# Routing Topologies of Wireless Sensor Networks for Health Monitoring of a Cultural Heritage Site
## 4 Performance Evaluation  
As previously mentioned, two parameters were selected to evaluate the performance of the routing topologies of WSNs, the percentage of received messages and the lifetime of the network. To analyze in more detail which topology gave the best performance, other communication parameters were measured, such as the number of hops required for every message to reach the base station, the parent identifier for each message, and the Received Signal Strength indicator (RSSI) values for each more.  
To compute the number of lost messages, messages were labeled with consecutive identification numbers and the missing numbers were spotted and summed. Representing this number of lost messages as a function of time, the behavior of the WSN can be analyzed and malfunctions can be detected.  
Energy efficiency and optimal performance are essential for WSNs that operate in remote environments with difficult access. Energy efficiency can be improved with an appropriate choice of the WSN topology and communication protocols, with the energy required for communication scaling with distance (d) in a d2 to d4 relation. Therefore, the lifetime of the WSN has been studied as an indicator of energy efficiency. Some computer simulations have been performed to study the energy efficiency using different topologies [27], and different assumptions about the radio parameters in transmit and receive modes also change the relative advantages of different topology and routing protocols.  
The performance of the WSN was also monitored using additional parameters, related to the routing of messages within the WSN, these parameters were the number of hops, the parent identifier, and the RSSI values.  
The number of hops is the number of times a packet travels from the source through the intermediate nodes to reach the base station. A data point with one hop indicates that the message was received directly by the base station, two hops means that there was one intermediate mode, and so on.  
Figure 1: WSN deployment on an upper floor of the CAEND institute.  
Figure 2: WSN deployment in the church of Talamanca de Jarama.  
The parent identifier is the identifier of the first note that receives the message. If the base station has a direct connection to the more sending the message, then the base station is identified as the parent.  
The RSSI values are measured for each note in every position and these values can be related with the parent identifier of each note.  
Henceforth, we use the expression \"crowd intensity\" to mean the number of people walking in the vicinity of the WSN, leading to signal interference. Crowd intensity was higher during working days from Monday to Friday, and lower during weekends and holiday periods. Three different experiments were carried out to evaluate the selected routing topologies: Experiments 1 and 2 were performed at the CAEND institute with high and low crowd intensity, respectively, and with no direct line of sight between notes. To check the robustness of the results obtained, the notes were exchanged but keeping the same general spatial configuration. Experiment 3 was performed at the church deployment with occasional high crowd intensities during masses and with direct line of sight between notes.