Beamforming with partial channel knowledge

A beamformer for use with a beamformee having NR receive antennas, wherein the beamformer knows respective channels associated with M receive antennas of the beamformee, wherein M is less than NR, and wherein a partial channel matrix describes a multiple input, multiple output (MIMO) channel between the beamformer and the M receive antennas, the beamformer comprising:

• multiple (NT) beamformer antennas;
• respective radio interfaces coupled to the multiple beamformer antennas;
• a controller coupled to the respective radio interfaces;
• and
• a driver executed by the controller to select steering vectors for simultaneously transmitting a plurality of streams (NS) to the beamformee, the driver configured to:
• construct a partial channel matrix that describes the MIMO channel;
• generate L independent vectors using the partial channel matrix, wherein L is a rank of the partial channel matrix;
• select a respective steering vector for each of the plurality of streams to be transmitted to the beamformee, including:
• if NS is less than or equal to L, select NS of the L independent vectors as the steering vectors;
• if NS is greater than L, (i) select the L independent vectors as steering vectors to steer L of the plurality of streams;
• and (ii) select NS−L orthogonal vectors in a null space of the L independent vectors.

A communication system comprising:

• a beamformee having NR receive antennas;
• a beamformer, wherein the beamformer knows respective channels associated with M receive antennas of the beamformee, wherein M is less than NR, and wherein a partial channel matrix describes a multiple input, multiple output (MIMO) channel between the beamformer and the M receive antennas, the beamformer including:
• multiple (NT) beamformer antennas,
• respective radio interfaces coupled to the multiple beamformer antennas,
• a controller coupled to the respective radio interfaces, and
• a driver executed by the controller, the driver configured to
• steer one or more of streams toward the M receive antennas of the beamformee using the partial channel matrix, wherein the beamformer has NS streams to transmit to the beamformee, and
• if NS is greater than a rank of the partial channel matrix between the beamformer and the beamformee, use the partial channel matrix to steer remaining streams through a null space of the partial channel matrix,
• wherein the NS streams are steered simultaneously.