notes and tweak to bit flipping

git-svn-id: https://svn.code.sf.net/p/freetel/code@2450 01035d8c-6547-0410-b346-abe4f91aad63

diff --git a/codec2-dev/octave/fsk_horus.m b/codec2-dev/octave/fsk_horus.m
index 409895b8d5805045dbda333fe82eb567324815d7..90269bbde4dd50bd6b04695feb57a4b9f2712398 100644 (file)
--- a/codec2-dev/octave/fsk_horus.m
+++ b/codec2-dev/octave/fsk_horus.m
@@ -67,6 +67,7 @@ function states = fsk_horus_init()
   states.f2 = 0;
   states.norm_rx_timing = 0;
   states.ppm = 0;
+  states.prev_pkt = [];
 endfunction
 
 
@@ -327,7 +328,7 @@ function [str crc_ok] = extract_ascii(states, rx_bits_buf, uw_loc1, uw_loc2)
 
     % build up array for CRC16 check
 
-    if ch_dec == 42
+    if ch_dec == 42 
       rx_crc = crc16(str_dec);
       ptx_crc = nstr+1;
     else
@@ -351,20 +352,27 @@ endfunction
 
 % Use soft decision information to find bits most likely in error.  I think
 % this is some form of maximum likelihood decoding.
-% 
-% TODO: ignore rs232 start and stop bits, ie remove from weakest bit list
-%       insert known good bits (copy from prev packet with gd CRC)
-%       use other apriori info, like if a lat or long isn't a digit, use last packet as guess
 
-function [str crc_ok] = sd_bit_flipping(states, rx_bits_log, rx_bits_sd_log, st, uw_loc);
+function [str crc_ok rx_bits_log_flipped] = sd_bit_flipping(states, rx_bits_log, rx_bits_sd_log, st, uw_loc);
+
+  % force algorithm to ignore rs232 sync bits by marking them as "very likely", they have
+  % no input to crc algorithm
+
+  nfield = states.nfield;
+  npad = states.npad;
+  for i=st:nfield+npad:uw_loc
+    rx_bits_sd_log(i+nfield:i+nfield+npad-1) = 1E6;
+  end
+
+  % make a list of bits with smallest soft decn values
 
   [dodgy_bits_mag dodgy_bits_index] = sort(abs(rx_bits_sd_log(st+length(states.uw):uw_loc)));
   dodgy_bits_index += length(states.uw) + st - 1;
-  nbits = 8;
-  ntries = nbits^2;
+  nbits = 6;
+  ntries = 2^nbits;
   str = "";
   crc_ok = 0;
-
+  
   % try various combinations of these bits
 
   for i=1:ntries-1
@@ -382,7 +390,7 @@ function [str crc_ok] = sd_bit_flipping(states, rx_bits_log, rx_bits_sd_log, st,
       str = str_flipped;
       crc_ok = crc_ok_flipped;
     end
-  end 
+  end
 endfunction
 
 
@@ -415,18 +423,22 @@ function extract_and_print_packets(states, rx_bits_log, rx_bits_sd_log)
       %save -ascii horus_msg.txt msg
 
       % simulate bit error for testing
-      %rx_bits_log(st+100) = xor(rx_bits_log(st+100),1);
+      %rx_bits_log(st+200) = xor(rx_bits_log(st+100),1);
       %rx_bits_sd_log(st+100) = 0;
 
       [str crc_ok] = extract_ascii(states, rx_bits_log, st, uw_loc);
 
       if crc_ok == 0
-        [str_flipped crc_flipped_ok] = sd_bit_flipping(states, rx_bits_log, rx_bits_sd_log, st, uw_loc); 
+        [str_flipped crc_flipped_ok rx_bits_log] = sd_bit_flipping(states, rx_bits_log, rx_bits_sd_log, st, uw_loc); 
         if crc_flipped_ok
           str = sprintf("%s fixed", str_flipped);
         end
       end
 
+      % update memory of previous packet, we use this to guess where errors may be
+      if crc_ok || crc_flipped_ok
+        states.prev_pkt = rx_bits_log(st+length(states.uw):uw_loc);
+      end
       printf("%s\n", str);
     end
    
@@ -437,7 +449,7 @@ endfunction
 % simulation of tx and rx side, add noise, channel impairments ----------------------
 
 function run_sim
-  frames = 100;
+  frames = 10;
   EbNodB = 26;
   timing_offset = 0.0; % see resample() for clock offset below
   test_frame_mode = 4;

diff --git a/codec2-dev/octave/fsk_horus_stream.m b/codec2-dev/octave/fsk_horus_stream.m
index 15e5bdce3ec3e3c86958ea0bc36d6a3d6ac2e110..4fc3c8a51f96399a01f2b22d05a7a5cfed5bf94a 100755 (executable)
--- a/codec2-dev/octave/fsk_horus_stream.m
+++ b/codec2-dev/octave/fsk_horus_stream.m
@@ -3,20 +3,20 @@
 % fsk_horus_stream.m
 % David Rowe 13 Oct 2015
 %
-% Experimental near space balloon FSK demodulator, takes 8kHz 16 bit samples from 
-% stdin, output txt string on stdout
+% Experimental real time near space balloon FSK demodulator, takes
+% 8kHz 16 bit samples from stdin, output txt string on stdout
 %
 % usage:
 %  $ chmod 777 fsk_horus_stream.m
 %  $ rec -t raw -r 8000 -s -2 -c 1 - -q | ./fsk_horus_stream.m
 %
-% or to test with a stored file:
+% OR to test with a stored file (8kHz 16-bit shorts):
 %  $ cat ~/Desktop/vk5arg-3.wav | ./fsk_horus_stream.m
 %
 
-% include library (make sure calls to test functions at bottom are disabled)
+% include modem library
 
-fsk_horus_as_a_lib = 1;
+fsk_horus_as_a_lib = 1; % make sure calls to test functions at bottom are disabled
 fsk_horus;  
 
 gps_log = "~/Desktop/gps_log.txt"
@@ -44,7 +44,7 @@ while c
 
   rx = [rx s'];
  
-  % demodulate to bit stream
+  % demodulate samples to bit stream
 
   while length(rx) > nin
     [rx_bits states] = fsk_horus_demod(states, rx(1:nin)');
@@ -79,6 +79,7 @@ while c
         [str_flipped crc_flipped_ok] = sd_bit_flipping(states, rx_bits_buf, rx_bits_sd_buf, uw_loc1, uw_loc2); 
         if crc_flipped_ok
           str = sprintf("%s fixed", str_flipped);
+          crc_ok = 1;
         end
       end
 
@@ -89,22 +90,23 @@ while c
       rx_bits_buf =  rx_bits_buf(uw_loc2-1:length(rx_bits_buf));
       rx_bits_sd_buf =  rx_bits_sd_buf(uw_loc2-1:length(rx_bits_sd_buf));
 
-      % extract GPS coords and save to log file for mapping software
-      % TODO: sanitise, make sure they are all numbers, decimal point in right place
+      if crc_ok
+        % extract GPS coords and save to log file for mapping software
 
-      str_split = strsplit(str,",");
-      if length(str_split) > 4
-        lat = str_split{1,4}; long = str_split{1,5};
-        f = fopen(gps_log,"at");
-        fprintf(f,"%s,%s\n", lat, long);
-        fclose(f);
-      end
+        str_split = strsplit(str,",");
+        if length(str_split) > 4
+          lat = str_split{1,4}; long = str_split{1,5};
+          f = fopen(gps_log,"at");
+          fprintf(f,"%s,%s\n", lat, long);
+          fclose(f);
+        end
 
-      % TODO: thin out log file to points_max points to lighten plotting load
+        % TODO: thin out log file to max_points to lighten plotting load
 
-      % tell foxtrotGPS to plot track
+        % tell foxtrotGPS to plot track
 
-      system(system_command);
+        system(system_command);
+      end
     end
   else
     % Truncate buffers if no UW found so they don't grow endlessly with no signal.
@@ -114,6 +116,7 @@ while c
       rx_bits_sd_buf = rx_bits_sd_buf(length(rx_bits_sd_buf)-length(uw):length(rx_bits_sd_buf));
     end
   end
+
   [s,c] = fread(stdin, N, "short");
 
 endwhile