Circular Rotation of Base Sequences for Reference Signal Orthogonality
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Solution Overview
Problem
In LTE networks, inter-UE interference due to orthogonal Demodulation Reference Signals (DMRS) from different UEs limits the effectiveness of Coordinated Multipoint Processing (CoMP) techniques, particularly when Sequence Group Hopping (SGH) is disabled, leading to increased interference and reduced gains in link quality.
Innovation Solution
The method involves generating and replicating base sequences for each Reference Signal (RS) spanned by an Orthogonal Cover Code (OCC), applying individual RS-specific circular rotations, and multiplying each RS with a respective OCC value, followed by mapping to a subframe and transmitting, while the receiving device converts the subframe to the frequency domain, extracts RSs, applies circular rotations, and performs matched filtering to achieve orthogonality and reduce interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Sequence Group Hopping (SGH) is disabled to achieve OCC-based orthogonality, then interference between RS from different UEs is reduced, but interference randomization capability is lost
Solution Approach 1:
The patent segments the base sequence into multiple segments and applies different circular shifts to each segment independently. This segmentation allows the system to maintain orthogonality through OCC while introducing variability through segment-specific circular shifts, effectively resolving the contradiction between reducing interference and maintaining randomization capability.
Solution Approach 2:
The patent introduces dynamic circular shift values that vary across different UEs and time instances, even when SGH is disabled. This dynamic adjustment of circular shifts provides continuous interference randomization while maintaining the orthogonality structure provided by OCC, thus resolving the contradiction between static orthogonality and dynamic randomization.
2Reliability
If orthogonal DMRS are used from different UEs to improve link quality, then CoMP effectiveness is enhanced, but inter-UE interference increases when SGH is disabled
Solution Approach 1:
The patent applies different local circular shift values to different UEs' base sequences, creating local variations in the signal characteristics. This allows each UE to maintain its orthogonal DMRS structure while introducing local differences that reduce inter-UE interference, thus resolving the contradiction between improving link quality and reducing interference.
Solution Approach 2:
The patent changes the circular shift parameter dynamically for different UEs and time instances, even when SGH is disabled. By modifying this parameter while maintaining the orthogonal structure, the system achieves both improved link quality through CoMP and reduced inter-UE interference through parameter differentiation.
3Object-affected harmful factors
If base sequences are replicated per RS spanned by OCC to achieve orthogonality, then orthogonality between UEs is improved, but sequence diversity is reduced
Solution Approach 1:
The patent introduces dynamic circular shift variations across different UEs and time instances for the replicated base sequences. This dynamic adjustment maintains the orthogonality structure provided by OCC replication while introducing diversity through varying circular shift values, thus resolving the contradiction between achieving orthogonality and maintaining sequence diversity.
Data Source
AI summary
A first and second communication device and respective method thereby are provided for performing a radio transmission. The method performed by the first communication device comprises generating a base sequence, and replicating the base sequence per each RS panned by an OCC. The method further comprises applying, to the base sequences, an individual RS-specific circular rotation, wherein each rotated base sequence corresponds to an RS. The method also comprises multiplying each RS with a respective value of the OCC, and mapping each frequency domain RS to a subframe. Still further, the method comprises converting the subframe to a time domain; and transmitting the subframe to the second communication device.