1 files changed, 133 insertions, 0 deletions
diff --git a/gr-digital/lib/digital_ofdm_sampler.cc b/gr-digital/lib/digital_ofdm_sampler.cc
new file mode 100644
index 000000000..cab8c2ba9
--- /dev/null
+++ b/gr-digital/lib/digital_ofdm_sampler.cc
@@ -0,0 +1,133 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2007,2008,2010,2011 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.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <digital_ofdm_sampler.h>
+#include <gr_io_signature.h>
+#include <gr_expj.h>
+#include <cstdio>
+
+digital_ofdm_sampler_sptr
+digital_make_ofdm_sampler (unsigned int fft_length, 
+			   unsigned int symbol_length,
+			   unsigned int timeout)
+{
+  return gnuradio::get_initial_sptr(new digital_ofdm_sampler (fft_length, symbol_length, timeout));
+}
+
+digital_ofdm_sampler::digital_ofdm_sampler (unsigned int fft_length, 
+					    unsigned int symbol_length,
+					    unsigned int timeout)
+  : gr_block ("ofdm_sampler",
+	      gr_make_io_signature2 (2, 2, sizeof (gr_complex), sizeof(char)),
+	      gr_make_io_signature2 (2, 2, sizeof (gr_complex)*fft_length, sizeof(char)*fft_length)),
+    d_state(STATE_NO_SIG), d_timeout_max(timeout), d_fft_length(fft_length), d_symbol_length(symbol_length)
+{
+  set_relative_rate(1.0/(double) fft_length);   // buffer allocator hint
+}
+
+void
+digital_ofdm_sampler::forecast (int noutput_items, gr_vector_int &ninput_items_required)
+{
+  // FIXME do we need more
+  //int nreqd  = (noutput_items-1) * d_symbol_length + d_fft_length;
+  int nreqd  = d_symbol_length + d_fft_length;
+  unsigned ninputs = ninput_items_required.size ();
+  for (unsigned i = 0; i < ninputs; i++)
+    ninput_items_required[i] = nreqd;
+}
+
+
+int
+digital_ofdm_sampler::general_work (int noutput_items,
+				    gr_vector_int &ninput_items,
+				    gr_vector_const_void_star &input_items,
+				    gr_vector_void_star &output_items)
+{
+  const gr_complex *iptr = (const gr_complex *) input_items[0];
+  const char *trigger = (const char *) input_items[1];
+
+  gr_complex *optr = (gr_complex *) output_items[0];
+  char *outsig = (char *) output_items[1];
+
+  //FIXME: we only process a single OFDM symbol at a time; after the preamble, we can 
+  // process a few at a time as long as we always look out for the next preamble.
+
+  unsigned int index=d_fft_length;  // start one fft length into the input so we can always look back this far
+
+  outsig[0] = 0; // set output to no signal by default
+
+  // Search for a preamble trigger signal during the next symbol length
+  while((d_state != STATE_PREAMBLE) && (index <= (d_symbol_length+d_fft_length))) {
+    if(trigger[index]) {
+      outsig[0] = 1; // tell the next block there is a preamble coming
+      d_state = STATE_PREAMBLE;
+    }
+    else
+      index++;
+  }
+  
+  unsigned int i, pos, ret;
+  switch(d_state) {
+  case(STATE_PREAMBLE):
+    // When we found a preamble trigger, get it and set the symbol boundary here
+    for(i = (index - d_fft_length + 1); i <= index; i++) {
+      *optr++ = iptr[i];
+    }
+    
+    d_timeout = d_timeout_max; // tell the system to expect at least this many symbols for a frame
+    d_state = STATE_FRAME;
+    consume_each(index - d_fft_length + 1); // consume up to one fft_length away to keep the history
+    ret = 1;
+    break;
+    
+  case(STATE_FRAME):
+    // use this state when we have processed a preamble and are getting the rest of the frames
+    //FIXME: we could also have a power squelch system here to enter STATE_NO_SIG if no power is received
+
+    // skip over fft length history and cyclic prefix
+    pos = d_symbol_length;         // keeps track of where we are in the input buffer
+    while(pos < d_symbol_length + d_fft_length) {
+      *optr++ = iptr[pos++];
+    }
+
+    if(d_timeout-- == 0) {
+      printf("TIMEOUT\n");
+      d_state = STATE_NO_SIG;
+    }
+
+    consume_each(d_symbol_length); // jump up by 1 fft length and the cyclic prefix length
+    ret = 1;
+    break;
+
+  case(STATE_NO_SIG):
+  default:
+    consume_each(index-d_fft_length); // consume everything we've gone through so far leaving the fft length history
+    ret = 0;
+    break;
+  }
+
+  return ret;
+}