[Commotion-dev] Serval Mesh Helper Device / ISM long-range meshing work

[Paul Gardner-Stephen]

Hello,

On Fri, Feb 8, 2013 at 1:16 AM, Ben West <ben at gowasabi.net> wrote:
> Likewise, Ubiquiti also sells 900MHz versions of their Nanostation and
> Bullet access points.  I understanding these units essentially just have
> 2.4/5.8GHz chipsets that have been translated to a different band, and with
> some consequent penalty in spectral efficiency.
>
> E.g.
> http://www.wirelessnetworkproducts.com/locom900.aspx

These sorts of units are quite interesting.  The range is in part due
to the +7.5db gain on the directional antennae at each end, and
perhaps more importantly, the front-to-back ratio that this affords to
help reject interference.  If they have done the band translation
"right", then the spectral efficiency could well be better rather than
worse, as 900MHz has substantially better propagation characteristics,
and over typical distances yields about +9db compared with similar
2.4GHz transmissions.

900MHz NanoStations and similar would be a useful addition to a
Commotion network, and you (or we) may wish to obtain some to test
out, but there are a few caveats, some common to all 900MHz
communications, and some specific to a NanoStation type product:

1. The ISM 915 band is only available in the Americas, Australia, New
Zealand, Israel and a few other countries.
2. The regulations on the use of this band, and its frequency range
vary substantially even among those countries. For example the US
requires 50 channels in the hopping scheme, while Australia requires
only 20, but the band in the US is almost twice as wide.
3. The power consumption of the unit will be relatively high if
transmitting at 1W.  This is perhaps more an issue for Serval-inspired
use-cases where mains power is assumed to be absent.
4. The higher bit-rates that the unit will use (compared to what we
are experimenting with) will reduce the maximum range that can be
achieved.

This is why we are looking at a solution where the radio is field
replaceable with one that is legal wherever the unit is to be used. It
is also why we are looking at a hand-held portable device that you
just shove in your other pocket, and any phone within WiFi range can
make use of it.

> I would like to assume OpenWRT and derivatives will run w/o complaint on
> such 900MHz units, but I'm guessing it's not that simple.

I imagine that it shouldn't be hard to put OpenWRT on the 900MHz NanoStations.

Paul.

> On Wed, Feb 6, 2013 at 11:00 PM, Paul Gardner-Stephen
> <paul at servalproject.org> wrote:
>>
>> Hi All,
>>
>> Just a heads up on some stuff we are doing at Serval that I think will
>> be of interest to Commotion deployments more generally.
>>
>> We are now actively working on what we call our "Mesh Helper Device",
>> the prototype of which will consist of a TP-LINK WR703N running
>> Commotion OpenWRT + servald, connected to an RFD900 ISM 915MHz band
>> packet radio and a rechargeable battery.
>>
>> This gives the potential for much greater range than just WiFi, as
>> well as offering some resistance for 2.4GHz jamming in places where
>> that is a problem.
>>
>> The RFD900s with current firmware in urban settings offer 5x to 10x
>> range compared with WiFi.  For example, I could receive a decent
>> signal with one radio sitting on my lounge, and the other radio with
>> me walking around the block, up to about 150m away -- with the signal
>> path obliquely through perhaps 8 or 10 houses, fences, cats, dogs,
>> trees and everything else.
>>
>> With good clear line of sight, and a low noise floor, ranges of 10km
>> or more are possible, with some evidence pointing to the actual limit
>> being around 80km - 120km in very ideal conditions.
>>
>> We have already managed to get Serval Mesh traffic, including some
>> Rhizome transfers (but not yet voice) running over one of these links:
>>
>> servalpaul.blogspot.com.au/2013/02/breaking-wifi-barrier-serval-mesh.html
>>
>> We think a complete Mesh Helper Device, including these really nice
>> radios could be built and sell for <US$200.  It may also be possible
>> to use a cheaper compatible (but slightly lower performance) radio and
>> get the price down to <US$100.
>>
>> The RFD900 firmware only does point-to-point communications, but it is
>> entirely possible to make it do "ad-hoc" point-to-multipoint
>> communications.  Perhaps this is something for us to look at as a
>> follow on after our current work block is complete.
>>
>> We are hoping to have a couple of these with us in New Zealand in a
>> couple of weeks for the KiwiEx field trial. General outline of our
>> thinking for KiwiEx at present is at:
>>
>>
>> http://developer.servalproject.org/dokuwiki/doku.php?id=content:exercises:kiwiex2013
>>
>> If there are other things people would like tested while we are there,
>> let me know, and we will endeavour to cover them.
>>
>> Paul.
>>
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>
>
>
> --
> Ben West
> http://gowasabi.net
> ben at gowasabi.net
> 314-246-9434