Modulation Designs for Visible Light Communications With Signal-Dependent Noise

This paper proposes efficient modulation design methods for single-carrier and multicarrier visible light communication systems with signal-dependent shot noise (SDSN). Improved constellations are obtained through solving optimization problems aiming at minimizing the system symbol error rate, subject to lighting constraints. For single-carrier systems, maximum likelihood based detection, is applied. Constellation and threshold values are optimized jointly. The proposed method outperforms both the uniform signaling and the square-root signaling. It is also observed that the uniform signaling outperforms the square-root signaling through the medium-to-high signal to noise region, while the latter performs better in lower SNR region. For multicarrier systems, we formulate a new channel model with the SDSN taken into account. By maximizing the minimum Euclidean distance between the symbols, improved constellations are designed under different lighting constraints. Furthermore, the multicarrier part of design embraces the DC-informative design framework, and thus achieve high power efficiency. The performance gain of our DC-informative optical OFDM (DCIO-OFDM) over OFDM-QPSK ranges from 5 to 30 dB even in moderate dimensional signal space.