Good Day,
The overarching goal of my project is to build and test a one-way
transmitter/receiver pair. The bare-bones block diagram is UDP input -->
16QAM modulation --> bladeRF Tx --> channel —> bladeRF Rx -->
polyphase clock --> 16QAM demod --> UDP output
When I sent this over the air I kept getting a garbage/unexpected output
so now I’m going through the system and simming things again. For now
I’ve cut out the UDP source and am testing specific values. My
questions/problems:
-
If I use a random source set to (0,1), or a constant source set to 0,
the Qt Gui Time sink displays a flat line @ 0. But if I use a random
source of (1,2) --which should output “1”-- or I use a constant source
of 1, the Gui Time sink doesn’t display a flat line @ 1 but a bunch of
discrete points, mostly 1’s but apparently also some 0’s. -
Likewise, input 0 gives a Gui Constellation output that one would
expect for a grey-coded symbol of “0000” (this and ONLY this
constellation point appears). However, input 1 doesn’t generate one
point at “1111”, but the full 16-point constellation, which means the
QAM Mod block is outputting a bunch of mixed 1’s and 0’s. I realize the
block causes ISI but why is it apparently so severe for an input of “1”
and not for an input of “0”? -
What is the exact constellation used by the QAM block? There are
multiple ways to grey-code 16QAM…you’ll notice that my LMS-DD
Equalizer is disabled. I think the QAM Constellation Object that I
specified doesn’t match the grey coding of the QAM Mod. -
Finally, I was testing my transmission @ 801MHz. I noticed that the
radio is broadcasting even if the UDP source has no inputs (i.e. I’ve
typed nothing, or not sent a file). How do I get the radio to NOT
broadcast unless it actually receives some data input? Can I not do this
in GNURadio, and have to dig into the python code by hand?
Tx Setup: Sony Laptop, i5 dual core 4GB RAM, bladeRFx40 over USB3.
Debian Jessie + GNURadio 3.7.5
Rx Setup: custom desktop, i7 quad core + 16GB RAM, bladeRFx40 over USB3,
GNURadio 3.7.5 live persistent USB thumb drive (16GB, over USB3).