Archived from groups: alt.internet.wireless (
More info?)
On Thu, 7 Oct 2004 14:30:04 -0700, "Tom C." <tomc70NO@SPAMcomcast.net>
wrote:
>Sorry Jeff, but I have to disagree with you. Three walls are not
>"impossible". I just got a Netgear WGT624 Wireless 108mps Router and I'm
>going through floor framing and SIX walls total. Typical 2-story house with
>wood framing and this router totally blankets my house with a Wi-Fi signal.
>At the farthest reach, the signal reduces to 11mps, which is still very
>good. Directly below my router is my dining room where my wife surfs the
>net with a 54mps connection.
>
>I switched from a 54mps Linksys Wireless Access Point which barely worked at
>the farthest reach. This new Netgear router is great and solved many
>problems.
>
>- Tom C.
Whee... Why don't I have such good luck? I have never made it
through that many walls with a reliable connection. What's your
secret? What client radios are you using? Any open doorways and
hallways? Who's your sorcerer?
Let's play with the numbers and see where they lead.
The WRT624 belches about +13dBm into a +2dBi antenna for a +15dBm
EIRP. At the other end is probably (my guess), an laptop with a built
in antenna. At 11Mbits/sec, it has about -83dBm sensitivity. Antenna
gain is a disgusting -2dBi.
When I did my own testing in 1999, the average wood framed residential
wall was good for -6dB of loss, while the floors were -10dB. Note
that this is only the *ADDED* loss contributed by the walls and
floors, and do not include any path loss over a distance.
My guess is your overall range is about 75ft from one end of the house
to the other.
Free space loss (dB) = 96.6 + 20 log F + 20 log D
Where:
F = Frequency (GHz)
D= Distance (miles)
logs are base 10, 5280 ft/mile
FSL = 96.6 + (20 log 2.4) + (20 log 75/5280)
FSL = 96.6 + 7.6 -40 = 64.2 dB loss.
(Somebody please check my math. I haven't had my morning coffee yet).
So, we start with the TX EIRP of +15dBm, loose 64.2dB over the
distance, and end up with a receive sensitivity of -83dBm. The fade
margin is:
+15dBm - 64.2dB -(-83dBm) = 34dB
That means that we can lose 34dB more signal and still just barely
communicate with the laptop over a distance of 75ft.
With my measurements of about -6dB for walls, and -10dB for floors,
that will give you about 5 walls, or 1 floor and 3 walls which can be
penetrated.
However, please note that the receiver sensitivity reference level is
at a BER (bit error rate) of 10^5, which is fairly lossy and would not
provide reliable communications. You would need at least +10dB more
signal to make it reliable. Therefore, my guess would be 4 walls, or
1 floor and 2 walls maximum.
Drivel: When I was making the loss measurements, we had a very
difficult time making sense of the numbers. A wall should be 6dB per
wall and should be linear for additional walls. Instead, additional
walls contributed less and less loss for each additional wall. After
about 4 walls, the signal level was strictly free space loss and the
additional walls had little effect. Huh? Eventually, we figured out
that as the number of walls increased, the tendency for the signal to
leak AROUND the walls became more pronounced. It was going out
windows, bouncing around stairwells, and generally avoided going
through the walls. This might be what's happening here. Any
possibility that instead of going through 6 walls, your signal is
going around some of them?
--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
e2cm0pnbla00hrlh96ggh1g924tace7gv@4ax.com...
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