## 6 Conclusions  
In this work, the spatial intersymbol interference from close-emitters within an OCC communication link was experimentally characterized in function of the transmitted wavelength, while the Normalized Power Signal to Interference Ratio (NPSIR) was introduced for measuring the chromatic interference independently of the chosen devices. Equations for easily determining the 2D pixel representation of real separation distances were deduced and validated. The NPSIR of the pictures taken with the distance that assures perfect spatial separation of the sources represents minimum interference, as expected, in the majority of the cases greater than 40 dB. However, when the pictures have limited or critical spatial separation, the results depend greatly on the selected wavelength. For the transmissions in Blue (Figure 13) the minimum normalized interference came from close sources emitting in Red although this interference could affect the transmission. Figure 21: Normalized Power Signal to Interference Ratio (NPSIR) projection Simulation. Bite Error Rate in function of the separation between sensors. The sensors transmitted OOK-NRZ signals in Red (S1), Green (S2) and Blue (S3). Figure 20: Monte Carlo Simulation. Bite Error Rate in function of the separation between sensors. The sensors transmitted On-Off Keying (OOK)-NRZ. signals in Red (S1), Green (S2) and Blue (S3). In the case of the LED transmitting in Green (Figure 14), close LEDs emitting in Blue and Red have similar influence over the communication link; but for transmissions in Red (Figure 15), there is no real interference from close emitters using Blue channel, but the communication could be affected by a LED sending messages in Green. The specific case of a device transmitting with white light (see Figure 16) presents almost the same interference from the different wavelength (Red, Blue, and Green) due to the fact that white light is produced by turning on the three LEDs at the same time. In all cases, the most significant interference comes from possible close emitters transmitting in white or in the same channel of the target LED. Similar to channel allocation in RF systems, it is important to have close emitters in orthogonal channels: Red, Blue, Green. The simulated scenario demonstrates the applicability of Equations (1) and (2) as an accurate tool for easily projecting distances into pixels under specific circumstances and the efficiency of Equation (4) for determining the interference independently of the system characteristics. Equations (1) and (2) were validated during the performance of the optical interference experiment with a mean error of less than one pixel. The simulated scenario also shows that the deployment of this system is feasible. Using OOK-NRZ modulation there is no significant BER produced by close emitters when the sensors are separated more than 4.50 cm (zero for the Monte Carlo simulation and less than \(2.85\times 10^{-15}\) for the NPSIR one), and the maximum BER of \(1.3\times 10^{-3}\) from the Monte Carlo simulation (\(5.44\times 10^{-4}\) from the NPSIR simulation), obtained for 2.00 cm separation, predicts that the communication link will work properly under real conditions. The Monte Carlo simulation also demonstrated that the spatial intersymbol interference from close-emitters working in the same wavelength affects the system significantly. The use of the three channels (red, green and blue) reduce this interference, so future system designs should take advantage of the chromatic nature of the images and assign the different colors to the emitters in a similar way as WiFi allocates frequency bands. Further research in this area is needed. The flickering problem will be addressed in future works, where the influence of external sources, such as solar radiation or illumination LEDs, should be taken into account. The presence of turbulence, particles and the temperature variation should also be characterized for outdoor environments.