Anyone work with GSM &3G?

Wed Jan 18, 2012 8:10 am   

I am seeking specific information regarding the signal structure of
GSM and 3G.

Does anyone here work for a Telco, or is familliar with the make up
and comparative capabilities of these?

In particular, I am interested in the types of modulation inherent to
these standards which are technically available (utilized or not) for
transmission of _analog_ signals, ie FM, PWM, etc.

Bob Sutton

Wed Jan 18, 2012 9:43 am   

On Tue, 17 Jan 2012 23:51:19 -0800 (PST), Daku <dakupoto_at_gmail.com>
wrote:


Thanks for the link. But it appears to be a bit of a labyrinth. I
suspect even a specialist would be hard pressed to navigate this.

Where are the signal specs?? Occupied frequencies, modulations, etc.

I found this: http://www.techmind.org/gsm/

If one wanted to FM the pulse train with an analog signal, which
component of the signal would be most suitable, without substantial
modifications to the transmitter?

Also the page cited does not give a comparison of the GSM signal
structure with that of 3G.

Bob Sutton

Wed Jan 18, 2012 9:51 am   

On Jan 18, 2:10 am, bobsut...@protolux.com (Bob Sutton) wrote:

Yes, I do work for a Telco, but with more mundane DOCSIS etc.,
Please check http://www.3gpp.org which has a huge collection
of protocol specification/standards documentation for GSM, UMTS
and related protocols, as well as links to other relevant sites.

Wed Jan 18, 2012 9:12 pm   

On Jan 18, 3:43 am, bobsut...@protolux.com (Bob Sutton) wrote:

My initial thought is that your questions are too simplistic to give
any sort of meaningful answer.
GSM and 3G (such as UMTS) are two very different things.

I agree 3gpp is too complex a signalling system for any one person to
digest. Don't bother.
As to occupied frequencies, etc..., that will depend on where the
devices are deployed as each country sets if frequency use
regulations, in concert with international treaties, etc...
You're unlikely to find a single document anywhere with this
information already compiled for you. (And even if you did, how
helpful would that really be?)
Furthermore, the technical parameters (occupied bandwidth,
modulations, etc..) also vary according to an almost bewildering set
of circumstances and conditions, not the least of which are those same
various regulatory environments in which the systems and designs are
intended to operate. So, to the extent you won't find the basics all
nicely summarized, don't expect to discover the drill-down either.

Also, (if I understand your question correctly), you appear to have a
fundamental misconception of how modern-day systems and networks are
built.
Essentially, they are all software-defined radios. So if you want to
"FM the pulse train" of anything with an analog signal (whatever that
means?), your question might really be about how to modify the
software.
Because frankly, if it can't be coded in software, these days it can't
be done.

As to GSM - though that is still a very widely deployed platform, it's
days are definitely numbered (in my humble opinion).
Capacity demands and the relentless march towards "progress" will
eventually push it out the back door in favor of 4G, LTE and future
network designs.

I assume you're either tinkering with some used wireless base station
gear, or are "inventing" some new hopeful intellectual property.
Either way, it certainly seems you are on the outside looking in -
meaning you don't come across as being tightly affiliated with a
carrier, or device manufacturer, supplier, etc....
Now I could be wrong, but my intent was simply to stress that whatever
you're attempting to do is very likely not a trivial undertaking in
any sense.
For the questions you've asked, I would expect a team of engineers to
have to work on a problem like that non-stop for a really large chunk
of time with an amazing budget and resource behind them.
If this is a home-brew project.... well, you can pretty much gather
where I see that's headed.

Best of luck to you though.
-mpm

Thu Jan 19, 2012 12:08 am   

On Wed, 18 Jan 2012 11:12:13 -0800 (PST), mpm <mpmillard_at_aol.com>
wrote:


With due respect, I was hoping for an answer from someone who had done
some study in this area. As I understand the basic GSM and 3G signal
standards are relatively fixed. For example, the carrier, modulation
and keying frequencies.

Accordinly, I would like to find a description of these, and their
characteristics. I am not concerned with local variants, only the
generic capabilities of the transmitter.

Furthermore, without direct experience, I do not see how anyone can
claim the controlling software canot be modified.

Thanks for your time, but someone please re-read my OP and provide a
bit of further information?

Bob Sutton

Thu Jan 19, 2012 1:51 am   

On 19 Jan., 00:08, bobsut...@protolux.com (Bob Sutton) wrote:

google? http://www.radio-electronics.com/info/cellulartelecomms/gsm_technical/gsm-radio-air-interface-slot-burst.php


it is partly so of course it can be modified, anything is possible in
theory

those who makes gsm chipset don't want competion to find out how they
do it, and those who control
the phone frequencies don't want people hacking the gsm baseband in
their phones, potentially screwing
up the network, so good luck


-Lasse

Thu Jan 19, 2012 9:10 am   

On Wed, 18 Jan 2012 15:51:27 -0800 (PST), "langwadt_at_fonz.dk"
<langwadt_at_fonz.dk> wrote:



Thanks. The info there is alot more accessible.

But I would still like to see a commented spectrum analysis plot of 2G
and 3G transmissions.

Bob

Fri Jan 20, 2012 4:33 pm   

On Jan 19, 3:10 am, bobsut...@protolux.com (Bob Sutton) wrote:

What do you mean by "spectrum analysis plot"?
Do you just want to see what these look like off-air with a spectrum
analyzer or receiver?
If so, I can send you that.

I don't see how such a plot would even remotely address what it is I
thought I understood your original post to be about.
Is it that you want to frequency modulate some portion of the
underlying "whatever" that constitutes the actual waveform that is
broadcast by a cellular or PCS 3G base station?
And whatever that FM'd portion is, it would constitute some additional
"information" that would be superimposed on the signal. Is that
correct?
(I'm using the terms "whatever" and "information" here as a
placeholders so we don't get into a pissing contest.)

Because if so, I'm certain that is not possible (at least for CDMA, W-
CDMA, UMTS and LTE) without totally destroying the usability of the
signaling format.
For one thing, you would lose UE synchronization with the network.

Otherwise, I have no idea what you're talking about.
My familarity is with the Ericsson UMTS, and Nokia GSM equip.
Again, best of luck. -mpm