Hi Everyone,
I apologize ahead of time if this question seems stupid or if the answer
already exists somewhere and I haven't been able to find it. I am working
with a group that is attempting to recreate a 56kb/sec RF Modem nominally
operating at 29MHz using Minimum Frequency Shift Keying. The end goal is to
have the modem we are building using gnuradio and the usrp to communicate
with one of the original hardware modems. As a proof of concept, I am
attempting to have my gnuradio code loopback on itself, to show that the
modulation-to-demodulation works as expected. I am attempting to do this by
simply reading from a file, modulating, passing it through a channel model,
demodulating, and writing to a new file. The problem I am encountering is
that the write data comes out as garbage, and I'm not sure what I'm doing
wrong. Here is the test code that I am trying to run:
-----
from gnuradio import gr, gru, blks2
from gnuradio import usrp
from gnuradio import eng_notation
import copy
import sys
from gmsk import gmsk_demod
class my_top_block(gr.top_block):
def __init__(self):
gr.top_block.__init__(self)
self._file_name = 'testdata.dat'
self.src = gr.file_source(gr.sizeof_char, self._file_name, False)
self.unpacker = gr.packed_to_unpacked_bb(1, gr.GR_LSB_FIRST)
self.mod = gr.cpfsk_bc(.5, 1, 2) #Modulation index = .5 for MSK, 1 bit
per symbol for BFSK, 2 samples per symbol
self.chanmod = blks2.channel_model()
#self.demod = gmsk_demod(2)
self.demod = gr.quadrature_demod_cf(1)
self.dec = gr.keep_one_in_n(gr.sizeof_float, 2) #2 Samples Per symbol
self.slicer = gr.binary_slicer_fb()
self.repack = gr.unpacked_to_packed_bb(1, gr.GR_LSB_FIRST)
self.out = gr.file_sink(gr.sizeof_char, 'outdata.dat')
self.out2 = gr.file_sink(gr.sizeof_char, 'testout.dat')
self.connect(self.src, self.unpacker, self.mod, self.chanmod,
self.demod, self.dec, self.slicer, self.repack, self.out)
#self.connect(self.src, self.unpacker, self.repack, self.out)
if __name__ == '__main__':
tb = my_top_block()
try:
tb.run()
except KeyboardInterrupt:
pass
-----
I originally tried this code, as seen from the commented section, using the
demodulation method from gmsk included in blks2, as per my understanding
that demodulating a gmsk signal would be the same as an msk signal. When
this did not work correctly, I then searched the boards and found that
demodulating a BFSK signal had been done using the method I show above, yet
I'm still recieving incorrect data on the write side. I would really
appreciate any help on this, as I've been trying to solve it on my own with
no success. The testfile 'testdata.dat' consists of a single line of text
'This is a test file for GNU Radio'. Below are some examples of the recieved
data that I have captured.
----
Run 1: Sensitivity = 1, Keep-N-In-One = 2
ZÚ HÚ H ]Ù Y [ Ù È S T YÚ
Run 2: Sensitivity = 20, Keep-N-In-One = 2
ZÚ HÚ H ]Ù Y [ Ù È S T YÚ
Run 3: Sensitivity = 1, Keep-N-In-One = 3
Ã<< ª "EURO £Š Õ) EURO a3 #Õ
Run 4: Sensitivity =1, Keep All samples
g g çá a çá a æg çá æ g g ç á á ff af g ç
-----
Thanks again for any help on this, I'm basically hitting my head against a
brick wall.
-Dan
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