Reducing FBI and MLI Using FSS Method for Adaptive Modulated VLC-OFDM System

In an adaptive modulation OFDM system, feedback information (FBI) is necessary to control the modulation level for each subcarrier. The FBI contains the estimated channel state information (CSI), as well as the power and noise levels for each subcarrier. In the transmitter side, the transmitted signal is modulated by using FBI and adaptively modulated packets are transmitted to the receiver side. In this case, the receiver is needed a modulation level information (MLI) to demodulate received packets. Since the MLI is generally transmitted as a data symbol, the throughput is degraded in the downlink, as a result of the MLI transmission. To reduce FBI and MLI, in this paper, we propose an adaptive modulation for VLC-OFDM using frequency symbol spreading (FSS).