## 3 The LOBIN Prototype: A Practical Study Case
### System Validation and Tests
#### 3.2.3 WCIS Tests  
The main goal of the WCI Subsystem tests was to determine the topology that suits better the target scenario. The first test deployment was composed of a network of DPs and a Gateway. In order to \begin{table}
\begin{tabular}{|c|c|c|c|} \hline
**Test** & **Ptx\_loc (s)** & **Tlisten (s)** & **Pbeacons (s)** \\ \hline
1 & 30 & 2 & 1 \\
2 & 9 & 2 & 1 \\
3 & 20 & 4 & 1 \\
4 & 15 & 2 & 0.5 \\
5 & 9 & 2 & 0.5 \\ \hline \end{tabular}
\end{table} 
Table 40: Location Subsystem Tested Configurations. cover approximately 300 m\({}^{2}\), five DPs and one Gateway were deployed, as Figure 10(A) shows. The main requirement the chosen topology has to meet is that the system supports at least five users ensuring that the percentage of lost packets is not more than 2% of those sent. It is worthwhile to remark upon the fact that these tests were run in a lab where intensive IEEE 802.11 tests were carried out in parallel. Thus, as it has been pointed out in Section 3.1.3, IEEE 802.15.4 channel 25 was selected in order to alleviate possible interference issues [73]. In addition, the WCIS was deployed in the roof of the lab, which is built of metal structures and the lab itself is plenty of metal structures, which may affect the propagation of the electromagnetic signal. First, a scenario composed by a network of DPs and a Gateway was tested. Obtained results show that this topology does not support high rate applications. Figure 10(B) shows that the percentage of lost packets increases non-linearly with the number of patients and greatly exceeds the maximum loss percentage allowed. This is due to the fact that the traffic handled by the network does not grow linearly with the number of patients, but higher, since it not only increases the traffic added by the sources, but also the traffic forwarded by the DPs. Similar issues were also reported in [25].Therefore, this configuration is suitable for applications that present low traffic load, but require high coverage (e.g., ordinary temperature checking on-demand or location fixing), but it does not work for high rate applications (e.g., real-time ECG monitoring) since it does not support more than 6 WDADs sending messages every 260 ms (\(\sim\)3.1 Kbps). The same network topology (_i.e._, DP network) duplicating the deployed infrastructure was also tested. In this scenario two different channels were used within the WCIS in order to split the traffic. Several pairs of IEEE 802.15.4 channels were tested and none of them yielded the expected improvement. Thus, it can be concluded that in such scenarios that present heavy traffic load, interference between IEEE 802.15.4 channels may occur with subsequent high data losses. Furthermore, this approach entails some drawbacks such as that LWTBs have to be programmed to work in one channel or another or that network infrastructure has to be duplicated, which means an increase on the deployment cost. Figure 10: **(A)** Distribution Point network test (**B**) Test results for DP network topology. Finally, the DP network was replaced by a network of Gateways (Figure 11). This topology was proved to provide the best results, presenting the lowest percentage of losses in scenarios with 8/10 WDADs and LWTBs. This percentage of losses was tested to be with a 95% confidence in the interval (0.2068%, 1.6585%) for 10 tests of about 15 minutes duration involving 10 users. Therefore, the obtained data were considered to fit a Gaussian distribution and the 95% confidence interval was computed using the formula below, \(\mu\) being the mean of the data, \(\sigma\) the standard deviation of the data, and n the length of the data (_i.e._, n = 100):  
\[(\mu-1.96\cdot\frac{\sigma}{\sqrt{n}},\mu+1.96\cdot\frac{\sigma}{\sqrt{n}}) \tag{3}\]  
This approach adds redundancy to the system and supports user mobility better, since sources may be within the coverage of different Gateways and so data may be forwarded to the Management Server several times, reducing the probability of packet losses even when a patient is moving.