Hello,
I've got a problem with the FIR
filters in GNU radio. Basically, at the moment I'm using it as a
platform to run some simulations on (as I've already written a load of
code on it for implementing a digital radio), and one of the tests I'm
doing is trying to find the BER through an equaliser. To do this I'm
loading a vector source up, running my flow graph with run() and upon
completion I'm checking a vector sink for errors. This works fine for a
fixed channel. The channel model I'm now using (a Watterson model which
I've coded into the flow graph), however, uses a FIR with a large number
of taps. Now the problem is that every time I run my flow graph with
run(), which presumably also calls wait(), the FIR seems to start from a
reset state. Is there any way to keep the contents of the FIR's shift
register in situ through calling run() multiple times? Every other
signal processing block I have maintains its state through this. For the
record I'm not calling stop() at all in the code, which I would expect
to reset everything.
I've set up a quick test case to describe
this problem,
So if I set up a little top_block like this, which
just sends a string of complex symbols valued +1+0j through a FIR
filter, and receives the result in block_out;
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class
my_top_block(gr.top_block):
def __init__(self):
gr.top_block.__init__(self)
self.data_rate = 1000;
self.totbits = 0;
self.toterrors = 0;
grey_const = ([1, -1])
length = 2
blank = [0x0,] * (length)
taps =
[1,] * 10
self.transmit_source = gr.vector_source_b(blank, False,
length);
self.unpack_for_mod =
gr.packed_to_unpacked_bb(1, gr.GR_MSB_FIRST)
self.symbol_mapper = gr.chunks_to_symbols_bc(grey_const)
self.fir = gr.fir_filter_ccc(1, taps)
self.v2s = gr.vector_to_stream(1, length)
self.connect(self.transmit_source, self.v2s, self.unpack_for_mod,
self.symbol_mapper, self.fir)
self.connect(self.fir, block_out)
-------------------------------------------------------------------------------------------------------------
Then
if I run it from main() like this;
-------------------------------------------------------------------------------------------------------------
def main ():
tb = my_top_block();
for a in range(20):
tb.run()
for n in block_out.data():
print n
block_out.clear()
tb.transmit_source.rewind()
-------------------------------------------------------------------------------------------------------------
I
get as output;
-------------------------------------------------------------------------------------------------------------
>>> gr_fir_ccc: using SSE
(1+0j)
(2+0j)
(3+0j)
(4+0j)
(5+0j)
(6+0j)
(7+0j)
(8+0j)
(9+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(1+0j)
(2+0j)
(3+0j)
(4+0j)
(5+0j)
(6+0j)
(7+0j)
(8+0j)
(9+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(10+0j)
(1+0j)
(2+0j)
(3+0j)
(4+0j)
(5+0j)
(6+0j)
(7+0j)
(8+0j)
.
.
etc
------------------------------------------------------------------------------------------------
Which
is wrong (after the first 10 outputs the output should always be
(10+0j). Is this a bug? Also does anyone know of any work around?
Cheers,
John