Abstract
Due to the massive insertion of embedded cameras in a wide variety of devices and the generalized use of LED lamps, Optical Camera Communication (OCC) has been proposed as a practical solution for future Internet of Things (IoT) and smart cities applications. Influence of mobility, weather conditions, solar radiation interference, and external light sources over Visible Light Communication (VLC) schemes have been addressed in previous works. Some authors have studied the spatial intersymbol interference from close emitters within an OCC system; however, it has not been characterized or measured in function of the different transmitted wavelengths. In this work, this interference has been experimentally characterized and the Normalized Power Signal to Interference Ratio (NPSIR) for easily determining the interference in other implementations, independently of the selected system devices, has been also proposed. A set of experiments in a darkroom, working with RGB multi-LED transmitters and a general purpose camera, were performed in order to obtain the NPSIR values and to validate the deduced equations for 2D pixel representation of real distances. These parameters were used in the simulation of a wireless sensor network scenario in a small office, where the Bit Error Rate (BER) of the communication link was calculated. The experiments show that the interference of other close emitters in terms of the distance and the used wavelength can be easily determined with the NPSIR. Finally, the simulation validates the applicability of the deduced equations for scaling the initial results into real scenarios.
Highlights
Nowadays, there is a trend in replacing fluorescent and halogen lamps, both indoor and outdoor, by LED-based ones, which are energy efficient and offer extended life cycles and high switching speed.This change affects street, traffic and car lights, opening the opportunity of deploying new communication systems over the fundaments of Optical CameraCommunications (OCC) [1] for a wide range of applications, e.g., in smart cities or V2X networks
If the emitter is LED1, the horizontal interference came from LED2 and LED4 contributed to the vertical one
The line color represents the wavelength of the interference, except for the black line that shows the interference from the LED turned on in white
Summary
There is a trend in replacing fluorescent and halogen lamps, both indoor and outdoor, by LED-based ones, which are energy efficient and offer extended life cycles and high switching speed. The attenuation introduced by fog in Free-space optical (FSO) communications was studied in [8], showing that it can be predicted according to visibility scenarios without using heavy computer codes These channel modeling research works were based on photodiode-based receivers. For slow data rate applications, such as in wireless sensor networks (WSN) which require transferring minimum amounts of data (for example temperature, pressure, humidity, or presence flags), the use of preexisting cameras-based infrastructure is a possible solution. Working with RGB multi-LED transmitters, such as LED matrices, and commercial middle range cost cameras For this purpose, the Normalized Power Signal to Interference Ratio (NPSIR) is presented in order to measure the chromatic interference independently of the chosen camera or the optical power transmitted by the LEDs. Some functions for determining the 2D pixel representation of real separation distances are deduced and validated.
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