Methods, apparatus, systems and procedures for uplink (ul) channel reciprocity

1. A method of uplink (UL) transmission implemented by a Wireless Transmit/Receive Unit (WTRU) using a plurality of Sounding Reference Signals (SRSs), the method comprising:

measuring, by the WTRU, one or more downlink (DL) reference signals (RSs);

precoding, by the WTRU, the plurality of SRSs using first precoding information which is based on the measured one or more DL RSs;

transmitting, by the WTRU to a network entity, the plurality of SRSs that are precoded;

receiving, by the WTRU, Downlink Control Information (DCI) including an indicator indicating second precoding information based on the precoded SRSs;

precoding, by the WTRU, UL data using the indicated second precoding information; and

transmitting, by the WTRU, the UL data that is precoded using the indicated second precoding information.

2. The method of claim 1 , wherein the transmitting of the SRSs that are precoded includes sending an indication to the network entity of a set of recommended precoders.

3. The method of claim 2 , further comprising identifying, by the WTRU via the DCI, a subset of the recommended precoders sent as the indication to the network entity based on the indicator included in the DCI.

4. The method of claim 2 , wherein the plurality of SRSs and the UL data are precoded differently.

5. The method of claim 1 , wherein the indicator is an index to identify the second precoding information.

6. The method of claim 2 , wherein the set of recommended precoders used to precode the plurality of the SRSs is determined by the WTRU based on the measured DL RSs.

7. The method of claim 3 , wherein the subset of recommended precoders associated with the second precoding information and indicated by the indicator in the DCI is used to any of generate a beam: (1) in a particular direction; (2) to avoid or to substantially avoid an interference direction; (3) to cancel or to reduce interference between or among the WTRU and one or more further WTRUs; or (4) having a null space that corresponds to an interference direction associated with at least one other WTRU.

8. The method of claim 6 , further comprising determining the first precoding information including determining a precoding vector or precoding matrix based on channel state information (CSI) RSs, as the measured DL RSs.

9. A Wireless Transmit/Receive Unit (WTRU) configured to transmit uplink (UL) data using a plurality of Sounding Reference Signals (SRSs), comprising:

a processor configured to:

measure one or more downlink (DL) reference signals (RSs), and

precode the plurality of SRSs using first precoding information which is based on the measured one or more DL RSs; and

a transceiver configured to:

transmit, to a network entity, the plurality of SRSs that are precoded, and

receive Downlink Control Information (DCI) including an indicator indicating second precoding information based on the precoded SRSs,

wherein:

the processor is configured to precode UL data using the indicated second precoding information, and

the transceiver is configured to transmit the uplink (UL) data that is precoded using the indicated second precoding information.

10. The WTRU of claim 9 , wherein the transceiver is configured to send an indication to the network entity of a set of recommended precoders.

11. The WTRU of claim 10 , wherein the processor is configured to identify via the DCI, a subset of the recommended precoders sent as the indication to the network entity based on the indicator included in the DCI.

12. The WTRU of claim 9 , wherein the plurality of SRSs and the UL data are precoded differently.

13. The WTRU of claim 9 , wherein the indicator is an index to identify the second precoding information.

14. The WTRU of claim 10 , wherein the processor is configured to determine the set of recommended precoders used to precode the plurality of the SRSs based on the measured DL RSs.

15. The WTRU of claim 11 , wherein the subset of recommended precoders associated with the second precoding information and indicated by the indicator in the DCI is used to any of generate a beam: (1) in a particular direction; (2) to avoid or to substantially avoid an interference direction; (3) to cancel or reduce interference between or among the WTRU and one or more further WTRUs; or (4) having a null space that corresponds to an interference direction associated with at least one other WTRU.

16. The WTRU of claim 14 , wherein the processor is configured to determine a precoding vector or precoding matrix based on channel state information (CSI) RSs, as the measured DL RSs.

17. A Network Access Point (NAP) configured to provide precoding assistance to a Wireless Transmit/Receive Unit (WTRU) using a plurality of Sounding Reference Signals (SRSs), the NAP comprising:

a transceiver configured to receive, from the WTRU, the plurality of SRSs that are precoded; and

a processor configured to:

determine precoders associated with the precoded SRSs that are recommended by the WTRU,

select a subset of the recommended precoders, and

transmit, to the WTRU, Downlink Control Information (DCI) including an indicator indicating the selected subset of recommended precoders,

wherein:

the transceiver is configured to receive UL data from the WTRU, and

the processor is configured to decode the UL data using the subset of recommended precoders.

18. The NAP of claim 17 , wherein the plurality of SRSs and the UL data are precoded differently.

19. The NAP of claim 17 , wherein the indicator is an index to identify the subset of recommended precoders.

20. The NAP of claim 17 , wherein the processor is configured to select the subset of recommended precoders indicated by the indicator in the DCI based on generation of a beam: (1) in a particular direction; (2) to avoid or to substantially avoid an interference direction; (3) to cancel or to reduce interference between or among the WTRU and one or more further WTRUs; or (4) having a null space that corresponds to an interference direction associated with at least one other WTRU.