Parallel Transmission Using $M$-Point DFT for Image-Sensor-Based Visible Light Communication

This paper proposes a parallel transmission (PT) system using M-point discrete Fourier transform (DFT) for image-sensor-based (IS-based) visible light communications (VLC). We make use of M-point inverse DFT (IDFT) to generate pulse width modulation (PWM) signals transmitted by M spatially aligned LEDs. The M PWM signals are pre-calculated to give N phase shifted carriers after M-point DFT, where N=⌊(M-1)/2⌋ and ⌊z⌋ stands for the maximum integer not exceeding z. Therefore, the IS receiver of a high-speed camera captures the LEDs to obtain the M inputs to the DFT from the luminance values of the captured LEDs. During a symbol interval equal to the exposure time of the high-speed camera, N log₂ P bits in total are simultaneously transmitted between the LEDs and IS-based receiver, when P-ary PSK is used for all the carriers. We experimentally demonstrate our PT system at the distance of nine meters between M PWM-modulated LEDs and a 2000-fps high-speed camera. Our experimental results validate that PSK symbols are demodulated without errors for smaller values of M and P, with controlling the aperture of the lens of the camera receiver.