How do wireless signals disperse themselves?

Maybe this question is unanswerable. Maybe not.

Just how are wireless signals dispersed from a wireless router? I mean
are they sent forth upwards, downwards, sideways. Do they cover an area
like a fog, seeping into every penetrable space until they reach their
maximum range or collide with an impenetrable or non-porous object such
as a cement wall or steel beam?

Thanks.

dejola wrote:
> Maybe this question is unanswerable. Maybe not.
>
> Just how are wireless signals dispersed from a wireless router? I mean
> are they sent forth upwards, downwards, sideways. Do they cover an area
> like a fog, seeping into every penetrable space until they reach their
> maximum range or collide with an impenetrable or non-porous object such
> as a cement wall or steel beam?
>
> Thanks.
>
http://www.atheros.com/pt/Methodolog...AN_Chariot.pdf
2. The radio environment—Several issues affect the way the radio signal
travels from one device to another:
• Radio energy attenuates when it propagates. As radio waves propagate
outwards spherically, the energy spreads over an ever-increasing area.
In free space, doubling the distance decreases the received power by a
factor of 4—the so-called 1/r2 behavior. Radio signals also attenuate
when they pass near or through objects such as floors, walls, furniture
and people. The attenuation increases with the object's conductivity
(due to metal or water content, for example). The combination of these
two attenuation effects reduces radio signal strength by 1/r3 to 1/r4,
or even 1/r5. In other words, each time you double the distance, the
received power might decrease by 8 to 16 times.
• Antenna designs affect how much radio-frequency (RF) energy is
transmitted or received and where it is directed.
• Scattering and multi-path cause fading effects. Signal strength can
change rapidly as a function of location because the received signal is
the sum of potentially numerous signals scattered from nearby objects.
As the transmitter or other objects in the environment move, the
scattered signals sometimes add together and sometimes cancel each
other. Fading can change significantly over distances of a wavelength or
so (12.5cm at 2.4 GHz and 6 cm at 5 GHz). Fading also occurs over time
as well as location. Even small changes in the environment (for example,
people or other objects moving) can affect the fading pattern. This
means that the received signal strength can also change quite quickly
over time, even when the receiver and transmitter are fixed.
• Scattering and multi-path results in delay spread. The received signal
might contain several slightly delayed copies of the transmitted signal,
as the scattered signals travel via different physical paths of
different lengths.

"dejola" <(E-Mail Removed)> wrote:
>Just how are wireless signals dispersed from a wireless router?

They tend to go out roughly perpendicular to the antenna(s), though
only roughly. You can pretty much consider the entire router to be an
isotropic (emits equally in all directions) radiator.

You can think of them as waves or particles, that will reflect from
some surfaces and be partially absorbed or blocked by others. Very
generally, you can go through a wall or two and a floor without too
much attenuation, assuming stick construction and no metal-faced
insulation in the way.

Multipath effects and interference will further complicate the issue,
as will the client radio, so it's not something subject to prior
analysis.

--
"dejola"

| Maybe this question is unanswerable. Maybe not.
|
| Just how are wireless signals dispersed from a wireless router? I mean
| are they sent forth upwards, downwards, sideways. Do they cover an area
| like a fog, seeping into every penetrable space until they reach their
| maximum range or collide with an impenetrable or non-porous object such
| as a cement wall or steel beam?

By way of a 2D example. Visualize a rock dropped into a still pond.

So long as there are no obstructions the signal propagates out in concentric
circles that get predictably weaker over distance. When the wave (in all
senses of the word) encounters a discontinuity the wave front is attenuated,
distorted, bent, blocked or reflected (sometime all of the above).

The effects are more complicate in 3D and by such elements as multi-path,
phase reversal and the polarization of the sending/receiving antenna
systems. (think a 5 foot broom handle passing through a door horizontal vs.
vertical enough force /power and part of the signal will make the trip.)

These are further complicated by the fact that some media/material are
transparent/translucent/opaque as a function of different frequencies. Then
there are the issues of path dynamics, i.e. the signal may pass,easily, from
the AP to the client but not from the client to the AP. Think CAN YOU HEAR
ME NOW?

That said the math for a full explanation is very complex and in someways
almost a black art.

Rob wrote:
> dejola wrote:
>
>> Maybe this question is unanswerable. Maybe not.
>>
>> Just how are wireless signals dispersed from a wireless router? I mean
>> are they sent forth upwards, downwards, sideways. Do they cover an area
>> like a fog, seeping into every penetrable space until they reach their
>> maximum range or collide with an impenetrable or non-porous object such
>> as a cement wall or steel beam?
>>
>> Thanks.
>>
> http://www.atheros.com/pt/Methodolog...AN_Chariot.pdf
> 2. The radio environment—Several issues affect the way the radio signal
> travels from one device to another:
> • Radio energy attenuates when it propagates. As radio waves propagate
> outwards spherically, the energy spreads over an ever-increasing area.
> In free space, doubling the distance decreases the received power by a
> factor of 4—the so-called 1/r2 behavior. Radio signals also attenuate
> when they pass near or through objects such as floors, walls, furniture
> and people. The attenuation increases with the object's conductivity
> (due to metal or water content, for example). The combination of these
> two attenuation effects reduces radio signal strength by 1/r3 to 1/r4,
> or even 1/r5. In other words, each time you double the distance, the
> received power might decrease by 8 to 16 times.
> • Antenna designs affect how much radio-frequency (RF) energy is
> transmitted or received and where it is directed.
> • Scattering and multi-path cause fading effects. Signal strength can
> change rapidly as a function of location because the received signal is
> the sum of potentially numerous signals scattered from nearby objects.
> As the transmitter or other objects in the environment move, the
> scattered signals sometimes add together and sometimes cancel each
> other. Fading can change significantly over distances of a wavelength or
> so (12.5cm at 2.4 GHz and 6 cm at 5 GHz). Fading also occurs over time
> as well as location. Even small changes in the environment (for example,
> people or other objects moving) can affect the fading pattern. This
> means that the received signal strength can also change quite quickly
> over time, even when the receiver and transmitter are fixed.
> • Scattering and multi-path results in delay spread. The received signal
> might contain several slightly delayed copies of the transmitted signal,
> as the scattered signals travel via different physical paths of
> different lengths.
Hi,
And it has vertcial and horizontal polarized componenet. Type of antenna
has lot to do with this. But no signal is 100% V or H. Matvching
antenna type at both end is good idea. Also there is technique using
diversity; frequency, space, polarization to combine received signal for
better reception quality.

dejola said the following on 1/5/2006 4:06:
> Maybe this question is unanswerable. Maybe not.
>
> Just how are wireless signals dispersed from a wireless router? I mean
> are they sent forth upwards, downwards, sideways. Do they cover an area
> like a fog, seeping into every penetrable space until they reach their
> maximum range or collide with an impenetrable or non-porous object such
> as a cement wall or steel beam?
>
> Thanks.
>

In my layman's view, I think of them as ripples in a pond, but the pond
has objects in it that cause the ripple to bounce around.

Lance
*****

"dejola" <(E-Mail Removed)> hath wroth:

>Just how are wireless signals dispersed from a wireless router? I mean
>are they sent forth upwards, downwards, sideways. Do they cover an area
>like a fog, seeping into every penetrable space until they reach their
>maximum range or collide with an impenetrable or non-porous object such
>as a cement wall or steel beam?

Wireless signals are not dispersed from a wireless router. They are
radiated from the antenna plugged into the wireless router. The
general idea is much like your fog, except that the fog is much
thicker in a plane perpendicular to the vertical antenna, than in line
with the antenna. Were you to represent this thickening of the fog as
a function of equal signal strength around the antenna, it would look
like a torus (donut).

The fog is also not static in that radio waves don't just sit there
looking like a donut and going nowhere. They radiate outwards at the
speed of light in all directions. It's just that the strength of
these waves are stronger in a plane perpendicular to the omni antenna.
Other equal signal strength shapes are possible with different antenna
geometry.

As the fog radiates away from the antenna, it occupies a larger and
large volume as it moves farther and farther away from the antenna.
The strength of the signal varies with the square of the distance from
the source. Double the distance and you get 1/4 the delivered signal
(i.e. -6dB).

The waves will begin to hit objects near the router and in the room.
These objects can be roughly classified as either translucent,
absorbent, or reflective. No object is truely transparent and many
are simultaneously both absorbent and reflective. Concrete is a good
example of both. The rebar inside reflects, while the water inside
absorbs. The exact effects are difficult to calculate and model.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558