UE-Specific Reference Signal Placement in sTTI for Low Latency
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Solution Overview
Problem
Current wireless communication systems face challenges in achieving low latency due to the existing structure of transmission time intervals (TTIs), which are not suitable for next-generation wireless communication systems requiring faster data rates and lower latency.
Innovation Solution
The proposed method involves a wireless communication system that coexists with a shorter subframe transmission time interval (sTTI) within the TTI, where a UE-specific reference signal is used for channel estimation, aligned with cell-specific reference signals, to maintain or improve channel estimation accuracy without introducing additional latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a shorter subframe transmission time interval (sTTI) is introduced to reduce latency, then user plane latency is reduced to 1 ms, but channel estimation accuracy may deteriorate due to limited reference signal resources
Solution Approach 1:
The patent combines cell-specific reference signals (CRS) and UE-specific reference signals (URS) in the same frequency resources within the sTTI structure. The CRS from previous TTI and the URS in current sTTI work together to perform channel estimation, effectively merging reference signal resources from different time domains to compensate for the limited resources in short TTIs.
Solution Approach 2:
The patent performs preliminary channel estimation using cell-specific reference signals received in the previous TTI before the actual data transmission in the sTTI. This preliminary action provides initial channel state information that can be refined with UE-specific reference signals, enabling faster and more accurate channel estimation within the constrained sTTI timeframe.
2Measurement precision
If UE-specific reference signal is placed in the first symbol of sTTI, then channel estimation for control channel is improved, but frequency resource alignment with subsequent cell-specific reference signal must be maintained
Solution Approach 1:
The patent applies different reference signal placement strategies for different purposes: UE-specific reference signals are placed in the first symbol specifically for control channel estimation, while cell-specific reference signals are placed in subsequent symbols for data channel estimation. This local optimization ensures each reference signal serves its specific function most effectively.
Solution Approach 2:
The patent resolves the frequency resource alignment issue by transitioning from time-domain separation to frequency-domain alignment. The UE-specific reference signal in the first symbol uses the same frequency resources as the cell-specific reference signal in subsequent symbols, creating a frequency-domain relationship that simplifies channel estimation across different time symbols.
3Measurement precision
If existing TTI structure is used, then channel estimation can be performed with sufficient reference signals, but latency requirement of 1 ms cannot be satisfied
Solution Approach 1:
The patent segments the reference signal resources across different time units: cell-specific reference signals are utilized from the previous TTI, while UE-specific reference signals are embedded within the current sTTI. This segmentation allows the system to maintain adequate reference signal resources for accurate channel estimation while reducing the overall transmission time interval to meet latency requirements.
Data Source
AI summary
Provided are a method and device for performing channel estimation in a wireless communication system. Specifically, user equipment receives a control channel in the first symbol of a plurality of symbols received for a short TTI (sTTI) set to be shorter than a TTI. The user equipment receives a data channel scheduled by the control channel in the remaining symbols other than the first symbol of the plurality of symbols received in the sTTI. The user equipment receives a user equipment (UE)-specific reference signal having the same frequency resource as a first cell-specific reference signal received in the TTI in the first symbol. The first cell-specific reference signal is received subsequent to the UE-specific reference signal, and the UE-specific reference signal is received in the sTTI. The user equipment decodes the control channel or the data channel using the UE-specific reference signal.