Synchronization Signal Alignment for LTE Frequency Synchronization
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Solution Overview
Problem
In LTE networks, frequency synchronization between user equipment (UE) and base stations is challenging due to misalignment with the 100 kHz channel raster, especially with NB-IoT operations, leading to potential connection failures and increased power consumption for UE, as existing methods fail to align with both the 100 kHz LTE channel raster and 15 kHz OFDM subcarrier spacing grid simultaneously.
Innovation Solution
A synchronization signal aligned with the 15 kHz LTE subcarrier spacing grid is positioned at the 100 kHz channel raster, with a bandwidth of less than or equal to six subcarriers, allowing UE to identify radio access technology and carrier frequency offset, while maintaining alignment with the channel raster to ensure efficient frequency synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the synchronization signal is aligned with the 100 kHz channel raster, then frequency synchronization is simplified, but alignment with the 15 kHz OFDM subcarrier spacing grid is lost
Solution Approach 1:
The synchronization signal is designed with different alignment characteristics for different purposes: it is aligned with the 100 kHz channel raster for easy frequency synchronization and UE scanning, while simultaneously being aligned with the 15 kHz OFDM subcarrier spacing grid to maintain orthogonality and avoid interference. This local quality differentiation allows the same signal to satisfy multiple alignment requirements.
2Adaptability or versatility
If the synchronization signal bandwidth is increased to cover more subcarriers, then frequency coverage is improved, but the signal becomes misaligned with the channel raster
Solution Approach 1:
The synchronization signal uses a limited bandwidth of 6 subcarriers (90 kHz) which is partial coverage rather than full coverage. This partial action is sufficient to achieve the synchronization objective while maintaining alignment with the channel raster, avoiding the excessive action that would cause misalignment.
3Measurement precision
If the synchronization signal is positioned at the carrier center frequency, then frequency offset is minimized, but alignment with the channel raster is lost
Solution Approach 1:
The synchronization signal is deliberately positioned asymmetrically relative to the carrier center frequency, specifically at the lower edge of the carrier bandwidth. This asymmetric positioning allows the signal to remain aligned with the channel raster while still providing sufficient frequency offset information for the UE to locate the carrier center frequency accurately.
4Ease of manufacture
If existing synchronization methods are used, then implementation is simple, but connection failures occur and power consumption increases
Solution Approach 1:
The invention changes key parameters of the synchronization signal including its bandwidth (6 subcarriers), positioning (lower edge of carrier), and alignment characteristics (simultaneous alignment with 100 kHz raster and 15 kHz subcarrier grid). These parameter changes resolve the fundamental conflict between implementation simplicity and connection reliability, enabling successful connections while maintaining ease of implementation.
Data Source
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AI summary
A method and apparatus may include configuring, by a base station, a synchronization signal. The synchronization signal may be aligned with a subcarrier spacing grid of a radio access technology. The synchronization signal may be positioned at a frequency location that is the same or about the same as a frequency step of a channel raster. The synchronization signal may be transmitted to a user equipment so that the center of the synchronization signal is transmitted with a frequency offset with respect to the center of the radio-access technology bandwidth.