Pointing, Acquisition, and Tracking (PAT) are critical aspects of both uplink and downlink Free Space Optical (FSO) communications systems, ensuring precise targeting of the optical signal from the transmitter to the receiver. PAT systems provide steering and tracking capabilities in order to establish and maintain an optical link, compensating for the relative satellite motion, atmospheric turbulence, vibration and jitter.
A novel method for achieving closed loop control between the steering mirrors of a dual channel free space optical communications terminal is presented. By modifying an off-the-shelf open loop stick-slip actuator, the control system achieves a pointing resolution of 0.002° with under a 15% increase in mass, resulting in a light weight solution suitable for small satellites.
Visible light communication (VLC) based on light-emitting diodes (LEDs) technology not only provides higher data rate for indoor wireless communications and offering room illumination but also has the potential for indoor localization. VLC-based indoor positioning using the received optical power levels from emitting LEDs is investigated. We consider both scenarios of line-of-sight (LOS) and LOS with non-LOS (LOSNLOS) positioning. The performance of the proposed system is evaluated under both noisy and noiseless channel as is the impact of different location codes on positioning error. The analytical model of the system with noise and the corresponding numerical evaluation for a range of signal-to-noise ratio (SNR) are presented. The results show that an accuracy of <10 cm on average is achievable at an SNR>12 dB.
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