[7 Wonderful Ideas] | Wi-Fi 7 Test Practice: SOC Chip and MIMO Scenarios
Tip: The original PDF download link is attached at the end of the article
In the previous article, we talked about the ultimate EVM analysis of Wi-Fi 7 , the factors that affect EVM testing such as frequency response and crest factor, and the channel estimation and tracking methods that need to be paid attention to during demodulation. Finally, we introduced the new FSW-K575 option for IQ noise cancellation to further improve EVM measurement performance through algorithms.
As Wi-Fi 7 has become a hot topic in recent years, the test items are also varied, and each manufacturer in the industry has its own focus, including:
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Power amplifier manufacturers focus on digital pre-distortion (DPD) and peak-to-average ratio (PAPR);
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Wireless equipment manufacturers are concerned about error vector magnitude (EVM) and IQ data imbalance;
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Semiconductor companies focus on IQ noise and noise figure (NF);
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System manufacturers are more concerned with overall metrics such as EVM, which affects network quality of service, as well as system validation for multi-user and MIMO.
These special projects also constitute an important part of Wi-Fi 7 testing, such as WLAN SOC (System On Chip) chip test solutions, noise coefficient tests, digital pre-distortion (DPD), MIMO test scenarios, etc.
In this article, we will continue to focus on Wi-Fi 7. In this series of technical solutions, we will use SOC chips and MIMO tests as demonstrations to explore the technical details of these important parameters.
WLAN SOC Test
Many manufacturers who do SOC chip testing, in addition to verifying a single device chip, of course also need to evaluate the entire Radio Frequency Integrated Circuit (RFIC) as a whole. SOC-level RFIC testing can verify whether the integration of the RF module with other processors, memory, analog IQ interface and other modules is correct, and whether the performance of the entire system meets the design requirements.
At this time, the system often needs to test many parameters, such as the noise figure of the RF receiving link, the DPD of the RF transmitting link, phase noise test, digital signal generation and demodulation, etc. At this time, the signal on the board is often I/Q separated, so that the in-phase I and orthogonal Q components can be processed and analyzed separately at the baseband level, and even the differential link can be used to improve the anti-interference performance, allowing the four ports of I+, I-, Q+, and Q- to test and calibrate each component separately. In addition, zero-frequency processing reduces the complexity of the equipment, reduces the external interference and signal distortion caused by the RF link, and makes it easier to simulate various signal conditions, such as frequency offset, amplitude, phase, and modulation mode. Such test boards often do not have RF interfaces. At this time, test instruments with analog IQ interfaces with high dynamic range and low noise levels are needed. The SMW200A vector signal generator and the FSVA3000 series signal and spectrum analyzer can not only be tested with RF interfaces, but also equipped with analog IQ interface inputs and outputs, making testing easier. Among them, the ±200MHz intermediate frequency bandwidth option of the FSVA3000 series signal and spectrum analyzer, which is specially designed for 320MHz bandwidth Wi-Fi7 analog IQ testing, has also become the first choice for SOC chip R&D companies.
Figure 1 SMW200A+FSVA3000 simulated IQ interface Wi-Fi7 test solution
Of course, the noise coefficient and DPD algorithms we just mentioned can be performed under the condition of simulating the IQ interface. With the help of the noise source, the equipment noise coefficient can be accurately obtained under both cold and hot load conditions. With the help of the signal source and the K18 option of the spectrum analyzer, the signal can be repeatedly iterated to correct the source file sent by the signal source, realize link DPD, and achieve the effect of expanding the linear area of signal strength.
MIMO Testing
In fact, MIMO scenario measurements are more widely used in R&D and certification tests. In order to fully reproduce the data in the transmitted signal and the crosstalk between antennas, the tests of all antennas need to be carried out simultaneously.
Let's first consider the signal generation end. The SMW200A signal generator can be configured with two independent channels. The internal baseband can be merged into one baseband to set up two spatial streams to achieve 2-stream signal output. When equipped with the RF front-end SGT100A vector signal source and connected to the analog IQ interface and digital IQ interface of the SMW200A, it can support up to 8-stream data testing.
Figure 2 Multi-stream signal generation in MIMO scenario
Taking 2-stream signal output as an example, set System Config to Coupled Source mode inside a dual-channel signal generator SMW200A, and equip the baseband with 2 spatial streams and antenna transmission matrix, which are mapped to RF port A and port B respectively. You can see that the interface forms a 2-stream output architecture. At this time, you can configure the basic information inside our data stream as required.
Figure 3 SMW200A Wi-Fi2 stream signal generation
Considering that the spectrum analyzer has only one RF input port, spatial division multiplexing requires two or more spectrum analyzers to complete the calculation of the coding matrix and signal demodulation. The WLAN option of FSW provides three different MIMO signal capture methods in Signal Capture:
1. Simultaneous requires that each signal stream corresponds to an instrument, these instruments communicate through the LAN port, and output the reference frequency to each slave in a selected host, and finally demodulate uniformly in the host, which has relatively high requirements for the test environment.
2. Sequential using OSP Switch Box uses an external R&S OSP series switch matrix to switch the data streams sent by multiple antennas, automatically collect the signals of each source in a time-sequential manner, and integrate them for calculation. This method is suitable for situations with a large number of antennas and is more inclined to the establishment of an automated test environment.
3. Sequential Manual manually switches multiple channel data streams. Each time you measure, change the direction of the RF cable connected to the spectrum analyzer. After all the data is collected, the instrument's calculation function is used to obtain complete demodulation information. Like method 2, if you want to collect multi-stream signal data in a sequential manner, whether you use a switch matrix or manual switching, the signal needs to meet the characteristics that the PPDU content of each stream data meets the same characteristics in time.
It is difficult to achieve this condition in actual MIMO signals. After all, each stream signal is assigned a different signal field when it is generated to suit multiple scenarios. Therefore, this test item is only applicable to laboratory R&D scenarios, and the MIMO signal generation capability is verified using a standard WLAN multi-stream signal generated by a signal source.
Figure 4 FSW capture of MIMO signals
Then we can do a simple MIMO signal analysis verification of a 2-stream signal directly connected to a signal source spectrum analyzer. Select the MIMO acquisition mode. After capturing the signal of two channels and calculating the results, FSW can obtain the time domain waveform and demodulation results of the collected MIMO signal according to my preset antenna transmission matrix. You can see the clear constellation diagram and demodulation EVM data of the two spatial streams:
Figure 5 Demodulation of Wi-Fi 7 MIMO signals
Here we only use the signal source and spectrum analyzer to directly connect to verify the MIMO signal receiving and transmitting function, which has scalable significance in the actual multi-channel transmission and reception test scenarios.
In this series of articles, we have explained the new technologies and challenges brought by Wi-Fi 7. Rohde & Schwarz uses test solutions of signal sources and spectrum analyzers to cope with these challenges. Through in-depth analysis of perforated spectrum emission templates, extreme EVM test optimization means and methods, as well as WLAN chip tests and device MIMO tests that simulate IQ interfaces in expanded applications, we provide effective support for performance optimization and quality assurance of Wi-Fi 7.
You can also read our Wi -Fi7 technology white paper (click the original text to get the download link ) and other test solution articles for more information. If you have other questions to discuss, please contact us. R&S will continue to be involved in the research and development and testing of Wi-Fi related products and make professional technical contributions.
【7 Wonderful Ideas】Previous Issues
Let's take a closer look at the extremely comprehensive test solution for Wi-Fi 7 (with white paper download)
Wi-Fi 7 Performance Evaluation: Extreme EVM Analysis
Wi-Fi 7 Testing Guide: Flexible Spectrum Allocation
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