In recent years, light-emitting diodes (LEDs) have emerged as eco-friendly replacements for incandescent light bulbs and fluorescent lamps because of high electric-to-optic conversion efficiency, long lifetime, small size, etc. LEDs also have an interesting feature that the light output can be modulated with high-frequency signals. Using this phenomenon, LED can be used for optical wireless communications, which is usually called visible light communications (VLC) [1–7]. VLC is emerging as a promising alternative for future indoor wireless communication because of its unregulated huge bandwidth (~400 THz), low power consumption, no electromagnetic interference (EMI) generation, etc.
Currently, the performance of VLC cannot surpass the current WiFi technology. Therefore, performance improvement of VLC is one of the key issues for commercialization. To improve the performance of VLC, a lot of techniques have been proposed including electrical and optical domain approaches. Electrical domain approaches include equalization , quadrature amplitude modulation (QAM) , and orthogonal frequency division multiplexing (OFDM) . Optical domain approaches include blue filtering , multiple-input multiple-output (MIMO) , wavelength-division multiplexing (WDM) [12, 13], and polarization division multiplexing (PDM) .
Recently, one of the optical domain approaches called “optical beamforming” technique has been proposed to enhance the performance of VLC. Optical beamforming is a technique to focus LED light on a desired target so that it can enhance the signal-to-noise ratio (SNR) of the received VLC signal [15, 16]. Since it does not depend on electrical signal formats, it can be widely used in various VLC schemes.
However, the previous demonstration of the VLC using optical beamforming could communicate with only a single target. In the real-life applications, multiple user devices should be accommodated. Therefore, in this paper, we propose and demonstrate a VLC technology using time-division multiple access (TDMA) optical beamforming to accommodate multiple user devices, which focuses LED light on each different target device in each different time slot.