802.11n Moves Ahead
By Suzanne Deffree -- EDN, March 15, 2006
The IEEE 802.11n task group has voted by 80 percent to establish the 1.0 draft of the 802.11n wireless LAN specification and submit it to letter balloting as its next step on the road to standardization. But the journey through the IEEE process is not without bumps.
The draft announcement came from an IEEE bi-monthly meeting in Denver, Colo., last week. Specifically, Draft 1.0 is based on work the IEEE 802.11n task group did in January, when it voted to make the Enhanced Wireless Consortium (EWC) proposal its first draft.
At its core, EWC-based 802.11n is expected to move at speeds up to 600Mbits/sec., a significant jump over former 802.11 family leader 802.11g’s speed and fast enough to stream high-definition video and data seamlessly through the home. The big difference between 802.11g and 802.11n is .11n’s use of MIMO, or multiple input multiple output technology, which allows for the increased speed. High hopes exist in the industry for the next-generation technology in terms of the connected home, with companies preparing to move WLAN beyond the PC and into consumer electronics like DVD players, gaming systems and digital cameras.
At this new stage, known as letter balloting, a completed 802.11n document has been presented to task group, which voted above the needed 75 percent that the document was technically sound and complete. Now, the IEEE enters a 40-day period where the approximately 500 working group members read the document, make comments and give it a thumbs up or down.
And Draft 1.0 is not without dispute. While Bill McFarland, CTO of wireless leader Atheros, notes that this stage mostly focuses on editorial additions or changes, there is always room for technical change.
“Historically, what happens is a draft becomes more stable over time,” he noted. “The fact that there was extremely little technical change between when the draft was first adopted in January and now when it became a 1.0 draft, we find very encouraging. But there is always the potential for change.”
One needed change, claims Airgo Networks, is that Draft 1.0 does not provide a 100 percent guarantee for interoperability with nearby legacy 802.11b/g networks. Specifically, if “pre-n” products are released to market based on Draft 1.0 of the standard, they will “severely degrade or even disable nearby 802.11b and 802.11g networks,” said the company.
"While several IEEE member companies continue to promote chip designs based on Draft 1.0 of the standard, most IEEE member companies remain committed to creating the best possible 802.11n standard for consumers who want the speed, range and reliability of MIMO technology," said Greg Raleigh, CEO of Airgo. "At the same time it is crucial to retain complete interoperability with existing 802.11b and 802.11g devices."
As explained by McFarland, the problem is an editorial one. The Atheros CTO said the original 802.11n draft had a specific mechanism in it for how to do interoperability with legacy devices. The new standard proposal has a 40MHz mode where it uses two channels in parallel at once and did include a specific mechanism for how to ensure 802.11n would not interfere unduly with the legacy devices that are operating on the adjacent channel. “In the process of the discussion, some companies wanted a higher degree of flexibility in how they go about ensuring that interoperability,” he said. “They advocated that the description given for how to do this in the text of the draft be described as a ‘may’ kind of thing, as a device ‘may use’ this kind of mechanism, and left it open that other mechanism be acceptable, as well. Many people in the working group said no, we should require this behavior, this should be a ‘shall.’ That issue about should it be a ‘may’ or a ‘shall’ was not able to be resolved in the meeting on the fly.”
To decide the issue, an ad hoc committee was formed. The committee is being chaired by Cisco and Motorola, and plans to start formulating a technical solution in bi-weekly conference calls starting March 23.
“The industry as a whole is conscious of this issue,” said McFarland. “It will all be straightened out by next year. I think a solution will be announced at the May [IEEE 802.11n] meeting.”
What’s Next?
The road to standardization does not come to an end after letter balloting. Once the working group has scrutinized the 1.0 draft, all of the comments have to be resolved, either by accepting the change and agreeing to it or refusing the change and stating a reason.
“Any changes have to be adopted by 75 percent of the working group, so the draft as it stands now is not trivial to change,” the Atheros CTO said. “You have to really get a lot of people to buy into the change that was suggested.”
After the comments are settled, another version of the draft is revised and sent out again.
“There will be another round of this, independent of what the vote turns out to be this time around,” McFarland noted. “It’s more important what the vote will be like on that second round; there’s where it’s really important to get to the 75 percent or more level. That enables us to go ahead and progress to yet more steps in the process.”
802.11n’s standard process will be more or less solidified in 2006, McFarland believes, with a 2007 completion expected.
