Visible Light Communication Based on High-Power LED

In this research, a Visible light communication (VLC) system using a high power (30W) white single LED is evaluated. Initial experiments were performed on a 30 W warm LED, measuring the bandwidth (BW) and data rate. Previous research has shown that these can be implemented in VLC but at limited data rates of less than 10 Mbps due to the LED bandwidth of around 3MHz. An RC compensator circuit was used to increase the bandwidth above 10MHz and a cool LED was used to increase the bandwidth by up to three times. Three differently rated LEDs (20, 30, and 50W) were examined to study the rating power effect on the performance. Experimental systems have shown that this change affects bandwidth, with increasing power resulting in a reduction in bandwidth.

A further focus of the work was to study the effect of six different colour temperature LEDs on bandwidth and data rate. The results show that increasing the colour temperature from within the range of 3,000K to 35,000K leads to an increase in bandwidth from 10MHz to 84MHz and improves data transmission by reducing the bit error rate (BER) to 10-11. The drawback of increasing the colour temperature results in changing the lighting colour from white to blue, which can adversely affect the human eye.

The second objective of this research was to improve the functionality of the VLC system by choosing the appropriate modulation technique. Three types of pulse position modulation (PPM) technique (DiPPM, Duo PPM, and Offset PPM) were implemented based on VLC using high power LEDs. The study found all techniques have similar performance with a minimal difference in the data rate. However, the offset PPM was distinguished from other techniques by recording the minimum BER at a data speed of 20 Mbps. This is due to the working technique of the offset PPM which converts signal pulses from 3- to 4-bits, whereas, other techniques were based on the end of each pulse. Thus, the intersymbol interference (ISI) is reduced in offset PPM compared to other techniques. To verify the results, the 30W LED was compared to a 1W LED which had been used by previous researchers. The results confirm that the high-power LED has the same performance as the low-power LED in VLC applications. Theoretical simulations are also presented.