Hello Naazira,
If you are talking about the dynamic threshold detection associated with free space optics then here is a link to a paper which may help you. I suggest you to go through it.
https://dru5cjyjifvrg.cloudfront.net/wp-content/uploads/2016/04/1255-6871-1-PB.pdf?448a95
This article deals with the construction of a modulator and demodulator for Free-Space Optical (FSO) communication. In FSO optics, the modulated optical signal is propagated in the constantly changing environment (atmosphere). The optical signal is strongly influenced by the actual composition of air, which is directly linked to the change in refractive index in the turbulent cells. This article examines primarily
the appropriate modulation format for FSO. For this purpose, one type of an OOK-NRZ modulator and one type of a demodulator were designed. This article also describes the construction of two types of photo detectors the high impedance and the transimpedance ones). All electronic constructions were tested in the MicroCap simulator and they were experimentally measured as well. For the OOK NRZ modulation the, maximum transmission speed achieved the value of 160 Mbps. Measuring the quality of the modulation formats was carried out under mechanical and thermal turbulences. The last part of this work gives the results of the measurements of fog influences.
I hope this will help a little.
Thanks