Hybrid Beamforming MCS Offset for Uplink Stability
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Solution Overview
Problem
Existing MIMO systems face challenges with synchronization, cost, and operational complexity due to the need for multiple RF chains in millimeter wave communication, particularly when dealing with drastic changes in the uplink channel caused by user equipment movement or rotation, which can render designated modulation and coding schemes unsupported.
Innovation Solution
A hybrid beamforming method where user equipment estimates an MCS offset based on channel variations between sounding reference signal transmission and uplink grant reception, allowing for adaptive modulation and coding scheme adjustments to ensure stable data transmission, even in environments with significant channel changes, by using a combination of digital and analog beamforming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple RF chains are used in MIMO system to increase data transmission rate, then communication capacity is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines digital beamforming and analog beamforming into a hybrid beamforming system. The digital beamforming handles spatial multiplexing and interference suppression, while analog beamforming provides directional focusing. This merging allows the system to achieve high data transmission rates without requiring a proportional increase in RF chains, as the analog beamforming can steer multiple beams using the same RF resources through phase shifting.
Solution Approach 2:
The patent segments the beamforming function into two distinct parts: digital beamforming (performed in baseband domain) and analog beamforming (performed in RF domain). This segmentation allows each part to specialize in specific tasks - digital processing handles complex signal separation while analog processing handles directional control - thereby achieving high capacity with fewer RF chains than would be required for full digital beamforming.
2Measurement precision
If digital beamforming is used with one RF chain per physical antenna, then beam sharpness is improved, but cost and operational complexity increase
Solution Approach 1:
The patent merges digital beamforming capabilities with analog beamforming in a hybrid architecture. The digital beamforming provides the computational power for precise beamforming weights and spatial processing, while the analog beamforming provides the physical phase shifting and amplitude control. This combination achieves beam sharpness comparable to full digital beamforming but with fewer RF chains, as the analog domain handles the intensive RF processing for multiple antennas.
3Device complexity
If analog beamforming is used to reduce implementation cost, then device complexity is reduced, but beam sharpness and flexibility deteriorate
Solution Approach 1:
The patent combines analog beamforming's cost advantages with digital beamforming's performance advantages. The analog beamforming section provides the low-complexity directional beam steering, while the digital beamforming section enhances beam sharpness through precise weight calculation and spatial processing. This hybrid approach achieves beam sharpness superior to pure analog beamforming while maintaining lower complexity and cost compared to full digital beamforming.
4Productivity
If MCS is determined based on sounding reference signal, then communication efficiency is improved, but reliability deteriorates when channel changes drastically
Solution Approach 1:
The patent applies preliminary action by having the UE predict future channel conditions and pre-determine an appropriate MCS before actual data transmission. The UE uses the sounding reference signal to estimate channel quality, then predicts how the channel will evolve, and selects an MCS that is robust to predicted channel variations. This preliminary MCS selection ensures that even if the channel changes drastically, the transmission remains reliable, as the MCS was chosen with future conditions in mind.
Solution Approach 2:
The patent implements feedback mechanisms where the UE monitors actual channel conditions and transmission outcomes, then adjusts its MCS prediction algorithm accordingly. The system uses feedback from channel quality indicators and transmission acknowledgments to refine the MCS selection process, improving both the accuracy of predictions and the reliability of transmissions over time.
Data Source
AI summary
Provided are a method and an apparatus for transmitting uplink data based on hybrid beamforming in a wireless communication system. Specifically, a user equipment (UE) receives a first modulation and coding scheme (MCS) determined based on a sounding reference signal from a base station (BS) through an uplink grant. The UE determines an MCS offset based on a variation of an uplink channel when the variation of the uplink channel between a subframe for transmitting the sounding reference signal and a subframe for receiving the uplink grant is a threshold or greater. The UE transmits uplink data to the BS using a second MCS acquired from the first MCS and the MCS offset.