Average transmit power reduction through power allocation for OFDM-based indoor wireless optical communications

This research investgates the physical layer aspect of power allocation in orthogonal frequency division multiplexing (OFDM) based indoor wireless optical communication (WOC) systems with intensity modulation and direct detection (IM/DD). The main objective is to reduce the average transmit optical power subject to a constraint on the bit error rate (BER). Based on the channel gain information, the considered approach is to use only the better half of the OFDM subcarriers while doubling the signal constellation sizes on those subcarriers. Simulation results indicate that the transmit power reduction can be significant, especially when the transmission bit rate reaches the order of 100 Mbps. In particular, about 8-10 dB of power reduction is observed for a 100-Mbps system operating with the BER requirement of at most 10^-4.