Hierarchical Beamforming Reduces Overhead in Massive MIMO Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current wireless access systems face challenges in performing effective beamforming, especially in massive multi-input multi-output (MIMO) systems, due to increased antenna numbers which lead to high reference signal and feedback overhead, affecting beamforming gain and system complexity.
Innovation Solution
The implementation of hierarchical beamforming, where a base station transmits initial and secondary beams with different steering vectors based on feedback information including signal strength, channel quality, and precoding matrix indication, allowing for adaptive beam angle determination and reduced overhead through a hierarchical approach.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of transmitting antennas is increased to improve beamforming gain and link quality, then beamforming performance is improved, but reference signal overhead and system complexity increase
Solution Approach 1:
The patent segments the beamforming process into two hierarchical stages: coarse beam selection and fine beam refinement. In the coarse stage, a reduced set of beamforming vectors is used to identify candidate beams, while in the fine stage, a larger set of vectors refines the selection. This segmentation allows the system to handle large antenna arrays without requiring the receiver to process all possible beams simultaneously, thereby reducing complexity while maintaining beamforming gain.
Solution Approach 2:
The patent introduces a hierarchical dimension to the beamforming codebook structure, organizing beamforming vectors into multiple levels (coarse and fine). Instead of presenting all N-dimensional beamforming options at once to the receiver, the system structures the search space hierarchically, allowing the receiver to first select from a smaller coarse set and then refine within a finer subset. This dimensional organization reduces the immediate complexity burden on the receiver while preserving the ability to exploit all N antennas for beamforming gain.
2Productivity
If the number of transmitting antennas is increased to generate more orthogonal beams, then the number of simultaneous receivers is increased, but reference signal overhead increases
Solution Approach 1:
The patent segments the reference signal transmission into coarse and fine stages, where coarse reference signals correspond to a reduced set of beamforming vectors and fine reference signals correspond to a larger set. By transmitting reference signals in this hierarchical manner rather than all at once, the system reduces the immediate reference signal overhead while still enabling support for multiple simultaneous receivers through the expanded fine-grained beam set.
Solution Approach 2:
The patent performs preliminary coarse beam selection before fine beam refinement. The coarse beamforming stage pre-identifies candidate beams that cover broad spatial regions, allowing the system to reduce reference signal overhead by not transmitting fine-grained reference signals for all possible beams simultaneously. Only after coarse selection does the system activate the finer reference signal set, thereby reducing overall overhead while maintaining the ability to serve multiple receivers.
3Measurement precision
If hierarchical beamforming with multiple stages is implemented, then beam quality is improved, but feedback overhead increases
Solution Approach 1:
The patent segments feedback transmission into two parts: coarse feedback indicating the selected coarse beam index and fine feedback indicating the selected fine beam index within the coarse beam. By segmenting the feedback this way rather than transmitting a single large-index feedback for all beams, the system reduces total feedback overhead. The coarse feedback requires fewer bits since it selects from a reduced set, and the fine feedback only needs to distinguish among a subset of beams within the selected coarse beam, not all beams globally.
Solution Approach 2:
The patent transforms the feedback problem from a single-dimensional large-index selection into a two-dimensional hierarchical selection (coarse index + fine index). This dimensional change reduces feedback overhead because the coarse index requires fewer bits and the fine index only needs to differentiate among a subset. The hierarchical dimensioning of feedback mirrors the hierarchical dimensioning of the beamforming codebook, allowing precise beam quality selection with reduced total feedback quantity.
Data Source
AI summary
A method for performing hierarchical beamforming in a wireless access system and a device therefor are disclosed. Particularly, the method comprises: an initial step for allowing a base station to transmit a plurality of first beams, to which different steering vectors are applied, to a terminal through corresponding reference signals, and a repetition step for allowing the base station to transmit a plurality of second beams, to which different steering vectors are applied, to the terminal through corresponding reference signals by considering feedback information that contains an index of one or more beams received from the terminal, wherein the repetition step can be repeated up to a predetermined number of times.