A method for blindly detecting a precoding matrix index used to transmit a data or control signal is provided. The method includes receiving at a mobile station (102) a common reference signal and user specific data and control signal weighted by precoding matrix. An objective function is applied to the received reference signal and user specific data and control signal that minimizes the objective function for each of at least one rank used to transmit the received user specific data and control signal and each of known possible modulation constellations used to transmit the received data/control signal to determine the precoding matrix index (PMI).