Enhanced Coding Based Modulation for OFDM-based Visible Light Communication

OFDM-based Visible Light Communication (VLC) has been developed and adopted recently as an alternative technology for indoor optical communication due to the abundant bandwidth available in the visible light spectrum. OFDM offers several advantages for VLC systems, such as an efficient use of the spectrum and a low complexity method for inter-symbol interference mitigation. However, the small dynamic operational range of the VLC optical front-end in these systems poses a challenge to an OFDM-based system. These issues lead to clipping of signal picks which will cause power efficiency loss and nonlinear distortion. Most of the existing techniques utilize part of the frequency bandwidth for battling clipping noise which compromises modulation bandwidth and data. This study offers a modulation technique based on Reed Solomon code and OFDM subcarrier index modulation to battle the clipping distortion while enhancing the data rate in OFDM -VLC. Unlike the traditional index modulation techniques, the new technique attempts to convey extra information by nulling a subset of subcarriers in the OFDM frame. In this technique, referred to as RS-OFDM-IM, data symbols are embedded onto both signal and nonsignal subcarriers. Due to the reduced number of active subcarriers, the OFDM signal shows a less bursty envelope, which will cause low clipping distortion. Furthermore, with the aid of the RS code algebraic structure in decoding of codewords and its erasure extraction property, the nulling diversity is achieved. This allows for a better bit-error-rate in OFDM-VLC that is superior to those of the existing techniques. The reduced BER and additional information transmitted by the index modulation lead to a throughput improvement in OFDM-VLC with clipping constraint. The theoretical BER bound and the throughput of RS-OFDM-IM are discussed and are compared with those of the traditional coding-based OFDM techniques in VLC.