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Re: [Discuss-gnuradio] USRP and GSM

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] USRP and GSM
Date: Sat, 29 Jan 2005 11:12:46 -0800
User-agent: Mutt/1.5.6i

On Sat, Jan 29, 2005 at 12:41:36AM +0000, Pete Chown wrote:
> I have to develop some equipment for receiving GSM 900 and GSM 1800. 
> (Fortunately, it doesn't have to receive both at the same time!) It would
> be good to do this with GNU Radio and the USRP, but I'm not sure what
> performance I can expect.  I hope you don't mind if I ask a few questions.
> The spectrum allocated to GSM is split into a number of carrier
> frequencies, which are 200kHz apart.  Each of these frequencies can carry
> up to eight channels, with a data rate of about 34kbps each.  (This
> includes framing bits and so on, so much less useful data is actually
> transmitted.)  As this data rate is quite low, presumably it would be well
> within the capacity of GNU Radio to decode it in real time?

Definitely possible in real time, though without further testing, 
I can't say how many RF channels we can handle concurrently.

> According to the wiki, the USRP can push about 6MHz of spectrum over the
> USB bus.  This is quite a bit lower than the frequency range allocated to
> GSM, so I assume it would not be possible to receive all the carrier
> frequencies at once.  However, no single base station uses all the
> frequencies.  Neighbouring cells must not interfere with each other, so
> they must use different frequencies.  So, does my 6MHz have to come from a
> single contiguous range of frequencies?  Alternatively, can I ask for a
> number of 200kHz bands, with some bands in between that I'm not interested
> in?

Assuming that the IF bandwidth of the RF front end is wider than 6
MHz, the bands do not have to be contiguous.  You can use the digital
down converters in the FPGA to select 1, 2 or 4 distinct bands.  You'd
probably then subdivide those bands into individual channels in software.

> Thanks for your time and for sharing GNU Radio.

You're welcome!


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