Adaptive Frequency Offset Estimation Using Quasi-Co-located Reference Signals
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Solution Overview
Problem
In CoMP scenarios of LTE wireless communication networks, frequency offsets between oscillators in different transmission points cause phase ramps, degrading demodulation performance, and existing methods struggle to accurately estimate and compensate for these offsets, especially when CRS and DM-RS ports are from different transmission points.
Innovation Solution
An adaptive scheme in User Equipment (UE) for estimating frequency offsets using quasi-co-located reference signals, selectively choosing between DM-RS, CSI-RS, and CRS based on the number of Resource Blocks and Signal to Noise Ratio (SNR) levels to minimize CRS usage and exploit the benefits of DM-RS and CSI-RS estimators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency offset estimation uses CRS from serving cell in CoMP scenarios, then frequency offset can be estimated, but demodulation performance degrades due to phase ramps from different transmission points
Solution Approach 1:
The patent segments the frequency offset estimation process by separating CRS-based estimation (for common frequency offset) from DM-RS-based estimation (for residual frequency offset). This allows the system to first estimate and compensate the common frequency offset using CRS from the serving cell, then perform a second estimation using DM-RS from the actual transmission point, thereby resolving the contradiction between being able to estimate frequency offset and maintaining demodulation performance.
Solution Approach 2:
The patent introduces an intermediary two-stage estimation process where CRS-based estimation serves as a preliminary step to remove the common frequency offset component, enabling the subsequent DM-RS-based estimation to focus only on residual offsets. This intermediary step resolves the contradiction by preparing the signal environment for more accurate final estimation.
2Measurement precision
If CRS is used for frequency offset estimation, then estimation can be performed, but reliance on CRS limits deployment flexibility for shared cell scenarios
Solution Approach 1:
The patent extracts the frequency offset estimation function from exclusive dependence on CRS and distributes it across multiple reference signals (CRS and DM-RS). By taking out the estimation capability from CRS alone and implementing it through a combination of CRS for common offset and DM-RS for residual offset, the system gains deployment flexibility for shared cell scenarios while maintaining estimation accuracy.
3Reliability
If strict clock accuracy requirements are imposed on transmission points, then frequency offset can be minimized, but system complexity and cost increase
Solution Approach 1:
The patent implements a feedback-based two-stage estimation approach where the first CRS-based estimation result is used to pre-compensate the signal, and then the second DM-RS-based estimation provides feedback on the remaining offset. This feedback mechanism allows the system to achieve good frequency offset control without requiring extremely strict clock accuracy, as the estimation and compensation process actively corrects for clock variations.
4Measurement precision
If DM-RS and CSI-RS estimators are fully utilized, then estimation accuracy improves, but system complexity increases
Solution Approach 1:
The patent implements a dynamic estimation system that adaptively selects and combines different estimation methods (CRS-based and DM-RS-based) based on the operational scenario. The system dynamically switches between using common frequency offset estimation from CRS and residual frequency offset estimation from DM-RS, optimizing accuracy for different conditions without requiring a permanently complex system structure.
Data Source
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AI summary
The present disclosure discloses a method used in a UE for estimating a frequency offset between a CRS of a serving cell of the UE and a DM-RS of a data transmission to be decoded by the UE, using a set of quasi-co-located reference signals. The method comprises: comparing a number of Resource Blocks, RBs, for the data transmission to a first threshold; selecting one or more quasi-co-located reference signals from the set of quasi-co-located reference signals based on a result of the comparison; and estimating the frequency offset based on the selected one or more quasi-co-located reference signals. The present disclosure also relates to a UE for estimating a frequency offset between a CRS of a serving cell of the UE and a DM-RS of a data transmission to be decoded by the UE, using a set of quasi-co-located reference signals.