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