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Did MIMO run over Eileen McCluskey’s bike as a kid? I’m slightly baffled by the treatment of MIMO technology in this otherwise reasonable set of consumer advice about Wi-Fi in the Boston Globe yesterday. It’s possible the single source cited in the article poisoned her information well.
“These Multi Input, Multi Output gadgets achieve excellent signal quality and range by hogging the wireless spectrum up to 219 yards away. If you live in the city or suburbs, your MIMO router will knock out your wireless-enabled neighbors’ connections.” Huh?
Here’s my letter to the editor just sent off to the Globe:
“Less Is More” (Apr. 9, 2005) contains a glaring error regarding multiple antenna wireless networking. The reporter says that MIMO (multiple not “multi” input/output) gateways hog spectrum and knock out neighbors’ reception. This is entirely untrue. MIMO gateways for Wi-Fi, unlike previous range-extending Wi-Fi, are more sensitive receivers not more powerful transmitters.
It used to be that to extend range, you pumped up the volume (increased signal power output), which could interfere with neighboring networks. MIMO uses several antennas to better reconcile radio signals as they reflect off walls and metal objects. This allows the technology to more discretely receive fainter or less clear signals from further away.
There is the danger that a newer form of Wi-Fi, called 802.11n, that will be on the market soon may interfere with older networks in some cases, but Wi-Fi product makers haven’t finalized the standard, and it’s one of their key concerns.
The other also states that MIMO won’t work with free Wi-Fi hotspots. This is entirely untrue. Current MIMO gateways and future gatweays that use MIMO as one piece in a faster Wi-Fi standard are entirely compatible with Wi-Fi equipment sold as long as ago as the first devices in 1999. MIMO devices won’t communicate at their highest possible speeds except with compatible devices from the same maker (today) or with the newer standard with any maker (in about 3 to 6 months).
Posted by Glennf at April 10, 2006 10:32 AM
Categories: MIMO, Mainstream Media
TrackBack URL for this entry:
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Glenn, if nothing else, you've at least provided readers one of the few plain-English explanations of MIMO technology I've read. Thanks for the clarity.
Posted by: kawika ![[TypeKey Profile Page]](http://wifinetnews.com/nav-commenters.gif)
at April 12, 2006 9:42 AM
I have seen increased interference from pre-n gear since the devices have an increased effective transmit power due to the additional required radios and power amplifiers. For example, a typical 11g AP has a single 20 dBm (100 mW) power amplifier (20 dBm PA's are relatively cost effective and hence fairly popular in consumer 11g gear). A typical pre-N solution would have two 20 dBm PA's -- one for each transmit radio chain. This exactly doubles the effective output power of the device, at least in the U.S. where legal power limits are much higher. So in addition to the increased interference from (optional) 40 Mhz channels, 11n devices will also generate more interference in practice due to higher effective output powers.
Posted by: billkish at April 11, 2006 2:59 AM
Well, there is a grain of truth to the accusation that MIMO equipment can negatively affect other networks, if you consider Atheros's Super G to be MIMO. Personally, I don't. Airgo's "True MIMO" is definitely MIMO, Video54's BeamFlex sorta-kinda might be, but Atheros relies primarily on channel bonding to get throughput. Channel bonding has been proven to pollute the local EM environment.
http://www.theregister.co.uk/2003/12/18/tests_confirm_atheros_super_g/ is a good starting point for looking into one set of experiments showing this effect. The confusion occurs because Atheros has been stubborn regarding this issue, and also because they also call their stuff MIMO when it's not.
Posted by: Platypus at April 10, 2006 1:20 PM