  Visible light communication (VLC) systems can provide illumination and
communication simultaneously via light emitting diodes (LEDs). Orthogonal
frequency division multiplexing (OFDM) waveforms transmitted in a VLC system
will have high peak-to-average power ratios (PAPRs). Since the transmitting LED
is dynamic-range limited, OFDM signal has to be scaled and biased to avoid
nonlinear distortion. Brightness control is an essential feature for the
illumination function. In this paper, we will analyze the performance of
dynamic range constrained visible light OFDM systems with biasing adjustment
and pulse width modulation (PWM) methods. We will investigate the trade-off
between duty cycle and forward ratio of PWM and find the optimum forward ratio
to maximize the achievable ergodic rates.
