MIMO Beamforming Phase Correction for Unsynchronized Oscillators
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Solution Overview
Problem
Beamforming in Multiple-Input Multiple-Output (MIMO) communication systems is sensitive to undesired phase and frequency offsets, which existing methods struggle to accurately measure and correct, especially when transmitters use unsynchronized Local Oscillator signals, leading to high differential phase noise.
Innovation Solution
A communication terminal and system that includes transmitters and receivers with a phase correction unit, utilizing Differential Phase-Locked Loops and unsynchronized or synchronized Local Oscillator signals to measure and correct phase shifts, and employing pilot symbols with interleaved sub-sequences to estimate and adjust the beamforming phase offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If phase-shifted replicas are transmitted from multiple antennas to produce directional high-gain transmission, then transmission directionality and gain are improved, but sensitivity to phase and frequency offsets increases
Solution Approach 1:
The patent implements feedback mechanisms where the receiver measures phase and frequency offsets and sends correction information back to the transmitter. The transmitter then adjusts its beamforming phase shifts based on this feedback to compensate for offsets, maintaining directional gain while reducing sensitivity to phase errors.
Solution Approach 2:
The system dynamically adjusts beamforming parameters (phase shifts and weights) based on measured channel conditions and offset values. By changing these parameters in response to detected phase and frequency offsets, the system maintains optimal directional transmission despite varying offset conditions.
2Measurement precision
If frequency offsets are measured and corrected using existing methods, then some phase accuracy is improved, but accuracy is insufficient in systems with unsynchronized LO signals
Solution Approach 1:
The patent introduces pilot symbols as intermediary reference signals that are transmitted through the channel. These known pilot symbols serve as a mediator between transmitter and receiver, allowing the receiver to measure both channel response and LO frequency offsets by comparing received pilots against transmitted pilot sequences, achieving accurate measurement even with unsynchronized LO signals.
Solution Approach 2:
The system transmits multiple pilot symbols across different time instances and frequencies, using more measurement opportunities than strictly necessary. This excessive sampling of the channel and offset characteristics through redundant pilot transmissions enables more robust and accurate offset estimation despite LO synchronization issues.
3Measurement precision
If pilot symbols are interleaved in sequences to estimate beamforming phase errors, then phase error estimation is improved, but signal processing complexity increases
Solution Approach 1:
The patent segments the beamforming correction process into distinct stages: first estimating channel response from pilots, then separately estimating frequency offsets, and finally computing phase corrections. This segmentation of the estimation process into modular steps reduces overall processing complexity while maintaining estimation accuracy.
Solution Approach 2:
The system performs preliminary estimation of frequency offsets and channel responses using pilot symbols before the actual data transmission and beamforming adjustment. By preparing correction values in advance based on pilot measurements, the system reduces the processing complexity during main data transmission while maintaining accurate phase error estimation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively corrects error components in phase and frequency offsets, reducing differential phase noise and improving the directional accuracy of transmitted signals, even in systems with unsynchronized transmitters, by measuring phase shifts and applying phase corrections based on pilot symbol magnitudes.
Implementation Method 1
the phase correction unit includes a Differential Phase-Locked Loop (DPLL), which is coupled to measure the phase shift
Implementation Method 2
first and second Local Oscillator (LO) generation units, which are coupled to produce respective first and second LO signals
Implementation Method 3
the first and second receivers are respectively coupled to down-convert the third and fourth RF signals to produce first and second received signals
Data Source
AI summary
A communication terminal includes first and second transmitters, which are coupled to produce respective first and second Radio Frequency (RF) signals that are phase-shifted with respect to one another by a beamforming phase offset, and to transmit the RF signals toward a remote communication terminal. The terminal includes a reception subsystem including first and second receivers and a phase correction unit. The first and second receivers are respectively coupled to receive third and fourth RF signals from the remote communication terminal. The phase correction unit is coupled to produce, responsively to the third and fourth RF signals, a phase correction for correcting an error component in the beamforming phase offset.