RACH Resource Configuration for Non-Terrestrial Networks
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Solution Overview
Problem
In non-terrestrial networks (NTN), the large differential timing advance (TA) between user equipment (UE) and the base station leads to confusion in scheduling Random Access Channel (RACH) occasions, causing issues with RACH resource allocation and coverage due to the long round-trip delay and wide cell range, resulting in potential misclassification of preambles during the random access procedure.
Innovation Solution
The proposed solution involves transmitting the estimated time advance (TA) in the preamble (Msg1) and configuring RACH resources based on this TA information, allowing the base station to accurately determine the TA and schedule messages, thereby reducing the differential TA and improving RACH resource allocation and coverage by grouping preambles according to their estimated TAs and configuring thresholds for TA-based RACH resource allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If RACH resources are allocated without TA information in Msg1, then the random access procedure can proceed with standard timing, but the gNB cannot accurately schedule Msg2 and Msg3 due to large differential TA in NTN
Solution Approach 1:
The UE performs preliminary TA estimation before transmitting Msg1 and carries this estimated TA information in the preamble. This allows the gNB to obtain TA information in advance (before Msg3), enabling accurate scheduling of Msg2 and Msg3 while maintaining standard RACH timing procedures
Solution Approach 2:
The estimated TA information carried in Msg1 acts as an intermediary that bridges the timing gap between UE and gNB. It provides the gNB with advance knowledge of the TA value, enabling accurate scheduling decisions without requiring the full 4-step RACH procedure to complete first
2Device complexity
If RACH occasions are scheduled with fixed timing in NTN, then the scheduling is simple, but preambles from UEs with different TAs may be misclassified due to large differential TA
Solution Approach 1:
The gNB obtains preliminary TA information from Msg1 before scheduling decisions are made. This allows the gNB to calculate accurate reception timing for Msg1 and set appropriate RAR window timing, preventing preamble misclassification while maintaining fixed scheduling patterns
Solution Approach 2:
The gNB uses the estimated TA from Msg1 to dynamically adjust scheduling parameters such as RAR window timing and Msg3 resource allocation. This parameter adjustment based on TA information ensures accurate preamble classification without requiring complex scheduling algorithms
3Adaptability or versatility
If the RAR window is set to cover the maximum round-trip delay in NTN, then all UEs can be accommodated, but the waiting time for UEs with smaller delay increases unnecessarily
Solution Approach 1:
The gNB uses the estimated TA from Msg1 to dynamically set the RAR window timing and duration for each UE. UEs with smaller delays receive their RAR earlier in the window, while UEs with maximum delay receive it at the appropriate later time. This eliminates unnecessary waiting time while maintaining full coverage
Solution Approach 2:
Different RAR timing is provided to different UEs based on their specific TA values. Each UE receives the RAR at a time locally optimized for its distance from the gNB, rather than using a uniform timing that must accommodate the maximum delay case for all UEs
Data Source
AI summary
Methods and apparatuses for optimization of RACH procedure in non-terrestrial network are disclosed. A method comprises transmitting a preamble on a RACH resource from an uplink time slot, which is a first time advance before corresponding downlink time slot; and monitoring a control signal from a first time offset after the end of the transmission of the preamble.