MIMO OTA Calibration via Inverse Radiation Matrix
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Solution Overview
Problem
Current MIMO test systems face limitations in accurately measuring the radiation channel matrix, particularly for larger dimensions, leading to inaccurate DUT performance measurements due to the need for wired connections and limitations in calibrating the radiation channel matrix.
Innovation Solution
A non-cable-conducted OTA radiated test system that uses an anechoic chamber with probe antennas to transmit predetermined signals, measure received power and relative phase, construct a radiation channel matrix, and calculate an inverse matrix for calibration, allowing for accurate DUT performance measurements without physical connections to antenna ports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a radiated two-stage (RTS) methodology is used to measure the radiation channel matrix, then the test setup is similar to MPAC OTA setup, but the radiation channel matrix includes values associated with properties of the DUT antennas and is limited to cases where the radiation channel matrix is not greater than a 2-by-2 matrix, making accurate measurement impossible for larger matrices
Solution Approach 1:
The patent extracts the DUT antenna properties from the radiation channel matrix measurement process by using a different measurement approach. Instead of directly measuring the radiation channel matrix that includes DUT antenna properties, the system measures the channel response between probe antennas and uses this to derive calibration information, thereby separating the measurement of transmission medium characteristics from DUT-specific antenna characteristics.
Solution Approach 2:
The patent inverts the traditional measurement approach by not directly measuring the radiation channel matrix between probe antennas and DUT antennas. Instead, it measures the channel response at the probe antennas and uses this inverted measurement strategy to calculate the inverse matrix, which is then applied to calibrate out the radiation channel effects from DUT performance measurements.
2Ease of operation
If cable-conducted MIMO test system is used, then wired connections can be made to antenna ports, but it requires breaking open the DUT to access antenna ports and taking active antenna effects into account
Solution Approach 1:
The patent introduces probe antennas as intermediary elements that mediate between the test system and the DUT. These probe antennas wirelessly transmit and receive signals to measure the channel response, serving as an intermediary that eliminates the need for direct wired connections to DUT antenna ports while still enabling channel characterization.
Solution Approach 2:
The patent replaces the mechanical wired connection system with a wireless electromagnetic field-based measurement system. Instead of using cables to physically connect to antenna ports, the system uses electromagnetic waves transmitted between probe antennas and DUT antennas to measure channel characteristics, thereby eliminating mechanical connections.
3Measurement precision
If inverse matrix of radiation channel matrix is calculated and multiplied by channel model, then calibration is performed, but the radiation channel matrix cannot be accurately measured for matrices greater than 2x2, resulting in inaccurate DUT performance measurements
Solution Approach 1:
The patent changes the dimensionality of the measurement approach by measuring channel responses at multiple probe antenna locations and using these measurements to construct the radiation channel matrix. This multi-dimensional measurement strategy enables accurate measurement of large-scale MIMO channels with many transmit and receive antennas, overcoming the limitation of traditional 2x2 matrix measurements.
Data Source
AI summary
A MIMO test system is provided that performs non-cable-conducted, over-the-air radiated calibration and test modes of operations. A DUT is located in an anechoic chamber having a plurality of probe antennas disposed therein. During the calibration mode, the test instrument causes predetermined signals to be transmitted over a transmission channel comprising a non-cable-conducted, OTA interface between probe antennas of the chamber and antenna ports of the DUT and obtains measurements of received power and relative phase. The test instrument uses the measurements to construct a radiation channel matrix associated with the transmission channel and obtains an inverse matrix of the radiation channel matrix. During the test mode, the test system performs a non-cable-conducted, OTA radiated test during which the test instrument applies the inverse matrix to DUT performance measurements obtained by the test instrument to calibrate out the radiation channel matrix from the DUT performance measurements.