NTN Uplink Doppler Compensation Using Periodic Transmission Gaps
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Solution Overview
Problem
Existing wireless communication systems in Non-Terrestrial Networks (NTNs) face challenges in maintaining coherent transmissions due to time-variant Doppler shifts, particularly for Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) satellites, which affect frequency and timing accuracy, leading to excessive signaling overhead and difficulties in achieving coherent demodulation.
Innovation Solution
The proposed method involves creating time gaps or muting portions of uplink transmissions to support Timing Advance (TA) and performing time-frequency compensation, adjusting transmit frequency and timing resolution to compensate for estimated Doppler shifts and time dilation, using satellite ephemeris and cyclic prefix durations for parameter configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If time-frequency compensation is performed continuously during uplink transmission to compensate for Doppler shifts, then coherent demodulation performance is improved, but transmission complexity and processing overhead increase
Solution Approach 1:
The patent segments the uplink transmission into multiple slots with time gaps between them. During these time gaps, the wireless communication device performs time-frequency compensation for Doppler shifts. This segmentation allows compensation to be performed periodically rather than continuously, reducing processing complexity while maintaining coherent demodulation performance across the transmission.
Solution Approach 2:
The patent performs time-frequency compensation in advance during time gaps before the actual data transmission slots. By preparing the frequency compensation beforehand, the device ensures that when data transmission occurs, the Doppler shift compensation is already in place, enabling coherent demodulation without requiring complex real-time processing during the data slots.
2Measurement precision
If time gaps are created or portions of uplink transmission are muted to perform frequency compensation, then Doppler shift compensation accuracy is improved, but transmission efficiency and data rate decrease
Solution Approach 1:
The patent implements periodic time-frequency compensation by creating time gaps at regular intervals during the uplink transmission. Instead of continuously muting transmission, the device periodically inserts short time gaps (e.g., every few slots) to perform compensation. This periodic approach maintains adequate Doppler compensation accuracy while minimizing the impact on overall transmission efficiency compared to continuous muting.
3Reliability
If transmit frequency is adjusted in real-time to compensate for time-variant Doppler shifts, then frequency offset compensation is improved, but device complexity and processing requirements increase
Solution Approach 1:
The patent implements dynamic frequency compensation by adjusting the transmit frequency based on the time-variant Doppler shift characteristics of LEO satellite communication. The device calculates the Doppler shift compensation value based on satellite ephemeris data and relative velocity, then applies this compensation dynamically during the time gaps. This dynamic approach adapts to changing satellite positions while using simplified processing compared to continuous real-time adjustment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables low-complexity methods for Doppler compensation, ensuring coherent demodulation and optimized receiver implementations, particularly for Narrowband Internet of Things (NB-IoT) and LTE for Machine Type Communication (LTE-M), improving coverage and reducing signaling overhead.
Implementation Method 1
the Doppler shift caused by satellite motion, leading to frequency and timing offsets that existing methods struggle to compensate for effectively
Implementation Method 2
allowing for autonomous compensation of Doppler shifts and time dilation, thereby ensuring coherent demodulation and optimized receiver performance
Data Source
AI summary
Systems and methods are disclosed herein for supporting coherent transmissions in a wireless network such as a Non-Terrestrial Network (NTN). In one embodiment, a method performed by a wireless communication device comprises starting an uplink transmission and performing one or more actions comprising creating a time gap within the uplink transmission and/or muting a portion of the uplink transmission to support a timing advance of the continued uplink transmission. The method further comprises performing time-frequency compensation during a time period created by performing the one or more actions and continuing the uplink transmission after performing the time-frequency compensation. In this manner, a low-complexity method for achieving a compensation for a time variant Doppler shift is provided. This offers a predictability that can be used in a wireless network such as, for example, an NTN for supporting coherent demodulation and optimized receiver implementations.