Multi-cell CSI-RS Patterns for LTE Extended Cyclic Prefix
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Solution Overview
Problem
The E-UTRA LTE-Advanced standard faces challenges in designing Channel State Information-Reference Symbol (CSI-RS) patterns to minimize interference and ensure accurate channel quality measurement across multiple cells, while maintaining compatibility with Rel. 8 UEs and avoiding collisions with existing reference signals.
Innovation Solution
The proposed solution introduces candidate multi-cell CSI-RS time-frequency patterns that do not require knowledge of LTE transmission mode 7, avoid collisions with specific antenna ports, and maintain the nested property, ensuring compatibility with DMRS Rank 1 and 2, and are forward compatible with proposed WF patterns for DMRS Rank 1 and 2, using CDM-T multiplexing and orthogonal cover codes to simplify implementation and reduce interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CSI-RS patterns are designed to minimize interference across multiple cells, then measurement precision is improved, but device complexity increases due to the need to avoid collisions with multiple reference signals
Solution Approach 1:
The patent segments the time-frequency resource grid into specific patterns for CSI-RS transmission, defining distinct OFDM symbol positions and resource block allocations that minimize interference. This segmentation allows systematic avoidance of collisions with CRS, UE-RS, and other signals while maintaining measurement accuracy.
Solution Approach 2:
The patent implements nested patterns where CSI-RS patterns for different numbers of antenna ports (2, 4, 8) are nested within each other. The pattern for 2 ports is contained within the 4 port pattern, which is contained within the 8 port pattern, simplifying implementation by allowing UEs to use the same pattern structure regardless of the number of active ports.
2Adaptability or versatility
If CSI-RS transmissions occur in multiple subframes to maximize coverage, then adaptability is improved, but loss of time increases due to extended measurement duration
Solution Approach 1:
The patent performs preliminary configuration by pre-defining the CSI-RS patterns and their corresponding subframe allocations before actual measurement. The eNodeB configures the UE with specific pattern indices that correspond to predetermined time-frequency resources, allowing rapid measurement without real-time pattern selection.
Solution Approach 2:
The patent employs periodic CSI-RS transmission patterns that repeat across multiple subframes with fixed periodicity. This periodic structure allows the UE to measure channel quality at regular intervals, balancing measurement accuracy with time efficiency by avoiding ad-hoc measurements.
3Ease of operation
If the CSI-RS pattern uses CDM-T multiplexing with orthogonal cover codes, then ease of operation is improved, but device complexity increases due to additional code requirements
Solution Approach 1:
The patent designs the orthogonal cover codes to serve multiple functions: they provide multiplexing for different antenna ports, enable interference avoidance, and maintain compatibility with existing UE implementations. The same code structure works for 2, 4, and 8 antenna port configurations, eliminating the need for separate code sets.
Data Source
AI summary
This invention is a method of wireless communication using candidate multi-cell CSI-RS time-frequency patterns in the invention. This invention avoids collision with antenna ports 0, 1, 2 and 3 used for transmitting cell-specific reference signals and port 5 used for transmitting demodulation reference signals. This invention satisfies the nested property requirement. This invention avoids collision with DM-RS signal for extended cyclic prefix transmission as long as DMRS Rank is less than or equal to 2. For ranks greater than 2, this invention produces patterns that may collide with Rel. 10 DM-RS for extended CP. The invention includes alternative patterns obtained by relabeling and/or reshuffling the CSI-RS antenna port numbers while preserving identical time-frequency resources assigned to CSI-RS in the time-frequency grid.