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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!
Eric