Optimum thresholds for optical on-off keying receivers operating in the turbulent atmosphere

It is well known that atmospheric turbulence causes degradations in the performance of atmospheric links. The focus of this study is the effect of scintillation on the performance of optical On-Off keying (OOK) links in horizontal atmospheric paths. A new approach to improving the performance of OOK links in the atmosphere is presented in this paper: optimum adaptive thresholding for anticipated, future scintillation values. We look first at the non-time varying irradiance case. The theory of minimum probability of error receivers for this case is well established. When the link operates in a turbulent atmosphere, however, this theory will not necessarily hold. A new adaptive predictive control (APC) approach is described, and to test its effectiveness, a specific link is assumed and the expected BER performance with and without APC was determined by computer simulation. We see that all measures of the BER are better for the APC receiver than the fixed threshold receiver. APC is shown to illustrate a simple way to improve the effectiveness of atmospheric links. Other areas of laser communications that APC might potentially benefit are all processes that satisfy the two criteria of slow time variation and sample-to-sample correlation.