UL spatial relation switch for PUCCH, PUSCH and SRS
Methods and apparatus are provided for a UE to determine a UL spatial relation for an UL transmission in response to an unknown UL spatial relation switch. The UE may determine whether the UL spatial relation is based on an SRS transmission in UL, a CSI-RS in DL, or an SSB in the DL. If the UL spatial relation is based on the SRS transmission, the UE may select the UL spatial relation for the UL transmission corresponding to a Tx beam of the SRS transmission. If the UL spatial relation is based on the CSI-RS or the SSB, the UE may select the UL spatial relation for the UL transmission based on whether the unknown UL spatial relation switch is due to a corresponding resource for beam training not being configured by a communication network or a corresponding beam information being expired.
1. A method for a user equipment (UE) to determine an uplink (UL) spatial relation for an UL transmission, the method comprising:
determining whether the UL spatial relation is for a sounding reference signal (SRS) transmission in the UL, a channel state indicator reference signal (CSI-RS) in a downlink (DL), or a synchronization signal block (SSB) in the DL;
when the UL spatial relation is for the SRS transmission, selecting the UL spatial relation for the UL transmission corresponding to a transmit (Tx) beam of the SRS transmission; and
when the UL spatial relation is for the CSI-RS or the SSB, using a receive (Rx) beam or active Transmission Configuration Indicator (TCI) for reception of a pathloss reference signal (PL-RS) to derive a corresponding Tx beam for the UL transmission.
2. The method of claim 1 , wherein the UL transmission is selected from a group comprising an SRS or a physical uplink control channel (PUCCH).
3. The method of claim 1 , wherein the PL-RS comprises an active pathloss reference signal that is on-use by the UE for UL power control.
4. The method of claim 1 , further comprising, when the UL spatial relation is for the CSI-RS or the SSB, generating an indication or request to the communication network to configure or reconfigure an available resource for UL spatial relation switching.
5. The method of claim 4 , wherein the indication or request is carried on one or more of a radio resource control (RRC) signal, a medium access control (MAC) protocol data unit (PDU), an uplink control information or other L1 indication), and a random access channel (RACH).
6. The method of claim 4 , wherein the UL transmission comprises a physical uplink control channel (PUCCH), and wherein the method further comprises not transmitting the PUCCH until the communication network configures or reconfigures the available resource for the UE to determine the UL spatial relation.