UE Grouping Reference Signal Transmission for Massive MIMO
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Solution Overview
Problem
In wireless communication systems, especially in massive MIMO schemes, pilot contamination due to correlated reference signals limits link performance, and as the number of antennas increases, the reference signal overhead becomes a significant issue, particularly in FDD schemes where downlink and uplink channels require separate estimation.
Innovation Solution
The proposed solution involves a UE grouping-based reference signal transmission scheme, where UEs are grouped to use orthogonal sequences for uplink reference signals, reducing pilot contamination and eliminating the need for increased reference signals with more antennas, by employing a TDD scheme that allows uplink reference signals to estimate downlink channels, thereby maintaining efficient channel estimation without increasing overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of antennas is increased in massive MIMO schemes, then the channel estimation accuracy is improved, but the reference signal overhead increases significantly
Solution Approach 1:
The patent divides UEs into multiple groups, where each group is assigned a specific orthogonal sequence for reference signal transmission. This segmentation allows the system to serve multiple UEs with different antenna ports using distinct orthogonal sequences, thereby improving channel estimation accuracy for massive MIMO without proportionally increasing the overall reference signal overhead, as the orthogonal sequences can be reused across different UE groups.
2Measurement precision
If reference signals are transmitted for each antenna port, then the channel estimation precision is improved, but the system complexity increases
Solution Approach 1:
The patent implements a universal reference signal structure where a single orthogonal sequence can serve multiple antenna ports through the grouping mechanism. Instead of requiring completely separate reference signals for each antenna port, the system uses a unified orthogonal sequence design that can be assigned to different UE groups serving different antenna ports, thereby reducing system complexity while maintaining the capability to estimate channels for multiple antenna ports accurately.
3Reliability
If orthogonal sequences are assigned to reduce pilot contamination, then the link performance is improved, but the reference signal overhead increases
Solution Approach 1:
The patent segments UEs into groups and assigns orthogonal sequences at the group level rather than at the individual UE level. This segmentation approach reduces pilot contamination within each group while allowing the same orthogonal sequence to be reused across different groups, thereby improving link performance without proportionally increasing the overall reference signal overhead.
Solution Approach 2:
The patent applies orthogonal sequencing partially - only within grouped UEs that share the same time-frequency resources. Not all UEs require unique orthogonal sequences simultaneously, as the grouping allows temporal and spatial separation. This partial application of orthogonal sequencing reduces pilot contamination where needed while avoiding unnecessary overhead in cases where interference is already naturally separated.
Data Source
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AI summary
Grouping based reference signal transmission scheme for massive MIMO is disclosed. UEs are grouped and each UE group receive first information on which of uplink transmission time units is enabled to transmit an uplink reference signal and second information on a sequence used for the uplink reference signal from a base station. The above first information is differently determined to second UE group other than a first UE group including the first UE. And, the second information is determined to assign orthogonal sequences to the first UE group.