Wireless (802.11) website?

[David A. Bandel]

On Tue, 9 Jul 2002 08:54:57 -0400 (EDT)
begin  Net Llama! <netllama at linux-sxs.org> spewed forth:

> On Mon, 8 Jul 2002, David A. Bandel wrote:
> > On Mon, 08 Jul 2002 20:12:14 -0700
> > begin  "Net Llama!" <netllama at linux-sxs.org> spewed forth:
> >
> > > i guess i'm showing my ignorance.  so a base-station/access-point is
> > > basically an embedded device that doesn't need an OS based driver to
> > > work?
> > >
> > > i guess i need "wireless for dumbies", cause i don't fully
> > > understand how it all comes together.
> > >
> >
> > commercial "access points" cannot be used as anything but that, they
> > can't be used as Master or Repeater stations.  It has to do with
> > proprietary code in the cards, and the big boys don't want anyone to
> > muck with their gravy trains.
> >
> > In a linux box, however, a wireless card in ad-hoc mode is basically
> > an ethernet card.  You do need to understand radio signals and how
> > they work, fresnell zones, and more, but that's not hard either.
> >
> > Tell me what you need, I'll give you more than you've ever wanted to
> > know.
> 
> OK, what i attempted to diagram in my previous email was, that i'm
> getting DSL activated this Friday at home.  My grand plan (excluding the
> WiFi
> stuff) is to run a Freesco box box that has 2 NICs, one plugged directly
> into the DSL router that the DSL provider gives me, and then the other
> plugged into a 10 port hub (yes, i know switches are better, but this is
> all i have on hand, and all i can afford right now).  I've got 2 linux
> boxes that my wife & I use, plus 2 laptops (also linux).  everything is
> a static (10.x.x.x) IP, and will have the Freesco box as its gateway to
> the internet.
> 
> Now my vision for wireless is to get 1 or 2 wireless cards for the
> laptops, and a base-station/access-point.  Plug the access-point into
> the hub, point it to the Freesco box as the gateway (as i'm already
> doing), and then get the laptops online anywhere in my house.
> 
> So, is this possible, or am i completely misunderstanding what wireless
> can do for me?

My suggestion for you is the following:
forget the access point, it's an unnecessary expense.
In one system that's always on (I suppose, but don't know, that it could
be the freesco box), put a PCI-PCMCIA bridge card (I recommend one with
the Ricoh chipset) and a wireless card.  Spend the money you saved on the
access point to buy something like the Orinoco Extender antenna (works
with Orinoco/Agere cards, whatever card you use you'll need a compatible
connector for the card).  Place the extender antenna at approx eye-level
(when you're standing).
Install WIFI cards in your laptops. Depending on your distance from the
desktop, and the geography of your house, you may need small antennas for
the laptops. The WIFI network will, of course, be a different network than
your desktops, so make sure your routing is correct if you need to talk to
your desktops.

On WIFI cards, antennas, and wireless:
Most current WIFI cards are 50mW in power with no antenna.  An antenna
effectively increases the power for both sending and receiving.  Outdoors,
you can easily go 1/2 mile without antennas.  Newer cars w/ 100mW and even
200mW can go to almost a mile.  An antenna extends the sensitivity and
range.
Wireless is LOS (line of site).  It will pass through glass, but not solid
objects.  It will work in your house because for the most part you'll be
inside the "ground plane" (fresnell zone).  An antenna, particularly one
place up high, increases the ground plane (which size is based on antenna
height and output power).  So while the signal can't see through walls, it
can travel around them if the walls are within the ground plane.  With
overlapping ground planes, you'll always have connectivity despite the LOS
limitations.

On amplifiers:
Some folks (often HAM operators) think amps will increase distance through
increased power.  While this is true, you run the risk of overmodulating
stations closer in.  WIFI works on SNR (signal to noise ratio).  Amps
boost both, signal and noise.  They do little to change the SNR very much.
 Imagine you get 50 e-mails a day, 10 of which are important.  Your SNR is
-.20.  This is good (actual WIFI calcs are much more complicated, with
93/93 being perfect). You can effectively process 100 e-mails per day, but
no more (limitation on your time).  Suddenly, you find yourself getting
500 messages per day, of which 100 are important.  While the SNR is the
same, you'll probably never see any of the 100 important messages because
you're drowning in the 400 spams. Same principal applies to amp'd signals.

What haven't I covered?  Lots.  How antennas (typically 3dbi to 24dbi)
boost effective power (power is measured at the antenna).  Signal polarity
(must say a word or two here).

Signal polarity:  If you use something like the Orinoco range extender
antennas, you'll see that they are similar to an omni.  That is, they have
a radiation pattern, 360 degrees around, but probably vertically about 22
degrees (except within the ground plane).  However, you'll find that if
you have two spaced out beyond the ground plane and you rotate one, even
though they are "pointed" at each other (signal-wise, meanining they are
perpendicular one to the other physically), the signal will decay and
perhaps even disappear.  
Note: You can effectively do "df" on a signal in the distance by
reorienting the antennas to find the lull, do this from different places,
and you can triangulate lines of bearing to get a df (direction finding)
on the remote site.

The above is probably more than you wanted to know, but should give you
good background to get you started.

Ciao,

David A. Bandel
-- 
Focus on the dream, not the competition.
		-- Nemesis Racing Team motto