What’s new with Wi-Fi 6E? More interference testing
Article By : Jessy Cavazos, Keysight Technologies
Because 6GHz bands are already being used by many devices, Wi-Fi 6E requires new tests to prevent interference.
Just like cellular standards, Wi-Fi standards continue to evolve. Wi-Fi 6E is the newest kid on the block. This standard enables wireless Internet of Things (IoT) devices to operate in the unlicensed 6GHz spectrum to access a lot more bandwidth.
Here’s the tricky part: 6GHz spectrum brings new restrictions to device manufacturers. Why? Because 6GHz bands are already being used by many devices. Wi-Fi 6E thus requires new tests to prevent interference.
First, let’s do a quick recap of Wi-Fi standards to position Wi-Fi 6E in the evolution of the standard.
Wi-Fi Standards Evolution
Wi-Fi is not new. The first Wi-Fi standard emerged in 1997. Over the years, the link rate increased from 1 to 2Mbps to 600 to 9608Mbps, but mostly using the same frequency bands. Wi-Fi 6E uses new spectrum for the first time in the history of the standard.
Wi-Fi 6E is an extension of Wi-Fi 6, also referred to as 802.11ax. Wi-Fi 6 uses orthogonal frequency division multiple access (OFDMA) technology to improve network performance and a higher-order quadrature amplitude modulation (QAM) format to increase data rates. Wi-Fi 6 devices operate in the 2.4 and 5GHz frequency bands while Wi-Fi 6E operate in the unlicensed 6GHz spectrum.
6GHz frequency bands have much more available bandwidth. These devices have access to 1,200MHz contiguous bandwidth in the U.S. and regions that follow Federal Communications Commission (FCC) regulations and 480 to 500MHz in Europe and the regions that follow the European Telecommunications Standards Institute (ETSI) standards based on the regulations from the Radio Equipment Directive (RED).
Preventing Interference
The additional bandwidth available in 6GHz bands holds significant potential for device manufacturers to deliver higher performance and new applications to end users. Wi-Fi 6E brings faster and more reliable Internet access to consumers for video streaming, online gaming, and video calling, but the standard is also particularly helpful for enterprises to accelerate their digital transformation.
IT departments can allow more devices onto their networks and improve user experience boosting productivity and innovation. High-density environments like airports, stadiums, conference centers, as well as educational and healthcare facilities can benefit tremendously from Wi-Fi 6E too because it enables them to handle a much larger number and greater variety of devices.
Taking advantage of the additional bandwidth available in 6GHz spectrum is not without challenges though. A major issue is that many users already use this spectrum including 5G cellular, Wi-Fi access points, satellite links, mobile TV broadcasts, and utility communication links. Also, incumbent carriers have priority over other users. As a result, the FCC and ETSI mandate several new tests to ensure the effective use of spectrum among them.
Contention-based protocol (CBP) test
The CBP test is an important new item mandated by the FCC. It is named after the use of a CBP in the device to prevent interference with incumbent carriers’ services. The FCC requires all equipment classes—access points and clients—to undergo and pass this test.
Figure 1 shows a CBP test setup. The setup consists of two signal analyzers and an additive white Gaussian noise (AWGN) signal source to produce a 10MHz-wide noise (incumbent signal) for the test signal. This test also requires a client device to communicate with the device under test (not shown in the figure), and signal conditioning components. The signal source needs to inject the incumbent signal at one frequency within the channel for a 20MHz channel and three different frequencies within the channel for a 160MHz channel.
Figure 1 Conducted CBP test setup diagram. Source: KDB 987594 D02 V01r01.
Adaptivity / Channel access mechanism (CAM) test
The adaptivity / CAM test is the ETSI equivalent of the FCC CBP test, albeit a lot more complicated. It focuses on the automatic mechanism a listen-before-talk (LBT) device uses to check a channel before transferring data on it. The standard also requires the device to check the probability of other devices to use the channel to ensure fair usage of available channels.
The CAM test is complex and time-consuming because it requires extensive data processing to calculate the results. Quantifying the probability of other devices to use the channel of interest requires dividing the minimum idle time by the maximum channel occupancy time (COT), which differs by device class. The COT measurement can require a lot of samples. Load-based equipment (LBE), for example, may need more than 10,000 samples with a resolution of one microsecond or less, which results in the measurement and collection of many data points.
Adaptivity testing also includes performing interference analysis by injecting various signals into the device to evaluate its ability to detect and respond to these signals. This test requires a 5G New Radio (NR) waveform to simulate the interference from 5G users. You also need a known signal level and bandwidth and applying the results of the occupied channel bandwidth (OCB) test that would have been performed previously.
Receiver selectivity test
Formerly known as receiver adjacent channel selectivity test, receiver selectivity is another new ETSI test related to interference. It consists of measuring the device’s capability to receive a wanted signal on its channel without exceeding a certain level of degradation due to the presence of an interfering signal in an adjacent channel.
The test consists of three main steps. The first step is to determine the minimum power value (Pmin) of the signal to the device with a packet error rate (PER) just under 10%. The next step is to add interference in the upper channel (20 and 40MHz above) and checking that the device has less or equal to 10% PER. The final step consists of adding interference in the channel below (20 and 40MHz below) and again checking the PER.
Figure 2 provides a setup for receiver selectivity testing. It includes passive components and may require a shielded room or Faraday cage. A variable attenuator and a packet measurement system are also necessary to find the Pmin value and determine the PER. Using signal conditioning components and a packet counter make the test more manageable by only requiring a few front-panel connections.
Figure 2 Receiver selectivity test setup with Keysight’s X8749A signal conditioning test set and packet counter.
Dual client test
The dual client test is another new test but from the FCC. Since a client device can connect to a standard-power access point, a low-power indoor one, or both, the FCC requires this test to verify that client devices with the flexibility to connect to both types of access points are able to switch between the two seamlessly. The dual client test verifies that these client devices can distinguish the different access point configurations and control the respective power levels.
Figure 3 shows a connected dual client test setup. This test will require golden low-power and standard-power access points, variable attenuators, and signal conditioning components.
Figure 3 Dual client connected test setup. Source: KDB 987594 D01 V01r02.
Addressing interference issues for Wi-Fi 6E devices
Wi-Fi 6E is an exciting newcomer in the Wi-Fi standard landscape. Significant additional bandwidth is at manufacturers’ fingertips to deliver greater performance and new applications to end users – consumers and enterprises. The standard also brings new challenges mainly because it uses 6 GHz spectrum. Six GHz bands are already used by many other devices including incumbent carriers who have priority over other users. New tests are necessary to prevent interference. For more information on these tests, measurement examples, and to learn about other new test requirements for Wi-Fi 6E devices, watch the webinar “Understanding Regulatory Testing for Wi-Fi 6E Devices”.
About the Author
Jessy Cavazos joined Keysight’s Industry Solutions Marketing team in January 2019 with a focus on 5G. Prior to that, Jessy was the Industry Director for the Test & Measurement practice at Frost & Sullivan. She joined the global consulting and market research company in 2002 and tracked the Test & Measurement industry for more than 15 years. Jessy has authored numerous market studies highlighting key opportunities and disruptive trends and has been published in industry-leading publications. Jessy holds a bachelor’s degree in international business from the Institut de Formation Internationale located in Rouen, France.
