Re: Got Interference? Data-Crowding Problems Loom for Wi-Fi]

["David Farber" <dave () farber net>]

---------------------------- Original Message ----------------------------
Subject: Re: [IP] Got Interference? Data-Crowding Problems Loom for Wi-Fi
From:    "Tim Pozar" <pozar () lns com>
Date:    Wed, July 18, 2007 3:16 pm
To:      "David P. Reed" <dpreed () reed com>
Cc:      dave () farber net
         "Dewayne Hendricks" <dewayne () warpspeed com>
         glenn () glennf com
--------------------------------------------------------------------------

Hi gang...

Certainly, you can look at the problems that folks are having with the
google deployment in Mnt. Some of this of it being interference based.

I personally have seen this problem with deployments such as in San
Francisco's Union Square point-to-multipoint public deployment.  In this
space there is a ticket sales booth that has a 2.4 GHz cordless phone.
 If you are sitting next to this booth and someone is on the phone you
will have a difficult time connecting.

Some years ago, I put in a 2.4GHz point to point link in the Sunset
District of San Francisco.   This link went between my house and a
friend's.  Things worked well for some weeks until we got to a point
where about 7PM every night the link would degrade significantly for
about 15 to 60 minutes.

I finally grabbed my spectrum analyzer out and wandered through the link
and found that on my friends side of the link (next door to him) a
neighbor was running a cordless phone talking to their mom every night.

We had to do a couple of things to mitigate this by changing frequency
and moving his antenna up a bit so the link had less attenuation due to
fresnel zone issues.

On a larger scale, you need to look at organizations like SF BANC.  They
have had to give up on the 2.4GHz band and are encounting more
interference on 5.8GHz at populated sites like Black Mountain outside of
Palo Alto.   With the fact that the bands they are trying to coordinate
are unlicensed, dealing with non-coordinated links are problematic.

Sites like San Francisco's main public safety communications site on
Twin Peaks are running into problems getting 5.8 GHz links out of there
to downtown SF.

Interference is real on the ISM bands.  If you want me to do some leg
work outside of my couple of personal examples, I can point folks to
this group.

Tim

David P. Reed wrote:
> When somebody says "we have definitely seen impact, we just haven't been
> able to quantify that impact," shouldn't one wonder just a little bit?
>
> If there is impact, one should be able to measure it.   And 802.11
> systems are *all* quite capable of measuring their achieved rates
> without any fancy extra equipment.
>
> It reminds me of the folks who said, a few years ago, that the Wifi in
> Sand Hill road hotspots were interfering with Porsche RF door locks.
> Repeated over and over, this story became true.
>
> I personally await one little actual data point.   There is no doubt
> that WiFi systems can be affected.  But qualitative, evidence free
> claims are just Chicken Little ravings that conflate 0.01% effects with
> Global EMP shutdown.
>
> David Farber wrote:
> > As I have been saying in every talk I have given for years djf
> >
> >
> >
> > ---------------------------- Original Message
> > ----------------------------
> > Subject: [Dewayne-Net] Got Interference? Data-Crowding Problems Loom for
> > Wi-Fi
> > From:    "Dewayne Hendricks" <dewayne () warpspeed com>
> > Date:    Tue, July 17, 2007 12:47 pm
> > To:      "Dewayne-Net Technology List" <xyzzy () warpspeed com>
> > --------------------------------------------------------------------------
> >
> >
> > [Note:  This item comes from reader Tim Pozar.  DLH]
> >
> > From: Tim Pozar <pozar () lns com>
> > Date: July 17, 2007 8:44:44 AM PDT
> > To: Dewayne Hendricks <dewayne () warpspeed com>
> > Subject: It isn't like I have been beating this drum for years now...
> >
> > And it can only get worse at 2.4 and 5.8GHz.
> >
> > Also funny how these articles don't cover all of the other users on
> > these bands such as TV ENG trucks, Ham radio operators and Public Safety
> > video links that can and do cause significant interference to poor old
> > "wifi".
> >
> > Tim
> > --
> > <http://www.wired.com/gadgets/wireless/news/2007/07/wifi_interference/>
> >
> > Got Interference? Data-Crowding Problems Loom for Wi-Fi
> > Robert Lemos Email 07.17.07 | 2:00 AM
> >
> > The airwaves in the city of Riverside, California, just got a lot more
> > crowded.
> >
> > On Monday July 9, the city switched on its municipal wireless network,
> > delivering free internet service to more than three square miles of the
> > downtown area. According to MetroFi, the wireless service provider that
> > teamed up with AT&T to build the network, the ad-supported service
> > offers up to 512-kbps download speeds to each resident in the area
> > covered.
> >
> > Yet, for many living in the inland empire's capital city, the free
> > service isn't a bonus, it's a burden. The new network adds even more
> > sources of interference to the already crowded wireless spectrum.
> >
> > MetroFi installed 25 to 30 wireless nodes per square mile to cover the
> > downtown Riverside area. Because wireless signals in the most commonly
> > used Wi-Fi band of 2.4 GHz are scattered by buildings and trees,
> > MetroFi's wireless nodes could interfere with other wireless networks in
> > the area, and vice versa.
> >
> > Craig Mathias, principal analyst and founder of wireless research firm
> > Farpoint Group, says such citywide Wi-Fi projects could overwhelm nearby
> > residential systems.
> >
> > "We have definitely seen a negative impact from these systems," he says.
> > "But we just haven't been able to quantify that impact."
> >
> > Interference on wireless networks will likely get worse before it gets
> > better. Sometimes, the most egregious offenders aren't nearby
> > residential networks or municipal Wi-Fi grids, but the myriad electronic
> > devices in people's homes. Poorly shielded microwave ovens leak radio
> > waves tuned to 2.45 GHz, the resonant frequency of water. Many cordless
> > phones operate in the 2.4-GHz band as well. Wireless keyboards,
> > Bluetooth devices, wireless security cameras and baby monitors can all
> > interfere with a Wi-Fi network.
> >
> > "It's a worse problem for a consumer than it is for an enterprise,
> > because you have a lot more wireless gizmos in your space," says Neil
> > Diener, chief technology officer for wireless-solutions provider Cognio.
> >
> > Most people don't notice interference problems unless the cacophony of
> > electronic signals causes their residential network connection to drop.
> > MetroFi, which has covered 77 square miles with wireless networks in the
> > San Francisco Bay Area, has received only five e-mail messages regarding
> > interference problems, the company said.
> >
> > Diener says the low level of concern is because consumers typically
> > underutilize their wireless networks. For most, wireless is a way to
> > connect to the internet. While even the best residential broadband
> > speeds may reach 5 Mbps, today's wireless network equipment makers boast
> > speeds up to 54 Mbps for popular 802.11g equipment.
> >
> > If the wireless network can maintain even slight connectivity, Wi-Fi
> > will outperform current broadband solutions, Diener says.
> >
> > "It's like when your arteries are partially clogged, you don't know it
> > until you have a heart attack," he says.
> >
> > As consumers push more bits over their wireless networks, the slowdowns
> > will likely become much more obvious.
> >
> > Apple TV uses next-generation wireless networking technology, dubbed
> > 802.11n, to shuffle multi-gigabyte video files to and from computers on
> > a home network. Cell phones that allow users to browse the internet and
> > even make calls using the local wireless network, such as BlackBerry
> > devices and the iPhone, are increasingly popular. Game consoles like the
> > PlayStation Portable allow players to connect to the internet and each
> > other using Wi-Fi.
> >
> > The next-generation of Wi-Fi has both benefits and drawbacks in terms of
> > interference.
> >
> > Wireless networks using the most popular protocols, known as 802.11b and
> > 802.11g, use a part of the unlicensed radio spectrum in the 2.4-GHz band
> > by default. The next-generation 802.11n also uses the spectrum by
> > default. While 802.11n access points use multiple antennas to allow the
> > devices to cope with interference and improve range, many consumers will
> > be tempted to use a new feature that doubles the speed of the device --
> > at the cost of hogging double the amount of spectrum bandwidth.
> >
> > That's a recipe for greater interference, says Farpoint Group's Mathias.
> >
> > "That will cream the bandwidth," he says.
> >
> > [snip]
> >
> >
> >
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