Beamforming with partial channel knowledge

A method, in a transmitter, for selecting steering vectors for simultaneously transmitting one or more streams between the transmitter and a receiver, wherein the receiver has NR receive antennas, wherein the transmitter knows respective channels associated with M receive antennas of the receiver, wherein M is less than NR, and wherein NS is the number of the one or more streams, the method comprising:

• constructing a partial channel matrix that describes a multiple input, multiple output (MIMO) channel between the transmitter and the M receive antennas;
• generating L independent vectors using the partial channel matrix, wherein L is a rank of the partial channel matrix;
• and
• when NS is greater than L,
• (i) selecting the L independent vectors as steering vectors to steer L streams of the one or more of streams;
• (ii) selecting NS−L orthogonal vectors in a null space of the L independent vectors as steering vectors to steer a remainder of the streams in the one or more streams;
• and
• (iii) respectively utilizing the steering vectors for transmitting (a) the L streams of the one or more of streams (NS), and (b) the remainder of the streams in the one or more streams (NS).