1 files changed, 34 insertions, 6 deletions
diff --git a/gr-digital/lib/packet_header_ofdm.cc b/gr-digital/lib/packet_header_ofdm.cc
index f163657bab..4893b866e2 100644
--- a/gr-digital/lib/packet_header_ofdm.cc
+++ b/gr-digital/lib/packet_header_ofdm.cc
@@ -24,6 +24,7 @@
 #endif
 
 #include <gnuradio/digital/packet_header_ofdm.h>
+#include <gnuradio/digital/lfsr.h>
 
 namespace gr {
   namespace digital {
@@ -46,11 +47,13 @@ namespace gr {
 		      const std::string &frame_len_tag_key,
 		      const std::string &num_tag_key,
 		      int bits_per_header_sym,
-		      int bits_per_payload_sym)
+		      int bits_per_payload_sym,
+		      bool scramble_header)
     {
       return packet_header_ofdm::sptr(
 	  new packet_header_ofdm(
-	    occupied_carriers, n_syms, len_tag_key, frame_len_tag_key, num_tag_key, bits_per_header_sym, bits_per_payload_sym
+	    occupied_carriers, n_syms, len_tag_key, frame_len_tag_key, num_tag_key,
+	    bits_per_header_sym, bits_per_payload_sym, scramble_header
 	  )
       );
     }
@@ -62,8 +65,9 @@ namespace gr {
 		    const std::string &frame_len_tag_key,
 		    const std::string &num_tag_key,
 		    int bits_per_header_sym,
-		    int bits_per_payload_sym)
-      : packet_header_default(
+		    int bits_per_payload_sym,
+		    bool scramble_header
+    ) : packet_header_default(
 	  _get_header_len_from_occupied_carriers(occupied_carriers, n_syms),
 	  len_tag_key,
 	  num_tag_key,
@@ -71,23 +75,47 @@ namespace gr {
       d_frame_len_tag_key(pmt::string_to_symbol(frame_len_tag_key)),
       d_occupied_carriers(occupied_carriers),
       d_syms_per_set(0),
-      d_bits_per_payload_sym(bits_per_payload_sym)
+      d_bits_per_payload_sym(bits_per_payload_sym),
+      d_scramble_mask(d_header_len, 0)
     {
       for (unsigned i = 0; i < d_occupied_carriers.size(); i++) {
 	d_syms_per_set += d_occupied_carriers[i].size();
       }
+
+      // Init scrambler mask
+      if (scramble_header) {
+	// These are just random values which already have OK PAPR:
+	gr::digital::lfsr shift_reg(0x8a, 0x6f, 7);
+	for (int i = 0; i < d_header_len; i++) {
+	  for (int k = 0; k < bits_per_header_sym; k++) {
+	    d_scramble_mask[i] ^= shift_reg.next_bit() << k;
+	  }
+	}
+      }
     }
 
     packet_header_ofdm::~packet_header_ofdm()
     {
     }
 
+    bool packet_header_ofdm::header_formatter(long packet_len, unsigned char *out, const std::vector<tag_t> &tags)
+    {
+      bool ret_val = packet_header_default::header_formatter(packet_len, out, tags);
+      for (int i = 0; i < d_header_len; i++) {
+      	out[i] ^= d_scramble_mask[i];
+      }
+      return ret_val;
+    }
 
     bool packet_header_ofdm::header_parser(
 	const unsigned char *in,
 	std::vector<tag_t> &tags)
     {
-      if (!packet_header_default::header_parser(in, tags)) {
+      std::vector<unsigned char> in_descrambled(d_header_len, 0);
+      for (int i = 0; i < d_header_len; i++) {
+      	in_descrambled[i] = in[i] ^ d_scramble_mask[i];
+      }
+      if (!packet_header_default::header_parser(&in_descrambled[0], tags)) {
 	return false;
       }
       int packet_len = 0; // # of bytes in this frame