CSI-RS Port Sharing via Frequency Domain Multiplexing
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Solution Overview
Problem
The existing CSI-RS overhead in 5G FDD systems is high due to the need for UE-specific CSI-RS transmission, which increases linearly with the number of tap delays considered for FD precoding, leading to inefficiencies in channel state information feedback.
Innovation Solution
The proposed method involves multiplexing precoded pilots of two or more UEs on the same time-frequency resource elements and applying cyclic shifts at the gNB, allowing CSI-RS ports to be shared among UEs, reducing the overhead by compensating for shifts at the UE side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If UE-specific CSI-RS transmission is used for FD precoding, then channel state information accuracy is improved, but CSI-RS overhead increases linearly with the number of tap delays
Solution Approach 1:
The patent merges multiple UE-specific CSI-RS transmissions into a single shared CSI-RS resource by multiplexing precoded pilots of different UEs in the frequency domain. The gNB applies different frequency shifts to the CSI-RS for different UEs, allowing multiple UEs to share the same time-frequency resource elements while maintaining separate channel state information feedback channels.
Solution Approach 2:
The patent introduces frequency domain shifting as an additional dimension to separate multiple UE signals. Instead of using separate time-frequency resources for each UE, the system multiplexes UEs in the frequency domain by applying different frequency shifts to their CSI-RS pilots, thereby reducing overhead while maintaining measurement precision.
2Quantity of substance
If multiple UEs share the same CSI-RS port, then CSI-RS overhead is reduced, but signal separation and channel state information accuracy become more difficult
Solution Approach 1:
The patent segments the frequency domain into different shifted frequency components for different UEs. Each UE is assigned a specific frequency shift that separates its signal from other UEs' signals in the frequency domain, enabling the gNB to distinguish and measure channel state information for each UE independently while sharing the same time-frequency resource.
3Productivity
If frequency domain shifting is applied for UE multiplexing, then resource efficiency is improved, but cyclic shift compensation complexity at UE side increases
Solution Approach 1:
The patent applies preliminary frequency shifting at the gNB side before transmitting the CSI-RS to the UE. The gNB pre-calculates and applies different frequency shifts to the CSI-RS pilots for different UEs, so that when the UE receives the signal, the frequency domain separation is already established, reducing the complexity of signal separation at the UE side.
Data Source
AI summary
In an enhanced frequency domain precoding environment, a solution for transmitting channel state information reference signal to user equipments from the same channel state information reference signal port using the determined cyclic shifts, where user equipments are to share the same channel state information reference signal port.