Short-distance visible light communication with simple clock data recovery for audio applications

As light emitting diodes (LEDs) of fast response time are wide-spreading in a variety of applications such as displays, lighting, traffic signals, and automobiles, many researches on transferring the data with the visible lights of LEDs have been conducted. This paper describes such a visible light communication system that supports the audio applications at the short distance up to 80 cm and the data bandwidth of 32 kHz. Especially, a simple clock data recovery (CDR) is used to achieve the optimum sampling and compensate for the frequency offset between transmitter and receiver. The proposed CDR obtains three samples per symbol and then adjusts the sampling point properly with the pattern of three samples over the frequency offset range of ±1.5% without changing the operating frequency of a receiver side. In the prototype system, a transmitter is composed of audio encoder, field programmable gate array, LED driver, and LEDs and a receiver consists of photodiode, comparator, field programmable gate array, and audio decoder. At the distance of 50 cm and the data rate of 32 kbps, the measured bit error rates are 0.101 and less than 10−8 without and with CDR, respectively.