Back-off mechanisms for inter-cell mobility

1 . A baseband processor configured to:

receive a unified transmission configuration indicator (TCI) from a first serving cell wherein the unified TCI includes a mapping between a TCI state and a second serving cell that is a candidate cell of a user equipment (UE) of the baseband processor and is not activated at a time of reception, wherein the mapping identifies beam information of the second serving cell;

in response to receiving the unified TCI,

output, for transmission, an acknowledgment (ACK) message to the first serving cell;

communicate with the second serving cell based on the indicated beam information of the unified TCI; and

configure a time window subsequent to transmission of the ACK message;

perform a fallback operation when a dedicated signaling from the second serving cell is not received within the time window, wherein the fallback operation comprises generating a scheduling request (SR) associated with the second serving cell; and

generating the SR based on a physical uplink control channel (PUCCH) resource of the second serving cell that is identified by the mapping between the TCI state and the second serving cell, the PUCCH resource being configured by a radio resource control (RRC) signaling from the first serving cell.

2 . The baseband processor of claim 1 , wherein the fallback operation comprises configuring operations to communicate with the first serving cell.

3 . The baseband processor of claim 1 , wherein the fallback operation comprises generating a contention based random access channel preamble (PRACH) associated with the second serving cell.

4 . The baseband processor of claim 3 , further configured to generate a medium access control (MAC) control element (CE) associated with Layer 1 (L1)/Layer 2 (L2)-centric inter-cell mobility communications in a message 3 (Msg3) RACH or a message A (MsgA) RACH, wherein the MAC CE includes a cell radio network temporary identifier (C-RNTI) of the second serving cell or a TCI to cell mapping used for selecting a PRACH resource for the second serving cell prior to receiving dedicated signaling from the second serving cell that configures the UE to communicate with the second serving cell.

5 . The baseband processor of claim 1 , wherein the fallback operation comprises generating a contention free random access channel preamble (PRACH) associated with the second serving cell, wherein the contention free PRACH is based on a radio resource control (RRC) signaling associated with the first serving cell.

6 . The baseband processor of claim 5 , further configured to receive a response message in at least one of a dedicated search space or control resource set wherein the at least one of the dedicated search space or control resource set is configured by the RRC signaling or a physical downlink control channel (PDCCH) of the second serving cell and based on a radio network temporary identifier (RNTI) of a user equipment (UE) associated with the baseband processor, wherein the response message is initiated by the contention free PRACH.

7 . A user equipment (UE), comprising:

a memory interface; and

processing circuitry communicatively coupled to the memory interface and configured to:

receive a unified transmission configuration indicator (TCI) from a first serving cell wherein the unified TCI includes a mapping between a TCI state and a second serving cell that is a candidate cell of the UE and is not activated at a time of reception, wherein the mapping identifies beam information of the second serving cell;

transmit, by a radio frequency circuitry, a negative acknowledgment (NACK)/discontinuous transmission (DTX) in response to the unified TCI;

maintain configuration for communication with the first serving cell;

configure a time window subsequent to generating the NACK/DTX;

perform a fallback operation when a dedicated signaling from the first serving cell is not received within the time window, wherein the fallback operation comprises generating a scheduling request (SR) associated with the second serving cell; and

generating the SR based on a physical uplink control channel (PUCCH) resource of the second serving cell that is identified by the mapping between the TCI state and the second serving cell, the PUCCH resource being configured by a radio resource control (RRC) signaling from the first serving cell.

8 . The UE of claim 7 , wherein the fallback operation comprises generating a contention based random access channel preamble (PRACH) associated with the first serving cell.

9 . The UE of claim 8 , further configured to, in response to generating the contention based PRACH, generate a message 3 (Msg3) RACH or a message A (MsgA) RACH wherein the Msg3 RACH or MsgA RACH includes a cell radio network temporary identifier (C-RNTI) associated with the first serving cell or a UE ID of the UE.

10 . The UE of claim 8 , further configured to:

perform measurements on one or more beams of the second serving cell, wherein beam information of the one or more beams of the second serving cell is indicated by the unified TCI; and

generate a message with at least one of a physical cell ID (PCI), a synchronization signal block (SSB), or channel state information reference signal (CSI-RS) of the second serving cell associated with the measurements on one or more beams of the second serving cell.

11 . The UE of claim 7 , wherein the fallback operation comprises generating a contention based random access channel preamble (PRACH) for the second serving cell.

12 . The UE of claim 11 , further configured to generate a message 3 (Msg3) RACH or a message A (MsgA) RACH wherein the Msg3 RACH or MsgA RACH includes a cell radio network temporary identifier (C-RNTI) associated with a cell of the second serving cell or a UE ID of the UE.

13 . The UE of claim 11 , further configured to:

perform measurements on one or more beams of the second serving cell;

determine a L1-RSRP of a beam of the second serving cell according to the measurements;

determine whether the L1-RSRP of the beam of the second serving cell satisfies a RSRP threshold; and

generate a contention based random access channel preamble (PRACH) associated with the second serving cell in response to determining that the RSRP threshold is satisfied by the L1-RSRP of the beam of the second serving cell.

14 . A method for a user equipment (UE), configured with operations comprising:

receiving a unified transmission configuration indicator (TCI) from a first serving cell wherein the unified TCI includes a mapping between a TCI state and a second serving cell that is a candidate cell of the UE and is not activated at a time of reception, wherein the mapping identifies beam information of the second serving cell;

in response to receiving the unified TCI,

transmitting an acknowledgment (ACK) message to the first serving cell;

communicating with the second serving cell based on the indicated beam information of the unified TCI;

configuring a time window subsequent to transmission of the ACK message;

performing a fallback operation when a dedicated signaling from the second serving cell is not received within the time window, wherein the fallback operation comprises generating a scheduling request (SR) associated with the second serving cell; and

generating the SR based on a physical uplink control channel (PUCCH) resource of the second serving cell that is identified by the mapping between the TCI state and the second serving cell, the PUCCH resource being configured by a radio resource control (RRC) signaling from the first serving cell.

15 . The method of claim 14 , further comprising awaiting a response time period subsequent to transmission of the ACK; and

communicating with the second serving cell at an expiration of the response time period.

16 . The method of claim 14 , further comprising:

prior to communicating with the second serving cell, generating an uplink signal for transmission with the second serving cell;

receiving a downlink confirmation associated with the second serving cell in response to generating the uplink signal;

waiting a response time period subsequent to receiving the downlink confirmation; and

communicating with the second serving cell at an expiration of the response time period.

17 . The method of claim 14 , wherein the uplink signal is associated with a sounding reference signal (SRS), and the operations comprise:

receiving a response message in at least one of a dedicated search space or control resource set wherein the at least one of the dedicated search space or control resource set is configured by a RRC or a physical downlink control channel (PDCCH) of the second serving cell and based on a radio network temporary identifier (RNTI).

18 . The method of claim 14 , wherein the uplink signal is associated with a physical uplink shared channel (PUSCH), and the operations comprise:

receiving a response message in a physical downlink control channel (PDCCH) associated with the second serving cell, wherein the PDCCH schedules a new transmission with a same hybrid automatic repeat request (HARQ) process as the PUSCH.

19 . The baseband processor of claim 1 , further configured to:

perform measurements on one or more beams of the second serving cell, wherein beam information of the one or more beams of the second serving cell are indicated by the unified TCI; and

generate a message with at least one of a physical cell ID (PCI), a synchronization signal block (SSB), or channel state information reference signal (CSI-RS) of the second serving cell associated with the measurements on one or more beams of the second serving cell.

20 . The UE of claim 11 , further configured to:

perform measurements on one or more beams of the second serving cell;

determine a L1-RSRP of a beam of the second serving cell according to the measurements;

determine whether the L1-RSRP of the beam of the second serving cell satisfies a RSRP threshold; and

generate a contention based random access channel preamble (PRACH) associated with the second serving cell in response to determining that the RSRP threshold is satisfied.