Re: [Discuss-gnuradio] On air 16_QAM transmission problem with USRP N210

[Tom Rondeau]

On Fri, May 2, 2014 at 11:08 AM, Martin Braun <address@hidden> wrote:

On 02.05.2014 16:59, zielalaoui wrote:

Hi to all,
I resolved my problem and I want to share the solution
The problem was the amplitude in the QAM demod block input. I checked the
constellation in the transmitter directly before UHD usrp block for being
sure the the constellation points are good depending on the samples/symbol
value (8 worked good). After that i just try to adapte the amplitude signal
in reception by adding gain for to have the same signal which i had in my
QAM simulation. Like that the transmission worked good.
Zakaria

Zakaria,

generally, your equalizer should be taking care of that. Adjusting gain is an unreliable method, since the actual attenuation of your signal over-the-air is a function of many things.

But nice that your experiment is working!

Martin

Zakaria,

First, great that you got it working!

Martin makes a good point in general. One reason I mentioned the amplitude in my post is because I know that our consetllation objects used in the constellation_receiver has some strange slicing requirements. They expect the constellation to have the symbols at certain points in complex space (instead of, for instance, estimating the maximum energy of the constellation and scaling based on that). Using the LMS_DD equalzier with the same constellation object for the QAM modulation you're using will do what Martin is suggesting.

Tom