Cell-Specific Reference Signal Shifting for Multi-Stream Interference
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In 3GPP LTE systems, minimizing interference among reference signals (RSs) of CoMP cells is crucial for accurate CSI measurement and high-performance CoMP operation, but existing methods are inefficient in multi-stream transmission scenarios.
Innovation Solution
The method involves cell-specific shifting of reference signal mapping patterns, where RSs for advanced UEs are circularly shifted in the subcarrier or frequency domain, and for legacy UEs, RSs are shifted differently or remain unshifted, preventing overlap and ensuring efficient CSI estimation and demodulation across multiple antenna ports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If reference signals for advanced UEs are transmitted using standard mapping patterns, then multi-stream transmission can be supported, but interference with reference signals from other cells increases
Solution Approach 1:
The patent applies parameter changes by introducing cell-specific shifting parameters (v-shift) that modify the frequency domain position of reference signals. Different cells use different shifting values to orthogonalize their reference signal mapping patterns, thereby reducing inter-cell interference while maintaining multi-stream transmission capability. The shifting is applied to the resource element positions where reference signals are mapped, changing the spatial parameters of signal transmission.
2Measurement precision
If reference signals are shifted to reduce interference, then measurement accuracy improves, but signal mapping complexity increases
Solution Approach 1:
The patent applies local quality by implementing cell-specific shifting only where necessary - at reference signal resource elements - while leaving other signal components unchanged. This targeted approach improves CSI measurement accuracy by reducing interference at critical measurement points without requiring system-wide restructuring of signal mapping, thus limiting the increase in overall system complexity.
Solution Approach 2:
The shifting mechanism uses simple parameter adjustments (v-shift values) that can be configured per cell. The complexity is managed by using predetermined shifting patterns and formulas that map reference signals to shifted positions based on cell identity, rather than requiring complex adaptive algorithms. This keeps the implementation relatively simple while achieving the measurement accuracy improvement.
3Adaptability or versatility
If different shifting patterns are used for advanced and legacy UEs, then backward compatibility is maintained, but reference signal overhead increases
Solution Approach 1:
The patent applies segmentation by dividing the reference signal handling into different groups: advanced UEs that support the new cell-specific shifting feature and legacy UEs that use traditional mapping patterns. This allows the system to apply interference reduction techniques selectively to advanced UEs without affecting legacy UE compatibility, while avoiding duplicate reference signals for the same UE group, thus controlling overhead.
Data Source
Figure 1~3
Figure 4~5
Figure 6
AI summary
A base station is provided. The base station comprises a downlink transmit path comprising circuitry configured to transmit a plurality of reference signals in one or more subframes. Each subframe comprises one or more resource blocks. Each resource block comprises S Orthogonal Frequency Division Multiplexing (OFDM) symbols. Each of the S OFDM symbols comprises N subcarriers, and each subcarrier of each OFDM symbol comprises a resource element. The base station further comprises a reference signal allocator configured to allocate the plurality of reference signals to selected resource elements of a resource block, and circularly shift the plurality of reference signals in a time domain of the resource block by an hshift value that is based at least partly upon a cell_ID of the base station.