Methods and systems for hybrid beamforming for MIMO communications

A method at a hybrid beamforming (BF) transmitter terminal for implementing single user multiple-input multiple-output (SU MIMO) communications with a hybrid BF receiver terminal, the method comprising:

• receiving, from the hybrid BF receiver terminal, feedback information to enable the hybrid BF transmitter terminal to implement a hybrid precoder using a radio frequency (RF) precoder matrix and a baseband precoder matrix;
• forming the RF precoder matrix and the baseband precoder matrix using the feedback information, wherein the feedback information indicates first two or more selected columns which have been selected by the hybrid BF receiver terminal from a first discrete Fourier transform (DFT) matrix, and the RF precoder matrix is formed using the first two or more selected columns, and the feedback information further indicates a selection, by the hybrid BF receiver terminal, of second one or more columns from a second DFT matrix to enable the hybrid BF transmitter terminal to select the second one or more columns from the second DFT matrix to form the baseband precoder matrix;
• and
• implementing the hybrid precoder using the RF precoder matrix at an analog RF precoder and the baseband precoder matrix at a digital baseband precoder, to perform hybrid beamforming operations.

A method at a receiver terminal for implementing multi-user multiple-input single-output (MU MISO) communications with a hybrid beamforming (BF) transmitter terminal, the method comprising:

• determining a set of one or more candidate radio frequency (RF) precoder vectors for enabling implementation of a hybrid precoder at the hybrid BF transmitter terminal;
• transmitting feedback information about the determined set of candidate RF precoder vectors to the hybrid BF transmitter terminal, the feedback information including information to enable the hybrid BF transmitter terminal to identify candidate columns, selected by the receiver terminal from a discrete Fourier transform (DFT) matrix, to form a RF precoder matrix for the hybrid precoder;
• and
• transmitting further feedback information about channel conditions to form a baseband precoder matrix for implementing the hybrid precoder;
• wherein the set of candidate RF precoder vectors is determined by selecting one or more candidate RF precoder vectors, from the DFT matrix, along which a known channel vector for the receiver terminal has a maximum projection.

A method at a hybrid beamforming (BF) transmitter terminal for implementing multi-user multiple-input single-output (MU MISO) communications with a plurality of receiver terminals, the method comprising:

• receiving, from the plurality of receiver terminals, respective feedback information indicating respective sets of one or more candidate RF precoder vectors to enable the hybrid BF transmitter terminal to form a RF precoder matrix for implementing a hybrid precoder;
• forming the RF precoder matrix by selecting, from the sets of candidate RF precoder vectors indicated in the feedback information, one or more preferred vectors indicated by the feedback information as vectors along which a respective channel vector, known to a respective receiver terminal, has a maximum projection;
• wherein the one or more preferred vectors are selected such that there is no repeated vector in the one or more preferred vectors;
• receiving, from the plurality of receiver terminals, respective further feedback information indicating channel conditions for forming an effective channel matrix;
• determining, using the effective channel matrix, a baseband precoder matrix for implementing the hybrid precoder;
• and
• implementing the hybrid precoder using the RF precoder matrix at an analog RF precoder and the baseband precoder matrix at a digital baseband precoder, to perform hybrid beamforming operations.