# An Effective Hybrid Routing Algorithm in WSN:
## 2 Related Works
### Minimum Hop Count WSN Routing Algorithm  
On the basis of the Directed Diffusion algorithm (DD) and the flooding algorithm, [PERSON] et al. [4] introduced the concept of hop count and proposed the minimum hop count (MHC) WSN routing algorithm. In the phase of data transmission, the algorithm determines the transmission path according to the hop count from the source node to the sink node. MHC routing algorithm has the potential advantages of shortest path, lowest energy consumption, and minimum time delay. However, the following two concerns disadvantages the original minimum hop count routing algorithm.  
1. The sink node periodically initiates flooding for route update. This kind of periodic flooding throughout the whole network may cause excessive cost and overhead in terms of energy due to redundant data transmissions.
2. There is no reasonable strategy to choose the next hop nodes for data transfer in the process of data transmission but forwarding the same data through all the parent nodes, which generates a large quantity of redundant information in the network and accelerates the energy consumption of the network.  
[PERSON] et al. [5] established routing tables for sensor nodes using a technique similar to the classical flooding method. In each node's routing table, it includes its neighbor nodes. They are marked as parent nodes, sibling nodes or child nodes respectively by recording their hop count values, together with their ID numbers, energy levels and time slots. A node's parent nodes are whose hop counts are one less than this node itself, sibling nodes are who have the same hop counts with this node itself, and the child nodes are whose hop counts are one more than this node itself. Based on the routing table, in accordance with the priority of the parent nodes and the sibling nodes, each sensor node can determine the best next-hop node which has the highest energy level. The proposed data routing protocol reduces some redundant data transmission by providing a next hop node selection approach.  
[PERSON] et al. [26] proposed an ACO-based ladder diffusion algorithm to solve the energy consumption and transmission routing problems in WSNs. The algorithm consists of two phases, namely the ladder diffusion phase and route-choosing phase. The ladder diffusion creates a ladder table for each sensor node, and the route-choosing phase integrates ACO to select and construct the route from a sensor node to the sink node. The proposed algorithm greatly reduces the energy consumption compared to the previous work by properly assigning the transmission route using the ACO. However, the algorithm has a main flaw that it does not consider the sensor nodes' residual energy when choosing the relay node. So the algorithm is easy to face in the \"Hot Spot\" and \"Energy Pole\" problems.  
[PERSON] et al. [27] modified [PERSON]'s method as an energy aware ladder diffusion (EALD) routing algorithm. The EALD adopts the ladder diffusion process similar to [26] in the first step. In the second step of its transmitting phase, in order to solve the 'Hot Spot' and 'Energy Pole' problems, an energy aware strategy is used to dynamically adjust the routes of transmitting according to the nodes' residual energy. The key strengths of this modified algorithm include low routing overhead, network load balancing and the extended network lifetime.