Turbo-DC-FSK: Joint Turbo Coding and FSK-Based Modulation for Visible Light Communications

In this article, we propose and analyze a joint Turbo coding and DC-FSK modulation scheme (Turbo-DC-FSK) dedicated to visible light communications (VLC). This method is an adaptation to satisfy the VLC requirements of the Turbo-FSK technique initially developed for the long range low power Radio Frequency context in CEA-LETI (during the PhD of Yoann Roth, in collaboration with Gipsa-lab). It requires a change in the modulation alphabet generation to get unipolar real baseband signal instead of a complex bipolar one. We propose, in this paper, to deal with real Discrete Cosine Transform (DCT) instead of complex Discrete Fourier Transform (DFT) to generate the Frequency Shift Keying (FSK) modulation alphabet. We, then, add a constant component (DC) to make the signal unipolar and positive. This scheme involves a FSK-based modulation at the transmitter side, i.e. DC-FSK, and a Turbo-decoder scheme at the receiver side, i.e. Bahl, Cocke, Jelinek and Raviv (BCJR) algorithm. Simulation results confirm that Turbo-DC-FSK can achieve around 4 dB energy gain over regular VLC state-of-the-art DC-FSK modulation at a BER = 10 ^-4 ans at same spectral efficiency. Using λ parallel branches, a desired balance between energy efficiency and spectral efficiency is achieved.