Uplink DMRS Orthogonality via Virtual Cell ID and Cyclic Shift Hopping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In wireless communication systems, particularly in 3GPP LTE-A, the performance of uplink demodulation reference signals (DMRS) is compromised due to high correlation among DMRS sequences with different lengths, leading to inter-cell interference and deteriorated demodulation performance in scenarios like CoMP scenario 4 and CoMP scenario 3, where macro cells and low-power RRHs share the same or different cell IDs.
Innovation Solution
The implementation of virtual cell identifiers, orthogonal cover codes, and cyclic shifts ensures orthogonality of uplink DMRSs across different user equipment, even when they belong to different cells with overlapping bandwidths, by allocating distinct identifiers and codes, and configuring cyclic shift hopping patterns based on cell IDs, thereby reducing inter-cell interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference signals are assigned to all subcarriers, then channel estimation performance is improved, but the amount of transmitted data decreases
Solution Approach 1:
The patent segments the reference signal assignment by introducing different reference signal patterns for different subcarrier groups. Specifically, it divides subcarriers into multiple groups and assigns reference signals to specific groups based on the subcarrier index modulo operation, allowing selective reference signal placement that balances estimation performance with data transmission capacity.
Solution Approach 2:
The patent applies local quality by making reference signal assignment density variable across different subcarrier regions. Instead of uniform assignment to all subcarriers, the system dynamically adjusts reference signal presence in specific subcarrier groups based on channel conditions and data requirements, optimizing local estimation quality where needed while preserving data transmission in other regions.
2Quantity of substance
If reference signals are assigned between data subcarriers, then the amount of transmitted data increases, but channel estimation performance deteriorates
Solution Approach 1:
The patent introduces dynamic reference signal assignment where the presence and position of reference signals change based on subcarrier index and configurable parameters. The system dynamically selects which subcarrier groups receive reference signals using modulo operations and configurable patterns, allowing adaptive optimization between data capacity and estimation performance based on varying channel conditions.
Solution Approach 2:
The patent changes key parameters of reference signal assignment including subcarrier group selection, assignment patterns, and density configurations. By modifying these parameters dynamically based on system conditions, the patent optimizes the balance between maintaining adequate channel estimation performance and maximizing data transmission capacity across different operational scenarios.
3Measurement precision
If virtual cell identifiers and orthogonal cover codes are allocated to ensure orthogonality, then demodulation accuracy improves, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-configuring virtual cell identifiers, orthogonal cover codes, and cyclic shift values for different user equipment before actual data transmission. These orthogonality-preserving parameters are assigned in advance based on cell ID and user equipment identification, ensuring that demodulation can proceed efficiently without real-time computation overhead during active transmission.
Solution Approach 2:
The patent uses copying by reusing standardized orthogonal cover code sequences and cyclic shift patterns across multiple user equipment and cells. Instead of creating unique complex sequences for each user, the system copies and adapts standardized patterns with different parameters (virtual cell IDs, cyclic shifts), maintaining orthogonality while reducing the complexity of sequence generation and management.
Data Source
AI summary
A method and a user equipment (UE) for transmitting a demodulation reference signal for a physical uplink shared channel (PUSCH) in a wireless communication system are discussed. The method according to an embodiment includes configuring a virtual cell identity (ID) which is different from a physical cell ID; generating a base sequence by using the virtual cell ID; obtaining a cyclic shift hopping pattern for each slot by using a UE-specific parameter; generating the demodulation reference signal for the PUSCH by using the base sequence and the cyclic shift hopping pattern for each slot; and transmitting the demodulation reference signal for the PUSCH to an eNodeB (eNB).