Apparatus and method for channel state information codeword construction for a cellular wireless communication system

A method for constructing a channel state information (CSI) codeword at a mobile station in a wireless communication system comprising a base station having a two-dimensional array of antennas, wherein the array comprises a plurality of groups of antennas, the method comprising:

• receiving from the base station a first configuration for a first set of reference signals and a second configuration for a second set of reference signals;
• estimating a first channel state with the first set of reference signals and a second channel state with the second set of reference signals;
• determining a co-phasing scalar component for each of the groups of antennas based on the first channel state;
• generating a matrix X comprising a plurality of column vectors selected from a codebook based on the second channel state, wherein each of the column vectors quantizes channel coefficients for one of the groups of antennas;
• generating a matrix P1, wherein the matrix P1 comprises a block diagonal matrix having the matrix X for each block diagonal element;
• generating a matrix P2 comprising a plurality of vector elements, wherein each vector element comprises one of the co-phasing scalar components and a column selector vector configured to select a column of the matrix X;
• transmitting to the base station a first precoding matrix information corresponding to the matrix P1 and a second precoding matrix information corresponding to the matrix P2;
• and
• transmitting to the base station a channel quality information (CQI), wherein the CQI is derived with a precoding matrix P defined by P=P1P2.

A base station in a wireless communication system, comprising:

• a two-dimensional array of antennas, wherein the array comprises a plurality of groups of antennas;
• and
• a base transceiver subsystem (BTS) controller configured:
• to transmit to a mobile station a first configuration for a first set of reference signals and a second configuration for a second set of reference signals;
• to receive from the mobile station a first precoding matrix information corresponding to a matrix P1 and a second precoding matrix information corresponding to a matrix P2,
• wherein a first channel state is estimated with the first set of reference signals and a second channel state is estimated with the second set of reference signals,
• wherein a co-phasing scalar component is determined for each of the groups of antennas based on the first channel state,
• wherein the matrix P1 comprises a block diagonal matrix having a matrix X for each block diagonal element,
• wherein the matrix P2 comprises a plurality of vector elements, wherein each vector element comprises one of the co-phasing scalar components and a column selector vector configured to select a column of the matrix X, and
• wherein the matrix X comprises a plurality of column vectors selected from a codebook based on the second channel state, wherein each of the column vectors quantizes channel coefficients for one of the groups of antennas;
• and
• to receive from the mobile station a channel quality information (CQI), wherein the CQI is derived with a precoding matrix P defined by P=P1P2.