REFERENCE SIGNALS AND LINK ADAPTATION FOR MASSIVE MIMO

• US 20170324455A1
• Filed: 05/02/2017
• Published: 11/09/2017
• Est. Priority Date: 05/09/2016
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: SORIAGA, Joseph Binamira, VITTHALADEVUNI, Pavan Kumar, KARAKUS, Can, JI, Tingfang
• Granted Patent: US 10,505,597 B2
• Time in Patent Office: Days
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0421 utilizing implicit feedback, e.g. steered pilot signals
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0456 Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/0691 using subgroups of transmit antennas
• CPC Class Codes: H04B 7/0695 using beam selection
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 5/0037 Inter-user or inter-terminal allocation
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 76/10 Connection setup
• CPC Class Codes: H04W 88/02 Terminal devices
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

Aspects of the present disclosure relate to wireless communications and, more particularly, to reference signals (RS) and link adaptation for massive multiple-input multiple-output (MIMO). In one aspect, a method is provided which may be performed by a wireless device such as a base station (BS). The method generally includes receiving sounding reference signals (SRS) and at least one of: feedback regarding interference or a whitening matrix from one or more user equipments (UEs), determining beamforming parameters for transmissions to a group of one or more UEs based, at least in part, on the SRS and at least one of: the feedback regarding interference or the whitening matrix, and transmitting channel state information reference signals (CSI-RS) to UEs in the group using the determined beamforming parameters.

Claims

1. A method for wireless communications by a base station (BS), comprising:

receiving sounding reference signals (SRS) and at least one of;

feedback regarding interference or a whitening matrix from one or more user equipments (UEs);

determining beamforming parameters for transmissions to a group of one or more UEs based, at least in part, on the SRS and at least one of;

the feedback regarding interference or the whitening matrix; and

transmitting channel state information reference signals (CSI-RS) to UEs in the group using the determined beamforming parameters.

2. The method of claim 1, wherein the beamforming parameters comprise at least one of:

which UEs are in the group, one or more precoders, or a number of spatial streams.

3. The method of claim 1, further comprising:

receiving CSI feedback from the at least one UE; and

determining the beamforming parameters for transmissions to the UE further based on the CSI feedback.

4. The method of claim 3, wherein the CSI feedback comprises at least one of:

a channel quality indication (CQI), rank indicator (RI), the feedback regarding interference, or a phase correction matrix.

5. The method of claim 4, further comprising:

determining different precoders, spatial streams, or UE groupings based on the phase correction matrix if the CSI feedback comprises the phase correction matrix.

6. The method of claim 1, wherein at least one of:

the feedback regarding interference or the whitening matrix is provided implicitly via a rotation used for the SRS.

7. The method of claim 1, further comprising:

performing channel estimation based on the received SRS; and

determining the beamforming parameters based on the channel estimation.

8. The method of claim 1, wherein:

the SRS is received in an uplink portion of a first subframe; and

the CSI-RS is transmitted in a downlink portion of a second subframe, wherein an amount of resources in the second subframe allocated for downlink transmissions is greater than an amount of resources allocated for uplink transmissions.

9. The method of claim 8, further comprising:

transmitting data in a downlink portion of a third subframe;

receiving an acknowledgment (ACK) or negative acknowledgment (NACK) for the data in an uplink portion of the third subframe;

sending another CSI-RS in a downlink portion of a fourth subframe if a negative acknowledgement (NACK) for the transmitted data is received; and

retransmitting the data in a downlink portion of a fifth subframe in response to the NACK, wherein an amount of resources in the fifth subframe allocated for downlink transmissions is greater than an amount of resources allocated for uplink transmissions.

10. The method of claim 1, wherein:

the SRS is received in an uplink portion of a first subframe; and

the CSI-RS is sent in a downlink portion of a second subframe, wherein an amount of resources in the second subframe allocated for uplink transmissions is greater than an amount of resources allocated for downlink transmissions.

11. The method of claim 10, further comprising:

transmitting data in a downlink portion of a third subframe;

receiving an acknowledgment (ACK) or negative acknowledgment (NACK) for the data in an uplink portion of the third subframe; and

retransmitting the data in a downlink portion of a fourth subframe in response to the NACK.

12. The method of claim 1, wherein:

CSI-RS is transmitted in a common downlink portion of every subframe.

13. The method of claim 1, further comprising:

determining a rotation of the SRS; and

determining the beamforming parameters based, at least in part, on the determined rotation.

14. A method for wireless communications by a user equipment (UE), comprising:

transmitting sounding reference signals (SRS) and at least one of;

feedback regarding interference or a whitening matrix to a base station (BS);

receiving beamformed channel state information reference signals (CSI-RS) from the BS;

determining CSI feedback based on the beamformed CSI-RS; and

transmitting the CSI feedback to the BS.

15. The method of claim 14, wherein the CSI feedback comprises at least one of:

a channel quality indication (CQI), a rank indicator (RI), the feedback regarding interference, or a phase correction matrix.

16. The method of claim 15, further comprising:

receiving another CSI-RS with different beamforming parameters based on the phase correction matrix if the CSI feedback comprises the phase correction matrix.

17. The method of claim 14, wherein:

the SRS is transmitted in an uplink portion of a first subframe; and

the CSI-RS is received in a downlink portion of a second subframe, wherein an amount of resources in the second subframe allocated for downlink transmissions is greater than an amount of resources allocated for uplink transmissions.

18. The method of claim 17, further comprising:

receiving data in a downlink portion of a third subframe;

transmitting an acknowledgment (ACK) or negative acknowledgment (NACK) for the data in an uplink portion of the third subframe;

receiving another CSI-RS in a downlink portion of a fourth subframe if a negative acknowledgement (NACK) for the data is transmitted; and

receiving a retransmission of the data in a downlink portion of a fifth subframe in response to the NACK, wherein the fifth subframe comprises a downlink-centric subframe, wherein an amount of resources allocated for downlink transmissions is greater than an amount of resources allocated for uplink transmissions.

19. The method of claim 14, wherein:

the SRS is transmitted in an uplink portion of a first subframe; and

the CSI-RS is received in a downlink portion of a second subframe, wherein an amount of resources in the second subframe allocated for uplink transmissions is greater than an amount of resources allocated for downlink transmissions.

20. The method of claim 19, further comprising:

receiving data in a downlink portion of a third subframe;

transmitting an acknowledgment (ACK) or negative acknowledgment (NACK) for the data in an uplink portion of the third subframe; and

receiving a retransmission of the data in a downlink portion of a fourth subframe in response to the NACK.

21. The method of claim 14, wherein:

CSI-RS is received in a common downlink portion of every subframe.

22. The method of claim 14, further comprising:

determining a rotation for the SRS, wherein transmitting the SRS comprises transmitting the rotated SRS.

23. A method for wireless communications, by a user equipment (UE), comprising:

transmitting one or more sounding reference signals (SRS) to a base station (BS);

receiving a data packet from the BS; and

reporting demodulation quality feedback to the BS based on the received data packet.

24. The method of claim 23, wherein the demodulation quality feedback comprises a demodulation quality indicator or a demodulation signal to interference plus noise ratio (SINR).

25. The method of claim 23, wherein the one or more SRS is transmitted in an uplink portion of a first subframe;

and

the data packet is transmitted in a downlink portion of a second subframe, wherein an amount of resources in the second subframe allocated for downlink transmissions is greater than an amount of resources allocated in the second subframe for uplink transmissions.

26. The method of claim 25, further comprising:

transmitting an acknowledgment (ACK) or negative acknowledgment (NACK), for the data packet, in an uplink portion of the second subframe, wherein the demodulation quality feedback is transmitted in an uplink portion of the second subframe.

27. The method of claim 25, wherein the demodulation quality feedback is transmitted in an uplink portion of a third subframe, and wherein an amount of resources in the third subframe allocated for uplink transmissions is greater than an amount of resources allocated in the third subframe for downlink transmissions.

28. A method for wireless communications, by a base station (BS), comprising:

receiving one or more sounding reference signals (SRS) from a user equipment (UE);

transmitting a data packet to the UE;

receiving demodulation quality feedback from the UE based on the data packet; and

selecting at least one of;

a modulation scheme or a coding rate for transmitting to the UE based on the demodulation quality feedback.

29. The method of claim 28, wherein the demodulation quality feedback comprises a demodulation quality indicator or a demodulation signal to interference plus noise ratio (SINR).

30. The method of claim 28, wherein the one or more SRS is received in an uplink portion of a first subframe;

and

the data packet is transmitted in a downlink portion of a second subframe, wherein an amount of resources in the second subframe allocated for downlink transmissions is greater than an amount of resources allocated in the second subframe for uplink transmissions.

31. The method of claim 30, further comprising:

receiving an acknowledgment (ACK) or negative acknowledgment (NACK), for the data packet, in an uplink portion of the second subframe, wherein the demodulation quality feedback is received in an uplink portion of the second subframe.

32. The method of claim 30, wherein the demodulation quality feedback is received in an uplink portion of a third subframe, wherein an amount of resources in the third subframe allocated for uplink transmissions is greater than an amount of resources allocated in the third subframe for downlink transmissions.

33. An apparatus for wireless communications by a base station (BS), comprising:

means for receiving sounding reference signals (SRS) and at least one of;

feedback regarding interference or a whitening matrix from one or more user equipments (UEs);

means for determining beamforming parameters for transmissions to a group of one or more UEs based, at least in part, on the SRS and at least one of;

the feedback regarding interference or the whitening matrix; and

means for transmitting channel state information reference signals (CSI-RS) to UEs in the group using the determined beamforming parameters.

34. An apparatus for wireless communications by a user equipment (UE), comprising:

means for transmitting sounding reference signals (SRS) and at least one of;

feedback regarding interference or a whitening matrix to a base station (BS);

means for receiving beamformed channel state information reference signals (CSI-RS) from the BS;

means for determining CSI feedback based on the beamformed CSI-RS; and

means for transmitting the CSI feedback to the BS.