Just because a device meets compliance specification doesn't mean it will meet user expectations. UNH-IOL now tests Wi-Fi devices in situations that go beyond compliance.
You probably have a Wi-Fi router at home and probably in your office as well. While all access points, routers, computers, phones, and other devices must comply with IEEE 802.11 and Ethernet Alliance standards, that's no assurance the device will meet your expectations. The UNH-IOL has announced Wi-Fi testing services that go beyond 802.11 specifications.
Why is such testing needed? IEEE specifications don't cover measurements such as throughput vs. signal strength, but users care about that because it affects connectivity and throughput. I can certainly see a performance decrease when a Wi-Fi device gets near the limits of my 802.11n router's range.
"You have to test the whole internet experience," said Lincoln Lavoie, UNH-IOL senior engineer for broadband technologies, "and that includes Wi-Fi connections. Users don't care if the problem is Wi-Fi to their devices or if a problem is with a router's internet connection. Service providers get blamed when a user's Wi-Fi stops working, even if the internet connection works." Engineers at UNH-IOL work with the Broadband Forum to define tests that relate measurements to the user experience. From the test plans students write test scripts to automate tests. Tests include:
- Throughput vs. signal strength (receiver sensitivity)
- Associated talkers
- Come and go (add/drop)
- Bandwidth loading
- Interference and noise from other devices such as cordless phones and Bluetooth devices
Video applies the most stress that a network can put on a receiver, at least in terms of throughput. Receiver sensitivity tests can show when the connection can support 4K HD, HD, or standard video, depending on the connection's signal strength.
"Broadband Forum testing helps manufacturers distinguish their products from competitors," added Leigh Chinitz, CTO at octoScope, whose company provides UNH-IOL with Wi-Fi test chambers and signal sources. "It also helps manufacturers identify the best applications for their equipment."
Figure 1 shows two routers in octoBox chambers manufactured by octoScope and located at UNH-IOL. The flat log-periodic antennas emulate the channel to and from equipment under test (EUT) while the Wi-Fi "rubber duck" antennas add interference. When testing a router's receive sensitivity, for example, the system adjusts transmit power sent to the log-periodic antennas to simulate RF distance from Wi-Fi devices and it adjusts noise power.
Figure 1 Four log-periodic antennas emulate the over-the-air channel to and from the equipment under test. Four Wi-Fi antennas add interference to the transmission channel. Photo courtesy of UNH-IOL.
According to Chinitz, one of the most difficult tests is association between two Wi-Fi devices, especially with low-data-rate devices connected to an access point through Wi-Fi extenders. It's easy for connections to drop.
Tests such as these, plus interoperability tests, go beyond compliance testing, enabling an improved wireless experience.—Martin Rowe covers test and measurement for EDN and EE Times. Contact him at [email protected]
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