[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] GMSK: GSM initial phase for a burst

From: Jeffrey Karrels
Subject: Re: [Discuss-gnuradio] GMSK: GSM initial phase for a burst
Date: Mon, 18 Jun 2007 16:02:34 -0400

Great suggestion!

I have attached a couple of things:
1) The IQ plot (1e6 sample rate)
2) The burst data (MATLAB array)
3) The da vs time plot. (1 symbol = 3.69us)

Another quick question.  I can now see that after the amplitude ramp
up that there is a short section of negative phase movement (.7
radians clockwise) prior to the remaining counterclockwise rotations.
Should I expect a full (-pi/2) to start off the burst? Is my sampling
rate just not high enough to catch the remaining rotation? Any other

Thank you for your time

On 6/18/07, Matt Ettus <address@hidden> wrote:
Jeffrey Karrels wrote:
> Hello everyone.
> I am looking at the frequency correction burst of a GSM signal.
> According to spec the original data defines 148 bits of 0 that are
> differentially encoded and GMSK modulated.  After the data goes
> through the differential encoder it ends up as [-1,1,1, (142 1s),
> 1,1,1].  I have taken this burst and plotted I vs Q (which is
> attached).  I was expecting to see the amplitude ramp up followed by a
> negative pi/2 phase shift, followed by 147 positive pi/2 phase shifts,
> and a ramp down. I never see the initial negative phase shift though.
> Am I missing something in my sanity? Any thoughts or ideas?

Its hard to read the graph like that.  Plot angle vs time or even
better, derivative of angle vs. time.


Attachment: fcch_data.zip
Description: Zip archive

Attachment: fcch_iq.png
Description: PNG image

Attachment: fcch_da.png
Description: PNG image

reply via email to

[Prev in Thread] Current Thread [Next in Thread]