Two-Stage Precoding for FD-MIMO Antenna Port Compression
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Solution Overview
Problem
FD-MIMO systems face challenges in designing efficient beamforming/precoding algorithms and CSI acquisition schemes due to the increased number of transmit antennas, leading to high overhead and complexity in CSI feedback, especially in traditional one-shot beamforming methods.
Innovation Solution
A two-stage precoding system is adopted, where UL channel estimation is used to acquire a long-term port precoding matrix that compresses a larger number of antenna elements to a smaller number of antenna ports, reducing overhead and complexity by allowing UE-specific beamforming in both azimuth and elevation using a two-dimensional antenna array.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional one-shot beamforming methods are used in FD-MIMO systems, then complete channel state information can be obtained, but overhead and complexity in CSI feedback increase significantly
Solution Approach 1:
The patent segments the precoding process into two distinct stages: first stage precoding (beamforming) that maps antenna elements to antenna ports, and second stage precoding (layer mapping) that maps layers to antenna ports. This segmentation allows the UE to report CSI only for antenna ports rather than all antenna elements, significantly reducing feedback overhead while maintaining channel state information accuracy through the first stage beamforming process.
Solution Approach 2:
The patent introduces antenna ports as an intermediary layer between antenna elements and data layers. The first stage precoding matrix acts as a mediator that transforms the channel characteristics from antenna elements to antenna ports, enabling the UE to provide simplified CSI feedback based on antenna ports while the eNB maintains full channel knowledge through the precoding transformation.
2Productivity
If the number of antenna ports is increased to support more users, then system capacity improves, but computational complexity at the UE increases
Solution Approach 1:
The patent divides the large-dimensional antenna array into multiple antenna ports through first stage precoding, allowing the UE to perform channel estimation and CSI reporting on a reduced dimensionality space. The eNB maintains the full-dimensional processing capability, thus system capacity is enhanced through increased antenna ports while UE computational complexity is reduced by operating on the compressed antenna port dimension rather than the full antenna element dimension.
3Power
If full-dimensional MIMO with two-dimensional antenna array is deployed, then beamforming gain and system capacity improve, but CSI acquisition overhead increases
Solution Approach 1:
The patent transforms the channel dimensionality by introducing antenna ports as an intermediate dimension between antenna elements and data layers. The first stage precoding matrix performs dimensionality reduction from the two-dimensional antenna array to a smaller set of antenna ports, enabling efficient CSI acquisition in this transformed dimension while preserving the beamforming gain benefits of the full-dimensional antenna array through the precoding transformation.
Data Source
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AI summary
Certain aspects of the present disclosure provide methods and apparatus for linear precoding in full-dimensional MIMO (FD-MIMO) systems. According to aspects, an eNB may compress a larger number of antenna elements to a smaller number of antenna ports. The eNB may use a port precoding matrix to transmit reference signals to a UE, receive feedback regarding CSI based on the reference signals, and transmit data to the UE, based on a mapping of multiple data layers and mapping of antenna ports to the physical antenna elements. Further, aspects include performing elevation beamforming by dynamically forming one or more vertical sectors based on UE feedback in the elevation domain.