Flexible Reference Symbol Patterns with Variable Subcarrier Spacing
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Solution Overview
Problem
The overhead associated with reference symbols in wireless communication systems is a concern due to their transmission occupying time-frequency resources that could otherwise be used for data or control information, especially when DFT spreading is not performed on reference symbols, leading to high reference symbol overhead.
Innovation Solution
The subcarrier spacing (SCS) of reference symbols is differentiated from that of information symbols, with reference symbols having a larger SCS and shorter length, allowing them to be time-division multiplexed with information symbols, thereby reducing overhead while improving channel estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If reference symbols are transmitted using the same subcarrier spacing as information symbols, then the reference symbol pattern is simple and easy to implement, but the reference symbol overhead becomes large and occupies excessive time-frequency resources
Solution Approach 1:
The patent changes the subcarrier spacing parameter specifically for reference symbols, making it different from the subcarrier spacing used for information symbols. This parameter change allows reference symbols to be more efficiently packed in the frequency domain, reducing the number of resource elements required for reference symbol transmission while maintaining the same channel estimation functionality, thereby reducing reference symbol overhead without significantly increasing system complexity
Solution Approach 2:
The patent segments the subcarrier spacing into different values for different symbol types: one subcarrier spacing value for reference symbols and another for information symbols. This segmentation allows optimized resource allocation where reference symbols use a spacing that minimizes their footprint in the time-frequency grid, reducing overall overhead while keeping the information symbol transmission unchanged
2Quantity of substance
If reference symbols are transmitted with larger subcarrier spacing and shorter length, then reference symbol overhead is reduced, but the reference symbol pattern becomes more complex and requires differentiated configuration
Solution Approach 1:
The patent applies parameter changes by configuring a specific subcarrier spacing value for reference symbols that is larger than the cyclic prefix length, and a different subcarrier spacing value for information symbols. This parameter differentiation reduces reference symbol overhead by optimizing their placement in the time-frequency grid, while the complexity is managed through standardized configuration procedures and clear signaling mechanisms
Solution Approach 2:
The patent introduces dynamic configuration capabilities where the subcarrier spacing for reference symbols can be adjusted based on system conditions, channel characteristics, and traffic requirements. This dynamic approach allows the system to optimize reference symbol overhead in real-time while adapting to changing conditions, with the complexity managed through flexible signaling and configuration protocols
3Measurement precision
If reference symbols occupy the entirety of several OFDM symbols at different time locations, then channel estimation is improved, but reference symbol overhead becomes high
Solution Approach 1:
The patent changes the subcarrier spacing parameter for reference symbols to be larger than the cyclic prefix length, which allows reference symbols to be positioned at specific time locations without requiring them to occupy entire OFDM symbols. This parameter change enables more efficient time-frequency resource utilization, distributing reference symbols across multiple locations to improve channel estimation accuracy while minimizing the total number of resource elements dedicated to reference symbols, thereby reducing overhead
Data Source
AI summary
A reference sequence may be transmitted in wireless communication, e.g. in order to perform channel estimation. The use of a reference sequence introduces overhead. In some embodiments, the subcarrier spacing (SCS) of the multi-carrier symbols (e.g. OFDM symbols) used to transmit one or more reference sequences is different from the SCS of the multi-carrier symbols used to transmit information (e.g. data). In some embodiments, an original reference sequence may be spread over multiple multi-carrier symbols, with each multi-carrier symbol carrying a respective reference sequence that is a portion of the original reference sequence. The technical benefit is possibly improved channel estimation because the original reference sequence is spread in time, but with the same overhead (in terms of total occupied time of reference symbols) as transmitting all of the original reference sequence at the same time.