Random Access Timing Advance Handling for NTN Propagation Delays
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Solution Overview
Problem
Existing random access procedures in communications networks, particularly in Non-Terrestrial Networks (NTNs) like satellite networks, face challenges due to large propagation delays, making it difficult to establish successful connections between UEs and network nodes.
Innovation Solution
A network node method that refrains from initially responding to a UE's first random access preamble, instead transmitting a Random Access Response (RAR) with estimated Timing Advance (TA) commands for multiple possible preambles, and subsequently checks for matching TA values in retransmitted preambles, allowing for efficient random access handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the network node responds to the first RA preamble with a RAR in the conventional random access procedure, then the connection establishment process can proceed normally in terrestrial networks, but the procedure fails in satellite networks due to large propagation delays causing timing misalignment
Solution Approach 1:
The network node performs preliminary actions by transmitting RAR messages for multiple possible RA preambles (including potential retransmissions) before actually receiving those preambles. This allows the UE to receive the RAR in advance and use the TA command for timing alignment when it eventually transmits the RA preamble or retransmission, compensating for the large propagation delays in satellite networks.
2Reliability
If the network node transmits multiple RAR messages for different RA preambles in advance, then timing alignment can be achieved despite propagation delays, but the network node must maintain and update TA values for multiple preambles increasing processing complexity
Solution Approach 1:
The network node creates a mapping between multiple RA preambles and their corresponding TA values, where each RAR message contains a TA command that can be universally applied regardless of which specific RA preamble the UE eventually transmits. This multi-functional approach allows a single RAR transmission to serve multiple potential RA preamble scenarios.
Solution Approach 2:
The network node dynamically updates TA values associated with different RA preambles based on received uplink signals. When a UE transmits an RA preamble or retransmission, the network node estimates the TA value from the received signal and updates the corresponding TA parameter in the mapping, ensuring accurate timing alignment for future communications.
3Productivity
If the conventional RAR window timing is used in satellite networks, then the procedure works for terrestrial networks with small delays, but the UE misses the RAR or experiences excessive delay due to large propagation delays in satellite networks
Solution Approach 1:
The network node transmits the RAR message in advance during a configured RAR window before the UE actually transmits its RA preamble or retransmission. This preliminary transmission ensures the UE receives the RAR and TA command early enough to perform timing alignment, overcoming the large propagation delays that would otherwise cause the UE to miss the RAR or experience excessive delays.
Data Source
AI summary
There is provided mechanisms for random access handling of a UE. A method is performed by a network node. The method comprises receiving, from the UE during a first RAO, a first RA preamble, whilst refraining from responding to the first RA preamble. The method comprises transmitting, towards the UE and without the network node first having received any retransmitted RA preamble from the UE, one RAR for each of N possible RA preambles, where each RAR comprises a TA command corresponding to a TA value estimated for the first RA preamble. The method comprises receiving, from the UE during a further RAO, a retransmitted RA preamble. The method comprises determining whether the TA value for the retransmitted RA preamble matches the TA value for the first RA preamble or not.