From 51c504ebb1ca21c5f7071826c1af03e45e391a65 Mon Sep 17 00:00:00 2001
From: Daniel Estévez <daniel@destevez.net>
Date: Sun, 6 Jun 2021 11:25:57 +0200
Subject: digital: Add NRZI option to differential en/decoder
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This adds an option to the differential encoder an decoder blocks
to perform NRZI encoding and decoding. NRZI only makes sense with
a modulus of 2, so the blocks constructors will throw and exception
if passed nrzi = true and a modulus different from 2.
The GRC blocks handle this by hiding the modulus field if the user
selects NRZI encoding.
A new unit test for the NRZI version of the blocks is added. Besides
checking that encode plus decode gives the original, this test also
compares the C++ implementation results against a Numpy implementation.
Additionally, a faster implementation of differential encoding/
decoding for modulus 2 is included here.
Signed-off-by: Daniel Estévez <daniel@destevez.net>
---
gr-digital/lib/diff_decoder_bb_impl.cc | 33 +++++++++++++++++++++++++++------
1 file changed, 27 insertions(+), 6 deletions(-)
(limited to 'gr-digital/lib/diff_decoder_bb_impl.cc')
diff --git a/gr-digital/lib/diff_decoder_bb_impl.cc b/gr-digital/lib/diff_decoder_bb_impl.cc
index 95e5c2e9c3..f9b093400d 100644
--- a/gr-digital/lib/diff_decoder_bb_impl.cc
+++ b/gr-digital/lib/diff_decoder_bb_impl.cc
@@ -1,6 +1,7 @@
/* -*- c++ -*- */
/*
* Copyright 2006,2010,2012 Free Software Foundation, Inc.
+ * Copyright 2021 Daniel Estevez <daniel@destevez.net>
*
* This file is part of GNU Radio
*
@@ -15,19 +16,27 @@
#include "diff_decoder_bb_impl.h"
#include <gnuradio/io_signature.h>
+#include <stdexcept>
+
namespace gr {
namespace digital {
-diff_decoder_bb::sptr diff_decoder_bb::make(unsigned int modulus)
+diff_decoder_bb::sptr diff_decoder_bb::make(unsigned int modulus,
+ enum diff_coding_type coding)
{
- return gnuradio::make_block_sptr<diff_decoder_bb_impl>(modulus);
+ return gnuradio::make_block_sptr<diff_decoder_bb_impl>(modulus, coding);
}
-diff_decoder_bb_impl::diff_decoder_bb_impl(unsigned int modulus)
+diff_decoder_bb_impl::diff_decoder_bb_impl(unsigned int modulus,
+ enum diff_coding_type coding)
: sync_block("diff_decoder_bb",
io_signature::make(1, 1, sizeof(unsigned char)),
io_signature::make(1, 1, sizeof(unsigned char))),
- d_modulus(modulus)
+ d_modulus(modulus),
+ d_coding(coding)
{
+ if (d_coding == DIFF_NRZI && d_modulus != 2) {
+ throw std::runtime_error("diff_decoder: NRZI only supported with modulus 2");
+ }
set_history(2); // need to look at two inputs
}
@@ -43,8 +52,20 @@ int diff_decoder_bb_impl::work(int noutput_items,
unsigned modulus = d_modulus;
- for (int i = 0; i < noutput_items; i++) {
- out[i] = (in[i] - in[i - 1]) % modulus;
+ if (d_coding == DIFF_NRZI) {
+ for (int i = 0; i < noutput_items; i++) {
+ out[i] = ~(in[i] ^ in[i - 1]) & 1;
+ }
+ } else if (modulus == 2) {
+ // optimized implementation for modulus 2
+ for (int i = 0; i < noutput_items; i++) {
+ out[i] = (in[i] ^ in[i - 1]) & 1;
+ }
+ } else {
+ // implementation for modulus != 2
+ for (int i = 0; i < noutput_items; i++) {
+ out[i] = (in[i] - in[i - 1]) % modulus;
+ }
}
return noutput_items;
--
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