Improved Error Correction for Visible Light Communications

The number of mobile device subscribers worldwide grows at an exponential rate every year. This generates a congestion in the radio frequency (RF) bandwidth that may create unreliable communication. Therefore alternative means of communications should be investigated to sustain the RF channel. Visible light communication (VLC) which is a subset of optical wireless communication (OWC) could be a potential complement to RF channels. VLC is defined as a short-range optical wireless communication through lightemitting diode (LED) source. This technology could decongest the RF channel in the sense that VLC could cover indoor wireless communication where short distance transmissions are widely used while RF channels apply mainly for outdoor communication. There are many advantages about the VLC channel including a low cost of deployment, higher security, lower interference, bigger and unregulated bandwidth compared to RF systems. However, the VLC field presents several challenges such as light beam flickering and dimming. In other words, how to achieve reliable communication that supports different light intensities while avoiding light blinking perceptible to human eyes? This thesis aims to bring some elements to address those challenges. In VLC channels, the flickering mitigation is most often imposed by the use of DC-free run-length limited (RLL) codes such 1B2B, 4B6B and 8B10B codes; due to their low error correction performance, a forward error correction (FEC) code is concatenated with RLL codes to improve the channel reliability. In this thesis, we present a new class of 4B6B codes, the most efficient and reliable in terms of error correction performance. This code was obtained from a permutation of the conventional 4B6B code based on some distance constraints. Furthermore, a flicker-free FEC coding using Knuth’s balancing algorithm is implemented; this is a non-RLL technique which achieves flicker-free communication using the famous Knuth’s algorithm introduced by Donald Knuth in 1986. Finally, we provide an efficient dimming scheme based on non-DC free codes which does not make use of puncturing, interleaving, compensation symbols (CS) insertion as some state-of-the-art (SOA) methods, therefore reduces the decoding complexity while improving the spectral efficiency.