# Comparative Study of Energy Efficient Routing Techniques in Wireless Sensor Networks
## 3 The Proposed Taxonomy
### Latency Aware and Energy-Efficient Routing
#### 3.9.4 Heuristic and Swarm-Based  
These protocols were inspired by natural behaviors as ant and bee colonies. Several protocols were developed based on this concept, such as the framework of ant colony optimization (ACO) [114; 115], mainly aiming to enhance the network lifespan. Protocols belonging to this class are further divided into four subcategories according to their functionalities, which are: SB data-centric, SB location, SB hierarchical and network flow and QoS-aware protocols. Each of these categories is detailed in the following. SB Data-Centric Routing Protocols  
Some swarm-based protocols are data-centric-based and aim to improve network reliability and lifespan using various techniques. Among those protocols, we find:  
* **Pheromone-based energy-aware Directed Diffusion (PEADD)** This protocol involves sensors with higher energy levels in the data gathering process in order to enhance the network lifetime [116]. Inspired from ant colonies, where a chemical substance known as a pheromone is used to sign food paths, PEADD increases routes with larger energy while others are reduced depending on the remaining energy to which the pheromone is linked. PEADD updates the pheromone level based on the amount of transmitted data. SB Location-Based Protocols  
Some swarm-based protocols use location information to estimate the distance between two sensors and to enhance the performance of the routing process in order to conserve energy in WSNs. Among the representative protocols of this class, we quote:  
* **Sensor-driven and cost-aware ant routing (SC)**Inspired by ant colonies, SC assumes that ants (sensors) know the location of the food (data) and aims to choose the best path to take initially. SC allows nodes to estimate routing costs through each of the sensor nodes, but when an obstacle arises in the routing path, SC suffers from redundant data and sensing errors [117]. SB Hierarchical Protocols  
Swarm-based hierarchical routing protocols define a specific structured similar to ant colonies where eggs and larvae are grouped according to their degree of similarity into small groups. Among these protocols, we find:  
* **Self-organizing data gathering scheme (SDG scheme)** SDG is designed as a hierarchical protocol and allows nodes to use another sink in needed to ensure scalability and reliability. In SDG, the node clustering mechanism is similar to the way in which larvae and eggs are grouped in ant colonies. Researchers found that SDG reaches more than 90% of reliability even in the presence of loss channels, but a significant amount of energy is lost through the exchange of control packets due to the proactive nature of this protocol [118]. Network Flow and QoS-Aware Protocols  
Satisfying the QoS of a network is the main objective of the routing protocols in WSNs. This category of protocols aims to deal with the loss of data packets and to guarantee their sequencing using some mechanisms inspired by behaviors observed in nature. Among these protocols, we find:  
* **Energy-efficient ACO-based QoS routing (EAQR)** EAQR is designed as a QoS aware routing protocol. It uses an improved ant colony optimization algorithm and a new dual pheromone heuristic model to ensure the QoS and balance the energy consumption over the network, but it presents some delays [119]. Table 10 establishes a comparison between heuristic and swarm-based routing protocols [120].