Wireless access test-bed through visible light and dimming compatible OFDM

Visible light communications (VLC) technology has a potential to complement the RF wireless technology for indoor coverage. It promises concurrent illumination control and wireless data transmission capabilities. The potential of advanced multi-carrier modulation techniques, i.e. orthogonal frequency-division multiplexing (OFDM), introduces new challenges in the development of driver circuits. The reverse polarity optical OFDM (RPO-OFDM) is a recent approach to realize compatibility between the analog OFDM signal and the industry well-known pulse-width modulation (PWM) for dimming control. In this paper, we present the implementation of a wireless access test-bed through visible light and dimming compatible RPO-OFDM. A driver topology capable of driving a string of light-emitting diodes (LEDs) using a RPO-OFDM signal is proposed. The driver alleviates the nonlinearity of LEDs by proper biasing and maintaining a quasi-linear range of operation, i.e. minimizes the OFDM signal clipping. Using a software defined radio (SDR) platform for online modulation and demodulation, and a range of un-coded quadrature amplitude modulation (QAM) constellations, the experimentally obtained measurements demonstrate linear wide-range dimming while independently maintaining a bit-error performance below the forward error correction (FEC). Error free bit-error rate (BER) performance without symbol level equalization is obtained for binary phase shift keying (BPSK) and 4-QAM.