Abstract: The disclosure relates to a method performed by an optical receiver, the method comprising receiving an optical communication signal comprised in a signal space, the signal comprising a set of received training symbols and a set of received payload symbols, determining a kernel operating in a feature space by using the set of training symbols and a reference set of training symbols indicative of an undistorted version of the training symbols, wherein determining a kernel further comprises determining at least an equalization mapping function ƒ configured to map received symbols to channel equalized symbols, and determining an error function (e) configured to generate a measure indicative of an error between symbols mapped by the equalization mapping function ƒ and an ideal equalization mapping function, performing nonlinear equalization of the payload symbols (C?1 to C?M) by performing linear equalization of the payload symbols (C?1 to C?M) in the feature space using the received training symbols (C1 to CN) a