Dear Ravi,
this is no good. We've told you several times now that you need to
fix things, and you just come back with your same broken
configuration and ask the same question. It's totally OK if you just
say "hi, sorry, I did not understand your answer, could you explain
this and that", but not addressing what we wrote is really getting
frustrating, for me at least.
Let me repeat what Tom and others have tried to explain to you:
There's no single "switch" you can flip so that your transmission
works. We have pointed out methods to help you optimize your
transmission, for example looking at the RX spectrum and adjusting
gains until it looks "good". We can't, just by looking at the
problems the receiver script has, tell you what you need to do.
Really. Please stop asking the same question over and over again,
and ask different questions. A clever one would, for example, be:
I've got this spectrum (screenshot), and it doesn't look like
<modulation I'm expecting>. Increasing the gain just made
things worse."
I hope this leads you to a path that promises more success than what
you're currently doing.
So: You've gotten a lot of responses. You might need to
consider how much consultation costs you would have caused if we
weren't doing this out of interest but for money -- so please
explain what you did not understand in our answers, we really
want to help!
Here's my rather comprehensive answer from last time:
I don't know whether your questions have been solved. I think Tom
has extensively discussed [1] a lot of things that can happen
here, so you're aware of the fact that transmission-wise, there's
the whole world of radio channel that could distort your signal.
So let's talk a bit about what's wrong with the hardware settings
you use:
Transmitter
No gain specified.
You should really specify the gain. That defines how much power
comes out of your antenna. For a start, you might want to use a
moderately high setting, so something like 25 would be good.
UHD Warning:
The hardware does not support the requested TX sample rate:
Target sample rate: 0.050000 MSps
Actual sample rate: 0.250000 MSps
Symbol Rate: 25000.000000
Requested sps: 2.000000
Given sample rate: 250000.000000
Actual sps for rate: 10.000000
Requested sample rate: 50000.000000
Actual sample rate: 250000.000000
I you must really fix that. As I've explained two weeks ago:
as the warning says, the sampling rates
you're trying to use on both TX and RX side are lower than the
minimum sampling rates. You should fix that. It's not hard, you
just need basic understanding of what the program does.
To spell this out: the data rate together with the samples per
symbol define your sample rate. For your USRP, this rate must be
at least 250kS/s. The effect of you not correcting your flow graph
is that the script generates a signal that the USRP converts to an
analog signal at five times the speed that you specify -- this
means all frequencies with your complex baseband are five times as
high!
..............................................................................................U...............................................................
Oh, that's bad. You're seeing an U like "Underrun", which means
your PC was too slow at supplying samples to the USRP. This
seriously breaks your signal. Now, I don't know your computer, but
I know that 250kS/s is really no load for any PC nowadays -- I
haven't seen any PC being too slow for this very low rate. How old
is your PC? Are you doing something else on it? Or are you running
in a virtual machine?
terminate
called after throwing an instance of 'uhd::runtime_error'
what(): RuntimeError: usb tx2 transfer status: 1
Aborted (core dumped).
That's even worse. It can happen if you cancel the script using
"ctrl+c", but this looks like there is something seriously wrong
with your USB2 controller. Again, what computer are you using?
Receiver
No gain specified.
Setting gain to 56.250000 (from [0.000000, 112.500000])
The same as above. More gain = more signal power, but don't overdo
it. You will need to experiment. As Tom explained, letting the
transmitter run and observing the spectrum with something like
usrp_spectrum_sense will help you determine settings that make
sense. First, however, I can not stress this enough, fix your
sample rate issue!
UHD Warning:
The hardware does not support the requested RX sample rate:
Target sample rate: 0.050000 MSps
Actual sample rate: 0.250000 MSps
Symbol Rate: 25000.000000
Requested sps: 2.000000
Given sample rate: 250000.000000
Actual sps for rate: 10.000000
Requested sample rate: 50000.000000
Actual sample rate: 250000.000000
The same as above. Both your RX and your TX are running at 250kS/s
instead of the 50kS/s that you specified. Luckily, this means that
the effect kind of cancels itself out -- still, fix that!
General
How would I be able to know if the USRP is maintained in the same
channel?
You set both TX and RX to the same frequency, and since there is
only one physical medium (the space between the RX and TX
antenna), you can be sure. There's no concept like "this specific
part of spectrum belongs to channel number 12" in the physical
world -- just frequencies, and Maxwell's Equations governing the
propagation of radio waves.
What commands do I need to give so that the packet is received
correctly as n_right=1.
Tom has explained enough that it's not like that. You will need to
find out yourself.
Best regards,
Marcus
PS: Do you have a preferred name to address you by? "Ravi" is as
fine to me as "John", so I'd suggest you pick one and stick with
that, because it's less confusing.
[1] "Communication Problems between 2 USRP" email thred
Best regards,
Marcus
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