Development and Experimental Evaluation of a Visible Light Communication System with Ambient Light Cancellation

Light emitting diodes (LEDs) hold several attractive characteristics such as low power consumption, fast switching times, high durability and size reduction to find applications in modern digital communications. This paper presents the design, implementation and suppression of interference due to ambient light sources of a visible light communication system (VLC). The transmitter of the designed VLC system uses White LEDs to modulate visible light with digital data using On-Off keying (OOK) modulation. Low cost transistors were used in the transmitter to switch the LEDs. In the receiver the modulated visible light is captured using high speed photodiodes. Moreover, general-purpose operational amplifiers were used in the receiver to implement the amplifier and comparators in order to perform signal detection. At present, the implemented VLC system is capable of operating at 100 kHz. Moreover, the speed can be further increased by using high speed transistors and operational amplifiers. In order to test the implemented VLC system and collect data, a real time measurement campaign was also carried out. Initial results demonstrated that the ambient light variations in the environment have a significant impact on the performance of the VLC system. In order to mitigate these deleterious impairments, a hardware setup was developed to cancel out the constant component of the ambient light effect. Further, the effects of CFL sources and variations of sun light condition cannot be treated as constant and a signal processing technique was utilized for cancellation. Distance between the transmitter and receiver also affects the system performance. Various arrangements of the transmitter and receiver were tested to increase the maximum transmitter-receiver distance. The approach makes VLC systems more immune to the ambient light variations and in particular enables successful integration into state-of-the art high speed indoor communications. Keywords— Visible Light Communications, Ambient Light Cancellation, Communication System Performance