected to receive the packets from respective members of that cluster, and then, it forwards the packet directly to the BS. In LEACH, energy efficiency is achieved by clustering and data fusion. By clustering, just the CH has a direct long-distance transmission to the BS; other nodes send their data to CH in short-distance transmission. By data fusion, the CH removes redundant data and fuses the received packets into a single packet. The cluster heads are selected randomly and changed periodically in time to achieve load balancing [11]. However, ignoring the energy level of the cluster head may make it a bottleneck node, and it does not consider reliability. There are several modified versions of LEACH, these modifications based on three titles, selection of CH, clustering, and data transmission. In LEACH-C, the selection of CH is centric and performed by BS based on the remaining energy and location of nodes [9]. In NEAHC, load balance and energy efficiency are achieved by selecting the CH based on remaining energy. Also, members with low energy are forced to switch between sleep and active status [12]. The authors of [13] propose the selection of CH and clustering based on practical swarm optimization and fuzzy logic; the fitness function depends on the distance between nodes and CH, the distance between CH and BS, and the minimum consumed energy. In [14], the firefly heuristic algorithm is used to select the CH based on distance, energy, and delay. In terms of clustering, CACD algorithm constructs clusters based on the energy depletion of the clusters and node density [15]. PEGASIS is an underlying chain-based routing protocol [16], it is a modification of LEACH, the nodes are grouped into a chain using a greedy algorithm, and each of them acts as chain head in turn; each node fuse the received packet into its packets, the fused packet is forwarded to the closest neighbor until it arrives at the chain leader. The chain leader aggregates the packets together and sends them directly to the BS. By selecting the chain leader, regardless of its energy, can result in a shorter lifespan. CHIRON [17] is a chain-based routing protocol that increases energy efficiency by dividing the network field into some smaller areas to create shorter chains for reducing data transmission delay and path duplication. The Energy-Efficient Chain-Based (EECB) routing protocol [18] modified PEGASIS by selecting the chain leader based on the residual energy and distance from the BS. The scheme in [19] selects the chain leaders from a group of nodes in the neighborhood of BS. The authors of [20] used a heuristic Ant Colony optimization to reduce delay and to find the optimal path with minimum transmission distance. Regarding the reliability, in [8], an energy-efficient and reliable protocol is proposed, predefined reliability is achieved by multipath routing. But, only two-hop paths are assumed. Researchers of [21], improve the reliability by finding the best location of CH. RE-AEDG [22] and GIN [23] protocols use the cooperative routing model to enhance reliability, where the transmitted packet is overheard by several neighbors and retransmitted by several neighbors too. Some researches use network coding to improve reliability [24; 25].