Re: [Discuss-gnuradio] OFDM / DAB demodulation

[Jens Elsner]

I resampled all the data to do a proof-of-concept. The frames are only a
small part
of the "chunk" variable. What I am getting is a fairly nice pi/4 DPSK.
Only that
in between OFDM Symbols (there are 76 in a frame) there is some sort of
random
phase jitter. And I am clueless what it could be. Frequency offset is
compensated,
the channel doesnt vary that fast.

Jens

4/1/2006, "Clark Pope" <address@hidden> вы писали:

>Resample is okay, but beware of any other filter operations you are doing on
>the data in a block-wise manner, e.g. chunks. You have to remember to save
>the initial conditions:
>
>[chunk_filt, z] = filter(b,a,chunk,z);
>
>This would cause phase discontinuities at the edges of each block.
>
>-Clark
>
>>From: Jens Elsner <address@hidden>
>>To: address@hidden
>>Subject: Re: [Discuss-gnuradio] OFDM / DAB demodulation
>>Date: Sat, 1 Apr 2006 10:48:29 +0200
>>
>>To resample, I used the Matlab "resample" function
>>
>>chunk_resamp = resample(chunk, 2048, 2000);
>>
>>It's basically an FIR low-pass - phase is linear.
>>
>>I'll try again today without resampling, but then the timing is
>>pretty much screwed up.
>>
>>Jens
>>
>>On Fri, Mar 31, 2006 at 04:28:14PM -0800, Eric Blossom wrote:
>> > On Fri, Mar 31, 2006 at 05:10:40PM -0500, Clark Pope wrote:
>> > > 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
>> > >
>> > > >>
>> > > >> 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.
>> >
>> > How did you resample from 2.000MHz to 2.048 MHz?
>> >
>> > Eric
>>
>>
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>
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