Making Massive MIMO Measurements

Massive MIMO Multiple Input, Multiple Output: A physical layer (PHY) configuration in which both transmitter and receiver use multiple antennas. is currently a BETA feature.

Massive MIMO Overview

This document provides a brief summary of the procedure for using the Keysight L8990A-016 3x32 switch matrix with the 89600 VSA software to make measurements on 32 ports of a massive MIMO radio (DUT Device under Test: An acronym used to describe some type of electrical apparatus connected to test instrumentation. The apparatus can range from a single component to a complex subsystem such as a mobile phone, base station or MSC.) using sequential acquisition to two ports at a time.

Port 1 of the DUT will be connected to the first port on the 2-channel analyzer (e.g. MXR or UXR oscilloscope) without going through the switch matrix. The user should try to add path loss and delay for this path to match the path loss and delay for signals going through the switch matrix. If MXR or UXR has 4 channels or 8 channels, connect the output of the switch matrix to the third port of MXR or UXR.

Examples

Example 1: Sequential Acquisition with Keysight 32-port Switch Matrix

The following measurement example performs a separate acquisition for each of four carriers in a 5G NR signal, resulting in one acquired carrier per measurement channel.

Required equipment and software:

Procedure

  1. Calibrate the switch matrix and all the cables from DUT to MXR/UXR

    1. Calibrate the PNA network analyzer using a calibration kit or ECal, then calibrate the switch matrix using the P7006A system calibration software and the PNA to generate *.s2p correction files for each path through the switch matrix to a DUT port.

    2. You can name the calibrations file with prefix Ch1, Ch2... or Port1, Port2... etc, so that you can use VSA System Calibration Utility to load all the 32 calibration files conveniently.

  2. Connect the hardware in Keysight Connection Expert.

    1. Run Keysight Connection Expert software and establish LAN Local Area Network: A communications network that serves users within a local geographical area, typically over distances of around 100m. Wireless LANs use wireless communicaitons to network devices so there is no need for data cabling. connections to the switch matrix and the MXR oscilloscope or other 2-channel phase coherent analyzer.

  3. Add switch matrix and analyzer to VSA hardware configurations

    1. Run VSA software. Go to Utilities > Hardware > Configurations, add a new hardware configuration, select the Keysight L8990 RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). Switch, and add it to the configuration list. In the box below step 2, select the switch matrix, then name the configuration and click OK.

    2. Add another new configuration for Keysight/Agilent Infiniium Series Oscilloscope to create the configuration for the MXR/UXR, and select this configuration to use for analysis measurements. Close the configuration window.

    3. Go to Utilities -> Hardware -> Switch and select the switch that was configured.

  4. Configure single channel analyzer parameters

    1. Go to Input > Trigger. If external trigger (Frame boundary) is present, select the external trigger and set the proper Level. If you are using VXT2 or XA series and there is no external frame trigger, you can select Periodic trigger and set the trigger period as 10ms.

    2. Go to MeasSetup > Frequency... and set the center frequency the same as the carrier frequency, then set the span as the carrier bandwidth.

    3. Go to Input > Analog... and set the Range based on the signal power level and possible attenuation between DUT and analyzer.

  5. Configure single channel 5G NR Measurement

    1. Configure 5G NR signal based on DUT's signal configuration.

    2. As we will expand the channel number from 1 to 32, in order to speed up the measurement, we need to minimize the data capture length. Go to 5G NR Demod Properties... > Time and change the Result Length to 1 subframe, and change the Acquisition Mode to Frame Trigger Is Present.

    3. Open the MIMO related traces, like DMRS MIMO Info, MIMO Eq Ch Freq Resp, Beam Weights.

    4. In order to avoid presetting the traces after changing the channel configuration, go to Utilities > Display Preferences > Trace and uncheck Preset Traces after changing Channel Configuration.

    5. Change the sweep mode to single mode. This will speed up the channel configuration process and also protect the switch matrix.

  6. Configure sequential acquisition

    1. Go to Utilities > Custom Solutions > Sequential Input Config.

    2. Enter the parameters under General as needed for the DUT. Note that the Analyzer Input Range should be the DUT output power minus the Switch Attenuation setting.

    3. Under Channel Mapping, enter the DUT Ch. Count (32) and the Analyzer Ch. Count (2).

    4. Check the box for Sequential Phase/Time Tracking On, then click Apply.

    5. If anything is invalid, an invalid configuration message will be displayed. Read the message carefully to see the root cause.

    6. After the change is applied successfully, a message will say that the changes are applied successfully. Restart the measurement and check the Massive MIMO results in NR measurement. This is the results without any system calibration.

  7. Load user correction files into VSA to calibrate switch matrix paths

    1. In VSA, go to Help > Examples and select Utilities > SystemCalibrationUtility. Run SystemCalibrationUtility.exe.

    2. Under Correction Application, Check Select corrections from folder, select the right folder path and right Prefix for the file, like Ch or Port.

    3. Click the Apply User-Corrections button.

    4. Go to Input > User Correction, to check whether all the files are applied for all the channels.

    5. Restart the measurement and check the Massive MIMO reuslts; this is the results with system calibration.

 

See Also

Measurements Dialog Box