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 $N=\lfloor(M-1)/2\rfloor$ and $\lfloor z\rfloor$ 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, $N\ \log_{2}P$ 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.