Questions about synchronization and modulation in benchmark

GNU Radio
1

Hello All,

I have problems in demodulating code from benchmark qpsk. please help me
with answering my question.

  1. Why there are no bpsk, qpsk or 8psk in the modulation option ?there
    are
    only dbpsk , dqpsk, d8psk.

  2. Is there any different synchronization besides gr_mpsk_receiver_cc?
    3.I don’t know about costas loop in detail, but in my knowledge, this
    module
    using modified Muller for the algorithms and I see that this method is
    just
    using 1 sample per symbol in recovering symbol timing with mu as a base
    for
    correction? am i right? if yes, may i know why they use just 1 sample
    per
    symbol?

  3. Is this costas loop just for differential modulation ? I have a
    problem
    in decoding the qpsk if frequency offset occurs.

    • In the transmitter side , I just took of the diff dec . and in the
      receiver side, I made diff_phasor as a delay detector and recovered it
      into
      qpsk based on preamble.
      (it works while i am using bencharmark loopback without frequency
      offset
      and time error)

  4. if no 3 is yes, please help me in solving this problem. I have no
    idea.

Best Regards,

Tim

2

Please help me anyone

Tim

On Fri, Jan 29, 2010 at 10:06 PM, Timothy Lawrence Sitorus <
[email protected]> wrote:

is just using 1 sample per symbol in recovering symbol timing with mu as a
4. if no 3 is yes, please help me in solving this problem. I have no idea.

Best Regards,

Tim

–

Best Regards,

Timothy Lawrence Sitorus
Komaba Campus Blding, 5th Floor,
Research Center for Advanced Science and Technology,
The University of Tokyo.
4-6-1, Komaba, Meguro-ku, Tokyo 153-8904, Japan.
Tel: +81-3-5452-5368
Fax: +81-3-5452-5369
Mail:[email protected] [email protected]
Mobile phone: 090-1860-2859

3

HI all,

Please anyone help me.

Is there anyone succeeded to modulate qpsk, even frequency offset
occurs?

Best Regards,
Tim

4

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

5

there is some work from Thomas S. 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:

Discuss-gnuradio mailing list
[email protected]
Discuss-gnuradio Info Page

–
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6

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 <

7

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 <

8

Thanks Mir

Please tell me if there is some results.

Tim

9

Hi Tom,

Thanks for answering all my questions. Recently I am reading the source
of
gr_mpsk_receiver module and starting to understand how the algorithm
consumes sps > 1 and produces one output.

Thanks for the information about dqpsk2.py. I didn’t now about it. I
will
test it soon.
Btw ,can you tell me why the phase ambiguity issues occur? is it
because
gr_mpsk_receiver do not divide clock recovery and frequency offset
separetely?
I checked dqpsk2.py source and saw that you are not using
gr_mpsk_receiver
anymore.

Thanks,

Tim

10

On Fri, Jan 29, 2010 at 7:06 AM, Timothy Lawrence Sitorus
[email protected] wrote:

Hello All,

I have problems in demodulating code from benchmark qpsk. please help me
with answering my question.

  1. Why there are no bpsk, qpsk or 8psk in the modulation option ?there are
    only dbpsk , dqpsk, d8psk.

We don’t use non-differential modulation because we didn’t want to
work into the code the phase ambiguity issues involved. It’s a simple
matter of removing the differential encoder in the modulator and
decoder in the demodulator, but then you’ll have to add your own
method of handling the phase rotation.

  1. Is there any different synchronization besides gr_mpsk_receiver_cc?

You can use the clock_recovery_mm_cc and costas_loop_cc blocks
separately. In the latest master in the Git repo, I have just added
dbpsk2 and dqpsk2 that use a whole different system of synchronization
that has proven much more robust. It still needs a little work, which
is why we haven’t replaced the old dbpsk and dqpsk modules, although
this should eventual obsolete them.

In the new way of synchronization in these blocks, I used a band-edge
filter frequency lock loop for frequency acquisition, a polyphase
filterbank clock recovery algorithm, and the Costas loop for phase
correction.

3.I don’t know about costas loop in detail, but in my knowledge, this module
using modified Muller for the algorithms and I see that this method is just
using 1 sample per symbol in recovering symbol timing with mu as a base for
correction? am i right? if yes, may i know why they use just 1 sample per
symbol?

No, the block takes in sps > 1 (2 or 4 samples generally) and produces
one output.

  1. Is this costas loop just for differential modulation ? I have a problem
    in decoding the qpsk if frequency offset occurs.
    • In the transmitter side , I just took of the diff dec . and in the
      receiver side, I made diff_phasor as a delay detector and recovered it into
      qpsk based on preamble.
      (it works while i am using bencharmark loopback without frequency offset
      and time error)

No, the costas loop is not specific to differential modulation and
will work with non-differential. It doesn’t have a wide bandwidth,
though, so this is probably your problem. It’s also why I switched the
frequency tracking method in the dXpsk2 modules.

Tom