CSI-RS Time and Frequency Synchronization with Lower CRS Overhead
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Solution Overview
Problem
The reliance on common reference signals (CRS) for time and frequency synchronization in LTE systems leads to energy inefficient transmission and limited capacity for control channels due to their constant transmission, even when no data is being transmitted, and interference between CRS signals from different cells.
Innovation Solution
Utilizing channel state information reference signals (CSI-RSs) for time and frequency synchronization by transmitting multiple non-zero power CSI-RSs in the same subframe, or combining CSI-RSs with other synchronization signals, to achieve synchronization performance similar to CRS but with lower overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common reference signals (CRS) are transmitted in every subframe for time and frequency synchronization, then synchronization reliability is improved, but energy consumption increases and transmission overhead increases
Solution Approach 1:
The patent applies periodic action by transmitting reference signals only in specific subframes rather than every subframe. The network configures user equipment to perform measurements on reference signals in periodically occurring subframes, reducing energy consumption while maintaining synchronization reliability through selective periodic transmission.
Solution Approach 2:
The patent extracts the essential synchronization function from continuous CRS transmission and implements it through selective reference signal transmission in specific subframes. This separates the synchronization function from constant full-bandwidth CRS transmission, achieving energy efficiency while maintaining reliability.
2Reliability
If common reference signals (CRS) are transmitted in every subframe for time and frequency synchronization, then synchronization reliability is improved, but transmission overhead increases
Solution Approach 1:
The patent reduces transmission overhead by implementing periodic reference signal transmission only in configured subframes instead of continuous transmission in every subframe. This periodic approach maintains synchronization reliability while significantly reducing the quantity of reference signal transmissions.
Solution Approach 2:
The patent applies partial action by transmitting reference signals only in necessary subframes rather than all subframes. The network configures specific subframes for reference signal transmission based on actual synchronization needs, reducing overhead while maintaining adequate synchronization performance.
3Area of stationary object
If common reference signals (CRS) are transmitted from multiple cells, then coverage is improved, but interference between CRS signals increases
Solution Approach 1:
The patent reduces interference by implementing periodic reference signal transmission in specific configured subframes rather than continuous transmission. This temporal separation reduces the probability of simultaneous transmissions from multiple cells, thereby reducing interference while maintaining coverage through selective transmission.
Data Source
AI summary
The scheduling flexibility of CSI reference signals enables time and frequency synchronization using multiple non-zero CSI-RSs transmitted in the same subframe, or using CSI-RSs transmitted in the same subframe with other synchronization signals. Also, multiple synchronization signals may be scheduled in the same subframe to enable fine time and frequency synchronization without cell-specific reference signals.