Hi George,
that flow graph doesn't frequency-hop :) It does something different,
rather cool. Please correct me if I got anything wrong about your
self-written blocks below:
What you do is:
"VCO generator":
Produces always the same 10240-long vector with pseudo-random values,
"Repeat":
Repeat that vector you get 100 times (but that makes no difference, you
could have just taken 100 vectors from "VCO generator", they are all the
same)
This does **not** repeat the elements within the vector 100 times
"VCO (complex)":
Takes every input values and uses it (scaled with a factor) as phase
increment relative to the last value it has generated.
With the uncorrelated random [0,1] source at the input, and the scaling
being such that the phase increment range is always [0;2pi], this just
generates a pseudo-random point on the unit circle each output item
"Complex Conj":
Well, takes the complex conjugate of each item individually – still just
points of uncorrelated random phase!
"Multiply":
You're multiplying the samples from your reception with a different
sample each from a repeating, white pseudorandom noise:
This is spectral whitening :) But not frequency hopping.
Best regards,
Marcus
On 4/28/23 14:03, George Katsimaglis wrote:
Hi,
Thanks for the answers.
I attach the Rx flowchart and grc of the frequency hopping. I have
successfully used it on QO100 satellite.
George SV1BDS
Στάλθηκε από το Ταχυδρομείο Yahoo σε Android
<https://go.onelink.me/107872968?pid=InProduct&c=Global_Internal_YGrowth_AndroidEmailSig__AndroidUsers&af_wl=ym&af_sub1=Internal&af_sub2=Global_YGrowth&af_sub3=EmailSignature>
Στις Πέμ, 27 Απρ, 2023 στις 14:57, ο χρήστηςMarcus Müller
<mmuel...@gnuradio.org> έγραψε:
Hi George,
> Also I have implemented 1.000.000 hops/sec frequency hopping at
QO100 satellite, spread
> over 1 MHz, using 10240 different frequencies.
> Is this project of general interest?
Well, that's impossible to say, but honestly: it probably is! And
also, you shouldn't care
too much :) It's cool in any case!
My advise is: Just put it out there.
But I do have signal theory questions:
We know that if a signal has a bandwidth of 1 MHz, we can
(complex) sample it and contain
all its signal content with a sampling rate of 1 MS/s.
If you're doing a million hops per second, how are you achieving a
bandwidth of only 1
MHz? That means that every hop only gets a single sample, and you
can't signify
"frequency" with just a single number.
So, I might have misunderstood you there, but it would seem what
you claim to have done is
mathematically not possible :(
> I create this script using Python to create QAM constellations
points.
> May be of general interest.
It's nice, but GNU Radio already comes with that!
from gnuradio import digital
constellation = digital.constellation_16qam()
points = constellation.points()
(and you can just use digital.constellation_16qam().points() in a
GRC block parameter, no
need to build a string!)
These are also power-normalized to 1.
If you don't want normalized (or different sizes of) QAM
constellation,
digital.qam.make_non_differential_constellation(M, gray_coded)
is your friend;
digital.qam.make_non_differential_constellation(4096, True)
makes a nice 4096-QAM, but it's average power isn't 1; you can fix
that
points = digital.qam.make_non_differential_constellation(4096, True)
average_pwr = sum(point**2 for point in points) / len(points)
print(f"Average power: {average_pwr}; normalization factor hence:
{average_pwr**(-1/2)}")
normalized_points = [ point * average_pwr**(-1/2) for point in
points ]
Similarly, since you're doing satellite communications, you might
be interested in PSKs,
an A-PSKs.
You can create a PSK using
digital.psk.psk_constellation(m=4, mod_code='gray', differential=True)
e.g.
digital.psk.psk_constellation(16, differential=False)
If you don't have GNU Radio but just python,
str([(i, j) for i in range(-n, n, 2) for j in range (-n, n, 2)])
does the same as your code, but might be a bit easier to read
(again, if you want to use
this in GRC, don't do the conversion to `str`; GRC accepts any
valid Python in its fields).
Best regards,
Marcus
