At 8/4/2010 09:55 PM, Jerry Richardson wrote:
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For UBNT 900 I have serious doubts you could cram more than 3x 5MHz
channels into the 30MHz and have it work without sync (behold the
power of Canopy!).
Yeah, sync... that's what I'd like. UBNT's AirMax has a degree of
it, of course. And MikroTik has put its own flavor of TDMA, nv2,
into beta. But they aren't as elaborate as Canopy or SkyPilot's
SyncMesh. You'd think that if the nodes could hear each other they
might be able to synchronize to some extent...
5MHz channels and 5MHz spacing might look like:
1 = 905.0 (902.5-907.5)
2 = 915.0 (912.5-917.5)
3 = 925.0 (922.5-927.5)
There are apparently four standard 5 MHz channels on the 900 band
(centered at 907, 912, 917 and 922). For the most part I'm finding
it possible to use two 120 degree sectors, with the rest of the
circle not required (usually over water). So I can keep 5 MHz
channels 10 MHz apart. Not ideal though.
I have doubts even that will scale well though. 900 is a different
animal with big fat lobes off the backs and sides of the antennas.
I suppose that the worst case is that the sectors will trigger each
others' CSMA, and thus the total throughput will be limited, but some
signal should get through. If the sectors are lightly loaded it
won't be so bad. Sound right?
- Jerry
From: wireless-boun...@wispa.org [mailto:wireless-boun...@wispa.org]
On Behalf Of Fred Goldstein
Sent: Wednesday, August 04, 2010 2:55 PM
To: fai...@snappydsl.net; WISPA General List
Subject: Re: [WISPA] Multiple sectors, one frequency?
At 8/4/2010 05:14 PM, Faisal Imtiaz wrote:
Well this is the formula we are using .... Under perfect conditions...
with 802.11n .... 40mhz channel = MCS 15 = 270/300mbps (air rate)
connection.
20mhz channel = MCS 15 = 130mbs (air
rate) connection
10mhz channel = MCS 15 = 65mbs (air
rate) connection.
5mhz channel = MCS 15 = 32.5mbs (air
rate) connection
802.11a/b/g radios are about 40%-50% efficient in terms
of air-rate to tcp thruput conversion.
802.11n radios are about 60-75% efficient ...
so....5mhz channel with a MCS 15 air rate of 32.5mbs should
translate into = 19mbps to 24mbps tcp thruput....
in the field you want to leave yourself plenty of headroom and
some margin.... a 5hz channel would be a bit on the margin for a
10x10mbs connection...
therefore using 10mhz channel should give you up to 30meg of
bandwidth capability on each of the cpe's....(i.e 15x15)
This all makes sense; I know that air rates don't translate diretcly
to throughput. The big question I'm still "rasslin'" with is
channel spacing. If I use 5 MHz channels (especially on 900), can
the sectors be 5 MHz apart? How about 10 MHz apart? Likewise, can
10 MHz channels be 10 or 20 apart? I'm drawing this big route map
(large-format printers are wonderful) with each AP's link and access
frequencies and trying to prevent conflicts... Thanks.
also:- this chart is a good reference when trying to decipher MCS rates ....
<http://en.wikipedia.org/wiki/IEEE_802.11n-2009>http://en.wikipedia.org/wiki/IEEE_802.11n-2009
Hope this helps.
Regards
Faisal Imtiaz
Snappy Internet & TelecomOn 8/4/2010 3:54 PM, Fred Goldstein wrote:
At 8/4/2010 03:37 PM, Jerry Richardson wrote:
It will not work.
But you would be surprised how well these run at 5 or 10 MHz channels.
With how much spacing between them? If I could put them on adjacent
10 MHz center frequencies, that would solve a lot of problems, and
even 5 MHz channels with 10 MHz spacing (and thus a 5 MHz guard band)
would be reasonable. But 20 MHz spacing is problematic.
How much throughput can a quarter-channel get? The Rocket data sheet
is not very complete; it doesn't even mention subchannel
support. The RM5 spec sheet says that MCS12 has -84 dB
sensitivity. That gets 78 Mbps in a full 20 Mbps channel, 162 in a
double-wide, and a bit more with the short guard interval. If I
could share 15 Mbps among the sector users, in 5 MHz, I think
everyone should be happy. And I'd expect -89 to -90 sensitivity.
Jerry Richardson
Sent Mobile
On Aug 4, 2010, at 12:33 PM, "Fred R. Goldstein"
<mailto:fgoldst...@ionary.com><fgoldst...@ionary.com>
wrote:
If I have a site with, say, Ubiquiti Rocket M5 radios plugged into
120 degree sector antennas, with Airmax (TDMA) turned on, do they
have to be on separate frequencies, or can they coexist on one?
The
5.8 GHz band is kind of crowded to be having three access frequencies
plus two or more backhaul frequencies... thanks.
--
Fred Goldstein k1io fgoldstein
"at" ionary.com
ionary
Consulting
<http://www.ionary.com/>http://www.ionary.com/
+1 617 795 2701
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