Wi Fi Propogation and Transmission - line of sight wi fi vs cordless

Could someone please explain to me as to why Wi Fi reception seems to
be line of sight dependent wheras cordless phone reception does not
seem to have this limitation.
My belief was that B and G are in a similar band as the cordless phone
frequencies .

On 18 Jun 2005 11:56:10 -0700, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>Could someone please explain to me as to why Wi Fi reception seems to
>be line of sight dependent wheras cordless phone reception does not
>seem to have this limitation.

I'll assume you're talking about a 2.4Ghz cordless phone. Please note
that there are many different types of cordless phones with different
frequencies and modulation methods.

- Wi-fi transmits at 1Mbits/sec to perhaps 54Mbits/sec over a 26MHz
signal bandwidth.
- Analog cordless phone does perhaps the equivalent of 0.005Mbits/sec
over a 0.025MHz bandwidth.
- Wi-Fi is highly sensitive to data waveform distortion caused by
reflections.
- Analog cordless phones are not.
- DSS (digital spread spectrum) cordless phones use the same spectrum
as Wi-Fi, but at a much much much lower data rate.

What happens is that for a given power level and bandwidth, you can
always trade speed for range. Wi-Fi goes quite fast, but not very
far. Cordless phones go quite slow, and therefore go quite far.

>My belief was that B and G are in a similar band as the cordless phone
>frequencies .

True. Cordless phones constitute a major source of interference to
Wi-Fi.


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

Jeff,

why is it that the cordless phone propogation seems to be somewhat of
a radius whereas even at a distance with lower transmission rates
Wi-Fi seems to be more of a line of sight propogation than a radius
pattern ?

On 18 Jun 2005 11:56:10 -0700, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>Could someone please explain to me as to why Wi Fi reception seems to
>be line of sight dependent wheras cordless phone reception does not
>seem to have this limitation.

where is this stated?

>My belief was that B and G are in a similar band as the cordless phone
>frequencies .

True for some phones.

>

WiFi does not need line of sight. My AP is upstairs and in a
cupboard.

Many offices have out of sight connections.

Cordless phones have a longer range when there is line of sight just
as WiFi does,
--
AnthonyL

On 18 Jun 2005 21:49:06 -0700, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:

>Jeff,

My me?

> why is it that the cordless phone propogation seems to be somewhat of
>a radius whereas even at a distance with lower transmission rates
>Wi-Fi seems to be more of a line of sight propogation than a radius
>pattern ?

The previous question was slightly confusing. This variation is worse
with no indication that you understood what I was previously trying to
explain. Please re-read my previous answer and rephrase your
question. I think you're asking about differences in coverage
patterns. If so, "line of sight" has no connection with the question.

I can't answer "why is it..." type questions because your statement
that follows is wrong. 2.4GHz propogation is the same no matter how
it is generated and what form of modulation and bandwidth used. What
is different is the ability of the system to recover from noise,
interference, reflections, multipath, variations in signal level, and
co-channel users. Because 802.11b/g requires a rather high S/N ratio
to operate, anything the trashes the S/N ratio will appear to have an
effect on reliability. However, the typical 2.4Ghz cordless phone can
operate with a rather lousy S/N ratio and can survive substantial
transmission imparement problems. The cordless phone is therefore
more reliable, but at the price of bandwidth and speed.

If both the 802.11b/g and the cordless phone systems used roughtly
identical antennas on both ends, their range and antenna patterns
would be roughly the same. There is nothing inherent in 802.11b/g
that would force it to be directional, which is what I'm guessing you
mean by "line of sight".

Are you asking why is it that your 2.4GHz cell phone works reliably
thoughout the house, while the 2.4GHz wireless router craps out as
soon as it goes through a wall or two? If so, it's again the ability
of the two systems to recover from S/N ratio imparements. The
cordless phone can tolerate enormous fades, lots of reflections, and
very low signal strengths, because of the narrow bandwidth. The
802.11b/g radios cannot, because of the wide bandwidth.


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