Distributed MIMO Calibration Using UE Feedback for Phase Alignment
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Solution Overview
Problem
The challenge of supporting a large number of CSI-RS antenna ports in low carrier frequency systems is limited by antenna form factor, restricting spectral efficiency and multi-user MIMO spatial multiplexing gains, especially in distributed MIMO networks where on-board calibration is difficult due to physical separation of antenna panels.
Innovation Solution
Implement over-the-air signaling mechanisms and UE-assisted calibration methods to calibrate phase and amplitude across distributed MIMO networks, utilizing UL RS transmission, channel estimation, and feedback for precise DL channel estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of CSI-RS antenna ports is increased to improve spectral efficiency and MIMO spatial multiplexing gains, then the spectral efficiency and MIMO performance are improved, but the antenna form factor size increases which is not feasible at low carrier frequencies
Solution Approach 1:
The patent divides the large number of antenna ports into multiple distributed antenna panels, each with a manageable number of elements. Instead of deploying all 32 antenna ports at a single location, the system segments them across multiple geographically distributed panels, allowing each panel to have a compact form factor while the aggregate system achieves the desired spectral efficiency through coordinated transmission.
2Area of stationary object
If distributed antenna panels are used to maintain compact form factor, then the antenna size constraint is satisfied, but phase and amplitude alignment becomes difficult due to physical separation
Solution Approach 1:
The patent implements a feedback-based calibration mechanism where the network node transmits calibration signals to the UE, which measures the received signals and reports channel state information including phase and amplitude characteristics. The network node uses this feedback to compute and apply calibration coefficients that compensate for the phase and amplitude differences introduced by physical separation, achieving precise alignment across distributed panels.
Solution Approach 2:
Instead of using mechanical or physical methods to align phases (such as precise physical positioning or hardware phase shifters), the patent substitutes these with signal processing and computational methods. The system uses digital signal processing to estimate and correct phase offsets based on channel measurements, replacing physical alignment mechanisms with software-based calibration.
3Ease of manufacture
If on-board calibration is used for centralized MIMO systems, then calibration is straightforward, but it becomes difficult to implement in distributed MIMO networks due to physical separation of antenna panels
Solution Approach 1:
The patent introduces the UE as an intermediary calibration assistant. Instead of requiring direct communication and calibration between physically separated antenna panels (which would be complex), the UE serves as a common reference point that receives signals from all panels. The UE measures and reports channel characteristics, enabling the network to compute calibration coefficients without requiring direct panel-to-panel calibration links.
Data Source
AI summary
Calibration in distributed multiple input multiple output (MIMO) networks. A method performed by a first base station (BS) includes receiving a first uplink (UL) reference signal (RS) and determining, based on the first UL RS and a second UL RS, a first phase offset for transmission of a first downlink (DL) RS to a user equipment (UE). The second UL RS is associated with a second BS. The first phase offset of the first DL RS is relative to a second DL RS associated with the second BS. The method further includes transmitting the first DL RS with the first phase offset; receiving UE feedback associated with the first DL RS and the second DL RS; and determining, based on the first phase offset and the received feedback, for a DL data transmission to the UE, a second phase offset between transmissions of the first BS and the second BS.