# Integration of Directional Antennas in an RSS Fingerprinting-Based Indoor Localization System
## 5 Experimental Tests
### Discussion  
Comparing the overall performance obtained for every configuration, it is clearly observed that the planning of the SRs is relevant, since different configurations of SRs may result in very different performances of the system for the same scenario. It is revealed that the more SRs, in general, the better the system performance achieved, according to the conclusions of [16; 29; 30]. However, it has been observed that this tendency is not always accomplished. Observing several configurations with the same or even a greater number of antennas, independently of the antenna type, it is shown that the same configurations with different SRs can obtain quite dissimilar performances, even degrading it if no proper antennas are included for the tag estimation. Regarding this phenomena, in Table 1, some of the configurations can be compared, and it can be conclude that adding more antennas is not always a feasible solution to enhance \(P_{S}\). This is clearly appreciated comparing Configuration #1_vs._#2, with three OAs each, for which different performances (44% and 52%, respectively) with the same number of OAs were obtained. Furthermore, this can be observed if we compare Configuration  
\begin{table}
\begin{tabular}{l l c c c c c c} \hline \hline \# & **Antennas ID** & \(P_{S1}\) **(\%)** & \(P_{S2}\) **(\%)** & \(P_{S3}\) **(\%)** & \(P_{S4}\) **(\%)** & \(P_{S5}\) **(\%)** & \(P_{S}\) **(\%)** \\ \hline
**1** & 3 OA = [  
#2 _vs._ #3, where the performance keeps constant with 53%, despite that two more OAs being employed for the location estimation in Configuration #3. Furthermore, observing Configuration #6 against #7, with five and eight Das, respectively, the performance decreases from 75.7% to 63.4%. From these observations, it can be derived that the increase of the number of antennas does not always enhance the performance, but planning must be also taken into account properly, since adding antennas arbitrarily might even produce the opposite effect. Regarding the inclusion of directional antennas, the results also confirm our assumptions about the spatial filtering properties to enhance the fingerprints' robustness and quality. It can be observed how the integration of directional antennas may improve performance in some rooms. This is proven by observing the performances obtained for Rooms 1 and 2 (corresponding to two offices with a similar area of 24.5 m\({}^{2}\)) in Configurations #1, #9, #10 and #11. The employment of just OAs in Configuration #1 does not improve the performance inside those rooms, it being not possible to distinguish between them, and attaining a poorer performance inside these areas: \(P_{S1}\) = 17% and \(P_{S2}\) = 7.8%. However, the insertion of a directional antenna may improve performance, as can be noted comparing Configurations #9 and #10, where DA1 and DA2 are included respectively, increasing significantly the performance in R1 and R2 up to \(P_{S1}\) = 71.4% and \(P_{S2}\) = 74%, respectively, with respect to the first cited configuration with only three OAs. Finally, DA1 and DA2 are combined with three OAs in Configuration #11, and a significant improvement for rooms R1 and R2 is achieved (\(P_{S1}\) = 70.8% and \(P_{S2}\) = 74.4%) at the same time, increasing the overall performance up to 79.4%. This example clearly demonstrates how the insertion of Das, suitably oriented and positioned, may further improve the performance in certain rooms due to the spatial discrimination enhancement associated with directive antennas, confirming our initial hypothesis. It should be also noted that comparing previous Configuration #11 (with three OAs and two DAs) with #6 (with 12 DAs) and #12 (with five AOs and 12 DAs), a similar performance is obtained, corroborating that the inclusion of more antennas is not worthwhile in this experimental case.