Experiments in Non-Line-of-Sight Li-Fi Channels

This paper presents a systematic experimental study of non-line-of-sight (NLOS) communication channels for a networked mobile optical communication system denoted as Li-Fi. The experimental setup uses high-power light-emitting diodes (LEDs) with wide beam at the transmitter (Tx) and large-area photodiodes (PDs) with wide field-of-view (FOV) at the receiver (Rx). A continuous-wave frequency-sweep based on a vector network analyzer (VNA) yields amplitude and phase responses of the Li-Fi channel at modulation frequencies of up to 200 MHz. Our experiments indicate that IR LEDs compared to white LEDs yield a gain of roughly 10 dBel and a significantly higher bandwidth. Moreover, NLOS signals are found between 25-37 dBel below LOS signals at the same Tx-Rx distance. Finally, NLOS signals have low-pass characteristics in general with a reduced cut-off frequency. Implications of these findings on the design of a mobile Li-Fi system are highlighted.