## 3 Experimental Results  
The environment where the experimental tests were carried out is a room with a surface of 55 m\({}^{2}\) and a height of 3.4 m. The LED transmitters were located in the ceiling of the room, distributed in the four corners of a square with a side of 1.2 m, and the receiver was placed at different locations  
Figure 5: Circuit for the amplification and filtering of the received signal \(v_{sum}\). Figure 6: Flowchart of the acquisition process at the receiver. on the floor. Therefore, emitters and receiver were placed at a distance of more than 3.4 m. The effective testing area below the transmitters was a surface of \(3\times 3\) m\({}^{2}\). The synchronization beacon was placed on the floor, as shown in Figure 7.  
In [21], it was shown that the algorithm used in this proposal obtains the best and worst results when the receiver is rotated the angles \(\beta=5^{\circ}\) and \(\beta=45^{\circ}\) on the Z axis, respectively. Note that the emitters are aligned with the X and Y axes (see Figure 7). Furthermore, it was also shown that those angles that meet \(90^{\circ}\cdot n\pm\beta\), where \(n\) is an integer and \(\beta\) is the rotation angle of the receiver, obtain similar performance results and, therefore, the study of the rotation of the receptor can be simplified to a single octant. Considering the square formed by the projections of the emitters on the floor, the experimental measurements were obtained hereinafter in seven points (P1 to P7) on the floor distributed in one of the octants of this square (P1, P2 and P5 inside the square, P3, P4, P6 and P7 outside, as is shown after in Figure 11a). At each point, the measurements were taken with the receiver rotated at angles \(\beta=\{5^{\circ},15^{\circ},30^{\circ},45^{\circ}\}\). A real signal received after the acquisition of the three channels can be observed in Figure 8: channels \(\upsilon_{fsum}\), \(\upsilon_{fLR}\), \(\upsilon_{fBT}\). It shows a total of ten LS consecutive sequences and each LS sequence has 16,200 samples (corresponding 46.02 ms). Figure 8: Real acquired signal (ten successive LS sequences) for each channel: \(\upsilon_{fsum}\), \(\upsilon_{fLR}\), \(\upsilon_{fBT}\). Figure 7: Setup for real experimentation and validation of the proposed system. The correct operation of the variable gain is relevant, since the signals maximize the dynamic range of the acquisition modules, reaching the value of 4000. Note also that the signal \(v_{sum}\) is better adapted to the automatic gain amplification than the signals \(v_{LR}\) and \(v_{BT}\), since \(v_{sum}\) collects the sum of all the energy received by the QADA, whereas \(v_{LR}\) and \(v_{BT}\) represent the difference in energy received between left/right and upper/lower half-planes, respectively. Figures 9 and 10 show the correlations of the experimentally received signals corresponding to all the beacons \(i=\{1,2,3,4\}\) for each of the channels \(v_{sum}\), \(v_{LR}\), \(v_{BT}\), and for every LS sequence. The correct simultaneous emission of the different LS codes by each of the transmitting beacons, the acquisition and USB transmission, and the simultaneous detection of the three channels have been verified. The zoom in Figure 10 shows the displacement of 10 samples between the different transmissions. Remember that the LS sequences are broadcasted simultaneously by each LED \(i\), with a 10-sample offset with regard to the previous one. Finally, Figure 11 shows the estimated positions for each of the points analyzed with the rotation angles \(\beta=\{5^{\circ},15^{\circ},30^{\circ},45^{\circ}\}\). The projections of the transmitters on the ground are represented by  
Figure 10: Zoom around the central peaks of the correlations presented in Figure 9.  
Figure 9: Correlation functions of the three acquired signals \(v_{sum}\), \(v_{\
ot{LR}}\) and \(v_{\
ot{BT}}\), with each one of the transmitted codes.