diff options
| author | Josh Morman <jmorman@perspectalabs.com> | 2019-12-04 11:05:55 -0500 |
|---|---|---|
| committer | Michael Dickens <michael.dickens@ettus.com> | 2020-01-26 16:48:40 -0500 |
| commit | be6647a101077e7fa471ed3a186da1b01025952b (patch) | |
| tree | b627f750455ad3df08c2ce2e91f1a0927d5562a1 /gr-digital/python/digital/generic_mod_demod.py | |
| parent | e55865dfe976a29641d037a52cbca3d77385d862 (diff) | |
digital: add filter response truncation to generic mod
The generic mod implementation is a convenience hier block to modulate
bits to symbols and apply an RRC filter. One downside is the output is
delayed by the length of the RRC filter (which is specified inside the
block). This adds an option to truncate the output according to the
length of the filter response such that the start of output is aligned to the first symbol.
Fixes #2920
Diffstat (limited to 'gr-digital/python/digital/generic_mod_demod.py')
| -rw-r--r-- | gr-digital/python/digital/generic_mod_demod.py | 20 |
1 files changed, 17 insertions, 3 deletions
diff --git a/gr-digital/python/digital/generic_mod_demod.py b/gr-digital/python/digital/generic_mod_demod.py index 2a0d2c44ce..bd0c849245 100644 --- a/gr-digital/python/digital/generic_mod_demod.py +++ b/gr-digital/python/digital/generic_mod_demod.py @@ -41,6 +41,7 @@ _def_samples_per_symbol = 2 _def_excess_bw = 0.35 _def_verbose = False _def_log = False +_def_truncate = False # Frequency correction _def_freq_bw = 2*math.pi/100.0 @@ -93,6 +94,7 @@ class generic_mod(gr.hier_block2): excess_bw: Root-raised cosine filter excess bandwidth (float) verbose: Print information about modulator? (boolean) log: Log modulation data to files? (boolean) + truncate: Truncate the modulated output to account for the RRC filter response (boolean) """ def __init__(self, constellation, @@ -101,7 +103,8 @@ class generic_mod(gr.hier_block2): pre_diff_code=True, excess_bw=_def_excess_bw, verbose=_def_verbose, - log=_def_log): + log=_def_log, + truncate=_def_truncate): gr.hier_block2.__init__(self, "generic_mod", gr.io_signature(1, 1, gr.sizeof_char), # Input signature @@ -133,7 +136,8 @@ class generic_mod(gr.hier_block2): # pulse shaping filter nfilts = 32 - ntaps = nfilts * 11 * int(self._samples_per_symbol) # make nfilts filters of ntaps each + ntaps_per_filt = 11 + ntaps = nfilts * ntaps_per_filt * int(self._samples_per_symbol) # make nfilts filters of ntaps each self.rrc_taps = filter.firdes.root_raised_cosine( nfilts, # gain nfilts, # sampling rate based on 32 filters in resampler @@ -143,13 +147,23 @@ class generic_mod(gr.hier_block2): self.rrc_filter = filter.pfb_arb_resampler_ccf(self._samples_per_symbol, self.rrc_taps) + # Remove the filter transient at the beginning of the transmission + if truncate: + fsps = float(self._samples_per_symbol) + len_filt_delay = (ntaps_per_filt*fsps*fsps-fsps)/2.0 # Length of delay through rrc filter + self.skiphead = blocks.skiphead(gr.sizeof_gr_complex*1, len_filt_delay) + # Connect self._blocks = [self, self.bytes2chunks] if self.pre_diff_code: self._blocks.append(self.symbol_mapper) if differential: self._blocks.append(self.diffenc) - self._blocks += [self.chunks2symbols, self.rrc_filter, self] + self._blocks += [self.chunks2symbols, self.rrc_filter] + + if truncate: + self._blocks.append(self.skiphead) + self._blocks.append(self) self.connect(*self._blocks) if verbose: |