FPGA-Based Pulse Compressor for Ultra Low Latency Visible Light Communications

Abstract

Visible Light Communication (VLC) represents an emerging technology where a short-range data connection is obtained by modulating the energy radiated by Light Emitting Diodes (LEDs) at frequencies from a few kHz up to hundreds of MHz. The bandwidth/distance performance of such links is a compromise related to the available Signal-to-Noise ratio (SNR). At present, VLC links with bandwidth beyond the Gb/s and distance limited to a few cm or distances up to 100 m but data rates of a few kb/s have been demonstrated. Chirp coding with pulse compression is a well-known technique capable of recovering useful data from low SNR signals, widely employed, for example, in radar. In spite of the possible advantages, its application in VLC has never been investigated. Unfortunately, the pulse compressor is quite calculation-intensive, and only devices like Field-Programmable-Gate-Arrays (FPGAs) can support a low-latency real-time implementation. In this paper we demonstrate a real-time VLC link based on chirp coding and pulse compression coded in FPGA. For example, a chirp with bandwidth and length of 1.7 MHz and 17.92 µs, respectively, is demonstrated to support a link at 1.56 Mb/s over 2.8 m distance and a latency below 40 µs. Moreover, the communication-distance increase achievable by chirps of increasing temporal length is demonstrated and compared to the theoretical background.