# 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
#### 5.1.1 Multi-Hop Clustering Technique
Also, because the source node does not have to convey the \(q\) bit message over a long distance to the destination, the multi-hop clustering technique technically solves the distance problem affiliated with WSN, thereby conserving the energy in the SNs and the total energy in the network. Despite the numerous advantages offered by the multi-hop clustering routing protocols [12; 13; 14; 15], designing an energy-efficient and energy-balanced multi-hop clustering routing protocol for WSNs can be a challenging problem. A reliable energy-balanced clustering routing protocol carries some important attributes. Besides the general problems in designing multi-hop routing protocols briefly explained in Section 4.2, the design of a reliable energy-balanced multi-hop clustering routing protocol has its own peculiar energy dissipation issues, for example, assuming we decide to use a multi-hop clustering routing protocol for the WSN of Figure 4. The first major load balancing issue is to select the set of nodes that will perform the CH duty. As simple as it may sound, the CH selection phase strongly indicates the network lifetime performance of the proposed clustering routing protocol. As depicted and explained in Figure 2, if the CH for a particular cluster is inactive or it has completely depleted its battery powered energy, all the SNs in that cluster or sub-network have been segregated from the whole network. The SNs in that cluster will not be able to access the BS for that particular data transmission round despite having sufficient battery energy left. Thus, it is desirable that a SN with sufficient battery energy is always selected as the CH in order to avoid network partitioning and to maintain the full functionality of the network. In this regard, developers of clustering routing protocols pay careful attention in selecting the CH. The CH nodes are selected based on some design decision metrics. Some authors select the CHs based on the residual energy of the SNs [55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82]. They choose the SNs with the highest residual energy as the CH nodes, mainly because the CH consumes more energy than the nCH nodes. This approach sounds reasonable but might not be as efficient. If the nodes selected to act as CH are at a distant position from the BS and the clustering routing algorithm assumes that the CH communicates directly with the BS, then the CH node will use up more energy in forwarding the aggregated information from its cluster members to the BS. In [83; 84; 85; 86; 87; 88], the authors select the CHs based on their proximity to the BS which is computed in the form of a distance metric. It is assumed that since the transmission distance \(d\) plays an important role in the energy dissipation model, the SNs with the shortest distances to the BS will consume less energy when forwarding packets to the BS. These selected SNs serving as CHs might be low on battery energy and if they are used continuously as CHs, they will completely deplete their energy, thereby resulting in untimely network partitioning. The authors in [89] selected the CHs based on their hop counts to the BS. As explained earlier, a small hop count from the source node to the BS helps to minimise the energy consumption in the network. However, this approach might suffer the same fate as using the shortest distance to the BS approach. Some authors select the CHs randomly based on some set threshold [90; 91; 92; 93]. They set a  
Figure 7: Typical example of a multi-hop clustering WSN. threshold such that any SN that does not meet this condition cannot be a CH. The majority of these threshold-based CH selection methods define this threshold based on the estimated average energy or residual energy in the network. Thus, they randomly choose the CH nodes from the SNs that meet the set conditions. Moreover, some literature [94] firstly divides the network into a virtual grid. Subsequently, they select the gateways or CHs based on their location in the grid.