1. A method for estimating a channel matrix for a channel between a transmitter and a receiver in a wireless multiple-input multiple-output (MIMO) network, wherein the receiver includes a set of M transmit antennas, and the receiver includes a set of N receive antennas, comprising the steps of buffering k symbols of a transmitted signal x(k) as a buffered signal x′(k); extending the buffered signal to a D th order polynomial signal u=D′(k)×′(k) of size M(P+1)(D+1), wherein D is a maximum polynomial order, D′(k) is an order extension matrix, P is a maximum length of a channel memory of k symbols; obtaining an estimate of an order-extended channel matrix G′(k) using an order extended recursive least-squares (RLS) process, on based u, a received signal y(k) corresponding to the transmitted signal x(k), and a signal correlation matrix R; refining the estimate using a sparse expectation-maximization (EM); and folding the order-extended channel matrix G′(k) to obtain an estimate of a channel matrix H′(k) as G′(k)D′(k), wherein the steps are performed in a processor of the receiver.