The Benefit of Frequency-selective Rate Adaptation for Optical Wireless Communications (invited paper)

In this paper, we evaluate the potential of adaptive transmission for optical wireless communications, used together with a real-valued, DC-biased optical (DCO) orthogonal frequency-division multiplexing (OFDM) waveform. Particularly, we include frequency-selective bit-and power-loading on top of DCO-OFDM. This combination is well known as discrete multi-tone (DMT). We work out the significant advantage of frequency-selective rate adaptation for operation in both, low signal-to-noise ratios and non-line-of-sight scenarios, as compared to using a fixed modulation format commonly applied over all subcarriers and switching between these formats. Our evaluation is based on the channel impulse responses (CIRs) provided by the IEEE task group for the 802.15.7r1 standard. Transmission bandwidth is up to 200 MHz, as supported by modern optical wireless frontends.