An Enhanced Adaptive Scheme With Pairwise Coding for OFDM-VLC System

For a visible light communication (VLC) system, different modulation formats and coding schemes are considered as the effective way to improve system performance under the limited bandwidth of light emitting diode. In this letter, we propose and experimentally demonstrate an enhanced adaptive scheme with pairwise coding (PWC) for an orthogonal frequency-division multiplexing (OFDM)-VLC system. Due to its no coding overhead and low complexity, it can be used to enhance the performance of the OFDM-VLC system. Through pairing the good and bad subcarriers, the signal-to-noise ratio (SNR) imbalance of this pair subcarrier is mitigated. Hence, it can lower the required SNR for a certain bit error ratio (BER). In the enhanced adaptive scheme with PWC, the lowfrequency subcarriers (SCs) are modulated by 16 quadrature amplitude modulation (16QAM), while the high-frequency SCs are modulated by 4QAM, and in the midst of them, 32QAM is used. The experimental results show that, it can achieve 1.1 dB Q(2) factor improvement compared with the conventional adaptive scheme and the BER can be up to 1.66x10(-5) using the proposed adaptive scheme with PWC.