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Re: [Discuss-gnuradio] GSM spectrum: Invisible 200kHz carriers?
From: |
TheOperator |
Subject: |
Re: [Discuss-gnuradio] GSM spectrum: Invisible 200kHz carriers? |
Date: |
Fri, 3 Jun 2011 01:14:26 -0700 (PDT) |
Ben Wojtowicz wrote:
> Are you saying that you are seeing 4MHz wide signals? Or are you seeing
> ~200KHz wide signals seperated by 4MHz?I see about 200kHz wide signals
> spaced 4MHz.
Ben Wojtowicz wrote:
> If you are seeing ~200KHz wide signals spaced by 4MHz, these most likely
> are
> GSM signals. The spec states that the spacing between adjacent channels
> is
> 200KHz, but that does not mean that an operator will place all of their
> channels next to each other. In fact, it would be bad if they did this.
> Keep in mind that the spacing between channels is 200KHz, but the occupied
> bandwidth of a GSM signal is ~270KHz. This means that if GSM channels are
> placed next to each other, ICI will increase significantly. Typically
> what
> is seen is a very sparse scattering of channels across the band.Thanks for
> the explanation, this makes sense. The channels are not exactly 200kHz
> wide however (see screenshots), but according to the frequencies, they
> have to be GSM.
I used this little system along with some GUI elements:
http://old.nabble.com/file/p31763653/gsm-900-blocks.png
The resulting spectrum looks like this:
http://old.nabble.com/file/p31763653/gsm-900.png
Such a peak has the following shape. Most of the power is distributed within
~50kHz. Do these smaller peaks have a special meaning?
http://old.nabble.com/file/p31763653/gsm-900-zoomed.png
--
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http://old.nabble.com/GSM-spectrum%3A-Invisible-200kHz-carriers--tp31761278p31763653.html
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