Control Design for Alignment Problem in Optical Wireless Communication

Student thesis: Doctoral Thesis

Abstract

Optical wireless communication (OWC) offers many benefits over established radio frequency–based communication links. Particularly in, high-data services, high security, and license-free operation, OWC link are becoming an attractive solution for the next generation of communication systems. In OWC, precise alignment of the incoming beam is necessary to close the communication link. However, precisely aligning the beam between the transceivers is challenging due to the laser beam’s narrowness and external disturbances that can significantly reduce, destroy, or scatter the beam signal. Therefore, designing optimized control strategies can significantly improve the alignment precision, which is the main motivation for this work. This thesis deploys standard and optimal control techniques, with an emphasis on optimized control strategies, to address the alignment problem in underwater optical wireless communication (UOWC) and in laser beam stabilizer systems within a vibrating environment. First, the UOWC system’s alignment problem was investigated in a vibrating scenario. For its effective control, the properties of light propagation were considered by accounting for the dynamical model that describes the propagation characteristics of the signal beam between transceivers. To control the UOWC system, we designed an observer-based optimal controller approach that combined the unconstrained and constrained optimal controllers, namely linear quadratic regulator (LQR) and model predictive control (MPC) with the extended Kalman filter (EKF). The latter enabled estimations of the beam dynamics from the power of the received beam signal. Extensive simulation tests were conducted that demonstrated the efficiency of the MPC algorithm compared to the LQR, fractional order proportional integral derivative (FOPID) and conventional PID controllers in terms of tracking and robustness against the disturbance levels. Second, the alignment problem in the laser beam stabilizer system was considered, whereby the designed control algorithms were tested experimentally in a vibrating disturbance. For this particular system, the LQR and MPC optimal controllers were designed both in simulation and experimental environments. The designed optimal control algorithms were compared to a conventional PID controller and its optimized variants (e.g., fractional and robust), demonstrating the MPC design’s outperformance in terms of tracking error and robustness to different voltage disturbance levels.
Date of AwardMar 2022
Original languageEnglish (US)
Awarding Institution
  • Computer, Electrical and Mathematical Sciences and Engineering
SupervisorTaousmeriem Laleg (Supervisor)

Keywords

  • Optical Wireless Communication
  • Control Alignment
  • FSO Alignmen

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