Help: Constellation Receiver

GNU Radio
1

I have gotten the “Constellation Receiver” block so it seems to run
without errors but I don’t see much out. I assume I am suppose to be
feeding it a complex baseband I/Q signal. What do the output “OUT,
SYMBOL, Error, Phase Freq” represent? I am getting signals out of the
Error/phase/freq outputs but nothing out of Out or Symbol.

Const Recv. Parameters: (suggestions anyone?)
Loop bandwidth == 6.28/100
Min Freq Deviation == 0.6
Max Freq Deviation == 0.9

Tom

REF:

Tom,

I am trying to use the Constellation Receiver Block and one of the
Parameters is “Constellation Object”. Is this a pointer to an object and
how/what creates this object? I have looked at the qam.py file but don’t
follow how this relates to placing a block down in gnuradio >>companion.
In GRC u can use

  1. from gnuradio import digital (Using Import block)
  2. my_const_obj = digital.constellation_qpsk() (Using variable block).
    To see other options for creating the constellation object see

http://gnuradio.org/doc/doxygen/classgr_1_1digital_1_1constellation.html
3) In constellation receiver>constellation Object parameter add
my_const_obj.base()

-Adeel

Sent from Yahoo! Mail on Android

2

On Wed, Aug 07, 2013 at 09:17:02AM -0700, tom sutherland wrote:

I have gotten the “Constellation Receiver” block so it seems to run without
errors but I don’t see much out. I assume I am suppose to be feeding it a
complex baseband I/Q signal. What do the output “OUT, SYMBOL, Error, Phase
Freq” represent? I am getting signals out of the Error/phase/freq outputs but
nothing out of Out or Symbol.

Hi Tom,

the constellation receiver is a combined block that does frequency,
phase and timing sync as well as the symbol demapping. The
error/phase/freq outputs are basically ‘debugging’ ports. I assume you
know how a Costas loop works? These ports transmit the error signal
which is part of this feedback loop.

Const Recv. Parameters: (suggestions anyone?)
Loop bandwidth == 6.28/100
Min Freq Deviation == 0.6
Max Freq Deviation == 0.9

Intuitively, I’d say the freq deviation params are off. The loop bw is
OK. To be honest, I keep forgetting how to set these myself, as they
affect the control loop rather than the actual receiver (have you read
these pages?:
http://gnuradio.org/doc/doxygen/classgr_1_1blocks_1_1control__loop.html

)

I don’t know the details of the block by heart, but I suggest you do the
following:
In GRC, connect a QPSK source into a channel model into a constellation
receiver. Start with very little noise, no freq offset.
Play around with the params, and see if the SYMBOL output looks like a
noisy QPSK constellation diagram. That gives you an idea of how the
params should look like. Then play around with frequency offset, phase,
timing etc. in the channel model.

Hope this helped,
MB

Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin B.
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT – University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association