Random Access Response Handling for Candidate Cell Timing Advance
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Solution Overview
Problem
In mobile communication systems, when a PRACH is transmitted for a candidate cell, the ambiguity in receiving an RAR from a serving cell can lead to unclear completion of the random access procedure, especially regarding MSG3 and MSG4 transmission and reception, necessitating a separate definition of the completion time point for the random access procedure related to the candidate cell.
Innovation Solution
A method involving a user equipment (UE) that receives configuration information for candidate cells, transmits a PRACH, and receives a RAR, which may include Timing Advance Command, UL grant, and Temporary C-RNTI fields, with reserved bits for these fields, allowing the UE to confirm the completion of the random access procedure based on additional information like PCI, RA-RNTI, and TAG ID, and HARQ-ACK, using DCI for subsequent operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RAR includes all standard fields (UL grant, Temporary C-RNTI, Timing Advance Command), then the random access procedure can be completed according to legacy specifications, but the signaling overhead increases and unnecessary information is transmitted when UL transmission is not required for the neighbor cell
Solution Approach 1:
The patent extracts and removes unnecessary fields (UL grant and Temporary C-RNTI) from the RAR message when the random access procedure is specifically for TA acquisition of a neighbor cell. Since UL transmission is not performed for the neighbor cell and the UE already has a C-RNTI, these fields are omitted to reduce signaling overhead while maintaining the essential Timing Advance Command field for TA acquisition.
2Device complexity
If the RAR is transmitted without explicit candidate cell identification, then the message format remains simple, but the UE cannot determine which candidate cell the RAR corresponds to, creating ambiguity in procedure completion
Solution Approach 1:
The patent introduces an intermediary mechanism where the DCI that triggered the PRACH transmission contains the candidate cell identification information. The UE uses this identification from the DCI to associate the received RAR with the specific candidate cell, resolving the ambiguity without complicating the RAR message format itself.
3Productivity
If the random access procedure follows the legacy completion criteria (MSG3 and MSG4 transmission), then the procedure can be completed according to existing standards, but the completion time point is incorrect for TA acquisition procedures where MSG3 and MSG4 are not transmitted
Solution Approach 1:
The patent changes the completion criterion parameter for the random access procedure. Instead of using the legacy MSG3/MSG4 transmission as the completion marker, the procedure is completed when the UE receives the RAR containing the Timing Advance Command for the candidate cell. This parameter change aligns the completion timing with the actual purpose of TA acquisition and enables faster handover preparation.
Data Source
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AI summary
A method according to an embodiment of the present disclosure comprises the steps of: receiving DCI; transmitting a PRACH; and receiving an RAR. The RAR includes at least one of i) a timing advance command field, ii) a UL grant field, and/or iii) a temporary C-RNTI field. On the basis that the PRACH is related to a second cell different from a first cell, the RAR without the UL grant field and/or the temporary C-RNTI field is received.