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Agreement on Bluetooth/WiFi protection leads to 802.11n draft

From "802.11n Draft Standard Nearly Ready," by Wayne Rash, eWeek, 24 January 2007:

"Last week's IEEE meeting in London demonstrated that the move to the next stage of Wi-Fi is nearly ready. At the meeting [on 19 January], 802.11n committee members unanimously approved draft standard version 1.10, and agreed to create version 2.0, which should be ready in the near future. The outstanding issues before the committee were resolved, clearing all remaining hurdles to the interim standard. This means that the Wi-Fi Alliance can publish specifications that will allow manufacturers to build 11n products knowing that they will be compatible.

" 'Every once in a while the stars kind of align. People had very realistic expectations. For the few remaining issues we had to find simple reliable solutions,' said Atheros Communications Chief Technology Officer Bill McFarland, who participated in the standards meetings.

"McFarland said that the primary hurdles were how to make sure that 11n devices would work with legacy 802.11 devices, and at the same time not interfere with them. Those devices include Wi-Fi devices using 802.11b and 11g, as well as Bluetooth devices.

"The approval of the draft standard, and the almost certain approval of Draft 2.0, has brought about a flurry of announcements... Intel announced on Jan. 23 that the company was taking advantage of the new standard to launch its Intel Next-Gen Wireless-N technology, which along with its 'Connect with Centrino' effort will allow products with Centrino Duo mobile technology to connect with Draft 11n access points....

"[Farpoint Group analyst Craig] Mathias said that the Wi-Fi Alliance, which actually sets the Wi-Fi specifications, is quite far along in its testing. 'We're expecting their spec in the first half of the year,' he said. Mathias added that the standards and the companion specifications were moving along quickly because 'the direction that the standards work was going to take was well known by the participants some time ago.'

"But he noted that just because the direction was known didn't mean the process was easy. 'It's been a very long, technically difficult politically charged process,' he said.

"Part of the problem was creating a new Wi-Fi standard and specification that uses more bandwidth and operates at higher speeds than existing communications operating on the same frequency. 'How do 11n devices which are able to use 40 MHz wide channel bands get along with legacy devices that are already in the 2.4 GHz band?' asked McFarland, referring to 802.11b, 11g and Bluetooth.

" 'We don't want these new 11n devices to interfere with the legacy devices,' McFarland said. 'So we needed to come up with a solution to use 40MHz when it's appropriate, but to drop back down to 20MHz bandwidth when we need to protect those devices.'

"McFarland said that the standards committee came up with three mechanisms to protect legacy devices, while still allowing 11n devices to operate as efficiently as possible. 'The first was a low-level physical layer, so that before you send a 40MHz packet, you have to listen to make sure no one is using that 20MHz. You have to use that same type of CSMA behavior in the secondary channel,' he said.

"The second tool is a high-level politeness algorithm which listens to see if there are 2.4GHz devices operating, and if they might be damaged. 'Then we don't send any 40 MHz packets,' McFarland said.

" 'The first two work well but they're not sensitive to Bluetooth,' McFarland explained, 'They can't actually detect Bluetooth, but they can detect power. So what is added is a third mechanism which is the intolerance indicator. Any device can send out a packet that says it can't tolerate interference as an 802.11 packet,' he said. McFarland said that normally this would mean that a computer running both Wi-Fi and Bluetooth would use its Wi-Fi radio to send out the intolerance packet, causing the 11n radios in range to restrict their bandwidth to 20MHz. McFarland said that not all Bluetooth devices will be able to produce the intolerance packet, because they can't generate a Wi-Fi packet. But he said that normally such devices, which mainly include cell phones and Bluetooth headsets, operate over such short distances that they're unlikely to suffer any interference.

"802.11n access points should begin to show up in consumer markets this year. McFarland said that there will be two types: those that can operate on both 11n frequencies of 2.4GHz and 5GHz at the same time, and those where you must choose one or the other. He said that he expects 5GHz 11n to grow in popularity.

" 'I'm sure that the products will be wonderful,' Mathias said. 'The Draft 11n products that we've been testing are much better than 11g. You're going to see a lot of consumer products around the middle of the year, then a number of enterprise products, then products aimed at home entertainment like digital video.' Mathias said that 802.11n would start to show up in cell phone handsets in 2008."

[802.11n - 26 January 2007]