Undersampled Pulse Width Modulation for Optical Camera Communications

Abstract : An undersampled pulse width modulation (UPWM) scheme is proposed to enable users to establish a non-flickering optical camera communications (OCC) link. With UPWM, only a digital light emitting diode (LED) driver is needed to send signals using a higher order modulation. Similar to other undersample-based modulation schemes for OCC, a dedicated preamble is required to assist the receiver to indicate the phase error introduced during the undersampling process, and to compensate for nonlinear distortion caused by the in-built gamma correction function of the camera. To test the performance of the UPWM-based OCC system, an experimental test-bed is developed. The experimental results show that the proposed system is able to achieve a data rate of 150 bps (spectrum efficiency of 5 bits/symbol) at a bit error rate of 6.76×10-4 , which is well below the forward error correction limit of 3.8×10 −3 , over a link span of 1 m using a Huawei Nexus 6P smartphone with a frame rate of 30 fps.