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Read this tutorial for detailed information on the VST video demos.
Table of Contents
802.11ac Comparison Demo
For this comparison demo, an 80 MHz 802.11ac signal is generated using either the Agilent MXG or the NI PXIe-5644R. The signal is routed to the analyzer (Agilent PXA or the NI PXIe-5644R) for analysis. For 802.11ac, error vector magnitude (EVM) is a challenging measurement to make because of the high signal-to-noise ratio (SNR) required for a 256 QAM modulated signal. The 802.11ac specification requires the EVM of devices to be at least -32 dB. Test instruments typically need to be at least 10 dB better than the specification. Time, amplitude, and phase compensation are turned on for both instruments. Channel tracking, however, is turned off. Carried frequency offset is set to preamble only instead of preamble and data. Typically, preamble only is about 2 dB worse in EVM than preamble and data.
Reference levels are adjusted to get the best possible range on both instruments. This is done using the adjust reference button for the Agilent PXA and using the reference level setting for the NI PXIe-5644R.
Agilent Setup Details
Generation
The Agilent N5182A is used to generate an 80 MHz 802.11ac MCS9 signal. Agilent signal studio is used to create the signal and then it is downloaded to the MXG. See some of the details for the setup below.
Center Frequency: 5.8 GHz
Power Level: -10 dBm
DC calibration is performed on the MXG before generation.
Figure 1: Signal Studio software is used to generate the 80 MHz 802.11ac signal.
Analysis
Agilent 89601 software is used to analyze the acquired signal on the Agilent PXA. The PXA has a bandwidth of 160 MHz; however, for this comparison, only 80 MHz is required.
See further details below.
Frequency: 5.8 GHz
Modulation Scheme: 256 QAM (MCS 9)
IQ Mismatch Compensation: On
Note: I/Q mismatch compensation compensates for any mismatches in the I and Q waveforms.
Amplitude Tracking: On
Amplitude tracking on the Agilent PXA is set to on. If the incoming signal has changing amplitude during the burst, turning amplitude tracking on compensates for this effect.
Phase Tracking: On
Setting phase tracking to on compensates for any phase mismatches during the burst.
Time Tracking: On
Number of averages: 10
Figure 2: Agilent 89601 software is used to analyze the incoming 802.11ac signal.
Figure 3: Time, amplitude, and phase tracking are turned on for the 802.11ac EVM measurement. IQ mismatch is also compensated to get the best EVM result.
NI Setup Details
Generation
The NI PXIe-5644R vector signal transceiver (VST) is used to generate an 80 MHz 802.11ac MCS9 signal. The NI WLAN Generation Toolkit is used to create the waveforms that are then downloaded to the NI PXIe-5644R. See some of the details for the setup below.
Center Frequency: 5.8 GHz
Power Level: -10 dBm
Figure 4: NI WLAN Generation Toolkit software is used to generate the 80 MHz 802.11ac signal.
Analysis
The NI WLAN Analysis Toolkit is used to analyze the acquired signal on the NI PXIe-5644R VST. See further details below.
Frequency: 5.8 GHz
Modulation Scheme: 256 QAM (MCS 9)
IQ Mismatch Compensation: On
Note: I/Q mismatch compensation compensates for any mismatches in the I and Q waveforms.
Amplitude Tracking: On
Amplitude tracking on the NI PXIe-5644R is set to on. If the incoming signal has changing amplitude during the burst, turning amplitude tracking on compensates for this effect.
Phase Tracking: On
Setting phase tracking to on compensates for any phase mismatches during the burst.
Time Tracking: On
Number of averages: 10
Figure 5: NI WLAN Analysis Toolkit software is used to analyze the incoming 802.11ac signal.
NI and Agilent Setup Table
| Setup Detail | National Instruments | Agilent |
| Analyzer | NI PXIe-5644R | Agilent PXA |
| Generator | NI PXIe-5644R | Agilent MXG |
| Analysis Software | NI WLAN Analysis Toolkit | Agilent 89601B |
| Generation Software | NI WLAN Generation Toolkit | Agilent Signal Studio for 802.11ac |
| Center Frequency | 5.8 GHz | 5.8 GHz |
| Amplitude | -10 dBm | -10 dBm |
| Channel Bandwidth | 80 MHz | 80 MHz |
| Averages | 10 | 10 |
| MCS/Modulation Scheme | 9/256 QAM | 9/256 QAM |
| Time Tracking | On | On |
| Phase Tracking | On | On |
| Amplitude Tracking | On | On |
| IQ Compensation | On | On |
| Synchronization Scheme | Backplane 10 MHz clocks synchronized | Sharing 10 MHz PXI clock |
Frequency Domain Trigger Demo
This is a demonstration of how a relatively small modification to the FPGA on the NI PXIe-5644R VST can enhance the functionality of the instrument. In this example, we add frequency domain triggering capability to the NI PXIe-5644R. Frequency domain triggering is useful if you are looking for a spur or noise in a specific part of the spectrum. It also helps prevent from continuously acquiring data and instead only acquiring the frequency components that are important to you. Almost all vector signal analyzers (VSAs) have a time domain trigger, but few can trigger in the frequency domain.
Setup Details
The RF transmitter on the NI PXIe-5644R VST is used to generate a single tone at 1 GHz, which is then looped back to the RF receiver on the same NI PXIe-5644R. The NI LabVIEW FPGA Module is used to reprogram the NI PXIe-5644R to incorporate a frequency domain trigger. A user-defined spectral mask threshold is downloaded to FPGA memory where it is compared to the incoming signal. If the signal exceeds the user-defined trigger threshold, the acquisition is triggered on the NI PXIe-5644R RF receiver and we begin acquiring the signal.
Figure 7: A LabVIEW front panel demonstrating a frequency domain triggered acquisition.
Channel Emulation Demo
A radio channel emulator is a tool for testing wireless communication in a real-word environment. Fading models are used to simulate air interference, reflections, moving users, and other naturally occurring phenomenon that can hamper an RF signal in a physical radio environment. This demonstration shows how the NI PXIe-5644R can be reprogrammed to become something completely different that a typical VSA+VSG could ever be. By programming mathematical fading models onto the FPGA of the NI PXIe-5644R VST, it becomes a real-time radio channel emulator.
Setup
This setup has two VSTs being used as a 2x2 MIMO channel emulator but could easily be expanded to support as many channels as desired. First, a 2x2 MIMO waveform is generated using two phase-coherent vector signal generators (VSGs). Two NI PXIe-5673E VSGs were used in this setup. The RF signals are generated from two VSGs into two phase-coherent NI PXIe-5644R VSTs, where mathematical fading models are applied that simulate air interference of a physical radio environment. The affected MIMO waveform is then generated out of the two NI PXIe-5644R VSTs and into two phase-coherent VSAs to be acquired and displayed to the user. Two NI PXIe-5663E VSAs were used in this setup.
Figure 8: This block diagram represents an example hardware setup to demonstrate a 2x2 MIMO channel emulator using two NI PXIe-5644R VSTs.
Figure 9: A LabVIEW front panel shows the effect of MIMO channel emulation implemented using two VSTs.
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