Re: [Discuss-gnuradio] OFDM / DAB demodulation

[Jens Elsner]

Forgot to answer your questions:
The subcarrier spacing is 1 KHz, 1536+DC Carrier (unused) = 1.537 MHz
I sampled 2 MHz (USRP, dec 32). Then I sampled up to 2.048 MHz since
1/2.048MHz is the basic timing unit in the standard.

I tried again without resampling - the random phase jitter is still
there. Plus the
timing problem - the standard requires 2.048 MHz to I get decimal offset
values.
For example at the 2.000 MHz the guard intervall has the length 492.1875.

Do you think downsampling will work better than upsampling? I'll try that
tomorrow.

3/31/2006, "Clark Pope" <address@hidden> вы писали:

>I would doubt that unless your USRP is defective. The phase noise should
>only become a major factor at baud rates below about 10 kbaud.
>
>What's the actual bandwidth of the DAB signal? Did you try collecting at 4
>MSPS and then downsampling to the FFT sample rate? Maybe the CIC or
>compensation filter transition are distorting the final result.
>
>-Clark
>
>>From: Jens Elsner <address@hidden>
>>To: address@hidden
>>Subject: Re: [Discuss-gnuradio] OFDM / DAB demodulation
>>Date: Fri, 31 Mar 2006 19:28:38 +0200
>>
>>After some thinking: Could this be phase noise? If it is, which
>>oscillator is at fault? The TVRX frontend? The max. phase jitter equals
>>roughly 100 Hz.
>>
>>On Fri, Mar 31, 2006 at 05:08:54PM +0200, Jens Elsner wrote:
>> > Good morning,
>> >
>> > I sampled a local DAB radio station at 225.648 MHz, decimation factor 32
>> > with the USRP/tvrx.
>> >
>> > DAB is using COFDM with pi/4-DPSK on 1536 subcarriers (see www.etsi.com,
>>standard
>> > EN300401 for details). I wrote some Matlab code to demodulate the
>> > signal. The data is resampled from 2 MHz (URSP) to 2.048 MHz (DAB
>>Standard).
>> > A frequency offset is compensated manually.
>> >
>> > It works so far, only one problem arises: The I/Q signal diagram jumps
>> > and jitters randomly by up to pi/8. What could be the problem? I am
>> > absolutely clueless - the frequency offset is compensated perfectly.
>> >
>> > My ultimate goal is to implement OFDM de/modulation and a DAB receiver
>> > in gnuradio.
>> >
>> > Greetings,
>> > Jens
>> >
>> >
>> >
>> > _______________________________________________
>> > Discuss-gnuradio mailing list
>> > address@hidden
>> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>>
>>
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