Physical layer design with analog front end for bidirectional DCO-OFDM visible light communications

Visible light communication (VLC) is a promising wireless communication technology that utilizes existing lighting system infrastructure. This paper presents the bidirectional VLC physical layer design that supports both pulse width modulation (PWM) and direct current-biased optical orthogonal frequency division multiplexing (DCO-OFDM) for downlink, and an infrared pulse position modulation (PPM) for uplink. The physical layer consists of an analog front end (AFE) and digital signal processing (DSP) circuits on both the transmitter and the receiver. The AFE circuit on the receiver is specifically designed to compensate for impairments in optical channels, such as ambient light and uneven distribution of light intensity. The evaluation results show that the designed AFE circuit minimizes the interference in the receiver without increasing the TX power. In addition, the PWM is found to be more robust in the optical channel than the DCO-OFDM. In respect of data transmission rate, however, it is observed that the DCO-OFDM is superior to the PWM; namely, the DCO-OFDM modulation using quadrature phase shift keying (QPSK) attains a data rate of 26.8 kbps, while the 2-PWM modulation achieves a data rate of 6.2 kbps.