# A Survey on an Energy-Efficient and Energy-Balanced Routing Protocol for Wireless Sensor Networks
## 5 Taxonomy for Energy-Efficient and Energy-Balanced Routing Protocols
### Multi-Hop Communication Method
#### 5.1.2 Load-Balanced Tree Technique
In spite of the numerous advantages offered by multipath routing protocols, designing a multipath routing protocol can be a challenging problem. A good multipath routing protocol takes into consideration several components to select the multiple paths and evenly distribute the traffic load over the discovered paths. The main components to be addressed in designing a multipath routing protocol include path discovery, path selection/load distribution, and path maintenance [16]. Since multipath routing is designed based on the multi-hop communication principle, the duty of the path discovery stage is to select the set of relay nodes that will form the multiple paths from the source node towards the destination. The path discovery stage is to select the set of relay nodes that will form the multiple paths from the source node towards the destination. the destination. After the set of intermediate nodes has been selected, the number of paths (path selection) to distribute the traffic load is also another vital component. Furthermore, as a result of resource constraints and the low battery power of the SNs, the selected paths are usually susceptible to error. Therefore, path maintenance is an essential component in designing a multipath routing protocol. Path maintenance helps to ensure reliable data transmission from the source node to the destination which is an important advantage of multipath routing protocols. Since the focus of this paper is on energy consumption reduction, we based our classification of the studied multipath routing protocols on the path discovery and path selection/load distribution steps as shown in Table 4. The importance of the path discovery and path selection/traffic distribution phases cannot be overemphasised in designing an energy-efficient and energy-balanced multipath routing protocol. During the path discovery phase, the set of relay nodes that will participate in constructing the multiple paths to the BS is selected. Researchers select the set of intermediate nodes based on different parameters. Some literature selects the participating relay nodes based on their residual energy (RE). This approach tends to prolong the lifetime of the SNs with low battery life. Nevertheless, this approach does not necessarily conserve the energy in the network during a particular data transmission round. This is because the participating nodes with a good energy level might be at large distances from each other. Thus, the SNs will consume more energy in relaying the sensed information to the BS. As such, some authors select the participating SNs based on other parameters such as hop count (HC), hop-distance, received signal strength/transmission power (RSS/TP), etc. All these mentioned design decision variables have their pros and cons when used in selecting the relaying nodes that will form multiple paths to the BS. For instance, using the distance between nodes as the yardstick in selecting the relaying nodes tends to reduce the transmission power; consequently, it minimise the energy consumption in conveying the sensed information. A drawback with this approach is that some of the participating nodes might be low on battery power and they will completely deplete their battery power when used consistently. Similarly, the HC will suffer the same fate as using the shortest distance approach when it is assumed as the design decision variable. In this regards, as shown in Table 4, most of the authors find a balance in using these decision variables. The authors select the set of intermediate nodes based on some mathematical formulations derived using a combination of some of these decision variables. Therefore, we grouped these multipath routing protocols based on the decision variables used in the path discovery phase as shown in Table 4. The multipath routing protocols that do not use any of these mentioned design decision variables in Table 4 are grouped under \"Others\".