Added typical signalization channels (CCCH, BCCH, SDCCH) decoder and demapper for BCCH.

The implementation is quite dirty at this moment.

1 files changed, 147 insertions, 0 deletions

diff --git a/lib/decoding/control_channels_decoder_impl.cc b/lib/decoding/control_channels_decoder_impl.cc
new file mode 100644
index 0000000..544e6bb
--- /dev/null
+++ b/lib/decoding/control_channels_decoder_impl.cc
@@ -0,0 +1,147 @@
+/* -*- c++ -*- */
+/* 
+ * Copyright 2014 <+YOU OR YOUR COMPANY+>.
+ * 
+ * This 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.
+ * 
+ * This software 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 this software; 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 <gnuradio/io_signature.h>
+#include <gsm/gsmtap.h>
+#include "control_channels_decoder_impl.h"
+
+namespace gr {
+  namespace gsm {
+
+    control_channels_decoder::sptr
+    control_channels_decoder::make()
+    {
+      return gnuradio::get_initial_sptr
+        (new control_channels_decoder_impl());
+    }
+
+    /*
+     * The private constructor
+     */
+    control_channels_decoder_impl::control_channels_decoder_impl()
+      : gr::block("control_channels_decoder",
+              gr::io_signature::make(0, 0, 0),
+              gr::io_signature::make(0, 0, 0)),
+              d_collected_bursts_num(0)
+    {
+        //initialize de/interleaver
+        int j, k, B;
+        for (k = 0; k < CONV_SIZE; k++)
+        {
+            B = k % 4;
+            j = 2 * ((49 * k) % 57) + ((k % 8) / 4);
+            interleave_trans[k] = B * 114 + j; //114=57 + 57
+        }
+
+        FC_init(&fc_ctx, 40, 184);
+        message_port_register_in(pmt::mp("bursts"));
+        set_msg_handler(pmt::mp("bursts"), boost::bind(&control_channels_decoder_impl::decode, this, _1));
+//        message_port_register_out(pmt::mp(""));
+    }
+
+    /*
+     * Our virtual destructor.
+     */
+    control_channels_decoder_impl::~control_channels_decoder_impl()
+    {
+    }
+
+    void control_channels_decoder_impl::decode(pmt::pmt_t msg)
+    {
+        unsigned char iBLOCK[BLOCKS*iBLOCK_SIZE], hl, hn, conv_data[CONV_SIZE], decoded_data[PARITY_OUTPUT_SIZE];
+        d_bursts[d_collected_bursts_num] = msg;
+        d_collected_bursts_num++;
+        //get convecutive bursts
+        pmt::pmt_t header_blob = pmt::car(msg);
+        gsmtap_hdr * header = (gsmtap_hdr *)pmt::blob_data(header_blob);
+        
+        if(d_collected_bursts_num==4)
+        {
+            d_collected_bursts_num=0;
+            //reorganize data
+            for(int ii = 0; ii < 4; ii++)
+            {
+                pmt::pmt_t burst_content = pmt::cdr(d_bursts[ii]);
+                int8_t * burst_bits = (int8_t *)pmt::blob_data(burst_content);
+
+                for(int jj = 0; jj < 57; jj++)
+                {
+                    iBLOCK[ii*iBLOCK_SIZE+jj] = burst_bits[jj + 3];
+                    iBLOCK[ii*iBLOCK_SIZE+jj+57] = burst_bits[jj + 88]; //88 = 3+57+1+26+1
+                }
+            }
+            //deinterleave
+            for (int k = 0; k < CONV_SIZE; k++)
+            {
+                conv_data[k] = iBLOCK[interleave_trans[k]];
+            }
+            //convolutional code decode
+            int errors = conv_decode(decoded_data, conv_data);
+            //std::cout << "Errors:" << errors << " " << parity_check(decoded_data) << std::endl;
+            // check parity
+            // If parity check error detected try to fix it.
+
+            if (parity_check(decoded_data))
+            {
+                FC_init(&fc_ctx, 40, 184);
+                unsigned char crc_result[PARITY_OUTPUT_SIZE];
+                if (FC_check_crc(&fc_ctx, decoded_data, crc_result) == 0)
+                {
+                    //("error: sacch: parity error (errors=%d fn=%d)\n", errors, ctx->fn);
+                    //std::cout << "Uncorrectable errors!" << std::endl;
+                    errors = -1;
+                } else {
+                    //DEBUGF("Successfully corrected parity bits! (errors=%d fn=%d)\n", errors, ctx->fn);
+                    //std::cout << "Corrected some errors" << std::endl;
+                    memcpy(decoded_data, crc_result, PARITY_OUTPUT_SIZE);
+                    errors = 0;
+                }
+            } else {
+                //std::cout << "Everything correct" << std::endl;
+            }
+           //compress bits
+           unsigned char outmsg[27];
+           unsigned char sbuf_len=224;
+           int i, j, c, pos=0;
+           for(i = 0; i < sbuf_len; i += 8) {
+                 for(j = 0, c = 0; (j < 8) && (i + j < sbuf_len); j++){
+                     c |= (!!decoded_data[i + j]) << j;
+                 }
+                 outmsg[pos++] = c & 0xff;
+             }
+
+           //printf("%6d %d:", (0 + 1), 0);
+           int jj=0;
+             while (jj < 23){
+                 printf(" %02x", outmsg[jj]);//decoded_data[jj]);
+                 jj++;
+               }
+             printf("\n");
+             fflush(stdout);
+        }
+        return;
+    }
+  } /* namespace gsm */
+} /* namespace gr */
+