IEEE slogs through thousands of 802.11n draft comments

A second draft of the proposed IEEE standard for 100+Mbps wireless LANs is being pushed back several months, with a vote on it likely for January 2007 instead of late fall.

The IEEE task group charged with crafting the 802.11n WLAN standard has been slogging through an astonishing 12,000 comments that were filed in response to draft 1.0, issued earlier this year. About half of that number, many of them very minor editorial changes, have already been resolved by the end of last month's regular meeting.

"There were a lot of duplicate comments, and three people filed comments for each and every blank line in the document," says Bill McFarland, CTO for Atheros Communications, a WLAN chip vendor. "The physical process of dealing with so many comments is tedious and time-consuming."

The task group has divided the comments into groups and assigned "tiger teams" of members to sift through them quickly during weekly conference calls between the regular meetings, McFarland says.

The underlying technology for 11n is the use of multiple antennas and signal processing, called multiple input multiple output or MIMO, that more than quadruples the current 20-24Mbps throughput for 802.11g and 11a WLANs (see: A MIMO Primer). MIMO also boosts WLAN ranges, maintaining higher throughput over longer distances than is currently possible.

In general, industry participants are optimistic that the remaining comments will be dealt with and a second draft completed, no later than the November meeting. Some members had thought the next draft would be ready at the September meeting. The new schedule would let the task group send out the draft for what's called a letter ballot in January.

That ballot would need backing by 75% of the task group members to be accepted, a critical step because it would signal that the draft has reached a level of stability that could unleash a new wave of radio chipsets and products based on the draft standard. Final ratification of the standard might not occur until early 2008, though typically it is very rare for any changes to be made during that last stage.

But at least some of the remaining issues are both more complex and potentially more divisive than those considered so far.

One issue is that 11n allows for the combining of two 20 MHz channels into one 40 MHz channel, to boost throughput. At least three methods have been proposed but, according to Atheros' McFarland, there's been no agreement so far on which one or ones to use.

The results are evident in the first crop of "draft 11n" high-throughput wireless gear which has been shipping for a few months (see Network World's new ClearChoice Tests on several of these access points and NICs).

"The initial crop of products have 'bad neighbor' characteristics in early tests," says Rolf De Vegt, senior director of business development at Airgo Networks, the first chipmaker to come out with a MIMO chipset, nearly 18 months ago. That means MIMO products can step on other WLAN transmissions and that MIMO products from different vendors don't work together well.

Other issues, says De Vegt, include deciding on what form of transmit beam forming to use, and Power Save Multi-polling, which is a technique to conserve power on handheld wireless devices by coordinating scheduled activity on the radio link, instead of randomly sending and receiving.

"There's not one issue that Airgo cites that can't be resolved," says William Bunch, director of product manager for archrival Broadcom. "We're anything but stalled."

Airgo has had the market to itself until this year, when both Broadcom and Atheros began shipping silicon based on the draft 11n document. By the end of the second quarter, Broadcom had already shipped 1 million chipsets. In the same period, Atheros, which doesn't cite unit shipments, said its draft 11n chipset accounted for 13% of its second quarter revenue.

"Draft 1.0 really can't be used to build interoperability around," says Airgo's De Vegt.

Bunch acknowledged interoperability has been a challenge, but noted that Atheros and Broadcom recently announced they'd surmounted many of those issue between them, by working together.

"Right now, the marketplace is putting a lot of pressure on vendors for more interoperability," says Atheros' McFarland. "It's going to be continuous evolution of the product lines."

"I've been stunned by the aggressiveness that the PC OEMs have toward this [draft 11n] technology," he says. "Their next laptop products [with draft 11n NICs] will come out before the end of this year, perhaps before the next 11n draft in November."

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