low-power Wifi

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Is there such a thing as low-power Wifi?

I want to create a WAP that has maybe a 10 or 20 foot range.  Is that reasonable?

Re: low-power Wifi
On Wed, 8 Aug 2012 08:08:49 -0700 (PDT), bob smith

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Several years ago I did something similar to that. I was suspecting my
neighbor was accessing my local network, so I remived the antennas
from my WRT54G router. I was still able to access it with my laptop
wirelessly, but only from within the same room. I eventually
instituted WAP protection, so I no longer need the antenna-less
protection.

Re: low-power Wifi
On Wed, 8 Aug 2012 08:08:49 -0700 (PDT), bob smith

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Some third party firmware, dd-wrt comes to mind, allows you to specify
the transmit power. You'd probably dial it down until you're
satisfied.


Re: low-power Wifi
On 8/8/2012 8:47 AM, Char Jackson wrote:
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Even if you dial down the power, you have the issue of wifi going into
the low speed fallback modes. That is, you dial down the power so 54mbps
just works, and you might find a long distance 1mbps user.

Now if you can dial down the power and force the wifi to only be at one
speed, then maybe you have a plan.

I find that not placing the wifi router too high helps in keeping it
local. Don't put it on a shelf.

Re: low-power Wifi

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Good points, thanks.


Re: low-power Wifi

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Good idea.  For coffee shops, I previously set the wireless router for
54Mbits/sec fixed speed to limit the range.  As a bonus, overall
performance improved since less air time was needed.  However,
retransmission increased dramatically.  

I stopped doing it that way because some laptops and devices did not
respond gracefully to a loss of signal at 54Mbit/sec associations.
Instead of going into standby when the signal disappeared, they would
disconnect, scan for other SSID's, and take forever to reconnect.
Users were complaining to the baristas that they "couldn't stay
connected".  My iPhone 3G was one of the devices with a problem.

There was also a problem with people arriving with 802.11b only
hardware.  I had thought all those were dead and being recycled, until
I realized that several of my ancient IBM Thinkpads (A30, A31, X30,
X31) come stock with 802.11b.  Also, lots of game pads are 802.11b
only.

I gave up and went back to auto speed at the coffee shops.


--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: low-power Wifi
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I was setting mine to 1 milliwatt from 15 foot away, no much change from 70
.

Greg

Re: low-power Wifi
On Wed, 8 Aug 2012 08:08:49 -0700 (PDT), bob smith

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Sure.  Some of the devices that have wi-fi built in have a very
limited range.  For example, the SD card for cameras:
<http://www.eye.fi
<(Amazon.com product link shortened)>

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I've been doing that at coffee shops for years.  Just use a terminator
for an antenna and you'll get some limited range.  It really depends
on the unit.  Most AP's have two antennas.  However, the one's with a
single antenna usually also have a 2nd antenna inside the box. Usually
that's a PIFA PCB antenna or chip antenna.  Don't try to just unplug
the outside antenna, as there's a huge difference between the MAIN and
AUX antennas.  The AP sits on the MAIN antenna all the time, unless
the error rate gets high enough to justify trying to use the AUX
antenna.  If you just use the AUX antenna, you'll have really lousy
association time and erratic disconnects as the AP keeps trying to use
the MAIN.  Fortunately, you can disable diversity in firmware such as
DD-WRT.

A few years ago, I worked on a project that was designed to restrict
the USABLE range of a coffee shop wireless to only the floor area. I'm
required to keep my big mouth shut on how it works, but I can assure
that I can measure range and block users outside the usable range.
However, it was expensive and somewhat messy.

A half-posterior approach that almost works is to use two access
points.  One is just a monitor, while the other actually does the
connecting.  By comparing the relative signal strengths for a given
MAC address, you can calculate a tolerable guess as to the location.
If the numbers are outside the acceptable limits, they get blocked
until it either recovers to acceptable limits, or disconnected if it
stays outside the limits.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Re: low-power Wifi
wrote:

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reasonable?

All of our "big Cisco" APs support turning down the power - e.g. the
AIR-AP1131AG-A-K9 supports setting the power down as as low as -1 dBm
(1 mW.)  Also you can pick and choose which data rates are mandatory/
supported/disabled.  (See e.g.
http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps6087/product_data_sheet0900aecd801b9058.html.)

What's the point, though, may I ask?

Aaron

Re: low-power Wifi
wrote:

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Nit pick:
-1dBm is about 0.8mw.  0dBm is 1mw.


--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

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