High Speed with MIMO: Who Cares?

By Eric Griffith

January 24, 2005

Chipmaker Airgo wants to clarify what really constitutes multiple-in/multiple-out tech in Wi-Fi—i.e., it's only what they're selling—but one analyst questions if it even matters so soon before high-speed 802.11n arrives.

Here is the definition of MIMO, according to Airgo Networks: two or more unique radio signals, in the same radio channel, where each signal carries different digital information.

According to the chipmaker, whose management pioneered the technology in academic papers several years ago, without adhering to that definition other companies are not actually providing multiple-in/multiple-out (MIMO, pronounced my-moe) in 802.11-based wireless networks. This is, of course, a direct shot by Airgo across the bow of competitors, notably Wi-Fi chipmaker Atheros Communications . That company has come out with a chip it calls MIMO, which will be using beam-forming, receive combining, and special multiplexing to increase range and throughput.

The point of that chip, says company spokesman Colin Macnab, is to "address the problems of robust high-rate signals in the home, driven by video transmission over wireless."

Other companies that say they support MIMO in silicon include Athena Semiconductor (working with Samsung) and Video54. The latter's CEO Selina Low says, "Other than marketing brand, there's no 'true MIMO.' It describes any system using multiple antennas and advanced digital signal processing to increase performance by managing multipath."

MIMO, as defined by Airgo above, will be the backbone someday of the future high-speed 802.11n standard (see below).

Bob Wheeler, analyst at the Linley Group, a firm that tracks the wireless chip market, agrees with Airgo.

"If you look at the literature, MIMO means multiple logical streams of data. Atheros is not doing that," he says. "Atheros falls back on their channel bonding," a technology they've had for some time that has caused controversy by allegedly interfering with other Wi-Fi networks.

That said, Wheeler also asks what may be the most important question: "Who cares? The question is, 'what is the value to the end user?' Does anyone care if it's true MIMO?"

He believes any company trying to get more data through all the floors of a large home to deliver digital video has a valid point—but that current 54Mbps 802.11a would be more than sufficient for the task, if done right. "The only place I see a need for the additional speed [of 11n] is in corporate networks," says Wheeler, "and no one will put something [that is for now] proprietary in such a network anyway."

Who cares? Airgo certainly does. The company CEO and president Greg Raleigh, who wrote some of the early MIMO academic papers, says, "There's no legal definition of MIMO. None of us anticipated someone claiming MIMO when they use beam-forming and diversity," technologies he says have been around for 50 years or more in wireless, including today's cellular base stations. He believes such technologies should be marketed as alternatives to MIMO, not as MIMO itself.

Raleigh says the use of the term MIMO by others will confuse consumers. However, he doesn't think the use of the term "Pre-N" is a problem. Pre-N refers to products currently shipping from Belkin with Airgo's "TRUE MIMO" branded chips. Belkin's is the first hardware available using Airgo's technology. Airgo says it is selling as well as 3% of the volume of Wi-Fi products in retail stores.

Raleigh says the products are only branded Pre-N (by Belkin, not by Airgo, it should be noted) to show their technological relationship to future 802.11n standard—not to indicate they'll work with future 11n-based products. He says that competitors "define [Pre-N] as if it should be upgradeable." (It won't be.)

Atheros's Macnab effectively agrees, and says "if you launch stuff that's pre-pre-pre anything, you know it won't be the final answer."

The Wi-Fi Alliance would probably beg to differ—it stated it would pull the 802.11g/a interoperability seal from any so-called Pre-N product that caused interference, in hopes of tempering use of the term in marketing. The Belkin products got the seal anyway.

Raleigh says if users of Pre-N products "want to interoperate with [final] 802.11n, they can buy new stuff in a couple years."

Perhaps that's the crux of the matter: the future.

Airgo and Atheros both stand on opposite sides in the battle for what will eventually be the IEEE 802.11n standard, a specification that promises to push wireless network data rates well above the 100Mbps mark. Airgo is part of the consortium called WWiSE (short for World-Wide Spectrum Efficiency), while Atheros stands with the heavyweights of TGn Sync. Other major proposals from Qualcomm and Motorola have recently been pulled or eliminated in votes during the latest meeting of the IEEE 802.11n Task Group.

Currently, TGn Sync's proposal is leading the way with 132 votes, versus 84 votes for WWiSE.

Raleigh accuses the TGn Sync group of being made up of members that all want to have their intellectual property built into the final 802.11n standard. "It's the first time in IEEE 802.11 history that so many non-chipset companies are participating," he claims, adding that "the percentage [of votes] going to WWiSE is increasing as OEMs see it as better for licensing."

Macnab sees it differently. "The WWiSE group at 802.11n, it's all sellers of 2.4GHz silicon," he says. "TGn Sync is who buys silicon—they'll have more power." (TGn Synch is also backed by chipmaker Intel , however—which certainly doesn't hurt on the power part.)

In the end, whoever can garner 75% of the vote will set the basis for the standard. Still, there will be a lot of work left to do even after that hoped-for, though not necessarily inevitable, compromise. Macnab hopes a published 802.11n specification will happen by March of 2007.

Linley Group's Wheeler says that TGn Sync is the "simpler way to get more throughput" for the straightforward reason that it uses twice the spectrum of today's WLANs. TGn Sync is calling for a 40MHz channel. However, this may not work in all countries, notably Japan, due to regulatory issues. Raleigh says that "the Japanese are quite offended that [TGn Sync member] Intel says they have to change regulatory rules." However, Wheeler thinks the presence of a giant like Sony on the TGn Sync member list might indicate this won't be a problem in the long run.

TGn Sync expects to deliver speeds of around 313Mbps using two antennas.

The WWiSE proposal calls for requiring only the 20MHz band, which it believes is friendlier to all countries (thus the "World-Wide" in the name) and provides better efficiency. Speed would start at 135 Mbps with two transmitting antennas as mandatory. More antennas would be optional, as would a 40MHz mode.

Airgo will benefit either way, since both proposals rely heavily on the use of MIMO as defined by Airgo (remember: two or more unique radio signals, in the same radio channel, where each signal carries different digital information). It will be the required mode of 802.11n. Airgo expects to meet the RAND standard for reasonable and non-discriminatory licensing—it's part of the overall WWiSE proposal. But that doesn't mean they'll just give it all away.

Raleigh says even after 802.11n has a final standard, "We're going to sell 11n on steroids—we'll always go beyond the basics."

"From the Airgo standpoint," says Wheeler, whether it's WWiSE or TGn Sync in the end, "they can't lose."

Originally published on .

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