Stephan Ludwig - 2012-03-26

Hi,

as you might have noticed already, I am trying to go through all the open
bugs/feature requests,discussions and try to get them into SVN as long as I
have knowledge about the topics there. Since there is a rule here on IT++not
to open a bug/feature request without prior discussion, I a posteriori start
the discussion, hoping that those albeit valuable requests/reports won't be
lost.

So i open up a discussion on feature request #3348928. qdelfin suggested
amending turbo.cpp/h by an additional (in add. to WCDMA/UMTS) interleaver
sequence generating function and already provided some code. I went through
that code and changed a bit, but since I cannot add it to the request, I will
post it here for discussion. Could you please verify that. Coding for LTE is
in the standard http://www.3gpp.org/FTP/Specs/latest/Rel-10/36_series/36212-a
50.zip
from page 14 onwards.

BTW: We should consider inheriting the special interleavers from
Sequence_Interleaver and not write a function for every special case. That
will require some changes in the method interface/constructors of the
Turbo_Codec class. What do you think?

ivec lte_turbo_interleaver_sequence(int interleaver_size)
// for standard see pp. 14 [url]http://www.3gpp.org/FTP/Specs/latest/Rel-10/36_series/36212-a50.zip[/url]
{
  ivec block_lengths; //Supported interleaver block lengths
  ivec f1_factors, f2_factors; //Interleaver parameters

  //Definitions of block lengths and associated f1 and f2 factors:
  ivec block_lengths("40 48 56 64 72 80 88 96 104 112 120 128 136 144 152 160 168 176 184 192 200 208 216 224 232 240 248 256 264 272 280 288 296 304 312 320 328 336 344 352 360 368 376 384 392 400 408 416 424 432 440 448 456 464 472 480 488 496 504 512 528 544 560 576 592 608 624 640 656 672 688 704 720 736 752 768 784 800 816 832 848 864 880 896 912 928 944 960 976 992 1008 1024 1056 1088 1120 1152 1184 1216 1248 1280 1312 1344 1376 1408 1440 1472 1504 1536 1568 1600 1632 1664 1696 1728 1760 1792 1824 1856 1888 1920 1952 1984 2016 2048 2112 2176 2240 2304 2368 2432 2496 2560 2624 2688 2752 2816 2880 2944 3008 3072 3136 3200 3264 3328 3392 3456 3520 3584 3648 3712 3776 3840 3904 3968 4032 4096 4160 4224 4288 4352 4416 4480 4544 4608 4672 4736 4800 4864 4928 4992 5056 5120 5184 5248 5312 5376 5440 5504 5568 5632 5696 5760 5824 5888 5952 6016 6080 6144");
  ivec f1_factors   (" 3  7 19  7  7 11  5 11   7  41 103  15   9  17   9  21 101  21  57  23  13  27  11  27  85  29  33  15  17  33 103  19  19  37  19  21  21 115 193  21 133  81  45  23 243 151 155  25  51  47  91  29  29 247  29  89  91 157  55  31  17  35 227  65  19  37  41  39 185  43  21 155  79 139  23 217  25  17 127  25 239  17 137 215  29  15 147  29  59  65   55   31   17  171   67   35   19   39   19  199   21  211   21   43  149   45   49   71   13   17   25  183   55  127   27   29   29   57   45   31   59  185  113   31   17  171  209  253  367  265  181   39   27  127  143   43   29   45  157   47   13  111  443   51   51  451  257   57  313  271  179  331  363  375  127   31   33   43   33  477   35  233  357  337   37   71   71   37   39  127   39   39   31  113   41  251   43   21   43   45   45  161   89  323   47   23   47  263");
  ivec f2_factors   ("10 12 42 16 18 20 22 24  26  84  90  32  34 108  38 120  84  44  46  48  50  52  36  56  58  60  62  32 198  68 210  36  74  76  78 120  82  84  86  44  90  46  94  48  98  40 102  52 106  72 110 168 114  58 118 180 122  62  84  64  66  68 420  96  74  76 234  80  82 252  86  44 120  92  94  48  98  80 102  52 106  48 110 112 114  58 118  60 122 124   84   64   66  204  140   72   74   76   78  240   82  252   86   88   60   92  846   48   28   80  102  104  954   96  110  112  114  116  354  120  610  124  420   64   66  136  420  216  444  456  468   80  164  504  172   88  300   92  188   96   28  240  204  104  212  192  220  336  228  232  236  120  244  248  168   64  130  264  134  408  138  280  142  480  146  444  120  152  462  234  158   80   96  902  166  336  170   86  174  176  178  120  182  184  186   94  190  480");
  const int MAX_INTERLEAVER_SIZE = 6144;
  const int MIN_INTERLEAVER_SIZE = 40;

  // Check the range of the interleaver size:
  it_assert(interleaver_size <= MAX_INTERLEAVER_SIZE, "lte_turbo_interleaver_sequence: The interleaver size is too large");
  it_assert(interleaver_size >= MIN_INTERLEAVER_SIZE, "lte_turbo_interleaver_sequence: The interleaver size is too small");

  // Check whether the given interleaver size is correct:
  int left, right, index, temp;
  bool search = true;

  // do a binary search for interleaver_size in block_lengths
  left = 0;
  right = block_lengths.size() - 1;
  temp = 0;
  while ( (search) && (left <= right) ) {
    index = (left + right) / 2;
    temp = block_lengths(index);
    if (temp == interleaver_size) {
      search = false;
    }
    else {
      if (temp > interleaver_size) {
        right = index - 1;
      }
      else {
        left = index + 1;
      }
    }
  }
  it_assert(!search, "lte_turbo_interleaver_sequence: The interleaver size is incorrect!");

  // Definitions of key parameters:
  int K = interleaver_size; // Interleaver size
  int f1_factor = f1_factors(index);
  int f2_factor = f2_factors(index);
  ivec I(K); //The interleaver sequence

  // Calculate the interleaver sequence:
  for (int i = 0; i < K; i++) {
    I(i) = (i*f1_factor + i*i*f2_factor) % K;
  }

  return I;
}