# A Survey of Using Swarm Intelligence Algorithms in IoT
## 3 Applications of Swarm Intelligence Algorithms in WSN
### WSN Routing Protocols Based on SI
#### 3.2.3 WSN Routing Protocols Based on ACO
Besides, considering large-scale WSNs, the inter-community retransmission and intra-community multi-path routing strategies are respectively used to improve the reliability and load balance of data transmission. The advantage of this strategy lies in the ability to organize and to run the network autonomously when the network is overloaded whilst the memory cost is very low. The CB-RACO method can achieve high data delivery rates in large-scale WSNs. Table 4 compares the routing algorithms. With respect to WSN routing protocol, the following factors need to be considered: first, because the energy of nodes is limited, the routing protocol design should be simple, efficient, and energy-saving and take into account the energy balance to extend the network life cycle. Second, the network can be extended to respond quickly to changes when nodes die, or new ones join. Third, convergence should be rapid. To sum up, from the literature, most routing algorithms in WSN are distributed, and only a few of them support QoS. Besides, the number of energy-aware protocols is relatively large because WSN requires energy saving. Finally, the PSO or ACO algorithms are popular for routing optimization in WSN applications and for multipath communication. The ACO is good at finding the optimal path. The design of WSN routing protocols has to not only take into account security, latency, packet loss rate, fault tolerance, and other issues but also to consider energy consumption, as do routing protocols in general networks. Factors to consider for WSN routing protocols and their solutions: energy saving (increase the number of clusters, prevent energy cavity made relay protection mechanisms to prevent low energy nodes, balance transmission distance, use mobile sinks, optimize multipath routing), average end-to-end delay, packet loss rate, fault tolerance (multipath routing), and safety. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Method**} & \multirow{2}{*}{**Year**} & **Key** & **Distributed (D/)** & **BestEffort** & **Single Path (S)/Multipath** & **Event-Driven** & **Fault** & **Energy** & **Loop** \\  & & **Technology** & **Centralized (C)** & **(B)/QoS (Q)** & **(M) Routing** & **(E)/Query-Based (Q)** & **Tolerant** & **Aware** & **Free** \\ \hline
[19] & 2018 & PSO & D & B & S & E & N & N & N \\
[20] & 2016 & PSO & D & B & S & Q & N & Y & N \\
[24] & 2019 & PSO & D & B & S & Q & N & Y & N \\
[30] & 2016 & PSO & D & B & S & QE & N & Y & N \\
[31] & 2017 & PSO & D & Q & M & E & Y & N & N \\
[25] & 2017 & ACO & D & B & S & E & Y & Y & N \\
[26] & 2016 & ACO & D & B & S & QE & N & Y & N \\
[27] & 2017 & EACO & D & B & M & E & Y & Y & N \\
[32] & 2017 & ACO & D & B & S & E & N & Y & N \\
[33] & 2019 & ACO & D & Q & S & E & Y & Y & N \\
[35] & 2017 & ACO & D & B & S/M & E & N & Y & N \\
[28] & 2017 & ABC & C & B & S & Q & N & N & N \\  & FCM & & & & & & & \\
[29] & 2017 & ABC & D & Q & S & E & N & Y & N \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Routing algorithms of WSN routing protocol based on SI.