Wi-Fi 7 is currently a future technology development trend that technology companies are focusing on. The performance specifications of Wi-Fi 7 products not only widen the bandwidth to 320M and comply with QAM4096, but also include a very important feature that a Wi-Fi 7 product should have: "Multi-Link Operation (MLO)". Among them, the Multi-RU Puncturing technology, which is derived from Wi-Fi 6 Preamble Puncturing under MLO, is a major characteristic of Wi-Fi 7 technology.

Signal coverage affects the quality of communication

If technology products need to support the aforementioned Wi-Fi 7 features during design and development, in addition to the transmission rate needing to reach QAM4096,the signal coverage is also one of the indicators for measuring Wi-Fi 7 communication quality. Especially since the application scenarios of Wi-Fi 7 communication products are diverse, each has different coverage range requirements.

Taking AP Router as an example, when the AP connects and transmits with multiple Stations, it is necessary to consider external interference from other Wi-Fi products and the attenuation conditions from various angles to check whether the signal coverage meets the requirements or to identify the locations of coverage dead zones. Coverage dead zones refer to areas where the signal cannot reach or where the coverage range cannot encompass, which may lead to communication interruptions or quality degradation. A high coverage rate indicates that the Wi-Fi signal can cover more areas, providing a wider service range.

The emission power of commercially available products in the 6GHz frequency band is limited by radio regulations, with AP at 16~18dBm, laptops (NB) at 12~15dBm, and smartphones at 12~13dBm. Wi-Fi 7 MCS13/BW:320MHz requires a receiving signal of -34dBm, not considering environmental factors and interference, with free space loss estimated at about 3 meters distance. In other words, if the antenna is to meet the Wi-Fi 7 specification requirements, the transmission distance and coverage need to reach 2~3 meters, at which point antenna chip manufacturers need sufficient experimental space to conduct far-field attenuation tests to demonstrate product performance (Figure 1).

 (Figure 1 Antenna test scenario)

Testing and validation are crucial for achieving the new performance of Wi-Fi 7. TRC has invented test antennas suitable for Wi-Fi 7 testing in accordance with the Wi-Fi 7 specifications, providing "left-hand circular polarized antennas" and "right-hand circular polarized antennas." Considering test coverage and angles, the arrangement angles of the test antennas are designed based on testing standards, allowing users to place the device under test on a turntable without needing to specifically distinguish between vertical or horizontal for testing. TRC has also launched various testing options in testing software to facilitate user testing.

Testing ensures chip compatibility

In addition, the chip compatibility of communication products is also one of the factors that Wi-Fi 7 product manufacturers need to consider. Different chips correspond to products from different brands, which may have compatibility issues with each other. To ensure that Wi-Fi 7 communication products can operate normally in different environments, avoid compatibility conflicts, and maintain communication quality, MLO testing, also known as "Multi-Link Operation simulation testing," is required.

TRC has launched the MLO Box to provide interactive connection capabilities between multiple STAs or multiple APs. Although the MLO Box reduces the testing space and uses an isolated box testing environment (Figure 2), the actual structural loss during testing can support a testing distance of 2 to 3 meters, consolidating the main testing items that Wi-Fi 7 products may face into one environment, constructed according to the requirements of Chapter 5 of the communication standard TR398.

 (Figure 2 Shielding Box Test Environment)

Due to the fact that over 70% of Wi-Fi internet access scenarios use mobile phones among various devices, MLO BOX has specially launched the Phone Box to simulate mobile phone connections to the AP, as well as various connection scenarios among different products and chip brands.

The Puncturing testing method follows TR398 6.5.2 AP Coexistence, calculating the bandwidth used by the STA based on throughput, and using spectrum to demonstrate the bandwidth used by the STA when it is interfered with. On the other hand, the Latency testing method follows TR398 6.2.6, testing the transmission connection time for 1 STA and 4 STAs.

The placement of the antenna is a noise issue

In addition to the performance of the antenna chip, manufacturers need to pay attention to the placement of the antenna chip when developing and designing Wi-Fi 7 products. The placement of the antenna has a significant impact on signal quality and noise levels; improper placement of the antenna can lead to noise issues, thereby affecting communication quality. Therefore, personnel responsible for the product design phase conduct tests known as EMI to assess the degradation of receiving sensitivity with each design of a housing. During the design of Wi-Fi 7 products, designers will control the noise from passive components to be less than the signal strength of -38dBm according to the Wi-Fi 7 QAM4096 specification, in order to maintain the performance of the Wi-Fi 7 antenna chip.

Looking back, in the application of Wi-Fi 7 QAM4096, in addition to the well-known laptops, mobile phones, and AP Routers, it actually also includes popular AR/VR/MR/XR products, such as smart glasses, smart helmets, and other wearable smart devices. Products like AR/VR/MR/XR especially require low-latency high-speed connection technology.

Taking the popular smart helmet as an example, the head-mounted device has a built-in Wi-Fi 7 antenna with a test reception sensitivity of about -47dBm, and the signal energy of each subcarrier at an interval of 78.125KHz is -83dBm. To perform QAM4096 demodulation, the noise within the 78.125KHz band must be less than -121dBm, which is only about 5dB higher than the general thermal noise (-174dBm/Hz=-126.1dBm/78.125KHz). The control computing unit, imaging, perception, and sound processing unit of the head-mounted device must have a broadband noise for data transmission that is less than -121dBm, or maintain proper isolation between the antenna and the noise source, thus requiring measurement of the noise distribution of the entire device.

However, when the spectrum analyzer has a resolution bandwidth of 100KHz, its Noise Floor level is -115dBm, making it impossible to measure the demodulation noise limit of QAM4096 at -121dBm. To address this, Shuoshu provides the Platform Noise Scanner for carrier noise testing, which uses a scanning probe to identify noise hotspot locations through the spectrum analyzer and reduces the attenuator's attenuation value to maintain a throughput of 2.5Gbps. This reduced attenuation value corresponds to the degradation of the receiving sensitivity for MCS13 at a bandwidth of 320MHz. During this test, the spectrum is used to identify 6 to 10 of the largest noise interference sources, and all parameter settings for the noise test as well as the throughput test settings must be taken into account to ensure stable re-measurability.