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,
It produces two different vectors depending of fh Boolean value. A sawtooth vector of values between -0.5 and 0.5 or the same random values between -0.5 and 0.5. The sawtooth values used in alignment phase (adjusting myblock).
"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
This block offloads the previous block as is too heavy to produce random numbers at the rate needed.
"My block"
Shift the vector in order to match the receiving keys.
"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
The VCO complex, with the values specified, produce frequencies between -500 kHz for -0.5 and +500 kHz for +0.5 input. This block creates the frequency change. All values between -0.5 and +0.5 produce frequencies between them.
VCO is voltage controlled oscillator. It produces frequencies depending of "voltage" input.
"Complex Conj":
Well, takes the complex conjugate of each item individually – still just
points of uncorrelated random phase!
Inverse the frequencies created.
"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.
It moves the USB voice signal by frequency created from previous steps.
You can better understand it considering frequencies rather than phases.
Best regards,
Marcus
Best regards,
George SV1BDS
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
>
> Στις Πέμ, 27 Απρ, 2023 στις 14:57, ο χρήστηςMarcus Müller
> 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
>
>