Low(er)-Cost Test Makes WiGig Even More Attractive

Low(er)-Cost Test Makes WiGig Even More Attractive

Saying you want WiGig (IEEE 802.11ad) for its wide swaths of spectrum and 7-Gb/s data rates is kind of like asking to move to the Arctic for wide-open space and loads and loads of free ice: You can have it, but at what cost? For designers, the cost factor starts to hit home when it comes time to start testing ICs and systems. Oops! But Tektronix’s new SignalVu option, the SV30, may get you over the hump. 

The attraction of WiGig is understandable, but it’s been a long and tortuous love affair. Its attraction starts with all that wonderful 8.64 GHz of unlicensed spectrum between 57.24 and 65.88 GHz, the lower and upper regions defined by the 802.11ad specification. Within that range, the spec has defined four 2.16-GHz channels through which it can transmit data at 7 Gb/s.

WiGig initially started out with Wilocity in 2007, and was bought by Qualcomm Atheros. Since then, the technology has been adopted and integrated into the Wi-Fi Alliance such that WiGig now includes both classic 802.11b/g/a/n/ac in the 2.4- and 5-GHz band as well as 60-GHz operation. This is good, as 60-GHz electromagnetic waves are absorbed by oxygen molecules and thus are limited in range.

Also, walls reflect almost all of their energy, so WiGig is limited to in-room apps and specified for ranges up to 10 m. The ability to fall back to 2.4- or 5-GHz operation keeps applications running well in most environments. Add in mesh networking, and limitations start to disappear.

The high end of WiGig (802.11ad) is divided into four 2.16-GHz-wide channels that cover the spectrum from 57.24 to 65.88 GHz to deliver up 7 Gb/s. The ability to fall back to 2.45- and 5-GHz Wi-Fi bands is a critical part of the specification. (Source: wikipedia.org/wiki/Wireless_Gigabit_Alliance)

Another attraction of 60 GHz is that higher frequencies mean small antennas and inductors. This can lead to smaller-footprint boards and end devices. However, the interesting twist is that the multipath reflections due to all of those waves bouncing off walls cause interference. The solution has been to use more antennas to perform multiple-input, multiple-output (MIMO) processing and apply beamforming techniques with arrays of antennas. That means some of those space and footprint gains go away, but it greatly improves data rates and point-to-point connection reliability and robustness.

While Qualcomm Atheros, Intel, and others have addressed the design issues, the Wi-Fi Alliance has been evolving its toolkit at 5 GHz by widening bandwidths, adopting higher-order modulation schemes, and adding more MIMO channels to increase throughput. Its latest adoption of IEEE 802.11ac can reach 1 Gb/s.

This stretching of baseline 2.45- and 5-GHz standards has impacted the adoption of 60-GHz technologies. However, as devices start to appear and test costs come down, it may be time to give 60 GHz another look.

At the 2016 CES show, TP-LINK showed off the Talon AD7200 802.11ad WiGig router based on Qualcomm Atheros ICs, which it expects to ship sometime this year. It’s actually a pretty slick design, with eight antennas that fold down into grooves in the housing (Fig. 1).

1. The Talon AD7200 802.11ad (WiGig) router from TP-LINK, which debuted at CES 2016, is expected to ship sometime this year. How many more devices will debut depends to a large degree on the full cost of testing—as measured in time, resources, and equipment—at both the IC and system level. (Courtesy of TP-LINK)

TP-LINK hasn’t quoted a price yet, and it only reaches 4.6 Gb/s. But if you’re looking to experiment with WiGig, Intel also has a module, the Wireless Gigabit Sink W1311, an “802.11ad wireless dock on a module” that works with the Intel tri-band Wireless-AC 18260.

While 60-GHz WiGig devices are starting to appear, the rate of appearance, and adoption, depends largely on cost, both for users as well as designers of the equipment. And for designers, it’s become increasingly the case over the past few years that test and debug is eating up a greater portion of test cost, in terms of time alone. However, at 60 GHz, that cost goes up dramatically due to the more expensive equipment required to perform those higher-frequency tests. The fact is, 60 GHz is hard, which is partly why TP-LINK has only reached the 4.6-Gbit/s mark up to this point.

To help out, Tektronix introduced the IEEE802.11ad Test Solution that, to hear Chris Loberg, senior technical marketing manager at Tektronix tell it, came about as a “pull” from IC manufacturers who wanted an easier, faster, less expensive way to test WiGig. To get there, the new solution provides “industry best” low error vector magnitude (EVM) out to 70 GHz that’s 13% to 20% lower than what’s out there already, according to Loberg.

Intended for designers trying to characterize and debug transmitter PHY silicon and systems, it’s actually an adoption of Tektronix’s SignalVu, called Option SV30, combined with a 70-GHz DPO70000SX Series ATI oscilloscope (Fig. 2). By being able to directly cover the 70-GHz band with low EVM, the solution avoids having to downconvert to an intermediate frequency.

2. The IEEE802.11ad solution from Tektronix aims to lower the cost of WiGig test by addressing 70-GHz test directly with the DPO70000SX Series ATI scope and a special version of SignalVu called Option SV30. (Courtesy of Tektronix)

Therefore, with one single box, the combination replaces two systems—and their associated synching and calibration requirements.  Tektronix also claims 20% greater accuracy and support for cross-correlation between the RF and time domains to speed up debug. Time is money. Literally.

Two other interesting features of the IEE802.11ad are live triggering on signals up to 70 GHz, as well as full de-embedding of cables, attenuators, and amplifiers with its Serial Data Link Visualizer (SDLA64).

While the whole point of the solution is to reduce costs, the new SV30 option isn’t cheap either, coming in at $9,000. But it beats buying a whole new system, especially if you’re lucky enough to already have a DPO700000SX handy.

Looking for parts? Go to SourceESB.

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