# Testbed for Experimental Characterization of Indoor Visible Light Communication Channels
## 5 Experimental Results
Figure 14: Experimental results with mockup when just one lamp is used to transmit data: (**a**) Measured throughput (\(R_{\text{max}}=31.1\) Mbps, \(R_{\text{mean}}=17.3\) Mbps, \(R_{\text{min}}=0.9\) Mbps for locations where communication was possible). (**b**) Measured mean SNR (\(\overline{\text{SNR}}_{\text{max}}=17.3\) dB, \(\overline{\text{SNR}}_{\text{mean}}=13.5\) dB, \(\overline{\text{SNR}}_{\text{min}}=-0.9\) dB for locations where communication was possible). When the four lamps are used to transmit the same information, the receiver can move freely throughout the room without experiencing a significant deterioration of the data rate as seen in the results presented in Figure 15. We can observe higher SNR values than those achieved for the one-lamp transmission (Figure 14) and thus the obtained data rates are greater too. The adaptive OFDM system was always able to work below the target BER of \(3.8\times 10^{-3}\). It is also noticeable how the measured illuminance throughout the mockup floor is above the recommendation for workplaces of at least 400 \(\mathrm{lx}\). More interestingly, these experimental results agree with the theoretical behavior predicted by simulations as depicted in Figures 9 and 11. Figure 16 compares the system performance for vertical pointing upward of the optical receiver and an orientation defined by its relative position with respect to all its serving lamps (in this case, the four lamps) calculated with Equation (14) when mockup walls are also added. Firstly, the inclusion of walls yields a significant increase in the obtained throughput and the measured mean SNR as compared with the results without walls presented in Figure 15, even at the center of the room, which demonstrates that the influence of light reflection cannot be ignored as it is usual in many studies where just LOS component is considered. We can see mean data rate improvements of about 5% at the central area of the room and of more than 10% at edge zones (outer rectangle of the matrix of receiver locations) while working below the target BER of \(3.8\times 10^{-3}\). In addition, an appropriate orientation of the optical receiver leads to an extra throughput enhancement of about 1% in average at edges zones but practically identical behavior at the central area of the room with a slightly more uniform distribution throughout the receiver plane. However, as it was also observed in simulation results, vertical orientation of the receiver still maintains a suitable throughput uniformity thanks to the contribution of reflected light, while being a simple solution because the receiver only requires a gyroscope (sensor usually incorporated in hand-held devices like smartphones) to correct its vertical orientation as compared with also requiring according to Equation (14) precise relative positioning information of all its serving lamps to be provided by a centralized system. Moreover, inaccuracies of this positioning information could lead to a worse performance than that obtained with the simpler solution of applying vertical orientation. In addition, there exist other practical impairments such as power intensity deviations among lamps that can affect more appreciably the overall system behavior. To summarize, Figure 17 illustrates the throughput maps for the different configurations evaluated with the experimental testbed: vertical receiver orientation for one-lamp transmission, four-lamp transmission with and without walls, and four-lamp transmission with walls and receiver orientation given by Equation (14). It is clear that perfect map symmetry is not observed for the measured data rates which is due to practical differences among distinct lamps. We can also see for Figure 17c,d that at locations close to the windows (along x-axis, \(y=0\)), the data rate experiences a slight decrease with respect to other equivalent positions where there are no windows, but not in such an evident way as it was observed in simulations.