This work presents a visible light communication system for the parallel transmission of high quality audio and video signals using white and red light emitting diodes (LEDs). For video transmission, we adopted the pulse width modulation scheme (PWM) at a carrier frequency of 15 MHz, while the analogue audio signal uses the Sony / Philips Digital standard. We show that high-quality simultaneous simultaneous audio and video signal transmissions over a 50 cm link range are possible without the need for optimized optics. For audio transmission, only the span of the link is doubled to 100 cm.
During the last four decades, technical progress in the development of light emitting diodes (LEDs) has been impressive. State-of-the-art LEDs emitting in the visible spectrum are small, robust, reliable, bright and highly efficient. Today, it is anticipated that LED lighting will be used in thousands of applications. Since LED lighting inherits the advantages of standard LEDs, it offers numerous advantages, such as considerable power reduction, extreme durability, downsizing, a greater degree of freedom for the form of illumination and a high resistance to shock and vibration. In addition, LED-based lighting requires less maintenance costs due to its long service life, and the chip per unit price of the luminous flux is continuously decreasing. Due to these characteristics, LEDs have become very attractive, not only for lighting, but also for indoor and outdoor decoration and advertising.
In addition to lighting, LEDs have found applications in data communications due to their fast switching time. As an optical source for indoor short-range communications, the visible LEDs are cheap and reliable, offering high data rate capabilities. It has been shown that an optical wireless communication link using high brightness LEDs supports a modulation bandwidth of up to 20 Mb / s. The theoretical background for visible light communication (VLC) systems is similar to those found in infrared (IR) communications, except that VLCs use a much wider visible spectrum as described in. In addition, we have seen several high - speed VLCs based on practice reported in. Through the use of flashlight LEDs, we have also reported a simplex link and a duplex link that combines the two simplex links.
A white LED-based VLC link was demonstrated for a non-return-to-zero (NRZ) 100 Mb / s data format using a low cost equalizer. A VLC link operating at 513 Mb / s has been reported based on the combination of discrete multithon (DMT), quadrature amplitude modulation (QAM), bit load and power load, as well as symmetric clipping. The application of VLCs for local area networks that offer full 10 Mb / s Ethernet binary rates at a short distance has been reported in. Recently, the application of LEDs to real services, such as audio and video signal transmissions, where frequency modulation (FM) has been used with a carrier frequency of 100 kHz has been investigated using 64 LEDs for audio signals and one Transmission rate of 2 Mb / S is used for video broadcasting. Amplitude (AM) and FM modulation have been adopted for audio and video transmissions in CATV systems, and transmissions of video and audio signals based on pulse width modulation (PWM) have been reported. However, analog-based modulation schemes adopted primarily in CATV systems are not ideal for LED-based communications. This is because the light intensity of the LEDs does not have a linear characteristic over all the direct current injected, becoming nonlinear at higher current levels. This problem is further acquitted in a higher modulation index or in a multiplexed analogue based system as in modulation of sub-carrier intensity. In addition, systems based on amplitude modulation are more vulnerable to noise than digital systems.