Estimating the channel state information (CSI) of several transmitters that use orthogonal space-time block codes (OSTBC) to communicate with a single receiver is considered. Based on rank revealing QR (RRQR) factorization and propagator method (PM), two new algorithms to estimate multiuser MIMO channels are proposed. The algorithm estimates the subspace spanned by the user channels use only a few training blocks to extract the users CSI from this subspace. Our both algorithms achieve better performance in comparison with reference LS based approach. Computer simulations are included to validate proposed methods