QoS Analysis and Signal Characteristics for Short-Range Visible-Light Communications

Visible-light communications (VLCs) are energy-efficient communication means and a popular alternative to the radio-frequency technology. VLCs are referred to as free-space optical communication systems which can be built upon the existing lighting infrastructure. Due to the cost-effectiveness concern, light emitting diodes (LEDs) are adopted as the visible-light sources. In this paper, we demonstrate a VLC prototype using white LEDs and pulse position modulation (PPM), which is aimed for short-range communications. Based on the acquired VLC signal waveforms, characteristics related to electronic components, LEDs, and photo diodes (PDs) are studied thoroughly. The non-square shape of received pulses is modeled by new template functions involving rising and setting time intervals. A new PPM demodulator is devised thereupon. Meanwhile, the probability density function of noise is derived using the Edgeworth expansion. As all of the aforementioned aspects are taken into account, the VLC quality-of-service (QoS) in terms of package error rate and throughput is studied in this work. Experiments are taken to justify the theoretical QoS metric and evaluate our proposed new PPM demodulator.