Is there any alternative to line of sight? -- Phridge brought to you by http://www.wifi-forum.com/

On Sun, 06 Mar 2005 23:09:08 GMT, in alt.internet.wireless , Phridge
<Phridge.1lhvua@WiFi-Forum_dot_com> wrote:

for what? Please leave some context in your posts.

On Sun, 06 Mar 2005 23:09:08 GMT, Phridge
<Phridge.1lhvua@WiFi-Forum_dot_com> wrote:

Maybe wire? ;-)

On Sun, 06 Mar 2005 23:09:08 +0000, Phridge wrote:

braille?

On Sun, 06 Mar 2005 23:09:08 GMT, Phridge
<Phridge.1lhvua@WiFi-Forum_dot_com> wrote:

Perhaps hindsight?  NLOS (non-line-o-sight) is the holy grail of
wireless connectivity.  Claims of amazing and miraculous connectivity
through a variety of obstructions are rampant.  My limited experience
on 2.4Ghz is that you can usually achieve a connection, but staying
connected 24x7 is almost always a marginal proposition.  Therefore, I
consider NLOS to be somewhat of a bad joke, along with "self
configuring" and "self healing" networks. 

The Pre-N (NINO) radios do a fairly good job of dealing with
obstructions by bouncing signals all over the place and then
attempting to put them all back together.  It's sorta a statistical
approach to redundant paths.  However, they require 3 antennas at each
and methinks such a derangement on a rooftop would not be
aesthetically acceptable.  (I said the same thing about pizza dish DBS
antennas with 3ea LNB's and was proven wrong).

In general, the best advice is to find some line of sight.  That could
mean a taller mast, inconvenient radio location, creative antennas, or
chain saw work.

However, all is not lost and there are some partial solutions.
However, in all cases, you'll need to either spend some real money, or
live with some performance losses.

1.  900MHz radios.  These will go through trees fairly well.  However,
they're slow.  115Kbit/sec to 750Kbit/sec is typical.  $150 to $500
per radio.  2-4 mile range through a forest.  25 miles with line of
sight.  Bug me if you want vendors.

2.  Repeaters and WDS bridges.  Instead of trying to get line-o-sight
directly, you find a place to locate a repeater that both ends can
see.  Single radio (simplex) repeaters will cause a 50% loss of
thruput.  This may not be significant if you're sharing a DSL or cable
mode.  Dual radio (duplex) repeaters on different channels do not have
this problem.  However, now you need 4 radios total instead of two.

3.  Big ugly antennas.  The rules for power output at 2.4Ghz are
rather weird for point to point links.  Legally, you can run a 24dBi
dish antenna with a +24dBm (250milliwatt) transmitter.  Given
sufficient antenna gain (notice I didn't say sufficient xmit power as
in a hang on power amplifier), you can sometime "drill" though a
building or line of trees.  If you can sorta see through the
obstruction somewhat, you have a chance.

4.  Spatial diversity.  Two radios at each end of a link.  Each one
has separate antennas.  Multiport router (Freesco.org) with some sort
of error detection script to optimize which link to use.  With
multilink, you also get twice the bandwidth through the link, but you
don't need that.  If one path goes down, the other one might be
functional.  One of my acquaintances did one of those with 4ea WRT54G
boxes in bridge mode.   When the trees sway one direction, one radio
link works.  When they sway the other direction, the other link is
active.  I've never seen the actual installation, but I've troubleshot
the system remotely.  It works.  However, if you're gonna do this,
make sure you have STP (spanning tree protocol) running and functional
or you may create a loop.

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