Hybrid Beamforming Using Partial CSI Subspaces for FDD Systems
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Solution Overview
Problem
Existing Hybrid Beamforming (HB) methods for MIMO wireless communication systems face challenges in practical implementation, particularly in FDD systems, due to the impracticality of full Channel State Information (CSI) availability, limitations in handling multiple MU-MIMO groups, and increased pilot overhead compared to TDD systems.
Innovation Solution
The proposed method constructs subspaces for each user based on principal angle information from partial CSI feedback, allowing for the derivation of a unified analog beamforming matrix for all users. This approach reduces the need for full CSI and minimizes pilot overhead, making it suitable for FDD systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full CSI is used to compute analog precoding matrix, then beamforming performance is improved, but pilot overhead increases substantially and implementation becomes impractical
Solution Approach 1:
The patent extracts only the essential phase information from the channel state, rather than using full CSI. By taking out only the phase component of channel coefficients to construct the analog precoding matrix, the system achieves acceptable beamforming performance while dramatically reducing pilot overhead and feedback requirements.
Solution Approach 2:
The patent applies partial action by using only partial CSI (phase information) instead of complete CSI for analog precoding matrix computation. This partial information approach is sufficient to achieve the main beamforming objective while avoiding the excessive resource consumption associated with full CSI acquisition.
2Productivity
If each antenna element has a dedicated RF chain, then signal processing capability is improved, but implementation cost and power consumption increase substantially
Solution Approach 1:
The patent merges multiple antenna signals through analog combining networks before feeding them to a reduced number of RF chains. By combining signals in the analog domain using phase shifters and summation networks, the system maintains signal processing capability while reducing the total number of expensive RF chains required.
Solution Approach 2:
The patent introduces analog combining networks as intermediary components between the antenna array and the RF chains. These intermediary networks process multiple antenna signals simultaneously in the analog domain, enabling efficient signal aggregation before digital conversion and reducing the burden on individual RF chains.
3Measurement precision
If full CSI is measured by downlink CSI-RS, then channel information accuracy is improved, but pilot overhead becomes huge due to large number of antennas
Solution Approach 1:
The patent extracts only the phase component from channel measurements rather than acquiring full complex CSI. This extraction approach maintains sufficient accuracy for analog precoding purposes while reducing the amount of data that needs to be measured, quantized, and fed back, thereby reducing pilot overhead.
4Productivity
If baseband precoding is applied to all antennas, then spatial multiplexing gain is improved, but baseband computation complexity increases hugely
Solution Approach 1:
The patent segments the beamforming function into two parts: analog beamforming at the RF stage and reduced baseband precoding. By dividing the overall signal processing into analog and digital domains, the system achieves spatial multiplexing gains through analog beamforming while keeping baseband computation complexity manageable.
Data Source
AI summary
This invention presents a method and systems for beamforming in wireless communication comprising a base station with a plural of antennas and radio frequency transmitting and receiving chains, a plural of base band transmitting paths and base band receiving paths, and a processor that constructs a subspace for each user equipment using the principal angle information contained in partial channel state information obtained on channels associated with a part of the BS antennas, derives an analog beamforming matrix and/or an analog combining matrix from the subspaces of all the user equipment selected for communication with the base station to achieve analog beamforming, and further performs beamforming at the base band.