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Re: [Discuss-gnuradio] benchmark experiment

From: Brian Padalino
Subject: Re: [Discuss-gnuradio] benchmark experiment
Date: Thu, 19 Jun 2008 16:19:14 -0400

On Thu, Jun 19, 2008 at 3:58 PM, mehdimolu <address@hidden> wrote:
> hi,
> I try to use benchmark in gnuradio. When I use gmsk which is default
> modulation scheme there is not error in detection of packets in the receiver
> but when I use other modulation options like dbpsk detection of all packets
> fail.
> why does it happen?
> thanks,
> Mehdi

You may have a problem with peak power output and
clipping/compression.  GMSK is a constant envelope waveform meaning
you have a 0dB PAPR (Peak-to-Average Power Ratio).  Because of this,
you can run your PA (power amplifier) at full power and in a
non-linear region and still get a great looking signal.

QPSK (when filtered through an RRC FIR filter), has about a 3dB PAPR
meaning the peaks of the signals are 3dB higher than your average
power you're transmitting.  Try backing off the amplitude
significantly and see if it fixes your problem.

Now, for future reference, you need to be a bit more specific with
your queries to this mailing list.  Describing EXACTLY what you are
doing is usually pretty helpful.  Links to web pages which contain
code, graphs, and even a pictorial diagram of what exactly you are
doing and what is failing is also helpful.

If you wish to create new functionality and would require help or
guidance - explaining what and why you are trying to do something is
also helpful.  There may possibly be code written or other people
interested.  Being verbose on this mailing list is extremely welcome
and encouraged!

What is NOT helpful is a 3 sentence e-mail describing a utility
provided in software and absolutely no other information with regards
to your physical setup.

I only point this out to help you with getting your questions answered
instead of having them go unanswered due to lack of information.
There is a lot of experience and knowledge on this mailing list, but
to tap into it you must know how to ask your questions.

Good luck in finding your answers.


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