Precoding method, base station and computing circuit

A base station, comprising:

• a plurality of antennas;
• a plurality of radio frequency (RF) chains;
• an analog precoder, coupled between the plurality of antennas and the plurality of RF chains, configured to perform a first precoding operation;
• a computing circuit, configured to perform the following steps:
• computing a relaxed beamforming matrix according to a plurality of desired channel correlation matrices and a plurality of interfering channel correlation matrices, wherein the relaxed beamforming matrix comprises a plurality of relaxed beamforming sub-matrices corresponding to the plurality of users, one relaxed beamforming sub-matrix is generated according to a desired channel correlation matrix and an interfering channel correlation matrix corresponding to one user;
• computing an approximated beamforming matrix according to the relaxed beamforming matrix, wherein entries within the approximated beamforming matrix have a constant magnitude;
• computing a plurality of degradations corresponding to the plurality of data streams according to a plurality of relaxed beamforming vectors within the relaxed beamforming matrix and a plurality of approximated beamforming vectors within the approximated beamforming matrix;
• selecting a selected data stream index according to the plurality of degradations;
• decomposing a selected relaxed beamforming vector corresponding to the selected data stream index into a first vector and a second vector, wherein entries within the first vector and the second vector have a constant magnitude;
• and
• updating the approximated beamforming matrix according to the first vector and augmenting the approximated beamforming matrix according to the second vector, to obtain an updated-and-augmented beamforming matrix;
• wherein the analog precoder performs the first precoding operation according to the updated-and-augmented beamforming matrix.

A computing circuit, disposed within a base station, wherein the base station comprises a computing circuit, an analog precoder, a plurality of antennas and a plurality of radio frequency (RF) chains, the analog precoder is coupled between the plurality of antennas and the plurality of RF chains, the computing circuit comprising:

• a processing unit;
• and
• a memory, configured to store a program code, wherein the computing circuit is further configured to perform the following steps:
• computing a relaxed beamforming matrix according to a plurality of desired channel correlation matrices and a plurality of interfering channel correlation matrices, wherein the relaxed beamforming matrix comprises a plurality of relaxed beamforming sub-matrices corresponding to the plurality of users, one relaxed beamforming sub-matrix is generated according to a desired channel correlation matrix and an interfering channel correlation matrix corresponding to one user;
• computing an approximated beamforming matrix according to the relaxed beamforming matrix, wherein entries within the approximated beamforming matrix have a constant magnitude;
• computing a plurality of degradations corresponding to the plurality of data streams according to a plurality of relaxed beamforming vectors within the relaxed beamforming matrix and a plurality of approximated beamforming vectors within the approximated beamforming matrix;
• selecting a selected data stream index according to the plurality of degradations;
• decomposing a selected relaxed beamforming vector corresponding to the selected data stream index into a first vector and a second vector, wherein entries within the first vector and the second vector have a constant magnitude;
• and
• updating the approximated beamforming matrix according to the first vector and augmenting the approximated beamforming matrix according to the second vector, to obtain an updated-and-augmented beamforming matrix;
• wherein the analog precoder performs a first precoding operation according to the updated-and-augmented beamforming matrix.