Re: [Discuss-gnuradio] USRP and GSM

[Berndt Josef Wulf]

On Saturday 29 January 2005 11:11, 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?
>
> 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?
>
> Thanks for your time and for sharing GNU Radio.

Hi Pete,

GSM900 defines 124 channels at 200kHz bandwidth for each, the uplink 
(890-915MHz) and the downlink (935-960MHz) bands. However, the number of 
channels used at any one location depends on factors such as site 
distributions, frequency re-use patterns, traffic density and is likely to be 
much smaller than the total number of channels available.

One solution may be to obtain network information from the BCCH carrier, 
interpreting its data and only processing the active GSM spectrum or cells of 
interest, hence managing the data bandwidth within the capabilities of the 
USRP.

cheerio Berndt

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