# 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
Some authors ignore the energy level of the SNs while distributing the load over the selected paths. They distribute the load based on the assigned rates on each path. In this case, they distribute more load to the paths with a high data transmission rate. This approach does not guarantee a load-balanced WSN or a reliable data transmission because the participating nodes might be low on battery energy and will deplete their battery energy completely during transmission. However, the approach avoids delay in data transmission which is very useful during real-time data transmission. Moreover, in order to reduce the transmission distance, thereby minimising the energy consumption, some literature uses decision variables such as the HC and the hop-distance to distribute the load traffic over the selected paths as shown in Table 4. Although the HC or hop-distance approach tends to reduce the energy consumption, even in real-time, both approaches suffer if the participating SNs have low residual energy. The authors in [143; 145] consider the total transmitted energy by each path as part of the decision variables before distributing the network load to these selected paths. The authors firstly measure the energy consumed by each path to convey the sensed information to the BS based on the distances between the participating nodes in that path. Subsequently, they distribute more load to the paths that will consume less energy in conveying the message to the BS. This approach will prolong the network lifetime if used with other parameters such as the RE as in the case of [143; 145]. For example, let us assume that this approach is used only in distributing the load over the selected paths. Accordingly, more load is distributed to the path that is measured to consume less energy in conveying the sensed information. If the participating nodes along that path are low on battery energy, they will deplete their energy completely during data transmission. As a result, the network functionality has been hampered. Therefore, as shown in Table 4--regarding the studied multipath routing protocols--most of the authors find a balance in selecting these decision variables while distributing the load over the selected paths. Furthermore, we grouped the multipath routing protocols that do not use any of these mentioned design decision variables in Table 4 under \"Others\" while any other design decision variables not mentioned in Table 4 that are used in distributing the load over the selected paths, together with those mentioned in Table 4, are classified under \"Others\". Additionally, in Table 4, we classified the studied multipath routing protocols based on the assumed network infrastructure as homogeneous and/or heterogeneous WSNs. Moreover, some of the studied routing protocols assume that the SNs are aware of their locations in selecting the multipath. Although, as explained earlier in Section 5.1.1, assuming that the SNs are aware of their locations may not be practical in reality; we classified the studied multipath routing protocols that base their design on this assumption. Finally, we classified the studied multipath routing protocols based on the optimization solution types or algorithms as shown in Table 4.