## 2 Routing Protocols in Large-Scale WSNs
### Energy Consumption Mitigation Algorithms
Then a next hop is calculated by the equation as follows:  
\[M=\underset{j\in T_{i}}{max}\Bigg{(}\alpha\times\frac{E_{j}}{E_{max}}+\beta \times\frac{C_{max}}{C_{j}}\Bigg{)}\times\mu\times I_{j} \tag{3}\]  
wherein \(E_{j}\) denotes the residual energy node \(j\), \(C_{j}\) denotes the path loss, and \(I_{j}\) denotes the event intension and \(\alpha\), \(\beta\), \(\mu\) separately denote the force of the residual energy, path loss and stimulated intension for route selection. The above equation means that more residual energy, less path loss and more event intension imply higher probability that the node will become the next hop of node \(i\). Then, the mobile agent will move to the next hop for data collection. Due to the limited buffer space in the mobile agent, in this protocol data is fused on those in-between nodes that can not only sense, but also forward data in order to reduce space occupation. To deliver the sensed data to the final destination (here the base station) in the higher level of the network a virtual cluster is formed wherein the base station acts as the cluster head. As in the local cluster, a multi-hop communication is adopted. The current cluster head will select the node which is the closest to the base station in the neighboring nodes as its next hop. If the distance from all neighbor nodes to the base station is longer than that from the node itself, the node will communicate with the base station directly. In the simulation part in [32], it was shown that DGMA is more scalable than EDMGP, which was presented in [33]. When the number of the sensor nodes increases, the energy consumption in DGMA increases more slowly. Furthermore, the dynamic cluster formation feature further reduces the energy consumption. The use of a mobile agent reduces energy consumption, but extends the delay for the cluster head to collect all the sensed data from all the member nodes. The chain-like route delivery of data by the cluster head makes the node closest to the base station overloaded and destroys the reliability. _DMSTRP_. [PERSON] _et al._ proposed a routing protocol named Dynamic Minimal Spanning Tree Routing Protocol (DMSTRP) in [34]. When the network size becomes larger, this scheme outperforms LEACH and Base Station Controlled Dynamic Clustering Protocol (BCDCP [35]) in terms of network lifetime and delay by introducing the concept OF Minimal Spanning Tree (MST) instead of THE clubs which are used in BCDCP to connect nodes in clusters. The main idea of DMSTRP is to use MSTs to replace clubs in two layers of the network: intra-cluster and inter-cluster. Because clubs are less effective than a spanning tree in connecting the nodes if the network area is larger, DMSTRP is an elegant solution in larger network areas. LEACH chooses clubs as the basic topology of the network, as shown in Figure 5(a), and managing clubs does not need multi-hops and thus makes the routing path simple. One step further in BCDCP, the CHs are connected by a tree instead of a club and the BS functions as the manager of the whole network, so BCDCP is more energy-efficient than LEACH. DMSTRP improves BCDCP further by connecting nodes in clusters by MSTs. In each cluster, all the nodes including the CH are connected by a MST and then the CH acts as the leader to collect data from the nodes on the tree. On the higher level, all the CHs connected by another MST cooperate to route data towards the BS. The data fusion process is handled during the packet transmission along the tree route. In DMSTRP, the structure of a MST is also utilized to alleviate the collisions among the transmitting nodes. Through reasonably arranging the transmitting sequence for the nodes within an intra-cluster, multiple nodes can transmit messages simultaneously, therefore increasing the throughput. The transmitting scheme is as follows: if a transmitter of a branch does not need to receive any data, this branch can be used to transmit data.