Re: [Discuss-gnuradio] Questions about synchronization and modulation in benchmark

I am not very good at this either but I will try the same thing first on my computer and see if I can help. 

On Tue, Feb 2, 2010 at 5:50 AM, Timothy Lawrence Sitorus <timothy.l.sitorus@gmail.com> wrote:

Hi Mir thank for the reply.

Sorry for my lack of information. Actually my problem is not in the modulator. But in the Frequency offset or timing error. I have removed the differential encoder in the path.
 The path worked when i executed it in one computer without usrp2(like benchmark_loopback.py). But when i executed it between two usrp2, I couldn't receive it in properly. the signal can't be locked.
I plot the result from gr.mpsk_receiver (see attached file).

Any suggest?

 

On Tue, Feb 2, 2010 at 5:21 PM, Mir M. Ali <mirmurtuza@gmail.com> wrote:

Check the source code of costas loop and Mueller Mueller clock recovery blocks. They have the link to the reference papers used for the implementation.

Regarding your bpsk/dbpsk question. There is a differential encoder block in the transmit_path of this modulator. Remove this from the connect path and you will get bpsk.

Thanks,
Mir

On Sun, Jan 31, 2010 at 2:54 AM, Timothy Lawrence Sitorus <timothy.l.sitorus@gmail.com> wrote:

Hi Adib

Thanks for the reply.

I check it in the net and download it. I don't know about costas loop and clock recovery in detail. may I know how they they estimate frequency offset, and recover it?
as far as I know,  they are using gr.quadrature_demod_cf(1) & and subtract it using gr.single_pole_iif_filter_ff(alpha) for frequency offset?is it right?

Tim

On Sun, Jan 31, 2010 at 4:03 PM, adib_sairi <adib_sairi@yahoo.com> wrote:

there is some work from Thomas Schmid which modulate and demodulate O-QPSK
which mean for IEEE802.15.4 standard.. you can search and download the code
online. good luck..

Adib

Timothy Lawrence Sitorus wrote:
>
> HI all,
>
> Please anyone help me.
>
> Is there anyone succeeded to modulate qpsk, even frequency offset occurs?
>
>
> Best Regards,
> Tim
>

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