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WiMAX demands conformance

Posted: 16 Dec 2008 ?? ?Print Version ?Bookmark and Share

Keywords:WiMAX? mobile Internet? standards testing? Wi-Fi?

Agilent WiMAX testing device

World Interoperability for Microwave Access, better known as WiMAX, has become the poster child of the mobile Internet world!a world where anything and anybody can be connected from anywhere.

The first leg in the WiMAX race is to provide broadband wireless access to a range of computing devices by extending the reach of current Wi-Fi nodes. Wi-Fi typically operates over 91.5m depending on how close the user is to a base station, while WiMAX extends that range to some 50km. Of course, capacity and demand can be limiting factors.

But WiMAX devices, terminals and base stations require rigorous testing and conformance to tight specification standards, more so than those required for Wi-Fi.

"The Wi-Fi Alliance has pretty much lost control of Wi-Fi," said Craig Mathias, principal of Farpoint Group consultancy. "There are lots of uncertified products on the market and no one really seems to care anymore!as long as the chips and reference designs are interoperable."

Mathias contends that such a state of affairs is unlikely in the WiMAX market, as carriers will insist on certified products. "They just don't need the headache of trying to figure out why something is not working."

Seal of approval
At last count, there were more than 400 WiMAX deployments in 133 countries, according to the WiMAX Forum, whose goal is to accelerate standards-based, interoperable solutions to the marketplace. The WiMAX Forum Certified program provides a sort of seal of approval for WiMAX products.

For WiMAX market participants, there are many challenges. "Compared with Wi-Fi, or even Wi-Fi MIMO, WiMAX Wave 2 specifications [increasing functions to test with each Wave of the IEEE805.16 spec] require more stringent parameter control, including frequency stability, modulation quality and power control," said John Lukez, head of product management at WiMAX test vendor LitePoint Corp. "Because the standard anticipates much greater range than Wi-Fi, and operating in an environment with greater potential for interference, there is more concern about power spectral density and tighter EVM [error vector magnitude] performance to avoid interference while providing higher data throughput."

While any testing solution must be accurate enough to ensure that WiMAX signals meet these more stringent specifications, "testing has to meet time and cost constraints that differ little from those of Wi-Fi," Lukez said. "It's a case, again, of having to do more!more accuracy and complex testing!without taking significantly longer or costing significantly more."

Interoperability for growth
WiMAX Forum defines and conducts conformance and interoperability testing to ensure that different vendor systems work seamlessly with one another. Successful testing gives the tested device a "WiMAX Forum Certified" designation. "The Forum goes to great lengths to warn vendors that claims like 'WiMAX-like' and 'WiMAX-compliant' are not WiMAX Forum Certified, which means their equipment isn't interoperable with other vendors' equipment," said Ron Resnick, president of WiMAX Forum.

WiMAX certification is crucial for the market to grow!without it, interoperability would be limited. "Interoperability is like any other standard," said Edwin Lowery, principal consultant for Verigy's Wireless Center of Expertise. "If everyone went their own way, you wouldn't be able to use your Compaq computer with the Sprint network, or use your Sprint handset in Europe etc. Compliance allows for interoperability. As an example, imagine if there were 10 different Bluetooth flavors. You could 'buy a Bluetooth,' but the device only works with this one compliant headset. What's the point of a standard if it only works with one product?"

"There is really only one solution: Make sure WiMAX devices are tested in production in ways that ensure they truly meet the standard's specifications," said Rob Brownstein, VP for market relations and communications at LitePoint. "This sounds simplistic but it's not. In development, one has some latitude with test time. In production, where pricing and margins can make or break a market, trading off testing comprehensiveness for time and cost is very tempting. The solution is not to give in to temptation."

Lowery explained specific challenges of WiMAX testing: "WiMAX supports multiple modulation types and multiple modulation bandwidths. To effectively test WiMAX, you need a mechanism to easily and effectively create the multiple waveforms used to test the DUT!that has to be part of the test strategy."

Lowery said that older 2G testers may not have the performance, phase noise and linearity required to test WiMAX to spec. The newer testers have the capability to perform the challenging EVM tests. "It is important to have good synchronization, good I/Q balance for your RF sources and I/Q balance between the AWGs [arbitrary waveform generators] and digitizers," he added.

WiMAX devices, terminals and base stations require rigorous testing and conformance to tight specification standards.

Possible problems
What sort of problems might "WiMAX-like" or "WiMAX-compliant" products create?

According to Lowery, such devices present the same challenge as any high-integration embedded wireless interface because WiMAX will be used openly in a conversational platform, either handsets or more likely PCs. "When I think of interference, I think you want to make sure you have a working WiMAX transceiver that doesn't affect other electronics in the system. If it's in a laptop, be very sure it's not interfering with, or isn't interfered with by, any radiated energy inside the laptop," Lowery said. "EMC is a big deal, and packaging and system designers in particular have to keep that in mind."

In October, the WiMAX Forum announced that 13 additional Mobile WiMAX devices have been designated as WiMAX Forum Certified. "WiMAX devices and networks have the most extensive certification and interoperability testing in the industry in place to guarantee network performance and consumer satisfaction," said Resnick during his keynote at WiMAX World 2008.

Products are currently certified under Release 1.0, which is based on the IEEE 802.16e-2005 standard. The focus of certification during the initial stages of Release 1.0 is on radio and protocol conformance, and on interoperability testing. Toward the end of 2008, Release 1.0 is expected to include testing for baseline network services, based on the WiMAX Network specifications developed by the forum's network working group.

Release 1.5, anticipated in 2009, is to be based on IEEE 802.16e Revision 2 and the corresponding updated version of the Mobile WiMAX System Profile. Release 2.0 (2010-11) is expected to be based on IEEE 802.16m.

- Nicolas Mokhoff
EE Times

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