NTN UE Frequency Pre-Compensation for Doppler Shift
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Solution Overview
Problem
In non-terrestrial network (NTN) communications, existing technologies face challenges in accurately compensating for propagation delay and Doppler shift, leading to signal distortion and degraded demodulation performance due to the need for precise timing and frequency synchronization across satellite links.
Innovation Solution
The proposed solution involves an apparatus that obtains a carrier frequency for NTN, generates an upconversion signal, and performs frequency pre-compensation by adjusting the phase of the signal using a pre-compensation frequency value, as well as timing compensation through a time compression factor, to maintain signal integrity across OFDM symbols without disrupting the constant phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency pre-compensation is applied by replacing carrier frequency with shifted frequency, then Doppler frequency shift is compensated, but constant phase across OFDM symbols is destroyed and demodulation performance degrades
Solution Approach 1:
The patent segments the frequency compensation process into two distinct parts: (1) a frequency shift applied only to the subcarrier spacing to compensate for Doppler effect, and (2) preservation of the original carrier frequency to maintain constant phase relationship across OFDM symbols. This segmentation allows independent optimization of frequency synchronization and phase coherence.
Solution Approach 2:
The patent applies different frequency adjustments to different components of the OFDM signal: subcarrier spacing receives a Doppler-compensated frequency shift while the carrier frequency remains unchanged. This local differentiation ensures that frequency synchronization is improved without compromising the constant phase property required for reliable demodulation.
2Reliability
If delay drift compensation is applied in NTN communications, then signal distortion is prevented, but timing synchronization complexity increases due to feeder link and service link delay variations
Solution Approach 1:
The patent applies preliminary delay drift compensation by pre-calculating and applying timing adjustments based on predicted satellite motion and link characteristics before signal transmission. This preliminary action prevents signal distortion proactively rather than requiring complex real-time adjustments during communication.
Solution Approach 2:
The patent introduces an intermediary timing compensation mechanism that separates the complex feeder link delay from the service link delay, allowing independent compensation of each component. This intermediary approach simplifies the overall timing synchronization by breaking down the complex delay structure into manageable segments.
3Measurement precision
If UE position and satellite velocity information are obtained for timing compensation, then propagation delay compensation accuracy is improved, but information acquisition overhead and processing complexity increase
Solution Approach 1:
The patent enables the UE to self-determine its position using integrated GNSS receiver and to self-calculate timing compensation parameters based on received satellite ephemeris data. This self-service approach allows accurate propagation delay compensation without requiring complex network-assisted positioning or extensive information exchange with the network.
Solution Approach 2:
The patent transforms the complex problem of propagation delay compensation into a parameter-based solution by using satellite position, velocity, and UE position parameters to directly calculate timing offsets. This parameter change approach converts a complex spatial-temporal synchronization problem into a straightforward computational task based on known orbital mechanics parameters.
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 effectively compensates for Doppler frequency shifts and delay drifts, ensuring accurate signal transmission and reception in NTN communications, thereby enhancing demodulation performance and preventing signal distortion.
Implementation Method 1
compensating for propagation delay and Doppler shift in wireless communications over a link
Implementation Method 2
compensating for propagation delay and delay drift on the service link
Data Source
AI summary
Various solutions for timing and frequency compensation in non-terrestrial network (NTN) communications are proposed. An apparatus implemented in a user equipment (UE) obtains a carrier frequency of an NTN. The apparatus generates an up-conversion signal by upconverting a baseband signal according to the carrier frequency. Then, the apparatus further obtains a pre-compensation frequency value. The apparatus performs an uplink (UL) frequency pre-compensation through adjusting a phase of the up-conversion signal according to the pre-compensation frequency value.