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Today's Topics:
1. Writing GRC block for preamble detection (Bakshi, Arjun)
----------------------------------------------------------------------
Message: 1
Date: Sun, 11 Jun 2017 02:51:17 +0000
From: "Bakshi, Arjun" <[email protected]>
To: "[email protected]" <[email protected]>
Subject: [USRP-users] Writing GRC block for preamble detection
Message-ID:
<mwhpr01mb22864558f623eb0949821397bc...@mwhpr01mb2286.prod.exchangelabs.com>
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Hello everyone,
I'm trying to build a GRC block in Python for the first time. I want a preamble
detection block. I've read the guided tutorial
here:https://wiki.gnuradio.org/index.php/Guided_Tutorial_GNU_Radio_in_Python ,
but am still unclear on what is happening under the hood.
I want to use a general/basic block that takes in len(preamble) floats and
returns 1 float (correlation value). My questions are:
1. What should the input output signature look like? I'm thinking that I
could write the signature as len(preamble):1, or in some M:N format like
1024:1024-len(preamble)+1. It is currently:
def __init__(self, preamble, th=0.8):
gr.basic_block.__init__(self,
name="pre_detect_ff",
in_sig=[(numpy.float32, len(preamble))],
out_sig=[numpy.float32])
2. What does the forecast function do? I think it tells gnuradio how to
slice the input stream so that each chunk can be used to generate the required
output. But Its not clear how the slicing is happening. My forecast function
looks like:
def forecast(self, noutput_items, ninput_items_required):
for i in range(len(ninput_items_required)):
ninput_items_required[i] = 1 # setting to len(self.preamble) gives
error, not enough inputs to generate output
# setting to 1
seems to make it work
3.
How do I use consume? I think consume tells gnuradio to move on to the next
chunk of data to process. I'm currently using it as follows in my general_work
function:
def general_work(self, input_items, output_items):
print "called gen work"
for i in range(input_items[0].shape[0]):
result = numpy.corrcoef(input_items[0][i], self.preamble)[0, 1]
if result > self.th:
result = 1.0
else:
result = 0.0
output_items[0][i] = result
# consume(0,1) # gives an error, undefined function, but this call
was added by gr_modtool
self.consume_each(1) # consume 1 data point on all streams (there
is only 1 stream)
return len(output_items[0])
I'm also having trouble with the QA tests(itemsize mismatch), but that my be
due to bugs in my class code. I'd really appreciate someone answering these
questions, and pointing out bugs in the code.
Thank you,
Arjun
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