12 Mar
2011
12 Mar
'11
11:33 p.m.
I was wondering how to transmit and receive using layer1. I have
been reading some of the gsm specs. I have been looking around in the
source code a lot, and there many functions that are used for transmit
and receive. Which are the right few to use? Is there any way to send
a text message to a different phone by simulating a base station? Do I
need two phones or one phone to transmit and receive as a base station?
Is there any way to make a half duplex base station on a BCCH channel
with only one subscriber phone at a time, and what would that entail
code-wise? Would it be legal to run a very low power base station in
the USA on a different unused cellular band/frequency? I have a lot of
free time since I do school at home and I could probably help develop
some new parts of the osmocom-bb project if you want me to. I know C,
some x86 assembly, and a few other languages. I have also had practice
fixing compile-time errors, and bugs in code. I apologize if this is
too many questions. You don't have to answer them all if you don't want to.
Thank you for helping,
Calvin E. Balke
13 Mar
13 Mar
2:34 p.m.
Hi,
I have been looking around in the source code a lot,
and there many
functions that are used for transmit and receive.
Yes there are ... The actual submission of L2 packets for TX to the DSP is
in prim_tx_nb.c.
This is what gives the DSP the command. But if _all_ the rest of the
environment (basically all the rest of L1) is not in the exact right
state ... it won't do what you ask.
There is no way around it, you have to see L1 in its globality to
understand.
Now if you want the higher function (from the host side), then it's the
L1CTL_DATA_REQ message you must look at.
Which are the right few to use?
Well they all have their role to play. It's not at all like network where
you have 'send a packet' ... here there is a whole context that matters.
Is there any way to send a text message to a different
phone by
simulating a base station?
No.
Do I need two phones or one phone to transmit and
receive as a base
station?
You need much more than that. And before you even think about this, get
more familiar about of a phone works as designed before trying to make it
do stuff it's not designed to do.
Is there any way to make a half duplex base station on
a BCCH channel
with only one subscriber phone at a time, and what would that entail
code-wise?
There is no way to make a 'half duplex' base station, it just won't work.
It's been tried with a modified OpenBTS and without a continuous RF power
signal on C0, the phones won't lock to it.
Would it be legal to run a very low power base station
in the USA on a
different unused cellular band/frequency?
No.
And since the phone can blast > 1W of RF power, you can easily disrupt
stuff so be careful.
For any testing of undesigned functions you should connect the phone in a
closed loop to some testing equipement (network analyzer / MS testers /
spectum analyzers ...).
Or at the very least disconnect the antenna, put a dummy load in its place
and test in a deep basement or something.
Cheers,
Sylvain
4815
days inactive
4816
days old
baseband-devel@lists.osmocom.org
1 comments
2 participants
participants (2)
-
246tnt＠gmail.com -
Calvin Balke