Non-Line of Sight Optical Wireless Relaying With the Photon Counting Receiver: A Count-and-Forward Protocol

We propose a count-and-forward relay framework for non-line of sight optical wireless relay communications. Both the relay and the destination employ an ideal photon counting receiver. The relay forwards on-off keying (OOK) modulated optical signals using discrete power levels corresponding to the number of received photons, and the destination employs maximum-likelihood detection. We formulate the forwarding power optimization problem that aims to minimize the destination detection error probability given the relay forwarding power budget. We pursue exact optimal solutions to two special cases. To solve the non-convex forwarding power optimization problem in general, we transform to a piecewise exponential approximation problem. Numerical results show that the proposed scheme outperforms the relay hard-decision forwarding scheme, and can approach the optimal power allocation performance based on simulated annealing.