NB-IoT Random Access Preamble Configuration for LEO Doppler
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge of providing ubiquitous coverage and ensuring service continuity for IoT devices in remote areas served by low-Earth-orbit (LEO) satellites is exacerbated by large Doppler shifts and long round-trip times, which impact the random access process in narrowband IoT (NB-IoT) systems.
Innovation Solution
The solution involves configuring random access preambles with adjusted subcarrier spacing, cyclic prefix lengths, and hopping patterns to compensate for time and frequency offsets, including disabling certain symbol groups and resource occasions, and using Zadoff-Chu or pseudo-noise sequences to enhance preamble capacity and reduce collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If narrowband IoT (NB-IoT) is used for remote area coverage via LEO satellite, then ubiquitous coverage and service continuity are improved, but large Doppler shifts and long round-trip times deteriorate the random access process performance
Solution Approach 1:
The patent modifies key parameters of the random access preamble including subcarrier spacing (increased to handle Doppler shifts), cyclic prefix length (extended to accommodate long round-trip times), and frequency hopping patterns (adjusted to compensate for satellite motion). These parameter changes enable the NB-IoT system to maintain reliable random access performance while achieving ubiquitous coverage through LEO satellite connectivity
2Device complexity
If standard random access preambles are used in LEO satellite scenarios, then implementation simplicity is maintained, but large Doppler shifts and long round-trip times cause significant degradation in access performance
Solution Approach 1:
The patent adjusts specific parameters of existing random access preambles including increasing subcarrier spacing to handle Doppler shifts, extending cyclic prefix length for long round-trip times, and modifying frequency hopping patterns. These targeted parameter changes improve access performance while maintaining compatibility with existing NB-IoT infrastructure and minimizing implementation complexity
3Measurement precision
If subcarrier spacing is increased to compensate for Doppler shifts, then frequency offset robustness is improved, but time offset compensation capability deteriorates
Solution Approach 1:
The patent increases subcarrier spacing to improve robustness against frequency offsets caused by Doppler shifts in LEO satellite scenarios. Simultaneously, it extends the cyclic prefix length to provide sufficient time guard interval for compensating long round-trip times, thereby balancing both frequency and time offset compensation capabilities
Solution Approach 2:
The patent implements dynamic frequency hopping patterns that adapt to the satellite's motion trajectory. The hopping patterns are designed to jump between frequency resources in a manner that compensates for the time-varying Doppler shift, allowing the system to maintain both frequency offset robustness and time synchronization
4Loss of time
If cyclic prefix length is extended to accommodate long round-trip times, then time offset tolerance is improved, but subcarrier spacing efficiency deteriorates
Solution Approach 1:
The patent extends the cyclic prefix length to accommodate the long round-trip times inherent in LEO satellite communication, providing sufficient time guard interval to prevent inter-symbol interference. Simultaneously, it increases subcarrier spacing to improve frequency offset robustness, balancing time tolerance requirements with spectral efficiency considerations
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A wireless communication method for use in a wireless terminal is disclosed. The wireless communication method comprises transmitting, to a wireless network node, a random access preamble selected from a plurality of predetermined preambles for a random access.