Performance analysis of indoor OFDM optical wireless communication systems

In this paper, the performance of indoor OFDM (orthogonal frequency division multiplexing) optical wireless (OW) communication systems in the presence of LED (light emitting diode) clipping distortions is analyzed. Two indoor OW OFDM techniques are considered. An ACO-OFDM (asymmetrically clipped optical OFDM) system produces half-wave symmetry time signal at the output of the OFDM modulator by special assignment of subcarriers. Therefore, bipolar-unipolar conversion is achieved by clipping the signal at the zero level at the expense of data rate reduction. The second technique, called DCO-OFDM (DC-biased optical OFDM), assigns data to all possible subcarriers to increase the data rate. However, half-wave symmetry signals cannot be achieved and a DC bias is needed to convert the bipolar signal to a unipolar signal before modulating the LED intensity. The performance of these systems, in terms of average electrical OFDM signal power versus bit-error-ratio (BER), DC power consumption, and transmitted optical power in the presence of additive white Gaussian noise (AWGN) channel and considering a practical LED model, are studied. Analytical results are validated through Monte Carlo simulation results and the results demonstrate close match. The results clearly highlight that LED clipping has significant impact on the performance of these systems and system design should consider optimizing the OFDM signal power, DC bias point, and LED dynamic range.