1. A data processing method in a channel equalizer of a receiver, the method comprising: estimating interference from a received signal at a first observation time, creating a first covariance matrix on the basis of the estimation and defining an inverse matrix of the first covariance matrix and a Cholesky decomposition matrix; removing selected covariance components from the Cholesky decomposition matrix; computing the inverse of a sub-matrix, which represents the common part of the first covariance matrix and a second covariance matrix, which includes covariance estimates of a second observation time, by using the aid of the Cholesky decomposition of the inverse matrix of the first covariance matrix; estimating interference from a received signal at a second observation time and determining additional covariance components on the basis of the estimation; creating the Cholesky decomposition of the inverse matrix of the second covariance matrix by using unitary rotations; and generating an output value of the channel equalizer by utilizing information obtained with the aid of the Cholesky decomposition of the inverse matrix of the second covariance matrix.