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

[Tom Rondeau]

On Wed, Apr 30, 2014 at 3:22 AM, Martin Braun <address@hidden> wrote:

On 29.04.2014 23:22, zielalaoui wrote:

Hi all,
I am trying to build transmission on air by using USRPs N210. The
transmission is good with MPSK modulations but when i try to use 16_QAM i
could not receive data (0 bytes at the reception). I tried to adapte
transmission power, gain at the tranmitter, gain at receiver, samp_rate but
the reception file still always empty. This is my flow graph:
Tx: file source => packet encoder => QAM mod => mult constant = 0.4 => UHD
usrp sink
Rx : UHD usrp source => QAM demod => packet decoder => file sink
samp_rate= 2M
samples/symbol = 8
centre frequency=2.4G
Any proposition will be appreciate
Thanks to all

There are lots of things that can go wrong. At 16-QAM, you'll likely have some bit error, and you have no FEC to compensate for that.

Martin

Also synchronization. That QAM Demod you have right after the USRP source block in your email suggests you aren't doing proper timing, freq, and phase recovery.

Tom