Merged r8195:8205 from jcorgan/ecc into trunk. Adds convolutional encoder

and decoder corresponding to the R=1/2, K=7 CCSDS standard ("Voyager").

This code is a GNU Radio wrapper around a 1995-era KA9Q portable-C 
implementation, and is designed for continuous streaming data, not packets.

The encoder takes MSB packed bytes and outputs channel symbols 0 or 1.

The decoder uses soft-decision Viterbi decoding on a floating point stream of
(possibly noise corrupted) [1.0, 1.0] symbols, and outputs MSB packed
decoded bytes.

Benchmarking on a 2.16 GHz Intel Core 2 Duo shows 4.7 Mbps decoding rate at 
100% CPU usage (single core).  (There is a newer KA9Q library that implements 
SIMD speed ups with correspondingly faster performance.)

The KA9Q library is placed into src/lib/viterbi.  It could use some cleanup,
file/function renaming, and refactoring, or even replacement with the newer
libfec code that is available.



git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@8206 221aa14e-8319-0410-a670-987f0aec2ac5

1 files changed, 88 insertions, 0 deletions

diff --git a/gnuradio-core/src/lib/viterbi/decode.cc b/gnuradio-core/src/lib/viterbi/decode.cc
new file mode 100644
index 000000000..6580e4d66
--- /dev/null
+++ b/gnuradio-core/src/lib/viterbi/decode.cc
@@ -0,0 +1,88 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2008 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+/*
+ * This is a minimal example demonstrating how to call the Viterbi decoder
+ * in continuous streaming mode.  It accepts data on stdin and writes to 
+ * stdout.
+ *
+ */
+
+extern "C" {
+#include "viterbi.h"
+}
+
+#include <cstdio>
+#include <cmath>
+
+#define MAXCHUNKSIZE 4096
+#define MAXENCSIZE MAXCHUNKSIZE*16
+
+int main()
+{
+  unsigned char data[MAXCHUNKSIZE];
+  signed char syms[MAXENCSIZE];
+  int count = 0;
+
+  // Initialize metric table
+  int mettab[2][256];
+  int amp = 100;
+  float RATE=0.5;
+  float ebn0 = 12.0;
+  float esn0 = RATE*pow(10.0, ebn0/10);
+  gen_met(mettab, amp, esn0, 0.0, 4);
+
+  // Initialize decoder state
+  struct viterbi_state state0[64];
+  struct viterbi_state state1[64];
+  unsigned char viterbi_in[16];
+  viterbi_chunks_init(state0);  
+
+  while (!feof(stdin)) {
+    unsigned int n = fread(syms, 1, MAXENCSIZE, stdin);
+    unsigned char *out = data;
+    
+    for (unsigned int i = 0; i < n; i++) {
+
+      // FIXME: This implements hard decoding by slicing the input stream
+      unsigned char sym = syms[i] > 0 ? -amp : amp;
+
+      // Write the symbol to the decoder input
+      viterbi_in[count % 4] = sym;
+
+      // Every four symbols, perform the butterfly2 operation
+      if ((count % 4) == 3) {
+        viterbi_butterfly2(viterbi_in, mettab, state0, state1);      
+
+	// Every sixteen symbols, perform the readback operation
+        if ((count > 64) && (count % 16) == 11) {
+          viterbi_get_output(state0, out);
+	  fwrite(out++, 1, 1, stdout);
+	}
+      }
+      
+      count++;
+    }    
+  }
+
+  return 0;
+}