Tokyo Polytechnic University scientists exploring low-cost, high-tech ‘communication with light‘ alternatives to Wi-Fi and Bluetooth have successfully demonstrated a high-speed visible light communication (VLC) system that uses rapid LED light pulses instead of radio waves to send digital data, without wires or radio signals.
Built using commercially available components, the light-based wireless communication system achieved a record-setting communication rate of 3.48 Mbit/s over distances of several meters in typical daylight conditions.
The research team behind the accomplishment suggests that their VLC system could enable specialized local data transmission alternatives where interference, external signal noise, or regulations make traditional radio-based systems impractical.
Potential futuristic applications for such technology may include intelligent transportation systems (ITS), in which traffic lights and streetlamps could be adapted to operate simultaneously as localized VLCs to enhance the safety of autonomous driving systems.
High Speed Communication with Light vs. Wi-FI and Bluetooth
Most wireless data transmission technologies, such as Wi-Fi and Bluetooth, use radio waves to communicate over the air. Some applications, like television remote controls, communicate using infrared light signals, although such applications are limited by range and data transmission rate.
More recently, engineers have explored high-speed visible-light communication as an alternative to radio waves and infrared signals. The most popular approach uses light generated by LEDs to send signals to a receiver a few feet away.
Although not yet commercially available, ‘communication with light’ systems using this method could offer several advantages in environments where traditional radio communication systems fail. These include areas with radio-wave congestion, external interference, or regulatory constraints limiting their use.
Still, these and other ‘communication with light’ systems suffer from data transmission limitations and can quickly degrade in the presence of other bright light sources. This sensitivity to ambient light and waveform distortion has limited their industrial and commercial applications,
Now, the Tokyo Polytechnic University team has revealed how a simple and affordable VLC system that overcomes several of these obstacles can be built using readily available, low-cost components.
Employing “Return to Zero” Logic and Light Suppression
The researchers started by employing a new 8B13B line coding scheme as the system’s core logic. According to a statement announcing the system’s successful demonstration, this coding scheme employs a “return to zero” format that balances the number of logical “1” and “0” bits. This approach allows the system to suppress the visible flicker inherent in LED-based systems, resulting in a more stable synchronization between the light source and receiver.
“By relying primarily on the rising edges of optical pulses, the system is robust against pulse-width variations caused by LED response characteristics, a phenomenon known as data-dependent pulse width shrinkage,” the study authors explained in their Electronics and Signal Processing paper.
Next, the team combined the new coding scheme with serializer/deserializer (SerDes) logic using Verilog HDL on a field-programmable gate array (FPGA). When the team connected this custom-built logic center to a Raspberry Pi with a standard serial peripheral interface (SPI), the VLC’s data communication circuit was complete.
To suppress background light, the researchers built a customized receiver containing multiple photodiodes and a narrow-band optical filter. The researchers said this design enabled reliable operation in outdoor environments “relevant to ITS applications.”
System Success in Direct Light Exceeding 90,000 Lux
To test their light-based communication system, the team placed the LED transmitter several meters from the receiver. All tests were conducted under relatively strong ambient light conditions to simulate the outdoor, daytime environments that have hindered previous light-based wireless communication systems.
“We evaluated the communication quality of the system in environments with ambient light interference and achieved stable communication over a distance of approximately 3 m between the light-emitting diode (LED) light source and receiver,” the researchers write.
As expected, the VLC maintained stable communications in simulated daylight conditions. In the most extreme test, these data rates were achieved in direct sunlight exceeding 90,000 lux.
“Although the overall communication speed relies on the data transfer frequency between the FPGA and Raspberry Pi, the bit rate was 3.48 Mbit/sec,” the study authors explained. They also highlighted the integrity of the received data, noting that the packet loss rate for packets consisting of 893 bits “was 10−4–10−5.”
Intelligent Transportation Systems and Autonomous Vehicles
To keep costs and complexity to a minimum, the team built their customized high-speed light-based communication system using commercially available components, including an FPGA, a Raspberry Pi, and all the electronic components for the LED driver and photodetector.
Along with the receiver and circuit diagrams, the study authors have released the FPGA SerDes source code as open source. The team said they hope that making their research, designs, and materials widely available will encourage other researchers and educators to teach and enhance the VLC concept, or to adapt it to other platforms.
When discussing potential applications, the researchers suggested that a VLC/traffic-light hybrid could transmit intersection or blind-spot video to vehicles, thereby increasing safety. They note that this type of integrated communication could be particularly advantageous in autonomous driving scenarios, where the car’s onboard AI can rapidly incorporate new information.
Although a light-based high-speed communication system offers potential ITS applications, the authors also noted that their design provides a “practical educational platform that integrates analog circuits, logic circuits, and software in a single communication system.”
The study “A study of SerDes logic for visible light communication using 8B13B code” was published in Electronics and Signal Processing.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.