Visible Light Communication (VLC) is emerging as a potential broadband transmission technology that may offer an unlimited bandwidth spectrum for high-quality wireless services. That’s critical as demand for mobile wireless services continues to grow and deployment of the Internet of Things (IoT) technologies magnifies.
The Center for Lighting Enabled Systems & Applications (LESA) at Rensselaer Polytechnic Institute says it has developed the world’s first high-speed visible-light transmission link with a fully integrated microchip receiver. VLC technology uses LED light instead of RF signals for high-speed wireless communications.
Sometimes called “LiFi” for “light fidelity,” the technology shares the same delivery mechanism as WiFi except that data is wirelessly transmitted using electromagnetic waves in the visible instead of the invisible RF electromagnetic range. LEDs transmit data through modulation that is so fast it’s imperceptible to the human eye and does not interfere with the quality of illumination, according to Troy, NY-based LESA.
Challenges remain to the commercialization of LiFi, such as continuous call connectivity during a handover from one device to another — enabling users to continue a call as they move between cell towers. Mona Hella, associate professor in the Department of Electrical, Computer, and Systems Engineering in the School of Engineering at Rensselaer, leads a LESA team that’s investigating new types of light sensors and signal processing circuits that could make VLC linking capability a reality. Her team is creating arrays of photodetectors that can serve as multichannel receivers and light sensors to allow the tracking of light, from one LED fixture to the next.
They’re also working to increase the bandwidth of the standard silicon-based photodiode to receive the high-speed data streams wirelessly from solid-state light sources. “Conventional photodiodes are photodetectors that convert light into current,” said Hella. “They are inexpensive to manufacture and are used in a multitude of applications in everything from cameras, smoke detectors, and CAT scanners, to barcode scanners and some airport security inspection equipment.”
Photodiodes integrated into optical receivers capture the light directly aimed at a subject needed for electric current generation. But they also capture unwanted light. Hella’s team is tackling enlarging the photodiode surface area to capture more incident light, without collecting unwanted light nor affecting the capacitance of the photodetector that limits the speed of the communication channel.
Hella says LiFi and other emerging VLC technologies are important elements in making smart lighting an inherent part of the IoT wireless infrastructure. By using LiFi to help bear the data load, higher bandwidth wireless communications are maintained as more IoT objects compete for RF bandwidth, according to LESA.
November 8, 2016
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