Antenna Calibration in Distributed Systems Using Loop-Back Phase Differences
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Solution Overview
Problem
Antenna calibration in distributed antenna systems (DAS) is challenging due to the complexity of minimizing phase and amplitude differences among multiple transceiver chains, especially in scenarios where centralized control units (CCUs) are not feasible, and existing methods fail to meet the strict calibration accuracy requirements for high-frequency subcarriers.
Innovation Solution
A method and apparatus for antenna calibration in DAS that transmit calibration signals from multiple antennas in the same frequency resource, obtaining receiver and transmitter side loop-back phase differences, and estimating time delay and initial phase differences using polynomial fits, without requiring a CCU, allowing for accurate calibration and reduced complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If antenna calibration is performed in distributed antenna systems using existing methods, then calibration can be achieved, but the complexity is high and calibration accuracy for high-frequency subcarriers is insufficient
Solution Approach 1:
The patent segments the calibration process into two independent parts: uplink calibration and downlink calibration. The uplink calibration determines receiver-side phase differences, while the downlink calibration determines transmitter-side phase differences. This segmentation allows each calibration process to be optimized independently, improving overall accuracy without proportionally increasing complexity.
Solution Approach 2:
The patent introduces a digital unit as an intermediary that coordinates the calibration process between distributed antennas. The digital unit manages signal transmission and reception, collects phase difference measurements, and performs polynomial fitting calculations. This intermediary structure enables centralized control of calibration without requiring a full centralized control unit, balancing accuracy requirements with system complexity.
2Measurement precision
If polynomial fits are used for estimating time delay and initial phase differences, then calibration accuracy is improved, but calculation complexity increases
Solution Approach 1:
The patent transforms the calibration problem from directly measuring phase differences to estimating time delay and initial phase parameters through polynomial fitting. By changing the parameters being estimated (from raw phase differences to time delay and initial phase), the system achieves more accurate results for high-frequency subcarriers while maintaining manageable calculation complexity through standardized polynomial operations.
3Productivity
If distributed antennas transmit calibration signals in the same frequency resource, then calibration efficiency is improved, but signal interference increases
Solution Approach 1:
The patent enables continuous calibration operations by allowing multiple distributed antennas to transmit calibration signals simultaneously in the same frequency resource. This continuous operation improves calibration efficiency by eliminating sequential timing constraints. The system manages potential interference through the digital unit's coordination and signal processing capabilities.
Data Source
AI summary
A method is implemented in a digital unit connected with a plurality of distributed antennas including a first antenna, a second antenna and a third antenna. The method comprises: causing transmitting a first signal from the first antenna, a second signal from the second antenna, and a third signal from the third antenna in a same frequency resource; obtaining a receiver and transmitter side loop-back phase difference between the first antenna and the second antenna based on the first signal received at the third antenna, the second signal received at the third antenna, the third signal received at the first antenna, and the third signal received at the second antenna; and obtaining estimations of a time delay difference and an initial phase difference between the first and second antennas based on the obtained loop-back phase difference.