Coefficient reporting for type II channel state information (CSI)

1. A method comprising:

receiving, at a user equipment (UE), a channel state information (CSI) configuration and a codebook configuration, the codebook configuration specifying a codebook;

determining a precoding matrix indicator (PMI) that specifies a precoding matrix associated with the codebook, wherein the precoding matrix is based on spatial-domain (SD) vectors and linear combining coefficients; and

transmitting a CSI report comprising the PMI in accordance with the CSI configuration, wherein parameters corresponding to the linear combining coefficients are reported using a plurality of bit fields in the CSI report, the parameters comprising at least an amplitude and a phase respectively reported using a first bit field and a second bit field of the plurality of bit fields.

2. The method of claim 1 , wherein the linear combining coefficients comprise a linear combining coefficient c that is represented as c=a ref ·a·b, wherein a ref is a reference amplitude, a is a differential amplitude, and b is a phase.

3. The method of claim 2 , wherein the PMI comprises the first bit field, the second bit field, and a third bit field of the plurality of bit fields, wherein the first bit field is used to report a ref , wherein the second bit field is used to report b, and wherein the third bit field is used to report a.

4. The method of claim 3 , wherein at least one potential value that is represented by the third bit field is a complex number.

5. The method of claim 3 , wherein at least one first potential value that is represented by the third bit field is a complex number, and wherein one or more second potential values that are represented by the third bit field are real numbers.

6. The method of claim 3 , wherein potential values represented by the second bit field follow a constellation of N phase-shift keying (N-PSK), where N is a number of points associated with the constellation.

7. The method of claim 6 , wherein at least one potential value represented by the third bit field is a complex number, wherein a phase of the complex number is equal to π/N.

8. The method of claim 1 , wherein the CSI report comprises a channel quality indicator (CQI), and wherein the CQI comprises information on a modulation and coding scheme for a downlink (DL) transmission.

9. The method of claim 8 , wherein the CSI report comprises a rank indicator (RI), the RI comprising information on a number of spatial layers for the DL transmission.

10. The method of claim 1 , wherein a column of the precoding matrix is based on a matrix of SD vectors, a matrix of linear combining coefficients, and a Fourier transformation matrix.

11. An apparatus comprising:

one or more processors;

circuitry configured to receive information comprising a channel state information (CSI) configuration and a codebook configuration, the codebook configuration specifying a codebook, and to transmit a CSI report in accordance with the CSI configuration; and

a memory storing instructions that, when executed by the one or more processors, cause the one or more processors to perform operations comprising:

determining a precoding matrix indicator (PMI) that specifies a precoding matrix associated with the codebook, wherein the precoding matrix is based on spatial-domain (SD) vectors and linear combining coefficients, wherein the CSI report comprises the PMI, and wherein parameters corresponding to the linear combining coefficients are reported using a plurality of bit fields in the CSI report, the parameters comprising at least an amplitude and a phase respectively reported using a first bit field and a second bit field of the plurality of bit fields.

12. The apparatus of claim 11 , wherein the linear combining coefficients comprise a linear combining coefficient c that is represented as c=a ref ·a·b, wherein a ref is a reference amplitude, a is a differential amplitude, and b is a phase.

13. The apparatus of claim 12 , wherein the PMI comprises the first bit field, the second bit field, and a third bit field of the plurality of bit fields, wherein the first bit field is used to report wherein the second bit field is used to report b, and wherein the third bit field is used to report a.

14. The apparatus of claim 13 , wherein potential values represented by the second bit field follow a constellation of N phase-shift keying (N-PSK), where N is a number of points associated with the constellation.

15. The apparatus of claim 14 , wherein at least one potential value represented by the second bit field is a complex number, wherein a phase of the complex number is equal to π/N.

16. The apparatus of claim 11 , wherein a column of the precoding matrix is represented as a linear combination of SD vectors and frequency-domain (FD) vectors.

17. The apparatus of claim 11 , wherein transmitting the CSI report comprises transmitting the CSI report via a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

18. The apparatus of claim 11 , wherein the CSI report comprises a channel quality indicator (CQI), and wherein the CQI comprises information on a modulation and coding scheme for a downlink (DL) transmission.

19. The apparatus of claim 11 , wherein a column of the precoding matrix is based on a matrix of SD vectors, a matrix of linear combining coefficients, and a Fourier transformation matrix.

20. The apparatus of claim 11 , wherein the codebook has a spatial resolution based on a digital Fourier transformation spatial domain vector.