DMRS Segmentation for Uplink Coordinated Relay Channel Estimation
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Solution Overview
Problem
In wireless communication systems, the inability of access nodes to accurately decode control information when relay nodes assist in retransmissions leads to system performance degradation due to the combined demodulation reference signals (DMRS) from both user equipment (UE) and relay nodes being different, making channel estimation for control information unreliable.
Innovation Solution
Implementing punctured or orthogonal DMRS patterns by relay nodes, where they transmit DMRS on a subset of subcarriers, allowing access nodes to perform separate channel estimation for data and control information using DMRS from the UE alone, and combining DMRS from both UE and relay nodes for data channel estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If relay nodes transmit combined DMRS with UE for coordinated retransmission, then data channel estimation is improved, but control information decoding reliability deteriorates
Solution Approach 1:
The patent segments the DMRS transmission by having the relay node transmit DMRS only on a subset of subcarriers (first set) while the UE transmits DMRS on all subcarriers (first and second sets). This segmentation allows the access node to separate control information (on first set subcarriers) from data (on second set subcarriers), resolving the contradiction between combined channel estimation and control information decoding reliability.
2Reliability
If relay nodes transmit DMRS on all subcarriers for coordinated transmission, then channel estimation coverage is improved, but control information separation deteriorates
Solution Approach 1:
The relay node segments its DMRS transmission to only occupy the first set of subcarriers, while the UE occupies both first and second sets. This creates clear spatial separation in the frequency domain, allowing the access node to easily separate control information from data without complex processing, thus improving channel estimation coverage while maintaining low separation complexity.
Solution Approach 2:
The patent introduces a frequency domain dimensionality change by assigning different subcarrier sets to different entities. The relay node uses the first set of subcarriers for DMRS, while the UE uses both first and second sets. This dimensional separation in the frequency domain enables straightforward control information separation while maintaining comprehensive channel estimation coverage.
3Ease of manufacture
If relay nodes use same DMRS pattern as UE for simplicity, then implementation ease is improved, but channel estimation accuracy deteriorates
Solution Approach 1:
The relay node applies local quality by using a different DMRS pattern (first set of subcarriers only) compared to the UE (both first and second sets). This localized differentiation in DMRS pattern allows the access node to accurately separate control information from data channels, improving overall channel estimation accuracy while maintaining relatively simple implementation through predefined subcarrier sets.
Data Source
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AI summary
A method is provided for an access node to perform channel estimation. The method includes, when a UE and a relay node are present in a cell with the access node, the access node receiving from the UE and from the relay node DMRS that are cyclically shifted relative to one another. The method further includes the access node performing a first channel estimation based on the DMRS that was transmitted by the UE, performing a second channel estimation based on the DMRS that was transmitted by the at least one relay node, combining the first channel estimation with the second channel estimation to derive a combined channel estimation, using the first channel estimation to demodulate control information received from the UE, and using the combined channel estimation to demodulate data received from both the UE and the at least one relay node.