Rank-2 CSI construction with 1-layer SRS

1. A base station (BS) in a wireless communication system, the BS comprising:

a transceiver configured to receive, from a user equipment (UE), a 1 st layer sounding reference signal (SRS); and

a processor operably connected to the transceiver, the processor configured to:

arrange the 1 st layer SRS based on two antenna polarizations of an antenna system of the BS,

identify a dominant direction of a channel based on the 1 st layer SRS,

identify a coefficient between two antenna polarizations based on the 1 st layer SRS, and

construct a 2-layer channel matrix based on the identified dominant direction and the identified coefficient,

wherein the transceiver is further configured to transmit, to the UE, a downlink signal via the antenna system based on the constructed 2-layer channel matrix.

2. The BS of claim 1 , wherein the processor is further configured to:

identify, based on the 1 st layer SRS, channel coefficients for the two antenna polarization directions, respectively;

switch the channel coefficients between the two antenna polarizations;

negate the channel coefficients for one of the two antenna polarizations to construct a 2 nd layer channel coefficients; and

combine the 1 st layer SRS and the 2 nd layer channel coefficients.

3. The BS of claim 1 , wherein the processor is further configured to:

identify an eigen direction and a pair of least-square (LS) fitted parameters for the two antenna polarizations;

configure a 1 st layer channel state information (CSI) based on the identified pair of LS fitted parameters and the eigen direction;

switch channel coefficients between the two antenna polarizations;

negate the channel coefficients for one of the two antenna polarizations to construct a 2 nd layer channel coefficients; and

normalize a 2-layer CSI to construct the 2-layer channel matrix.

4. The BS of claim 1 , wherein the processor is further configured to:

arrange 1 st layer SRS channel coefficients, based on directions of the two antenna polarizations, into a N×2 channel matrix;

perform a singular value decomposition of the N×2 channel matrix to obtain dominant channel directions of co-polarization array and the identified coefficient between cross-polarizations; and

determine a 2 nd layer channel state information (CSI) based on the performed singular value decomposition according to the dominant channel directions of co-polarization and a linear combination of the identified coefficient between the cross-polarizations, wherein a 1 st layer CSI is unchanged.

5. The BS of claim 1 , wherein:

the processor is further configured to:

configure a pool of random precoders;

identify channel quality indicator (CQI) received from the UE; and

select a multi-user multi-input multi-output (MU-MIMO) precoder from the pool of random precoders based on the identified CQI, the 1 st layer SRS of the UE, and a 2 nd layer precoder of the UE being served in the wireless communication system; and

the transceiver is further configured to transmit, to the UE, the selected MU-MIMO precoder via a downlink channel.

6. The BS of claim 1 , wherein:

the transceiver is further configured to receive, from the UE, rank information for a rank adaptation; and

the processor is further configured to:

determine orthogonality of a pool of UEs according to both layers of rank-2 UE; and

determine whether the rank information includes a rank-1 or a rank-2.

7. The BS of claim 6 , wherein the processor is further configured to:

schedule a set of UEs based on the determined rank information based on a network loading status belong to the BS;

adjust CQI of each layer of the layers of rank-2 UE; and

determine modulation coding scheme (MCS) for each layer based on the adjusted CQI.

8. A method of a base station (BS) in a wireless communication system, the method comprising:

receiving, from a user equipment (UE), a 1 st layer sounding reference signal (SRS);

arranging the 1 st layer SRS based on two antenna polarizations of an antenna system of the BS;

identifying a dominant direction of a channel based on the 1 st layer SRS;

identifying a coefficient between two antenna polarizations based on the 1 st layer SRS;

constructing a 2-layer channel matrix based on the identified dominant direction and the identified coefficient; and

transmitting, to the UE, a downlink signal via the antenna system based on the constructed 2-layer channel matrix.

9. The method of claim 8 , further comprising:

identifying, based on the 1 st layer SRS, channel coefficients for the two antenna polarization directions, respectively;

switching the channel coefficients between the two antenna polarizations;

negating the channel coefficients for one of the two antenna polarizations to construct a 2 nd layer channel coefficients; and

combining the 1 st layer SRS and the 2 nd layer channel coefficients.

10. The method of claim 8 , further comprising:

identifying an eigen direction and a pair of least-square (LS) fitted parameters for the two antenna polarizations;

configuring a 1 st layer channel state information (CSI) based on the identified pair of LS fitted parameters and the eigen direction;

switching channel coefficients between the two antenna polarizations;

negating the channel coefficient for one of the two antenna polarizations to construct a 2 nd layer channel coefficients; and

normalizing a 2-layer CSI to construct the 2-layer channel matrix.

11. The method of claim 8 , further comprising:

arranging 1 st layer SRS channel coefficients, based on directions of the two antenna polarizations, into a N×2 channel matrix;

performing a singular value decomposition of the N×2 channel matrix to obtain dominant channel directions of co-polarization array and the identified coefficient between cross-polarizations; and

determining a 2 nd layer channel state information (CSI) based on the performed singular value decomposition according to the dominant channel directions of co-polarization and a linear combination of the identified coefficient between the cross-polarizations, wherein a layer CSI is unchanged.

12. The method of claim 8 , further comprising:

configuring a pool of random precoders;

identifying channel quality indicator (CQI) received from the UE;

selecting a multi-user multi-input multi-output (MU-MIMO) precoder from the pool of random precoders based on the identified CQI, the 1 st layer SRS of the UE, and a 2 nd layer precoder of the UE being served in the wireless communication system; and

transmitting, to the UE, the selected MU-MIMO precoder via a downlink channel.

13. The method of claim 8 , further comprising:

receiving, from the UE, rank information for a rank adaptation;

determining orthogonality of a pool of UEs according to both layers of rank-2 UE; and

determining whether the rank information includes a rank-1 or a rank-2.

14. The method of claim 13 , further comprising:

scheduling a set of UEs based on the determined rank information based on a network loading status belong to the BS;

adjusting CQI of each layer of the layers of rank-2 UE; and

determining modulation coding scheme (MCS) for each layer based on the adjusted CQI.

15. A non-transitory computer-readable medium comprising program code, that when executed by at least one processor of a base station (BS) in a wireless communication system, causes the BS to:

receive, from a user equipment (UE), a 1 st layer sounding reference signal (SRS);

arrange the 1 st layer SRS based on two antenna polarizations of an antenna system of the BS;

identify a dominant direction of a channel based on the 1 st layer SRS;

identify a coefficient between two antenna polarizations based on the 1 st layer SRS;

construct a 2-layer channel matrix based on the identified dominant direction and the identified coefficient; and

transmit, to the UE, a downlink signal via the antenna system based on the constructed 2-layer channel matrix.

16. The computer-readable medium of claim 15 , further comprising program code, that when executed by the at least one processor, causes the BS to:

identify, based on the 1 st layer SRS, channel coefficients for the two antenna polarization directions, respectively;

switch the channel coefficients between the two antenna polarizations;

negate the channel coefficients for one of the two antenna polarizations to construct a 2 nd layer channel coefficients; and

combine the 1 st layer SRS and the 2 nd layer channel coefficients.

17. The computer-readable medium of claim 15 , further comprising program code, that when executed by the at least one processor, causes the BS to:

identify an eigen direction and a pair of least-square (LS) fitted parameters for the two antenna polarizations;

configure a 1 st layer channel state information (CSI) based on the identified pair of LS fitted parameters and the eigen direction;

switch channel coefficients between the two antenna polarizations;

negate the channel coefficients for one of the two antenna polarizations to construct a 2 nd layer channel coefficients; and

normalize a 2-layer CSI to construct the 2-layer channel matrix.

18. The computer-readable medium of claim 15 , further comprising program code, that when executed by the at least one processor, causes the BS to:

arrange 1 st layer SRS channel coefficients, based on directions of the two antenna polarizations, into a N×2 channel matrix;

perform a singular value decomposition of the N×2 channel matrix to obtain dominant channel directions of co-polarization array and the identified coefficient between cross-polarizations; and

determine a 2 nd layer channel state information (CSI) based on the performed singular value decomposition according to the dominant channel directions of co-polarization and a linear combination of the identified coefficient between the cross-polarizations, wherein a 1 st layer CSI is unchanged.

19. The computer-readable medium of claim 15 , further comprising program code, that when executed by the at least one processor, causes the BS to:

configure a pool of random precoders;

identify channel quality indicator (CQI) received from the UE;

select a multi-user multi-input multi-output (MU-MIMO) precoder from the pool of random precoders based on the identified CQI, the 1 st layer SRS of the UE, and a 2 nd layer precoder of the UE being served in the wireless communication system; and

transmit, to the UE, the selected MU-MIMO precoder via a downlink channel.

20. The computer-readable medium of claim 15 , further comprising program code, that when executed by the at least one processor, causes the BS to:

receive, from the UE, rank information for a rank adaptation;

determine orthogonality of a pool of UEs according to both layers of rank-2 UE;

determine whether the rank information includes a rank-1 or a rank-2;

schedule a set of UEs based on the determined rank information based on a network loading status belong to the BS;

adjust CQI of each layer of the layers of rank-2 UE; and

determine modulation coding scheme (MCS) for each layer based on the adjusted CQI.