Electronic Design

Next-Generation Wi-Fi 802.11n Is Almost Here

We haven't been waiting for the next generation of Wi-Fi as long as the Ultra-Wideband (UWB) people have been waiting for their standard. But it is taking longer than most of us expected. For a while, it looked like 11n was going to go the way of the UWB standards fiasco—that is, no formal single industry standard replacing multiple solutions.

But as of January 19, the IEEE's 802.11n Task Group accepted a joint proposal submitted by the Enhanced Wireless Consortium (EWC) as Draft 1.0 of the standard. There's still lots of work to do, but most members agree that we should see a final ratification of a standard in about a year. The Wi-Fi Alliance then can begin its testing and certification process, which has been the key factor in the success of the whole wireless local-area network movement.

The whole 802.11n process started a couple of years ago in a quest for ever-higher data rates. The 802.11a/g standards provide up to 54 Mbits/s. However, few users actually achieve it in practice. We all would like to see a faster version of the standard, especially if we're going to transmit video, the current hot topic in all wireless applications.

The 802.11n Task Group boiled the initial 30 or so proposals down into two camps. And then the battle began. The two groups tried but couldn't reach a consensus. That's business as usual, as members of these standards groups battle for their own ideas, intellectual property, and egos.

After a bit of muddling around, a few concerned companies wanting to move ahead formed the EWC to help overcome the process clog. It put together a joint proposal that most members agreed to. With a bit of further tweaking, the EWC was ready to submit the agreed-upon joint proposal to the IEEE. That's the Draft 1.0 that the IEEE accepted recently.

The lack of a standard didn't stop some companies from developing and selling chips and products using "pre-n" techniques to achieve higher speeds. Belkin, Linksys, Netgear, and others have products with speeds greater than 100 Mbits/s on the market.

All of these products are 802.11a/b/g-compatible. They also use one of the core concepts of 11n, which is multiple input/multiple output (MIMO). This technique uses multiple radios and antennas with spatial division multiplexing to transmit parallel data streams over multiple paths for higher speeds, longer range, and greater reliability.

BRINGING IT HOME
I recently tested a Belkin "pre-n" router in my home network (Fig. 1). This unit uses three antennas and Airgo chips, and it really made a big difference in coverage. After significantly repositioning my other 11g router, I linked a PC, an iMac, and a laptop to the DSL line. But it wasn't easy, and I still can't take my laptop out in the backyard.

There were no distance or orientation limits with the Belkin unit, and the speed was higher. MIMO is great. The extended range and reliability of the 11n products probably will be the bigger benefit and selling point. While speeds will be up to about 300 Mbits/s with a 600-Mbit/s maximum, I don't see the need until we get some wireless video products to connect.

Several companies have been selling chips that produce data rates faster than the 54 Mbits/s offered by 802.11a/g. The second-generation chips from MIMO pioneer Airgo have been remarkably successful. My Belkin router uses them. Airgo also offers a third-generation True MIMO chip with a 240-Mbit/s max data rate. The company eventually will offer a fully 11n-compatible chip.

Some other semiconductor companies have announced chips that comply with the 11n standard. Atheros' XSPAN family uses the company's Signal Sustain Technology. Its AR5008 is a triple-radio, single-chip solution that can deliver up to 300 Mbits/s in common usage, though the sustained rate likely will range from 150 to 180 Mbits/s.

Broadcom's BCM2055 multiple radio chip supports 2x2, 3x3, or 4x4 antenna arrangements. It can be combined with the BCM4321 media-access controller (MAC) and baseband chip to make a complete radio. The BCM4704 and BCM4705 are fifth-and sixth-generation network processors that match up with the radio to make a complete product.

Also on the scene with 11n products is Marvell. Its 88W8060 is a radio chip, while the 88W8360 and 88W8361 chips feature the MAC and baseband. Marvell's 88W8660 and 88F5181 CPUs run at 500 MHz to assist in implementing routers, gateways, and other 11n products. These CPUs are based on Marvell's Feroceon ARM processor, which boasts high speed and low power consumption.

Metalink has expanded its WLANPlus product line to cover 11n. These chip sets can achieve 300 Mbits/s. The company uses MIPS 32-bit processors in its products. Look for more chips shortly, with final end products from all the usual suppliers later this year or early next year.

SiGe Semiconductor's SE2545A10 integrates two full dual-band (2.4 GHz and 5 GHz) transmit/receive chains for 11n applications. All of the circuits between the antenna and the transceiver are included, such as the T/R switches, diplexers, filters, and power detectors as well as the transmitter power amplifiers (PAs). This front-end module is designed to interface to existing 11n transceivers (Fig. 2). The SE2545A10 is shipping now. An A30 variation with PAs with higher transmit power will be available later in March.

WHAT'S NEXT FOR 11n
The big issue here is if these new chips will be fully 11ncompliant by the time the 11n Task Group gets finished with the standardization-process. Lots of last-minute tweaking and multiple new versions are the norm. Some say the changes can be met with firmware updates, but that remains to be seen.

In any case, we all hope the 11n Task Group will be kind and bring us minimal changes and a ratified standard as soon as possible. The Wi-Fi Alliance then can begin its testing, which is expected by March 2007.

The big use of 11n, of course, is expected to be video transport. It isn't here yet. But we are beginning to see TV sets, DVD players, and other products that can benefit from a wireless connection. The question is if 802.11n will beat out UWB as the wireless technology of choice to transport video.

Despite the lack of one formal standard, the industry has pretty much settled on the guidelines set down by the WiMedia Alliance as the way to go. This is a UWB radio using orthogonal frequency-division multiplexing that can achieve from 100 to 480 Mbits/s at a range to 30 m.

While 11n can beat that range, UWB is smaller and cheaper, and it uses less power. It will be an interesting battle to witness. I expect both technologies to find their niches.

802.11n Task Group
grouper.ieee.org/groups/802/11/

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