# 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
Besides, we classified any other design decision variables not mentioned in Table 4 that are used in selecting the set of relay nodes, together with those mentioned in Table 4, under \"Others\". \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Multipath Routing**} & \multirow{2}{*}{**HM**} & \multirow{2}{*}{**HT**} & \multirow{2}{*}{**LA**} & \multicolumn{6}{c}{**Path**} & \multicolumn{6}{c}{**Path Selection/**} \\  & & & & & & **Discovery** & & & & **Load Distribution** & & **Optimization** \\  & & & & & & & & & & & & & & **Approach** \\ \hline
2000 & [143] & ✓ & & & ✓ & ✓ & & & & ✓ & ✓ & & & & H \\
2002 & [144] & & ✓ & & ✓ & ✓ & & & ✓ & & ✓ & & & & H \\
2004 & [145] & ✓ & & ✓ & ✓ & & & & ✓ & ✓ & & & & & H \\
2007 & [146] & ✓ & & & ✓ & ✓ & & & ✓ & ✓ & & & & & & H \\
2007 & [147] & ✓ & & ✓ & ✓ & ✓ & & & ✓ & & ✓ & & & & H \\
2007 & [148] & ✓ & & ✓ & ✓ & & & & ✓ & ✓ & & & & & H \\
2008 & [149] & ✓ & ✓ & ✓ & & & ✓ & & ✓ & & & & ✓ & H \\
2008 & [150] & ✓ & ✓ & ✓ & & ✓ & & ✓ & & & & & ✓ & H \\
2010 & [151] & ✓ & & & & & ✓ & ✓ & & ✓ & & & ✓ & H \\
2011 & [152] & ✓ & ✓ & ✓ & ✓ & & & ✓ & ✓ & & & ✓ & & H \\
2012 & [153] & ✓ & & & ✓ & ✓ & & & & & & ✓ & & & H \\
2012 & [154] & ✓ & & & ✓ & ✓ & & & & & ✓ & & & H \\
2014 & [155] & ✓ & & & ✓ & & & & ✓ & ✓ & & ✓ & & H \\
2014 & [156] & ✓ & & & ✓ & & & ✓ & ✓ & & ✓ & & ✓ & H \\
2015 & [157] & ✓ & & & ✓ & & & & ✓ & & ✓ & ✓ & & H \\
2015 & [158] & ✓ & ✓ & ✓ & & & & & ✓ & ✓ & ✓ & & H \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Decision variables for multipath load-balanced tree routing towards the BS. The path selection/load distribution phase is very important in designing an energy-efficient and energy-balanced multipath routing protocol. During this phase, the number of paths to distribute the traffic load is firstly determined. Subsequently, this phase aims to reduce the energy consumption in distributing the load from the source node towards the destination. Choosing an adequate number of paths is vital in the design of a reliable multipath routing protocol. A multipath routing protocol may use only the most cost efficient path for data transmission and the other paths for fault-tolerance [16; 159; 160; 161]. On the other hand, some multipath routing protocols use multiple paths synchronously to provide an evenly distributed traffic load or a reliable data transmission [162; 163; 164; 165]. Thus, the number of chosen paths is important in order to improve the performance of the attributes of multipath routing protocols. Once the given number of paths has been selected, the multipath routing protocol finds a way to evenly balance the network load over the chosen paths. In Table 4, we classified the studied multipath routing protocols based on the parameters that the authors employ in distributing the network load over the selected paths. As shown in the table, authors of the studied multipath routing protocols consider parameters such as RE, HC, total transmitted energy (TE), transmission distance, and data transmission rate in distributing the network over the chosen paths. These parameters must be carefully selected because they all offer different advantages and disadvantages. For instance, using the RE as the decision variable in selecting the paths will prolong the network lifetime for a reasonable duration while also ensuring a reliable data transmission. This is because more load is distributed to the paths where the participating SNs have a good energy level. As such, it is guaranteed that the sensed information will reach its destination since all the nodes along that path have sufficient energy to receive and transmit the sensed information towards the destination. A common disadvantage associated with this approach is the transmission distance problem. This high RE path might require a large distance to eventually convey the sensed information to the BS. As explained in Section 4.1, the larger the distance, the more energy consumed in conveying the \(q\) bit message.