Enhanced node B and method for precoding with reduced quantization error

A method performed by a serving enhanced Node B (eNB) for precoding symbols for multiple-input multiple output (MIMO) beamforming in an orthogonal frequency division multiple access (OFDMA) broadband wireless access network, the method comprising:

• receiving, from a user equipment (UE), first and second precoding-matrix indicator (PMI) reports on an uplink channel;
• computing a single subband precoder matrix from both the PMI reports;
• and
• precoding symbols for MIMO beamforming using the computed single subband precoder matrix for an OFDMA downlink transmission,
• wherein each of the first and second PMI reports include a PMI associated with a same subband of a single channel between the serving eNB and the UE,
• wherein the PMIs of the first and second PMI reports correspond to precoding matrices of a same codebook,
• wherein the first PMI report includes a first subband PMI,
• wherein the second PMI report includes a second subband PMI,
• wherein the second subband PMI is selected by the UE after selecting the first subband PMI by searching candidate precoder matrices that when combined with a precoder matrix indicated by the first subband PMI, results in a more accurate precoder for the same subband of the single channel between the serving eNB and the UE,
• wherein computing the single subband precoder matrix comprises performing an interpolation on corresponding vectors of precoder matrices indicated by the first subband PMI and the second subband PMI, the interpolation including weighting and combining the corresponding vectors of the precoder matrices to generate an interpolated precoding matrix corresponding to the single subband precoder matrix,
• wherein the first subband PMI and the second subband PMI correspond to precoding matrices selected from the same codebook that is based on a matrix of Discrete Fourier Transform (DFT) vectors,
• wherein when both the first and second subband PMIs indicate DFT vectors, vectors of the interpolated precoding matrix are generated from a weighted average of phases of the DFT vectors, and
• wherein when either the first and second subband PMIs do not indicate a DFT vector, each element of the vectors of the interpolated precoding matrix is generated from a weighted average of phases of corresponding elements of the vectors.