Temporal Spectrum Sensing for Optical Wireless Scattering Communications

Due to the unlicensed spectrum nature of the optical wireless communication, for a transceiver pair, the receiver needs to periodically sense the communication media, aiming to better schedule its transmission. Considering that the data symbols or channel parameters are unknown, we adopt a generalized likelihood ratio test (GLRT), which is known to be optimal with unknown parameters based on finite samples. This paper proposes two detection rules on whether there are optical signals falling into the receiver field of view within certain time slot(s), based on the sum number of received photons over all sensing slots, as well as the number of received photons in each slot. The formal one is named the sum-counting test and the latter one is named as the general GLRT. We design the corresponding detection schemes for both on-off keying (OOK) and pulse-position modulation (PPM) signal formats. We also provide asymptotic results on the miss detection probability. Numerical results show that, for OOK signal format, the general GLRT outperforms the sum-counting test at the cost of higher computational complexity, but for PPM signal format both detection schemes perform virtually the same.