Since last year’s finalization of the 802.11n standard, there’s been a steady rise in laptops and other wireless local-area network (WLAN) devices shipping with multiple-input multiple-output (MIMO) radios. Such strong market demand, even accelerated delivery schedules, can be “nice problems” to have—that is, if makers of RF receivers, chip sets, and WLAN devices weren’t faced with a not-so-nice problem: increasing “coverage gaps” in testing.

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The growing gaps in MIMO receiver testing stem from a mix of factors: increased test complexity, the limitations of traditional test equipment, the drain on engineering time, and overall cost of test (COT). The larger frames and exponentially greater combinations of speeds, clients, and channel models inherent in 802.11n, and especially 3x3 MIMO, are rapidly pushing today’s testing approach for I/Q waveform generation into obsolescence. With test parameters that are orders of magnitude greater, RF design teams face the distasteful prospect of sending products to market with critical undetected faults.

Fortunately, an emerging alternative to I/Q-based testing known as real-time RF signal-generation stands to significantly expand test coverage while minimizing DSP engineering efforts, capital expenditures, and overall test costs. To gauge the importance of this new approach, it’s best to take a more in-depth look at the growing challenge in current RF testing.

Tim Bennington-Davis, vice president of engineering, has nearly 30 years of experience in the development of high-performance test and measurement equipment. He previously held various positions in engineering and management at Tektronix Inc. and most recently was the director of optomechancial engineering at InFocus Corp.

802.11n Commands Good Memory And Higher “I/Qs”

Both traditional I/Q signal generation and the emerging real-time model adhere to one common principle: The only way to prove how a product will perform under fire is to fire at it. To date, 802.11n MIMO represents one of the most demanding design environments RF and baseband ever encountered by engineers. Thus, the job of comprehensively testing every likely deployment scenario becomes that much more onerous.

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