NTN Random Access Signaling for PRACH Timing-Frequency Ambiguity
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Solution Overview
Problem
The existing NR standard is designed primarily for terrestrial networks and faces challenges in supporting Non-Terrestrial Networks (NTN) due to issues with timing and frequency ambiguities in PRACH formats, particularly with Zadoff-Chu sequences, leading to difficulties in separating delay and frequency shifts during random access procedures.
Innovation Solution
Introduce new PRACH formats based on two Zadoff-Chu sequences to address timing and frequency ambiguities, allowing for improved UL timing and frequency estimation in NTN, and support different random access procedures tailored for NTN environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If existing NR standard PRACH formats with Zadoff-Chu sequences are used, then the system maintains compatibility with terrestrial networks, but timing and frequency ambiguities cannot be resolved in NTN environments
Solution Approach 1:
The patent segments the random access procedure by introducing separate PRACH formats specifically designed for NTN (Format A and Format B) distinct from terrestrial formats. Format A uses two different Zadoff-Chu sequences with specific root indices to separately estimate frequency and timing, while Format B uses a single sequence for combined estimation. This segmentation allows NTN-specific optimization without affecting terrestrial network operation.
Solution Approach 2:
The patent changes key parameters of the PRACH format including using two different Zadoff-Chu sequence root indices (u0 and u1) with specific relationships (u1 = (u0 + 1) mod 61 or u1 = (u0 - 1) mod 61), adjusting cyclic shifts, and modifying timing relationships between sequences. These parameter changes enable the system to resolve both timing and frequency offsets simultaneously in NTN environments where large Doppler shifts and delays occur.
2Measurement precision
If new PRACH formats with two Zadoff-Chu sequences are introduced for NTN, then timing and frequency estimation accuracy is improved, but the complexity of the random access procedure increases
Solution Approach 1:
The patent introduces dynamic selection mechanisms where the network can configure and indicate which PRACH format (A or B) should be used based on current NTN conditions. The WD dynamically adapts its transmission strategy by selecting the appropriate format based on network configuration and capability indicators, allowing flexibility to manage complexity while maintaining estimation accuracy.
Solution Approach 2:
The patent implements preliminary capability signaling where the WD indicates its NTN support capability and preferred PRACH format before actual random access. The network pre-configures the appropriate format based on this indication, allowing the WD to prepare the correct transmission parameters in advance, thereby reducing real-time processing complexity during the actual access procedure.
3Reliability
If separate PRACH formats for NTN are implemented, then random access reliability in NTN is enhanced, but the standardization and implementation difficulty increases
Solution Approach 1:
The patent designs the NTN-specific PRACH formats to be universally applicable across different NTN scenarios (LEO, MEO, GEO satellites) and different WD capabilities. The same Format A and Format B structures can be used regardless of specific orbital parameters or device types, providing a universal solution that reduces the need for multiple specialized implementations while maintaining high reliability across diverse NTN environments.
Data Source
AI summary
In one embodiment, a method implemented in a wireless device, WD, includes receiving at least one first random access, RA, indicator that indicates information relating to a non-terrestrial network, NTN, access; and determining a random access, RA, based at least in part on the at least one first RA indicator. In one embodiment, a method implemented by a network node includes sending at least one first random access, RA, indicator that indicates information relating to a non-terrestrial network, NTN, access; and allowing the WD to perform a random access, RA, that is based at least in part on the at least one first RA indicator.