1 Sep
2011
1 Sep
'11
2:30 p.m.
On Thu, Sep 1, 2011 at 7:30 PM,
<baseband-devel-request(a)lists.osmocom.org> wrote:
Hello,
Thank you Dieter and Scott for your fast responses.
---------- Forwarded message ----------
From: "Dieter Spaar" <spaar(a)mirider.augusta.de>
To: baseband-devel(a)lists.osmocom.org
Date: Thu, 01 Sep 2011 07:59:31 CEST
Subject: Re: 900MHz packet radio?
Hello Paul,
On Thu, 1 Sep 2011 13:41:11 +0930, "Paul Gardner-Stephen"
<paul(a)servalproject.org> wrote:
I had assumed that the modulation would be fixed in this way, and it
is not an issue for what I am wanting to do. In fact, it makes a lot
of sense to keep the GSM modulation for simplicity.
So, as the open-source group with the most experience reprogramming
baseband radios, what is the feasibility of creating a
proof-of-concept using the types of phones you already work with to
send and receive arbitrary data packets without reliance on a cell
tower (even for time synchronisation)?
It depends a lot on what you want to use on the lower layers
(e.g. Modulation). The TI Calypso based phones have a built-in
GMSK hardware modulator, so it is GMSK. Also the symbolrate is
fixed to the one used by GSM. Then there is the DSP which does the signal processing
work. Its
again tied to the GSM standard (format of the burst and length).
It might be possible to put something else into the relativ small
RAM inside the DSP, but this could be a huge effort.
This seems to me to be the hardest part of the whole process.
When you say a huge effort, do you think it would be possible for
someone to be able to get something working if they were able to work
on it full-time for a few months?
Besides that you have to modify the hardware of the
phone (remove
a filter) so that the phone can receive another phone. But this
is probably the smallest problem of all.
Indeed, this is the smallest problem I think. In fact, if we use the
part of the ISM915 band that is right next to the GSM band, then my
understanding is the filter will only attenuate by a few db --
although I am happy to be corrected on this point.
Best regards,
Dieter
--
Dieter Spaar, Germany spaar(a)mirider.augusta.de
---------- Forwarded message ----------
From: Scott Weisman <sweisman(a)pobox.com>
To: baseband-devel <baseband-devel(a)lists.osmocom.org>
Date: Thu, 1 Sep 2011 10:18:21 +0300
Subject: Re: 900MHz packet radio?
I think you would be better taking your existing hardware, which must be somewhat custom
to begin with (since it works over wifi) and use something like a HopeRF module
(http://www.hoperf.com/) or similar. HopeRF has transceivers with power output up 100mW,
data rates up to 256kbps, and a choice of 4 different bands (315, 433, 868, 915). This
sounds like it would be a far easier choice to incorporate into your already-working
system than hacking OsmocomBB-capable phones.
There is a lot of development from many different companies in this area and quite a bit
of hacker activity as well.
We are exploring that path simultaneously, and have a batch of the
exactly the HopeRF modules that we will use, to demonstrate the range
and utility of using the ISM band for long-range mesh telephony.
But it is important also that we prove that it can be done using the
baseband radio in a phone.
We all know that it can if we have the freedom to design the baseband
radio from scratch, but that it can also be done it is also important
that I show that for handsets where the baseband radio can be
reprogrammed without changing the hardware.
It all boils down to being able to deflect any straw arguments that
might be raised against the feasibility of long-range mesh telephony
using baseband radio.
Paul.
Scott
On Thu, Sep 1, 2011 at 7:11 AM, Paul Gardner-Stephen <paul(a)servalproject.org>
wrote:
Greetings all,
At the Serval Project we have created a mobile mesh telephony system
that currently works over wifi.
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baseband-devel mailing list
baseband-devel(a)lists.osmocom.org
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From the outset, we have wanted to get it working
on the ISM915 and/or
ISM868 bands that are located adjacent to the GSM 850/900
frequency
allocations.
My initial investigations and enquiries indicate that this should be
possible by creative programming of the baseband processor in many
models of phones. The trick, as I suspect you well know, is the
difficulty in getting the information and tools required to reprogram
these radios.
I am now in a position to potentially fund further work on this.
So, as the open-source group with the most experience reprogramming
baseband radios, what is the feasibility of creating a
proof-of-concept using the types of phones you already work with to
send and receive arbitrary data packets without reliance on a cell
tower (even for time synchronisation)?
I know there are a lot of constraints and problems, but I am most
interested in creative solutions that can get us to a working
prototype, however crude, that can be used to demonstrate the
feasibility of what I am proposing.
If this discussion is off-topic here, I am happy to hold the
conversation at the serval-project-developers google group, but I am
equally comfortable with it continuing here.
Thanks in advance,
Paul Gardner-Stephen.
Shuttleworth Telecommunications Fellow at Flinders University.