User grouping for multi-user MIMO

1. A method comprising, by a computing device associated with a base station of a wireless network:

receiving, from a plurality of user equipments (UEs) associated with the base station, sounding reference signal (SRS);

sending, to a distributed unit (DU) associated with the base station, information regarding one or more beams selected for each of the plurality of UEs based on the received SRS;

receiving, from the DU, information regarding a subset of the plurality of UEs selected for downlink data transmissions for a resource block group (RBG), multi-user data to be transmitted to UEs in the subset, and identities of beams to be associated with the UEs in the subset; and

transmitting pre-coded multi-user data to the UEs in the subset for the RBG using Multiple-Input Multiple-Output (MIMO) technologies, wherein the pre-coded multi-user data is prepared using a precoding matrix computed based on inverse-DFT (IDFT) vectors corresponding to the selected beams for the subset of the plurality of UEs.

2. The method of claim 1 , further comprising:

computing, for each of the plurality of UEs, a channel matrix by performing SRS-based downlink channel estimations based on the received SRS, wherein the channel matrix is between an antenna array for the UE and an antenna array for the base station;

estimating, for each of the plurality of UEs, strengths or signal-to-noise ratios (SNRs) of a plurality of pre-determined beams for the UE by performing a two-dimensional discrete Fourier transform (2D-DFT) on the computed channel matrix; and

selecting, for each of the plurality of UEs, the one or more beams among the plurality of pre-determined beams based on the estimated strengths.

3. The method of claim 2 , wherein an SRS-based downlink channel estimation is an SRS-based least squares channel estimation.

4. The method of claim 2 , wherein the estimated strengths or SNRs of the selected one or more beams are also sent to the DU.

5. The method of claim 4 , wherein the DU selects the subset of the plurality of UEs based on the strengths or SNRs of the selected one or more beams.

6. The method of claim 5 , further comprising sending channel quality indicators (CQIs) received from the plurality of UEs to the DU.

7. The method of claim 6 , wherein the DU selects the subset of the plurality of UEs further based on the CQIs.

8. The method of claim 7 , wherein the DU selects the subset of the plurality of UEs further based on downlink traffic information associated with each of the plurality of UEs.

9. The method of claim 8 , wherein the downlink traffic information associated with a UE comprises traffic class type, hybrid automatic repeat request (HARQ) retransmission information, and any pre-scheduled persistent or semi-persistent transmission allocations.

10. The method of claim 1 , wherein each of the beams to be associated with the UEs in the subset corresponds to a discrete Fourier transform (DFT) vector.

11. The method of claim 10 , wherein the pre-coded multi-user data is created based on a precoding matrix for the RBG.

12. The method of claim 10 , wherein the precoding matrix for the RBG is computed by:

establishing a maMIMO channel matrix by calculating inverse-DFT (IDFT) vectors of the DFT vectors corresponding to the beams to be associated with the UEs in the subset;

calculating a regularized pseudo-inverse of the maMIMO channel matrix; and

normalizing power of each column of the regularized pseudo-inverse of the maMIMO channel matrix such that a transmit power level for each UE in the selected subset equals to each other.

13. The method of claim 12 , wherein calculating an IDFT vector of a DTF vector is calculating a complex conjugate of the DFT vector.

14. One or more computer-readable non-transitory storage media embodying software that is operable when executed, by a computing device associated with a base station of a wireless network, to:

receive, from a plurality of user equipments (UEs) associated with the base station, sounding reference signal (SRS);

send, to a distributed unit (DU) associated with the base station, information regarding one or more beams selected for each of the plurality of UEs based on the received SRS;

receive, from the DU, information regarding a subset of the plurality of UEs selected for downlink data transmissions for a resource block group (RBG), multi-user data to be transmitted to UEs in the subset, and identities of beams to be associated with the UEs in the subset; and

transmit pre-coded multi-user data to the UEs in the subset for the RBG using Multiple-Input Multiple-Output (MIMO) technologies, wherein the pre-coded multi-user data is prepared using a precoding matrix computed based on inverse-DFT (IDFT) vectors corresponding to the selected beams for the subset of the plurality of UEs.

15. The media of claim 14 , wherein the software is further operable when executed to:

compute, for each of the plurality of UEs, a channel matrix by performing SRS-based downlink channel estimations based on the received SRS, wherein the channel matrix is between an antenna array for the UE and an antenna array for the base station;

estimate, for each of the plurality of UEs, strengths or signal-to-noise ratios (SNRs) of a plurality of pre-determined beams for the UE by performing a two-dimensional discrete Fourier transform (2D-DFT) on the computed channel matrix; and

select, for each of the plurality of UEs, the one or more beams among the plurality of pre-determined beams based on the estimated strengths.

16. The media of claim 15 , wherein an SRS-based downlink channel estimation is an SRS-based least squares channel estimation.

17. The media of claim 15 , wherein the estimated strengths or SNRs of the selected one or more beams are also sent to the DU.

18. The media of claim 17 , wherein the DU selects the subset of the plurality of UEs based on the strengths or SNRs of the selected one or more beams.

19. The media of claim 18 , wherein the SRS-based downlink channel estimation is an SRS-based least squares channel estimation.

20. A computing device associated with a base station of a wireless network comprising:

one or more processors; and

one or more computer-readable non-transitory storage media coupled to one or more of the processors and comprising instructions operable when executed by one or more of the processors to cause the system to:

receive, from a plurality of user equipments (UEs) associated with the base station, sounding reference signal (SRS);

send, to a distributed unit (DU) associated with the base station, information regarding one or more beams selected for each of the plurality of UEs based on the received SRS;

receive, from the DU, information regarding a subset of the plurality of UEs selected for downlink data transmissions for a resource block group (RBG), multi-user data to be transmitted to UEs in the subset, and identities of beams to be associated with the UEs in the subset; and

transmit pre-coded multi-user data to the UEs in the subset for the RBG using Multiple-Input Multiple-Output (MIMO) technologies, wherein the pre-coded multi-user data is prepared using a precoding matrix computed based on inverse-DFT (IDFT) vectors corresponding to the selected beams for the subset of the plurality of UEs.