Tokyo Polytechnic University develops visible light data link that works in direct sunlight
A research team at Tokyo Polytechnic University (TPU) developed a visible light communication (VLC) system that uses light-emitting diode (LED) lamps to transmit data reliably in outdoor conditions, including direct sunlight. The system achieved data transmission speeds of up to 3.48 megabits per second (Mbit/s) over distances of about 3 meters while exposed to strong ambient light reported at more than 90,000 lux.
VLC is designed to carry data through visible light rather than conventional radio frequencies, which can reduce reliance on crowded radio spectrum and avoid interference in settings where wireless networks face congestion or restrictions. The TPU system targets stable transmission in environments where background light and waveform distortion can disrupt VLC performance, particularly in outdoor use cases.
The system’s design centers on a line-coding approach called 8B13B, implemented as a serializer/deserializer (SerDes) on a field-programmable gate array (FPGA). Data are generated by a Raspberry Pi and transferred to the FPGA using a serial peripheral interface (SPI), then modulated onto LED light pulses for transmission. On the receiver side, the setup uses multiple photodiodes and a narrow-band optical filter to suppress background light and maintain signal detection outdoors.
The coding method relies primarily on the rising edges of optical pulses, improving resilience to pulse-width variations that can occur due to LED response characteristics. The return-to-zero format and balanced bit structure were described as supporting synchronization and reducing visible flicker during transmission.
Testing was carried out in an outdoor environment under sunlight with the transmitter and receiver separated by roughly 3 meters. The reported performance included stable reception under strong ambient light and a maximum data rate of 3.48 Mbit/s, positioning the system for short-range data links using widely available components rather than specialized hardware.
The work highlights applications in intelligent transportation systems (ITS), where traffic lights, street lamps, and other city lighting infrastructure can act as communication points for vehicles. The same approach can support low-cost optical data links for transport, monitoring, and safety functions, including scenarios tied to driver assistance and automated driving environments.
