Message-ID: <004a01c0b2f4$da2d7370$687a37c0@w2ksn>
From: "Stewart Nelson" <sn@scgroup.com>
To: rsgb_lf_group@blacksheep.org
References: <65AECDF1F89AD411900400508BFC869F9C03F4@pdw-mail-1.dera.gov.uk>
Subject: LF: Re: RE: Re: WOLF - Transmit?
Date: Thu, 22 Mar 2001 09:23:41 -0800
Organization: SC Group
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Hi Andy and all,

Sorry that I don't have a good document on the format, but
here is the code used to generate it; I hope that it is
enough info for you to build something compatible with WOLF.

You can run WOLF in the "EEPROM" mode to see if a given
message encoding matches your software.  If you have trouble,
let me know and I'll try to help.

Transmission involves radix-40 encode, convolutional encode,
interleave, and reference bit insertion.

#define MSGLEN 15  /* source message len in chars */
#define MSGLENW 5  /* radix 40 message len in 16-bit words */
#define WLEN 16   /* bits in 3-character coded group */
#define MSGLENB 80  /* message length in bits */
#define RRATE 6   /* reciprocal of code rate */

/* Radix-40 encoder */
/* Future versions may use codes >=64000 for
   control functions, CRC, etc. */
/* in: ASCII string, up to 15 chars
   out: array of 16 bit words, radix-40 encoded */
void encr40(char *in, ushort out[])
{
  int ch, fill, val, i;
  fill = 0;
  val = 0;
  for (i = 0; i < MSGLEN; ++i) {
    if (fill)
      ch = 0;
    else if (!(ch = *in++))
      fill = 1;
    else if (ch >= 'A' && ch <= 'Z')
      ch = ch - 'A' + 1;
    else if (ch >= 'a' && ch <= 'z')
      ch = ch - 'a' + 1;
    else if (ch >= '0' && ch <= '9')
      ch = ch - '0' + 27;
    else if (ch == ' ')
      ch = 0;
    else if (ch == '.')
      ch = 37;
    else if (ch == '/')
      ch = 38;
    else
      ch = 39;
    val = val * 40 + ch;
    if (i % 3 == 2) {
      *out++ = val;
      val = 0;
    }
  }
}

/* These values are bit-reversed from those in the NASA paper
   because the register shifts left */

int cnvcod[] = {042631, 047245, 073363, 056507, 077267, 064537};

/* tail-biting encoder
   in: array of radix-40 encoded 16 bit words
   out: baseband signal in xmit order, array of chars */
void enccnv(ushort in[], char out[])
{
  int sr, i, j, k, b, t;
  sr = in[MSGLENW-1];  /* init sr to last 15 bits */
  for (i = 0; i < MSGLENW; ++i) {
    for (j = 0; j < WLEN; ++j) {
      sr = (sr << 1) | (in[i] >> (15-j)) & 1;
      for (k = 0; k < RRATE; ++k) {
        b = 0;
        for (t = sr & cnvcod[k]; t; t &= t-1)
          b ^= 1;
        /* store */
#if INTLV
        out[k*MSGLENB + (j&7)*10 + ((j&8)>>3) + i*2] = b;
#else
        out[k*MSGLENB + j + i*WLEN] = b;
#endif
      }
    }
  }
}

char pnpat[] = {
0,0,1,1,1,1,1,0,1,0,1,0,1,1,0,0,0,0,1,1,0,1,0,1,1,0,0,1,0,1,0,0,1,0,0,0,1,0,0,1,
1,0,1,0,0,0,0,0,1,1,1,0,1,0,1,0,1,1,1,0,0,0,1,0,1,1,0,0,0,1,0,1,1,1,1,0,1,0,1,1,
1,1,0,0,1,0,0,0,1,0,0,1,1,1,0,1,0,1,0,0,0,1,0,1,1,0,0,0,1,0,1,0,1,1,0,1,1,0,1,0,
1,0,1,1,0,0,0,0,0,1,0,1,1,0,1,1,0,1,0,0,0,1,0,1,1,1,0,0,0,1,1,1,1,0,1,1,1,0,0,1,
1,0,1,1,0,1,0,0,1,1,1,0,1,0,0,1,1,0,1,0,1,0,0,1,0,0,0,1,1,1,0,1,0,0,1,0,0,0,1,1,
0,0,1,0,1,0,1,1,1,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,1,0,1,1,1,1,1,1,0,1,1,0,0,1,1,1,
1,1,0,1,0,0,1,0,1,0,1,0,1,1,0,1,0,0,1,0,1,0,0,0,1,0,1,0,1,1,0,0,0,0,0,0,0,0,0,0,
1,1,1,1,1,1,0,1,0,1,1,0,0,1,0,0,1,1,0,1,0,1,1,0,1,1,1,0,0,1,0,1,0,1,0,1,1,1,1,0,
1,1,0,0,1,0,0,0,0,0,0,1,1,1,1,1,0,0,1,1,0,0,0,1,1,1,1,1,0,1,0,0,0,0,0,0,1,0,0,1,
0,1,0,0,0,1,1,0,0,1,0,1,0,1,0,0,1,1,0,1,1,1,0,0,1,1,1,0,0,1,1,1,1,1,0,1,1,0,1,0,
1,0,0,1,1,1,0,0,0,0,0,1,0,0,1,0,1,0,0,0,0,1,1,0,0,0,0,1,1,0,1,0,1,1,1,0,1,0,1,1,
1,0,0,0,1,1,1,1,1,0,0,0,1,1,0,1,0,0,1,1,1,1,1,1,0,1,0,0,1,0,0,1,0,1,0,0,0,1,1,1,
};

Notes:  The interleave function is far from optimum but a lot better than
nothing.  The PN pattern was chosen literally at random, selecting for low
autocorrelation and for low autocorrelation with short substrings, but is
also far from optimum.  I would greatly appreciate it if you find a good
replacement pattern.

Hope this is useful.

73,

Stewart KK7KA


----- Original Message -----
From: "Talbot Andrew" <ACTALBOT@dera.gov.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, March 22, 2001 7:02 AM
Subject: LF: RE: Re: WOLF - Transmit?


> I would like add Wolf coding to my PIC based BPSK generator.
> Stuart, can you reveal the exact coding details, I can't find them in
> any of the documentation on the Web.   Just a comment that the mesage
> data is interleaved (?) with a PN Sequence to assist clock recovery and
> timing.
>
> Andy  G4JNT