This is a system for secure low probability of detection communications across a free-space optical (FSO) channel. The system utilizes an LED-based source which transmits signals with distributions that match the distribution of the background solar radiation, which hides the signals. The transmitted signals are modulated according to a phase-shift keying (PSK) which is encoded and transmitted to allow for decoding on the receiver end. The free-space optical link is established using a spatial light modulator (SLM)-based beam steering approach. This low-cost approach achieves reliable covert communications with a high data rate in the saturation turbulence regime. Background: Physical-layer security and encryption schemes are concerned with protecting the content of the transmitted message rather than protecting the users’ privacy. In the low probability of detecting and intercepting communications, the main goal is to provide private communication that is extremely difficult to intercept. Similar covert communications solutions have required that a Gaussian noise reference be provided on the receiver side of the channel, which is impractical and difficult to arrange in many applications. This system overcomes this challenge, providing a more practical solution. Applications:
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