WSJT-X/lib/qra/qra64/qra64.c

/*
qra64.c 
Encoding/decoding functions for the QRA64 mode

(c) 2016 - Nico Palermo, IV3NWV

-------------------------------------------------------------------------------

   qracodes 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 of the License, or
   (at your option) any later version.
   qracodes 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 qracodes source distribution.  
   If not, see <http://www.gnu.org/licenses/>.

-----------------------------------------------------------------------------

Code used in this sowftware release:

QRA13_64_64_IRR_E: K=13 N=64 Q=64 irregular QRA code (defined in 
qra13_64_64_irr_e.h /.c)

Codes with K=13 are designed to include a CRC as the 13th information symbol
and improve the code UER (Undetected Error Rate).
The CRC symbol is not sent along the channel (the codes are punctured) and the 
resulting code is a (12,63) code 
*/
//----------------------------------------------------------------------------

#include <stdlib.h>
#include <math.h>

#include "qra64.h"
#include "../qracodes/qracodes.h"
#include "../qracodes/qra13_64_64_irr_e.h"
#include "../qracodes/pdmath.h"

// Code parameters of the QRA64 mode 
#define QRA64_CODE  qra_13_64_64_irr_e
#define QRA64_NMSG  218        // Must much value indicated in QRA64_CODE.NMSG

#define QRA64_KC (QRA64_K+1)   // Information symbols (crc included)
#define QRA64_NC (QRA64_N+1)   // Codeword length (as defined in the code)
#define QRA64_NITER 100	       // max number of iterations per decode

// static functions declarations ----------------------------------------------
static int  calc_crc6(const int *x, int sz);
static void ix_mask(float *dst, const float *src, const int *mask, 
		    const int *x);
static int  qra64_do_decode(int *x, const float *pix, const int *ap_mask, 
			    const int *ap_x);

// a-priori information masks for fields in JT65-like msgs --------------------
#define MASK_CQQRZ      0xFFFFFFC // CQ/QRZ calls common bits
#define MASK_CALL1      0xFFFFFFF
#define MASK_CALL2      0xFFFFFFF
#define MASK_GRIDFULL	0xFFFF
#define MASK_GRIDBIT	0x8000	  // b[15] is 1 for free text, 0 otherwise
// ----------------------------------------------------------------------------

qra64codec *qra64_init(int flags, const int mycall)
{

  // Eb/No value for which we optimize the decoder metric
  const float EbNodBMetric = 2.8f; 
  const float EbNoMetric   = (float)pow(10,EbNodBMetric/10);
  const float R = 1.0f*(QRA64_KC)/(QRA64_NC);	

  qra64codec *pcodec = (qra64codec*)malloc(sizeof(qra64codec));

  if (!pcodec)
    return 0;	// can't allocate memory

  pcodec->decEsNoMetric   = 1.0f*QRA64_m*R*EbNoMetric;
  pcodec->apflags			= flags;

  if (flags!=QRA_AUTOAP)
    return pcodec;

  // initialize messages and mask for decoding with a-priori information

  pcodec->apmycall  = mycall;
  pcodec->apsrccall = 0;	

  // encode CQ/QRZ messages and masks
  // NOTE: Here we handle only CQ and QRZ msgs
  // 'CQ nnn', 'CQ DX' and 'DE' msgs 
  // will be handled by the decoder as messages with no a-priori knowledge
  encodemsg_jt65(pcodec->apmsg_cqqrz, CALL_CQ, 0, GRID_BLANK);
  encodemsg_jt65(pcodec->apmask_cqqrz, MASK_CQQRZ,0, MASK_GRIDBIT);     // AP27
  encodemsg_jt65(pcodec->apmask_cqqrz_ooo, MASK_CQQRZ,0, MASK_GRIDFULL);// AP42

  // encode [mycall ? x] messages and set masks
  encodemsg_jt65(pcodec->apmsg_call1,  mycall,  0, GRID_BLANK);
  encodemsg_jt65(pcodec->apmask_call1, MASK_CALL1, 0, MASK_GRIDBIT);	// AP29
  encodemsg_jt65(pcodec->apmask_call1_ooo, MASK_CALL1,0, MASK_GRIDFULL);// AP44

  // set mask for  [mycall srccall ?] messages
  encodemsg_jt65(pcodec->apmask_call1_call2,MASK_CALL1,MASK_CALL2, 
		 MASK_GRIDBIT);                                         // AP56
  return pcodec;
}

void qra64_encode(qra64codec *pcodec, int *y, const int *x)
{
  int encx[QRA64_KC];	// encoder input buffer
  int ency[QRA64_NC];	// encoder output buffer

  int call1,call2,grid;

  memcpy(encx,x,QRA64_K*sizeof(int));		// Copy input to encoder buffer
  encx[QRA64_K]=calc_crc6(encx,QRA64_K);	// Compute and add crc symbol
  qra_encode(&QRA64_CODE, ency, encx);	 // encode msg+crc using given QRA code

  // copy codeword to output puncturing the crc symbol 
  memcpy(y,ency,QRA64_K*sizeof(int));		// copy information symbols 
  memcpy(y+QRA64_K,ency+QRA64_KC,QRA64_C*sizeof(int)); // copy parity symbols 

  if (pcodec->apflags!=QRA_AUTOAP)
    return;

  // look if the msg sent is a std type message (bit15 of grid field = 0)
  if ((x[9]&0x80)==1)
    return;	// no, it's a text message

  // It's a [call1 call2 grid] message

  // We assume that call2 is our call (but we don't check it)
  // call1 the station callsign we are calling or indicates a general call (CQ/QRZ/etc..)
  decodemsg_jt65(&call1,&call2,&grid,x);
	
  if ((call1>=CALL_CQ && call1<=CALL_CQ999) || call1==CALL_CQDX || 
      call1==CALL_DE) {
    // We are making a general call; don't know who might reply (srccall)
    // Reset apsrccall to 0 so decoder won't look for [mycall srccall ?] msgs
    pcodec->apsrccall = 0;
  } else {
    // We are replying to someone named call1
    // Set apmsg_call1_call2 so decoder will try for [mycall call1 ?] msgs
    pcodec->apsrccall = call1;
    encodemsg_jt65(pcodec->apmsg_call1_call2, pcodec->apmycall, 
		   pcodec->apsrccall, 0);
  }
}

int qra64_decode(qra64codec *pcodec, int *x, const float *rxen)
{
  int k;
  float *srctmp, *dsttmp;
  float ix[QRA64_NC*QRA64_M];		// (depunctured) intrisic information
  int rc;
  
  if (QRA64_NMSG!=QRA64_CODE.NMSG)      // sanity check 
    return -16;				// QRA64_NMSG define is wrong

  // compute symbols intrinsic probabilities from received energy observations
  qra_mfskbesselmetric(ix, rxen, QRA64_m, QRA64_N,pcodec->decEsNoMetric);

  // de-puncture observations adding a uniform distribution for the crc symbol

  // move check symbols distributions one symbol towards the end
  dsttmp = PD_ROWADDR(ix,QRA64_M, QRA64_NC-1);	//Point to last symbol prob dist
  srctmp = dsttmp-QRA64_M;              // source is the previous pd
  for (k=0;k<QRA64_C;k++) {
    pd_init(dsttmp,srctmp,QRA64_M);
    dsttmp -=QRA64_M;
    srctmp -=QRA64_M;
  }
  // Initialize crc prob to a uniform distribution
  pd_init(dsttmp,pd_uniform(QRA64_m),QRA64_M);

  // Attempt to decode without a-priori info --------------------------------
  rc = qra64_do_decode(x, ix, NULL, NULL);
  if (rc>=0) return 0;                        // successfull decode with AP0

  if (pcodec->apflags!=QRA_AUTOAP) return rc; // rc<0 = unsuccessful decode

  // Attempt to decode CQ calls
  rc = qra64_do_decode(x,ix,pcodec->apmask_cqqrz, pcodec->apmsg_cqqrz); // AP27
  if (rc>=0) return 1;	                      // decoded [cq/qrz ? ?]

  rc = qra64_do_decode(x, ix, pcodec->apmask_cqqrz_ooo, 
		       pcodec->apmsg_cqqrz);	                        // AP42
  if (rc>=0) return 2;	                      // decoded [cq ? ooo]

  // attempt to decode calls directed to us (mycall)
  rc = qra64_do_decode(x, ix, pcodec->apmask_call1, 
		       pcodec->apmsg_call1);		                // AP29
  if (rc>=0) return 3;	                      // decoded [mycall ? ?]

  rc = qra64_do_decode(x, ix, pcodec->apmask_call1_ooo, 
		       pcodec->apmsg_call1);	                        // AP44
  if (rc>=0) return 4;	// decoded [mycall ? ooo]

  // if apsrccall is set attempt to decode [mycall srccall ?] msgs
  if (pcodec->apsrccall==0) return rc; // nothing more to do

  rc = qra64_do_decode(x, ix, pcodec->apmask_call1_call2, 
		       pcodec->apmsg_call1_call2);	                // AP57
  if (rc>=0) return 5;	// decoded [mycall srccall ?]	

  return rc;	
}

// Static functions definitions ----------------------------------------------

// Decode with given a-priori information 
static int qra64_do_decode(int *x, const float *pix, const int *ap_mask, 
			   const int *ap_x)
{
  int rc;
  const float *ixsrc;
  float ix_masked[QRA64_NC*QRA64_M];  // Masked intrinsic information
  float ex[QRA64_NC*QRA64_M];	      // Extrinsic information from the decoder

  float v2cmsg[QRA64_NMSG*QRA64_M];   // buffers for the decoder messages
  float c2vmsg[QRA64_NMSG*QRA64_M];
  int   xdec[QRA64_KC];

  if (ap_mask==NULL) {   // no a-priori information
    ixsrc = pix;	 // intrinsic source is what passed as argument
  } else {	
    // a-priori information provided
    // mask channel observations with a-priori 
    ix_mask(ix_masked,pix,ap_mask,ap_x);
    ixsrc = ix_masked;	// intrinsic source is the masked version
  }

  // run the decoding algorithm
  rc = qra_extrinsic(&QRA64_CODE,ex,ixsrc,QRA64_NITER,v2cmsg,c2vmsg);
  if (rc<0)
    return -1;	// no convergence in given iterations

  // decode 
  qra_mapdecode(&QRA64_CODE,xdec,ex,ixsrc);

  // verify crc
  if (calc_crc6(xdec,QRA64_K)!=xdec[QRA64_K]) // crc doesn't match (detected error)
    return -2;	// decoding was succesfull but crc doesn't match

  // success. copy decoded message to output buffer
  memcpy(x,xdec,QRA64_K*sizeof(int));

  return 0;
}
// crc functions --------------------------------------------------------------
// crc-6 generator polynomial
// g(x) = x^6 + a5*x^5 + ... + a1*x + a0

// g(x) = x^6 + x + 1  
#define CRC6_GEN_POL 0x30  // MSB=a0 LSB=a5    

// g(x) = x^6 + x^2 + x + 1 (See:  https://users.ece.cmu.edu/~koopman/crc/)
// #define CRC6_GEN_POL 0x38  // MSB=a0 LSB=a5. Simulation results are similar

static int calc_crc6(const int *x, int sz)
{
  // todo: compute it faster using a look up table
  int k,j,t,sr = 0;
  for (k=0;k<sz;k++) {
    t = x[k];
    for (j=0;j<6;j++) {
      if ((t^sr)&0x01)
	sr = (sr>>1) ^ CRC6_GEN_POL;
      else
	sr = (sr>>1);
      t>>=1;
    }
  }
  return sr;
}

static void ix_mask(float *dst, const float *src, const int *mask, 
		    const int *x)
{
  // mask intrinsic information (channel observations) with a priori knowledge
	
  int k,kk, smask;
  float *row;

  memcpy(dst,src,(QRA64_NC*QRA64_M)*sizeof(float));

  for (k=0;k<QRA64_K;k++) {	// we can mask only information symbols distrib
    smask = mask[k];
    row = PD_ROWADDR(dst,QRA64_M,k);
    if (smask) {
      for (kk=0;kk<QRA64_M;kk++) 
	if (((kk^x[k])&smask)!=0)
	  *(row+kk) = 0.f;

      pd_norm(row,QRA64_m);
    }
  }
}

// encode/decode msgs as done in JT65
void encodemsg_jt65(int *y, const int call1, const int call2, const int grid)
{
  y[0]= (call1>>22)&0x3F;
  y[1]= (call1>>16)&0x3F;
  y[2]= (call1>>10)&0x3F;
  y[3]= (call1>>4)&0x3F;
  y[4]= (call1<<2)&0x3F;

  y[4] |= (call2>>26)&0x3F;
  y[5]= (call2>>20)&0x3F;
  y[6]= (call2>>14)&0x3F;
  y[7]= (call2>>8)&0x3F;
  y[8]= (call2>>2)&0x3F;
  y[9]= (call2<<4)&0x3F;

  y[9] |= (grid>>12)&0x3F;
  y[10]= (grid>>6)&0x3F;
  y[11]= (grid)&0x3F;

}
void decodemsg_jt65(int *call1, int *call2, int *grid, const int *x)
{
  int nc1, nc2, ng;

  nc1 = x[4]>>2;
  nc1 |= x[3]<<4;
  nc1 |= x[2]<<10;
  nc1 |= x[1]<<16;
  nc1 |= x[0]<<22;

  nc2 = x[9]>>4;
  nc2 |= x[8]<<2;
  nc2 |= x[7]<<8;
  nc2 |= x[6]<<14;
  nc2 |= x[5]<<20;
  nc2 |= (x[4]&0x03)<<26;

  ng   = x[11];
  ng  |= x[10]<<6;
  ng  |= (x[9]&0x0F)<<12;

  *call1 = nc1;
  *call2 = nc2;
  *grid  = ng;
}