Timing advance resource management

A user equipment apparatus comprising:

• at least one processor;
• and
• at least one memory storing instructions which, when executed by the at least one processor, cause the user equipment apparatus at least to:
• establish a connection with a control network node via a serving cell, the control network node supporting at least one of central unit-control plane (CU-CP) functionality or a layer 3 protocol of a radio access network, wherein the serving cell is supported by a source network node which supports at least one of distributed unit (DU) functionality or a layer 2 protocol of the radio access network;
• receive, from the control network node and from the source network node, a plurality of timing advance (TA) cell configurations for a set of timing advance (TA) cells, wherein the plurality of TA cell configurations comprises a TA-associated random access (RA) configuration for TA acquisition for a specific TA cell of the plurality of TA cells, wherein the set of TA cells comprises:
• first TA cells comprising candidate target cells with which the UE may connect, and
• other TA cells which are requested by at least one of the candidate target cells and which the UE may connect with in case the UE connects with the at least one of the candidate target cells;
• acquire TA for the specific TA cell based on the TA-associated RA configuration and an associated TA acquisition request;
• acquire a separate TA value for each of the candidate target cells;
• and
• acquire TA for the other TA cells,
• wherein the TA-associated RA configuration comprises a contention-free random access (CFRA) configuration,
• wherein the TA-associated RA configuration further comprises:
• a timer on validity of CFRA resources corresponding to the CFRA configuration, the timer comprising:
• a time length, a timer trigger, a timer starting point, a timer stopping point, conditions for timer reset, and conditions for timer restart;
• information indicating that the CFRA resources are valid before receiving a cell switch command, before a cell switch, and after a cell switch;
• and
• information indicating that the CFRA resources are valid for a number of RA transmissions during a time period, and
• wherein the TA-associated RA configuration further comprises gaps, for performing RF tuning and RA preamble transmission, based on:
• an RA occasion of the specific TA cell being on a different frequency than an active frequency band of the UE with the serving cell, and
• a RAR reception configuration specifying a frequency for receiving RAR that is a different frequency than the active frequency band of the UE with the serving cell,
• wherein the instructions, when executed by the at least one processor, further cause the user equipment apparatus to:
• generate information regarding TA cell channel quality and information regarding handover probability, by performing:
• selecting a particular CFRA resource of the CFRA configuration for acquiring TA, and
• transmitting a random access preamble of the TA-associated RA configuration to acquire TA;
• receive, from a TA network node which supports the specific TA cell and supports at least one of distributed unit (DU) functionality or a layer 2 protocol of a radio access network, a random access response (RAR), wherein the RAR comprises:
• validity indicator for a TA value,
• a time alignment timer (TAT),
• uplink resources usable after a handover,
• validity timer for the uplink resources,
• a TA command,
• a timing advance group (TAG) associated with the TA command,
• TAG information including cells or TCI-state IDs,
• TAG timer, and
• validity conditions of TA command;
• and
• connect with the at least one of the candidate target cells and with the other TA cells which were requested by the at least one of the candidate target cells.