// qra65.c
// Encoding/decoding functions for the QRA65 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 .
// -----------------------------------------------------------------------------
// 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
#include
#include "qra65.h"
#include "..\qracodes\qracodes.h"
#include "..\qracodes\qra13_64_64_irr_e.h"
#include "..\qracodes\pdmath.h"
// Code parameters of the QRA65 mode
#define QRA65_CODE qra_13_64_64_irr_e
#define QRA65_NMSG 218 // this must much the value indicated in QRA65_CODE.NMSG
#define QRA65_KC (QRA65_K+1) // information symbols crc included (as defined in the code)
#define QRA65_NC (QRA65_N+1) // codeword length (as defined in the code)
#define QRA65_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 qra65_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 0 for all the messages which are not text
// -------------------------------------------------------------------------------
qra65codec *qra65_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*(QRA65_KC)/(QRA65_NC);
qra65codec *pcodec = (qra65codec*)malloc(sizeof(qra65codec));
if (!pcodec)
return 0; // can't allocate memory
pcodec->decEsNoMetric = 1.0f*QRA65_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 (26+1)
encodemsg_jt65(pcodec->apmask_cqqrz_ooo, MASK_CQQRZ,0, MASK_GRIDFULL); // AP42 (26+16)
// 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 (28+1)
encodemsg_jt65(pcodec->apmask_call1_ooo, MASK_CALL1, 0, MASK_GRIDFULL); // AP44 (28+16)
// set mask for [mycall srccall ?] messages
encodemsg_jt65(pcodec->apmask_call1_call2,MASK_CALL1, MASK_CALL2, MASK_GRIDBIT); // AP56 (28+28)
return pcodec;
}
void qra65_encode(qra65codec *pcodec, int *y, const int *x)
{
int encx[QRA65_KC]; // encoder input buffer
int ency[QRA65_NC]; // encoder output buffer
int call1,call2,grid;
memcpy(encx,x,QRA65_K*sizeof(int)); // copy input to the encoder buffer
encx[QRA65_K]=calc_crc6(encx,QRA65_K); // compute and add the crc symbol
qra_encode(&QRA65_CODE, ency, encx); // encode msg+crc using the given QRA code
// copy codeword to output puncturing the crc symbol
memcpy(y,ency,QRA65_K*sizeof(int)); // copy the information symbols
memcpy(y+QRA65_K,ency+QRA65_KC,QRA65_C*sizeof(int)); // copy the parity check 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, so we still don't know who can reply us (srccall)
// reset apsrccall to 0 so that the decoder won't look for [mycall srccall ?] msgs
pcodec->apsrccall = 0;
}
else {
// we are replying someone named call1
// set apmsg_call1_call2 so that the decoder will attempt to decode [mycall call1 ?] msgs
pcodec->apsrccall = call1;
encodemsg_jt65(pcodec->apmsg_call1_call2, pcodec->apmycall, pcodec->apsrccall, 0);
}
}
int qra65_decode(qra65codec *pcodec, int *x, const float *rxen)
{
uint k;
float *srctmp, *dsttmp;
float ix[QRA65_NC*QRA65_M]; // (depunctured) intrisic information to the decoder
int rc;
// sanity check
if (QRA65_NMSG!=QRA65_CODE.NMSG)
return -16; // QRA65_NMSG define is wrong
// compute symbols intrinsic probabilities from received energy observations
qra_mfskbesselmetric(ix, rxen, QRA65_m, QRA65_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,QRA65_M, QRA65_NC-1); // point to the last symbol prob dist
srctmp = dsttmp-QRA65_M; // source is the previous pd
for (k=0;k=0) return 0; // successfull decode with 0 ap
if (pcodec->apflags!=QRA_AUTOAP) return rc; // rc<0 = unsuccessful decode
// attempt to decode CQ calls
rc = qra65_do_decode(x, ix, pcodec->apmask_cqqrz, pcodec->apmsg_cqqrz); // 27 bit AP
if (rc>=0) return 1; // decoded [cq/qrz ? ?]
rc = qra65_do_decode(x, ix, pcodec->apmask_cqqrz_ooo, pcodec->apmsg_cqqrz); // 44 bit AP
if (rc>=0) return 2; // decoded [cq ? ooo]
// attempt to decode calls directed to us (mycall)
rc = qra65_do_decode(x, ix, pcodec->apmask_call1, pcodec->apmsg_call1); // 29 bit AP
if (rc>=0) return 3; // decoded [mycall ? ?]
rc = qra65_do_decode(x, ix, pcodec->apmask_call1_ooo, pcodec->apmsg_call1); // 45 bit AP
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 = qra65_do_decode(x, ix, pcodec->apmask_call1_call2, pcodec->apmsg_call1_call2); // 57 bit AP
if (rc>=0) return 5; // decoded [mycall srccall ?]
return rc;
}
// static functions definitions ----------------------------------------------------------------
// decode with given a-priori information
static int qra65_do_decode(int *x, const float *pix, const int *ap_mask, const int *ap_x)
{
int rc;
const float *ixsrc;
float ix_masked[QRA65_NC*QRA65_M]; // (masked) intrinsic information to the decoder
float ex[QRA65_NC*QRA65_M]; // extrinsic information from the decoder
float v2cmsg[QRA65_NMSG*QRA65_M]; // buffers for the decoder messages
float c2vmsg[QRA65_NMSG*QRA65_M];
int xdec[QRA65_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(&QRA65_CODE,ex,ixsrc,QRA65_NITER,v2cmsg,c2vmsg);
if (rc<0)
return -1; // no convergence in given iterations
// decode
qra_mapdecode(&QRA65_CODE,xdec,ex,ixsrc);
// verify crc
if (calc_crc6(xdec,QRA65_K)!=xdec[QRA65_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,QRA65_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 (as suggested by Joe. 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>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
uint k,kk, smask;
float *row;
memcpy(dst,src,(QRA65_NC*QRA65_M)*sizeof(float));
for (k=0;k>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;
}