Conjugate Gradient Derived Kernel Affine Projection Method for Post-distortion in Visible Light Communication Systems

With the explosive growth in the demand of spectrum, conventional radio frequency systems are increasingly facing the challenge of catering to high-speed transmissions. Visible light communication (VLC) has been considered as a promising supplement technique, since it can provide efficient energy efficiency and unlimited bandwidth. However, the nonlinearity effect is one of the fundamental problems in the VLC systems, which usually brings distortion to the transmitted signal and deteriorates the system performance. Aiming at this problem, numerous post-distortion schemes are proposed, where the kernel methods over reproducing kernel Hilbert spaces are identified to have successful applications. In this paper, we present a new post-distortion method with low computational cost, by utilizing the conjugate gradient (CG) based kernel affine projection algorithm (KAPA), where the objective parameters are updated adaptively along the conjugate direction. Simulation results show that the proposed CG-KAPA based post-distorter can efficiently mitigate nonlinear impairment in VLC systems, which can provide better bit error rate performance with fast convergence over the commonly-used gradient descent algorithms.