Multi-LED optical OFDM modulation for visible light communication

The limited modulation bandwidth and nonlinearity of light-emitting diodes (LEDs) are the important factors that constrain the high-speed transmission of visible light communication (VLC). As a LED lamp includes multiple LED chips and the superposition characteristics of light is approximately linear, a multi-LED optical orthogonal frequency division multiplexing (OFDM) system is proposed. The multiple LED chips are used to transmit multiple asymmetrically clipped optical OFDM (ACO-OFDM) and unipolar OFDM (U-OFDM) signals in parallel, while the signals can be recovered at the receiver. When adopting the same M-ary quadrature amplitude modulation (M-QAM), its spectral efficiency is higher than the conventional ACO-OFDM system. The power of the multi-LED transmission system is split equally to each branch, and the amplitude range of the signal is smaller, thus it has better anti-nonlinearity performance. At last, its advantages are verified by the simulation comparisons with other optical OFDM systems.