A SPAD-Based Visible Light Communications Receiver Employing Higher Order Modulation

This paper studies complex modulation schemes, including orthogonal frequency-division multiplexing (OFDM), received by a single photon avalanche diode (SPAD) array integrated circuit (IC). A SPAD operates in the Geiger mode, and is able to detect single photons. This feature enables order of magnitude receiver sensitivity in intensity modulation (IM) / direct detection (DD) Visible Light Communication (VLC) systems. The tradeoff between received power and bit error ratio (BER) using both pulse-amplitude modulation (PAM) and OFDM is shown. A first order model of the noise in a digital SPAD receiver is derived. The noise in the experimental receiver chip approaches the predicted noise in our model, and we achieve receiver sensitivity of -64 dBm with a 100 kbit/s signal at a BER of 10^-5. It is concluded that future improvements in SPAD VLC receiver architecture will allow sensitivity to approach the quantum limit.