Random Access Completion for Low-Latency L1/L2 Cell Mobility
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Solution Overview
Problem
Existing random access procedures in wireless communication networks, particularly during inter-cell mobility, result in prolonged delays and increased overhead due to layer 3 signaling, leading to longer interruptions and inefficiencies.
Innovation Solution
Implement a mechanism for acquiring timing advance (TA) of candidate cells using PDCCH ordered RACH, allowing completion determination of random access procedures on candidate cells through transmission of preambles or reception of PDCCH transmissions, thereby enabling L1/L2 mobility enhancements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If layer 3 signaling is used for serving cell changes, then reliability is improved, but delay and overhead increase
Solution Approach 1:
The patent segments the mobility procedure into two parts: timing advance acquisition (handled quickly at L1/L2) and serving cell change execution (handled at L3). This allows the time-critical TA acquisition to be separated from the more complex cell change signaling, reducing overall delay while maintaining reliability.
Solution Approach 2:
The patent performs timing advance acquisition as a preliminary action before the actual serving cell change is executed. By obtaining TA information in advance through PDCCH ordered RACH on candidate cells, the system prepares necessary parameters beforehand, avoiding delays during the critical cell switch moment.
2Reliability
If complete layer 1 reset is performed for serving cell changes, then reliability is improved, but interruption time increases
Solution Approach 1:
The patent performs timing advance acquisition as a preliminary action before the actual serving cell change is executed. By obtaining TA information in advance through PDCCH ordered RACH on candidate cells, the system prepares necessary parameters beforehand, avoiding delays during the critical cell switch moment.
Solution Approach 2:
The patent enables dynamic timing advance adjustment by allowing UEs to acquire TA for candidate cells before switching. This dynamic approach allows the system to adapt TA values in real-time based on the target cell, eliminating the need for complete layer 1 reset and reducing interruption time.
3Speed
If PDCCH ordered RACH is used for TA acquisition, then mobility speed is improved, but device complexity increases
Solution Approach 1:
The patent reuses the existing PDCCH ordered RACH mechanism, originally designed for other purposes, to also serve timing advance acquisition for L1/L2 mobility. This multi-functional use of an existing procedure avoids creating entirely new complex mechanisms while achieving the desired mobility speed improvement.
Data Source
AI summary
A random access apparatus, applicable to a terminal equipment, includes: a transmitter configured to transmit a random access preamble on a L1/L2 triggered mobility (LTM) candidate cell on a determined physical random access channel (PRACH) occasion corresponding to a selected synchronization signal block (SSB); and processor circuitry configured to, when a terminal equipment transmits the random access preamble on the LTM candidate cell, and/or when the terminal equipment receives a physical downlink control channel (PDCCH) transmission in a search space or a control resource set (coreset) related to the LTM candidate cell, determine that a random access procedure on the LTM candidate cell is completed.