Spatial and temporal characteristics of received radio signals in a multiple user radio system can be estimated based on signals received from the users. In one embodiment, the invention includes measuring radio frequency signals received at different elements of an antenna system over time, the received signals corresponding at least in part to transmissions received from a system user, accumulating the signal measurements into a first matrix, and generating a second matrix representing the transmissions of the system user. The invention further includes cross-correlating the first and second matrices to form a first cross-correlation matrix, cross-correlating the first matrix with itself to form a second cross-correlation matrix, and multiplying the second cross-correlation matrix with a product of the first cross-correlation matrix to form a fifth matrix in which the elements of the fifth matrix characterize the radio channel traversed by transmissions of the system user.