MIMO Products Muddle Wireless Market

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The Promised Land of wireless networking now is 802.11n, which alleges 100-megabits-per-second-plus speed on data throughput. But because ratification of this specification isn't expected until late 2006, vendors have begun offering products with enhanced speed, range, and coverage using a mix of proprietary technologies.

In December, Belkin began offering what it calls "pre-N" routers and adapters. D-Link, Linksys, and Netgear have since announced multiple-input/multiple-output (MIMO) products; Actiontec Electronics, Buffalo Technology, and SMC Networks have similar plans in motion.

In one sense, this is good news for small offices and consumers whose current wireless networks fall short, and for early adopters experimenting with network media adapters and Media PCs to stream content among TVs, stereos, and PCs. The products all tout double (or more than double) the throughput and range of today's standards-based 802.11g and 802.11a products, which makes them suitable (at least in theory) to carry multiple streams of high-definition television.

But in another sense, the rejection of standards turns the WLAN industry on its head, since for several years the industry has enjoyed enormous growth partly because of its adherence to standards and insistence on interoperability.

Three Flavors of MIMO

The new MIMO market breaks down into three camps. Belkin and Linksys offer MIMO gear based on Airgo Networks' chip set. Netgear has partnered with smart-antenna vendor Video54 and plans to ship gear this spring. D-Link (as well as SMC, soon) is using Atheros Communications' new Super G with MIMO chip set in products available now.

In a general sense, MIMO uses multiple antennas and radios in the same frequency to transmit data, and is the basis for the 802.11n spec.

Airgo's CEO Greg Raleigh, who wrote the first academic paper on MIMO in 1996 at Stanford and has 26 patents in the field, says "True MIMO" (a term Airgo has patented) requires not only multiple antennas and radios on both the transmit and receive sides of the link but also the ability to do spacial multiplexing. Spacial multiplexing allows for the transmission of multiple distinct datastreams over multiple radios in the same band at the same time, effectively doubling (or tripling) data throughput. Think of it as sipping milk through two (or more) straws at once.

Specifically, Airgo's MIMO chip set transmits two distinct datastreams simultaneously at 54 megabits per second to yield 108 mbps. Linksys, which uses the Airgo chip in its new Wireless-G Broadband Router with SRX, says it gets about 40 mpbs actual throughput.

However, Atheros, and Netgear with Video54, are pushing to broaden the definition of MIMO to not require spacial multiplexing. Atheros CEO Craig Barratt says, "Our position is that MIMO is any system that has multiple antennas at both ends of the link being used concurrently. How you actually use them is subject to various choices in implementation."

Video54's BeamFlex technology uses seven internal antennas to transmit and receive the same data over multiple paths simultaneously. This strengthens the signal, resulting in fewer lost packets and errors, as well as increased performance and distance. But it uses only one radio and one transceiver, and sends only one datastream.

Atheros's new MIMO chip set uses four antennas and two radios, which send data over two transceivers simultaneously and sounds more like Airgo's MIMO. But the two radios transmit the same datastream simultaneously, which isn't spacial multiplexing.

It comes to this: Raleigh argues that MIMO is spacial multiplexing. Barratt argues that spacial multiplexing is a feature of MIMO.

"We're worked up about this because we've worked hard on this technology, and we feel that it's being pirated," Raleigh says.

Won't Play Well With Others

When shopping, users need to put any assumptions of interoperability aside. Even though Belkin's and Linksys's products use the Airgo chip set, they won't necessarily work together--Linksys says they won't, Belkin says they will.

Although Belkin calls its products pre-N, no vendors claim their MIMO products will interoperate with the final 802.11n spec. Linksys's Malachy Moynihan, vice president of engineering and product marketing, objects to Belkin's use of the term, saying it misleads users into assuming its products will work with final 802.11n gear. Moynihan says he expects Linksys to come out with three distinct MIMO-based iterations between now and 802.11n's ratification, and that each might not be backward-compatible with its predecessor.

Atheros's Barratt says Netgear's Video54 implementation works well with the Atheros Super G with MIMO products. "We think Video54 is a very desirable stepping stone, one that maintains backward compatibility."

All the vendors claim their products will improve overall performance in a mixed 802.11b/g network, even with the addition of just one new MIMO client or router. And all seem to agree that products that rely simply on smart-antenna technology, like Netgear's, won't cause network problems.

However, Airgo rivals insist they've found that Airgo products interact poorly in a mixed environment, delivering lower data rates than you'd typically get on a standard 802.11g network. Raleigh says Airgo's products work seamlessly with both 802.11b and 802.11g gear, and adds that the Atheros MIMO chip set is based on the Atheros Super G chip set, which uses channel bonding to reach 108-mbps "turbo" speeds. Channel bonding is notoriously disruptive to standard 802.11b/g networks.

This story, "MIMO Products Muddle Wireless Market" was originally published by Network World.

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