802.11

[David Bandel]

On 1/4/06, Man-wai CHANG <mwchang at i-cable.com> wrote:
>
> Why are they "a", "g" and "n"?

802.11a:  5GHz (actually 4.9GHz to 6.1GHz) usually OFDM, but can be DSSS, 54Mb+
802.11b:  2.4GHz (DSSS or FHSS) -- old, slow, 11Mb
802.11g:  2.4GHz (OFDM) faster -- 54Mb+

OFDM: orthagonic frequency division and multiplexing (means the signal
can take multiple paths and the signal can be recombined by the signal
processor in the radio to get signal where there are obstructions to
lines of sight -- note that this means reflected signal as found in
other than the 1st fresnal zone -- also note that rocks, buildings
made of concrete, glass, and/or metal, roads, deserts, water, are
reflective surfaces, but trees are not.)

The + means that many systems can basically do channel bonding and go
into "turbo" mode where they actually get 108Mb.

Throughput is another story.  But my 802.11a networks see 12Mb+
throughput on a 36Mb connection.  This slow throughput is actually a
function more of the slow ack times required for the distances
involved (I have 20+ mile links -- several).  Throughput also suffers
as number of radio connections increases.

You can calculate the radius of your fresnel zone (required
object-free area) for any line-of-sight shot at my web page
(http://www.pananix.com), look for the RF calculations link.

Ciao,

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