1. A method, comprising: calculating a two-by-two channel matrix representation representing properties of a radio channel between a transmission antenna array of a radio transmitter and a reception antenna array of a radio receiver; examining mutual proportions of a first eigenvalue and a second eigenvalue of the channel matrix representation with a test function including elements of a solution of roots of a quadratic characteristic equation of the two-by-two channel matrix representation, wherein the test function comprises a discriminant of the solution of the roots of the quadratic characteristic equation without a square root operation; and determining the number of available spatially parallel communication streams between the transmission antenna array and reception antenna array from the mutual proportions of the eigenvalues.