DMRS Sequence Design for Interference Reduction
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Solution Overview
Problem
In new radio (NR) systems, the use of Gold sequence segments for downlink demodulation reference signals (DMRS) results in poor cross-correlation between segments, leading to strong interference and compromised channel estimation performance.
Innovation Solution
A signal sending method that determines specific sequences for subcarrier groups to ensure good cross-correlation, using sequences such as {1, −3, −1, 3, −1, 3, −3, −3, −3, 3, −3, −1, 3, 1, −1, 1, −3} for improved interference reduction and channel estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If Gold sequence segments are used for downlink DMRS, then the sequence length is reduced to fit available resources, but cross-correlation between segments deteriorates leading to strong interference
Solution Approach 1:
The patent changes the fundamental parameter of sequence generation from Gold sequences to Zadoff-Chu (ZC) sequences. ZC sequences have inherent mathematical properties that provide constant amplitude and optimal autocorrelation/cross-correlation characteristics. By changing the sequence type parameter, the system achieves good cross-correlation performance even with shorter sequence lengths suitable for NR resource constraints.
Solution Approach 2:
The patent combines multiple ZC sequences with different root indices (u values) to create a composite sequence structure. Each ZC sequence is generated with a specific root index, and by selecting sequences with carefully chosen root indices, the system achieves low cross-correlation between different cell DMRS while maintaining good autocorrelation within each sequence. This composite approach using multiple ZC sequences resolves the contradiction between sequence length and cross-correlation performance.
2Quantity of substance
If segments of Gold sequence are used, then the sequence fits the available time-frequency resources, but interference between signals increases
Solution Approach 1:
The patent changes the sequence generation algorithm from Gold sequence generation to Zadoff-Chu sequence generation. ZC sequences have constant amplitude and optimal correlation properties that inherently reduce signal interference. The mathematical structure of ZC sequences ensures that even short segments maintain low cross-correlation with sequences from other cells, thereby reducing interference without requiring long sequence lengths.
Solution Approach 2:
The patent converts the limitation of short sequence length (which would normally cause poor correlation) into an advantage by using ZC sequences. The constant amplitude property of ZC sequences means that shorter sequences do not suffer the same degradation in correlation performance as Gold sequences. Additionally, the system uses the available short sequence length to implement cyclic shifts and root index variations, transforming the constraint into a mechanism for generating multiple orthogonal sequences that reduce interference.
3Device complexity
If Gold sequence segments are used for DMRS, then resource allocation is simplified, but channel estimation performance is compromised
Solution Approach 1:
The patent changes the sequence type to Zadoff-Chu sequences, which have superior autocorrelation and cross-correlation properties. These mathematical properties enable more accurate channel estimation because the correlation peak is sharper and interference from other sequences is lower. The constant amplitude property of ZC sequences also simplifies the channel estimation process by removing amplitude variations that would otherwise need to be compensated for.
Solution Approach 2:
The patent creates a composite structure using multiple ZC sequences with different root indices and cyclic shifts. This composite approach provides both good autocorrelation (for accurate channel estimation of the desired signal) and low cross-correlation (for rejecting interference from other cells). The combination of these properties in a unified ZC-based framework maintains resource allocation simplicity while dramatically improving channel estimation performance.
Data Source
AI summary
A signal sending method, a signal receiving method, and a device for signal transmission or receiving are provided. A part that is of a first signal and that is carried on a kth subcarrier in an ith subcarrier group in N subcarrier groups is xi,n<sub2>id</sub2>(k), and a sequence {si,n<sub2>id</sub2>(k)} related to xi,n<sub2>id</sub2>(k) is one of enumerated sequences. The enumerated sequences are sequences with relatively good cross-correlation. Therefore, for two subcarrier groups, provided that selected {si,n<sub2>id</sub2>(k)} is two of the enumerated sequences, cross-correlation between signals carried in the two subcarrier groups can be ensured to be relatively good, thereby reducing interference between the signals and improving channel estimation performance.