Improved Dimming Scheme based on Non-DC Free RLL Codes for VLC

The dimming control is crucial for visible light communication (VLC) channels to maintain data transmission at different levels of lighting brightness. However, ensuring the dimming control while keeping a flicker-free channel remains a challenging task in VLC. Conventional techniques use the interleaving of compensation symbols (CS) applied on balanced codewords, usually obtained via run-length limited (RLL) codes. However, CS increases the redundancy used and are just thrown away during the decoding. Moreover, the interleaving step may increase the latency of the system. In this letter, new families of non-DC free RLL codes with variable weights are proposed. The dimming control can therefore be achieved without CS. Simulations stipulate that the proposed 4B7B code in FEC-coded channels achieve dimming ratios of 29% and 71% while improving on redundancy and error correction performance. For a 29% and 71% dimming ratios, at a BER of 10−4, gains in dB of 0.8 and 0.6 versus 3 and 2.6 are reported between the coded proposed RLL against the coded 1B2B and 4B6B with CS respectively.