Optimal automatic gain control using improved linear quadratic regulator and kalman filtering for vlc-based optical wireless communication systems

Abstract Visible Light Communication (VLC) is a promising technology for beyond-5G and sixth-generation (6G) wireless networks due to its large unlicensed bandwidth, high data rates, and immunity to electromagnetic interference. However, optical channel variations, ambient light interference, receiver mobility, and hardware nonlinearities cause significant fluctuations in received signal amplitude, degrading Automatic Gain Control (AGC) performance and increasing bit error rate (BER) and estimation error. To overcome these limitations, this paper proposes an Improved Linear Quadratic Regulator–based AGC (ILQR-AGC) integrated with Kalman Filtering (KF) for VLC systems. The ILQR adaptively updates state and control weighting matrices according to channel conditions, while the Kalman Filter provides recursive minimum mean square error state estimation for robust gain adaptation. Simulation results show convergence within 35 iterations, outperforming the Extended Kalman Filter (EKF) (90), Linear Quadratic Regulator (LQR) (180), Recursive Least Squares (RLS) (320), Least Mean Square (LMS) (620), and Fixed AGC (>900). At a BER of 10 −3 , the proposed method requires only 10 dB SNR, achieving up to 25 dB SNR improvement, an MSE of 2.08 × 10 −7 , EVM of 4.52 %, and 87 % lower computational complexity. Monte Carlo simulations validate its robustness and suitability for real-time high-speed VLC applications.