# Classification between Failed Nodes and Left Nodes in Mobile Asset Tracking Systems +
## 5 Performance Evaluation
### Simulation  
#### 5.1.1 Environment  
Two simulated networks are constructed for the simulations: one is for a grid model, and the other is for a real deployment. The simulated network for a real deployment is equal to that of the medical asset tracking system in Figure 3. A summary of the environment is shown in Table 1. Each mobile node wakes during every report interval, broadcasts a heartbeat message, collects responses from its neighbors and generates the neighbor data. In this simulation, 10 mobile nodes leave the monitoring area through a door, and 11 mobile nodes fail in the area. Although the communication range of actual nodes is 30 m in the free space, it is estimated to be reduced to about 12 m in the emergency room by the indoor path loss model defined by the International Telecommunication Union (ITU) [27].  
The performance of the proposed method is compared in terms of the report interval, moving speed, missing neighbor rate and elevator waiting time. The report interval indicates the period of time during which a mobile node collects and sends its neighbor data to the sink node. In this simulation, the moving speed of a mobile node is assumed to be less than or equal to 1.1 m/s because the node attached to a mobile medical asset in an emergency room moves slowly with a patient. It is slower than the range of normal walking speeds, 1.2\(\sim\)1.4 m/s, of a person; however, it is faster than the walking speeds, 0.6 m/s, of hospitalized patients [28]. The missing neighbor rate is affected by data collisions. If the number of collisions increases, the missing neighbor rate increases, and the number of neighbors of a mobile node decreases. The elevator waiting time is the time required to take an elevator when a mobile node goes to another department. Figures 5 and 6 show the results of this experiment. In the figures, the metric, \(SR(success\ rate)\), is defined as \(SR=(FF+LL)/(F+L)\), where \(FF\) and \(LL\) indicate the numbers of failed nodes and left nodes, which are determined by the proposed method, respectively; \(F\) indicates the number of failed nodes and is set to 11; and \(L\) indicates that of left nodes and is set to 10.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Area & 40 m \(\times\) 30 m \\ Number of anchor nodes (grid pattern) & 36 \\ Number of anchor nodes (real deployment) & 38 \\ Number of mobile nodes & 21 \\ Communication range & 12 m \\ Average neighbor count (grid pattern) & 7.95 \\ Average neighbor count (real deployment) & 10.04 \\ Minimum length of both Q and R & 2 \\ Maximum length of both Q and R & 5 \\ Mobility model & Random Waypoint \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of simulation environment.  
Figure 5: Detection results of both failed and left nodes in a grid model according to the parameter changes. (**a**) Report interval; (**b**) Moving speed; (**c**) Missing neighbor rate; (**d**) Elevator waiting time.  
Figure 6: Detection results of both failed and left nodes in a real deployment model according to the parameter changes. (**a**) Report interval; (**b**) Moving speed; (**c**) Missing neighbor rate; (**d**) Elevator waiting time.