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horusdemodlib/src/fsk.c

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32 KiB
C
Czysty Bezpośredni odnośnik Wina Historia

/*---------------------------------------------------------------------------*\
FILE........: fsk.c
AUTHOR......: Brady O'Brien & David Rowe
DATE CREATED: 7 January 2016
C Implementation of 2/4FSK modulator/demodulator, based on octave/fsk_lib.m
\*---------------------------------------------------------------------------*/
/*
Copyright (C) 2016-2020 David Rowe
All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License version 2.1, as
published by the Free Software Foundation. This program 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 Lesser General Public License
along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
/*---------------------------------------------------------------------------*\
DEFINES
\*---------------------------------------------------------------------------*/
/* Define this to enable EbNodB estimate */
/* This needs square roots, may take more cpu time than it's worth */
#define EST_EBNO
/* This is a flag to make the mod/demod allocate their memory on the stack instead of the heap */
/* At large sample rates, there's not enough stack space to run the demod */
#define DEMOD_ALLOC_STACK
/* This is a flag for the freq. estimator to use a precomputed/rt computed hann window table
On platforms with slow cosf, this will produce a substantial speedup at the cost of a small
amount of memory
*/
#define USE_HANN_TABLE
/* This flag turns on run-time hann table generation. If USE_HANN_TABLE is unset,
this flag has no effect. If USE_HANN_TABLE is set and this flag is set, the
hann table will be allocated and generated when fsk_init or fsk_init_hbr is
called. If this flag is not set, a hann function table of size fsk->Ndft MUST
be provided. On small platforms, this can be used with a precomputed table to
save memory at the cost of flash space.
*/
#define GENERATE_HANN_TABLE_RUNTIME
/* Turn off table generation if on cortex M4 to save memory */
#ifdef CORTEX_M4
#undef USE_HANN_TABLE
#endif
/*---------------------------------------------------------------------------*\
INCLUDES
\*---------------------------------------------------------------------------*/
#include <assert.h>
#include <stdlib.h>
#include <stdint.h>
#include <math.h>
#include "fsk.h"
#include "comp_prim.h"
#include "kiss_fftr.h"
#include "modem_probe.h"
/*---------------------------------------------------------------------------*\
FUNCTIONS
\*---------------------------------------------------------------------------*/
static void stats_init(struct FSK *fsk);
#ifdef USE_HANN_TABLE
/*
This is used by fsk_create and fsk_create_hbr to generate a hann function
table
*/
static void fsk_generate_hann_table(struct FSK* fsk){
int Ndft = fsk->Ndft;
size_t i;
for(i=0; i<Ndft; i++){
fsk->hann_table[i] = 0.5 - 0.5 * cosf(2.0 * M_PI * (float)i / (float) (Ndft-1));
}
}
#endif
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_create_core
AUTHOR......: Brady O'Brien
DATE CREATED: 7 January 2016
In this version of the demod the stdanard/hbr modes have been
largely combined at they shared so much common code. The
fsk_create/fsk_create_hbr function interface has been retained to
maximise compatability with existing applications.
\*---------------------------------------------------------------------------*/
struct FSK * fsk_create_core(int Fs, int Rs, int M, int P, int Nsym, int tx_f1, int tx_fs)
{
struct FSK *fsk;
int i;
/* Check configuration validity */
assert(Fs > 0 );
assert(Rs > 0 );
assert(tx_f1 > 0);
assert(tx_fs > 0);
assert(P > 0);
assert(Nsym > 0);
/* Ts (Fs/Rs) must be an integer */
assert( (Fs%Rs) == 0 );
/* Ts/P (Fs/Rs/P) must be an integer */
assert( ((Fs/Rs)%P) == 0 );
assert( M==2 || M==4);
fsk = (struct FSK*) malloc(sizeof(struct FSK)); assert(fsk != NULL);
// Need enough bins to with 10% of tone centre
float bin_width_Hz = 0.1*Rs;
float Ndft = (float)Fs/bin_width_Hz;
Ndft = pow(2.0, ceil(log2(Ndft)));
/* Set constant config parameters */
fsk->Fs = Fs;
fsk->Rs = Rs;
fsk->Ts = Fs/Rs;
fsk->burst_mode = 0;
fsk->P = P;
fsk->Nsym = Nsym;
fsk->N = fsk->Ts*fsk->Nsym;
fsk->Ndft = Ndft;
fsk->tc = 0.1;
fsk->Nmem = fsk->N+(2*fsk->Ts);
fsk->f1_tx = tx_f1;
fsk->fs_tx = tx_fs;
fsk->nin = fsk->N;
fsk->lock_nin = 0;
fsk->mode = M==2 ? MODE_2FSK : MODE_4FSK;
fsk->Nbits = M==2 ? fsk->Nsym : fsk->Nsym*2;
fsk->est_min = 0;
fsk->est_max = Fs;
fsk->est_space = 0.75*Rs;
//printf("C.....: M: %d Fs: %d Rs: %d Ts: %d nsym: %d nbit: %d N: %d Ndft: %d fmin: %d fmax: %d\n",
// M, fsk->Fs, fsk->Rs, fsk->Ts, fsk->Nsym, fsk->Nbits, fsk->N, fsk->Ndft, fsk->est_min, fsk->est_max);
/* Set up rx state */
for(i=0; i<M; i++)
fsk->phi_c[i] = comp_exp_j(0);
fsk->f_dc = (COMP*)malloc(M*fsk->Nmem*sizeof(COMP)); assert(fsk->f_dc != NULL);
for(i=0; i<M*fsk->Nmem; i++)
fsk->f_dc[i] = comp0();
fsk->fft_cfg = kiss_fft_alloc(Ndft,0,NULL,NULL); assert(fsk->fft_cfg != NULL);
fsk->Sf = (float*)malloc(sizeof(float)*fsk->Ndft); assert(fsk->Sf != NULL);
#ifdef USE_HANN_TABLE
#ifdef GENERATE_HANN_TABLE_RUNTIME
fsk->hann_table = (float*)malloc(sizeof(float)*fsk->Ndft); assert(fsk->hann_table != NULL);
fsk_generate_hann_table(fsk);
#else
fsk->hann_table = NULL;
#endif
#endif
for(i=0;i<Ndft;i++)fsk->Sf[i] = 0;
fsk->norm_rx_timing = 0;
/* Set up tx state */
fsk->tx_phase_c = comp_exp_j(0);
/* Set up demod stats */
fsk->EbNodB = 0;
for( i=0; i<M; i++)
fsk->f_est[i] = 0;
fsk->ppm = 0;
fsk->stats = (struct MODEM_STATS*)malloc(sizeof(struct MODEM_STATS)); assert(fsk->stats != NULL);
stats_init(fsk);
fsk->normalise_eye = 1;
return fsk;
}
/*---------------------------------------------------------------------------* \
FUNCTION....: fsk_create
AUTHOR......: Brady O'Brien
DATE CREATED: 7 January 2016
Create and initialize an instance of the FSK modem. Returns a pointer
to the modem state/config struct. One modem config struct may be used
for both mod and demod.
\*---------------------------------------------------------------------------*/
struct FSK * fsk_create(int Fs, int Rs, int M, int tx_f1, int tx_fs) {
return fsk_create_core(Fs, Rs, M, FSK_DEFAULT_P, FSK_DEFAULT_NSYM, tx_f1, tx_fs);
}
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_create_hbr
AUTHOR......: Brady O'Brien
DATE CREATED: 11 February 2016
Alternate version of create allows user defined decimation P and
Nsym. In the current version of the demod it's simply an alias for
the default core function.
P is the decimation rate, so the intermal demod processing happens
at Fs/P Hz. Nsym is the number of symbols we average demod
parameters like symbol timing over.
\*---------------------------------------------------------------------------*/
struct FSK * fsk_create_hbr(int Fs, int Rs, int M, int P, int Nsym, int tx_f1, int tx_fs) {
return fsk_create_core(Fs, Rs, M, P, Nsym, tx_f1, tx_fs);
}
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_destroy
AUTHOR......: Brady O'Brien
DATE CREATED: 11 February 2016
Call this to free all memory and shut down the modem.
\*---------------------------------------------------------------------------*/
void fsk_destroy(struct FSK *fsk){
free(fsk->f_dc);
free(fsk->fft_cfg);
free(fsk->stats);
free(fsk->hann_table);
free(fsk);
}
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_mod
AUTHOR......: Brady O'Brien
DATE CREATED: 11 February 2016
FSK modulator function, real valued output samples.
\*---------------------------------------------------------------------------*/
void fsk_mod(struct FSK *fsk,float fsk_out[],uint8_t tx_bits[]){
COMP tx_phase_c = fsk->tx_phase_c; /* Current complex TX phase */
int f1_tx = fsk->f1_tx; /* '0' frequency */
int fs_tx = fsk->fs_tx; /* space between frequencies */
int Ts = fsk->Ts; /* samples-per-symbol */
int Fs = fsk->Fs; /* sample freq */
int M = fsk->mode;
COMP dosc_f[M]; /* phase shift per sample */
COMP dph; /* phase shift of current bit */
size_t i,j,m,bit_i,sym;
/* Init the per sample phase shift complex numbers */
for( m=0; m<M; m++){
dosc_f[m] = comp_exp_j(2*M_PI*((float)(f1_tx+(fs_tx*m))/(float)(Fs)));
}
bit_i = 0;
for( i=0; i<fsk->Nsym; i++){
sym = 0;
/* Pack the symbol number from the bit stream */
for( m=M; m>>=1; ){
uint8_t bit = tx_bits[bit_i];
bit = (bit==1)?1:0;
sym = (sym<<1)|bit;
bit_i++;
}
/* Look up symbol phase shift */
dph = dosc_f[sym];
/* Spin the oscillator for a symbol period */
for(j=0; j<Ts; j++){
tx_phase_c = cmult(tx_phase_c,dph);
fsk_out[i*Ts+j] = 2*tx_phase_c.real;
}
}
/* Normalize TX phase to prevent drift */
tx_phase_c = comp_normalize(tx_phase_c);
/* save TX phase */
fsk->tx_phase_c = tx_phase_c;
}
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_mod_c
AUTHOR......: Brady O'Brien
DATE CREATED: 11 February 2016
FSK modulator function, complex valued output samples.
\*---------------------------------------------------------------------------*/
void fsk_mod_c(struct FSK *fsk,COMP fsk_out[],uint8_t tx_bits[]){
COMP tx_phase_c = fsk->tx_phase_c; /* Current complex TX phase */
int f1_tx = fsk->f1_tx; /* '0' frequency */
int fs_tx = fsk->fs_tx; /* space between frequencies */
int Ts = fsk->Ts; /* samples-per-symbol */
int Fs = fsk->Fs; /* sample freq */
int M = fsk->mode;
COMP dosc_f[M]; /* phase shift per sample */
COMP dph; /* phase shift of current bit */
size_t i,j,bit_i,sym;
int m;
/* Init the per sample phase shift complex numbers */
for( m=0; m<M; m++){
dosc_f[m] = comp_exp_j(2*M_PI*((float)(f1_tx+(fs_tx*m))/(float)(Fs)));
}
bit_i = 0;
for( i=0; i<fsk->Nsym; i++){
sym = 0;
/* Pack the symbol number from the bit stream */
for( m=M; m>>=1; ){
uint8_t bit = tx_bits[bit_i];
bit = (bit==1)?1:0;
sym = (sym<<1)|bit;
bit_i++;
}
/* Look up symbol phase shift */
dph = dosc_f[sym];
/* Spin the oscillator for a symbol period */
for(j=0; j<Ts; j++){
tx_phase_c = cmult(tx_phase_c,dph);
fsk_out[i*Ts+j] = fcmult(2,tx_phase_c);
}
}
/* Normalize TX phase to prevent drift */
tx_phase_c = comp_normalize(tx_phase_c);
/* save TX phase */
fsk->tx_phase_c = tx_phase_c;
}
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_mod_ext_vco
AUTHOR......: David Rowe
DATE CREATED: February 2018
Modulator that assume an external VCO. The output is a voltage
that changes for each symbol.
\*---------------------------------------------------------------------------*/
void fsk_mod_ext_vco(struct FSK *fsk, float vco_out[], uint8_t tx_bits[]) {
int f1_tx = fsk->f1_tx; /* '0' frequency */
int fs_tx = fsk->fs_tx; /* space between frequencies */
int Ts = fsk->Ts; /* samples-per-symbol */
int M = fsk->mode;
int i, j, m, sym, bit_i;
bit_i = 0;
for(i=0; i<fsk->Nsym; i++) {
/* generate the symbol number from the bit stream,
e.g. 0,1 for 2FSK, 0,1,2,3 for 4FSK */
sym = 0;
/* unpack the symbol number from the bit stream */
for( m=M; m>>=1; ){
uint8_t bit = tx_bits[bit_i];
bit = (bit==1)?1:0;
sym = (sym<<1)|bit;
bit_i++;
}
/*
Map 'sym' to VCO frequency
Note: drive is inverted, a higher tone drives VCO voltage lower
*/
//fprintf(stderr, "i: %d sym: %d freq: %f\n", i, sym, f1_tx + fs_tx*(float)sym);
for(j=0; j<Ts; j++) {
vco_out[i*Ts+j] = f1_tx + fs_tx*(float)sym;
}
}
}
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_nin
AUTHOR......: Brady O'Brien
DATE CREATED: 11 February 2016
Call me before each call to fsk_demod() to determine how many new
samples you should pass in. the number of samples will vary due to
timing variations.
\*---------------------------------------------------------------------------*/
uint32_t fsk_nin(struct FSK *fsk){
return (uint32_t)fsk->nin;
}
/*
* Internal function to estimate the frequencies of the FSK tones.
* This is split off because it is fairly complicated, needs a bunch of memory, and probably
* takes more cycles than the rest of the demod.
* Parameters:
* fsk - FSK struct from demod containing FSK config
* fsk_in - block of samples in this demod cycles, must be nin long
* freqs - Array for the estimated frequencies
* M - number of frequency peaks to find
*/
void fsk_demod_freq_est(struct FSK *fsk, COMP fsk_in[], float *freqs, int M) {
int Ndft = fsk->Ndft;
int Fs = fsk->Fs;
int nin = fsk->nin;
size_t i,j;
float hann;
float max;
int imax;
kiss_fft_cfg fft_cfg = fsk->fft_cfg;
int freqi[M];
int st,en,f_zero;
/* Array to do complex FFT from using kiss_fft */
#ifdef DEMOD_ALLOC_STACK
kiss_fft_cpx *fftin = (kiss_fft_cpx*)alloca(sizeof(kiss_fft_cpx)*Ndft);
kiss_fft_cpx *fftout = (kiss_fft_cpx*)alloca(sizeof(kiss_fft_cpx)*Ndft);
#else
kiss_fft_cpx *fftin = (kiss_fft_cpx*)malloc(sizeof(kiss_fft_cpx)*Ndft);
kiss_fft_cpx *fftout = (kiss_fft_cpx*)malloc(sizeof(kiss_fft_cpx)*Ndft);
#endif
st = (fsk->est_min*Ndft)/Fs + Ndft/2; if (st < 0) st = 0;
en = (fsk->est_max*Ndft)/Fs + Ndft/2; if (en > Ndft) en = Ndft;
//fprintf(stderr, "min: %d max: %d st: %d en: %d\n", fsk->est_min, fsk->est_max, st, en);
f_zero = (fsk->est_space*Ndft)/Fs;
int numffts = floor((float)nin/(Ndft/2)) - 1;
for(j=0; j<numffts; j++){
int a = j*Ndft/2;
//fprintf(stderr, "numffts: %d j: %d a: %d\n", numffts, (int)j, a);
/* Copy FSK buffer into reals of FFT buffer and apply a hann window */
for(i=0; i<Ndft; i++){
#ifdef USE_HANN_TABLE
hann = fsk->hann_table[i];
#else
hann = 0.5 - 0.5 * cosf(2.0 * M_PI * (float)i / (float) (fft_samps-1));
#endif
fftin[i].r = hann*fsk_in[i+a].real;
fftin[i].i = hann*fsk_in[i+a].imag;
}
/* Do the FFT */
kiss_fft(fft_cfg,fftin,fftout);
/* FFT shift to put DC bin at Ndft/2 */
kiss_fft_cpx tmp;
for(i=0; i<Ndft/2; i++) {
tmp = fftout[i];
fftout[i] = fftout[i+Ndft/2];
fftout[i+Ndft/2] = tmp;
}
/* Find the magnitude^2 of each freq slot */
for(i=0; i<Ndft; i++) {
fftout[i].r = (fftout[i].r*fftout[i].r) + (fftout[i].i*fftout[i].i) ;
}
/* Mix back in with the previous fft block */
/* Copy new fft est into imag of fftout for frequency divination below */
float tc = fsk->tc;
for(i=0; i<Ndft; i++){
fsk->Sf[i] = (fsk->Sf[i]*(1-tc)) + (sqrtf(fftout[i].r)*tc);
fftout[i].i = fsk->Sf[i];
}
}
modem_probe_samp_f("t_Sf",fsk->Sf,Ndft);
max = 0;
/* Find the M frequency peaks here */
for(i=0; i<M; i++){
imax = 0;
max = 0;
for(j=st;j<en;j++){
if(fftout[j].i > max){
max = fftout[j].i;
imax = j;
}
}
/* Blank out FMax +/-Fspace/2 */
int f_min, f_max;
f_min = imax - f_zero;
f_min = f_min < 0 ? 0 : f_min;
f_max = imax + f_zero;
f_max = f_max > Ndft ? Ndft : f_max;
for(j=f_min; j<f_max; j++)
fftout[j].i = 0;
/* Stick the freq index on the list */
freqi[i] = imax - Ndft/2;
}
/* Gnome sort the freq list */
/* My favorite sort of sort*/
i = 1;
while(i<M){
if(freqi[i] >= freqi[i-1]) i++;
else{
j = freqi[i];
freqi[i] = freqi[i-1];
freqi[i-1] = j;
if(i>1) i--;
}
}
/* Convert freqs from indices to frequencies */
for(i=0; i<M; i++){
freqs[i] = (float)(freqi[i])*((float)Fs/(float)Ndft);
}
/* Search for each tone method 2 - correlate with mask with non-zero entries at tone spacings ----- */
/* construct mask */
float mask[Ndft];
for(i=0; i<Ndft; i++) mask[i] = 0.0;
for(i=0;i<3; i++) mask[i] = 1.0;
int bin=0;
for(int m=1; m<=M-1; m++) {
bin = round((float)m*fsk->fs_tx*Ndft/Fs)-1;
for(i=bin; i<=bin+2; i++) mask[i] = 1.0;
}
int len_mask = bin+2+1;
#ifdef MODEMPROBE_ENABLE
modem_probe_samp_f("t_mask",mask,len_mask);
#endif
/* drag mask over Sf, looking for peak in correlation */
int b_max = st; float corr_max = 0.0;
float *Sf = fsk->Sf;
for (int b=st; b<en-len_mask; b++) {
float corr = 0.0;
for(i=0; i<len_mask; i++)
corr += mask[i] * Sf[b+i];
if (corr > corr_max) {
corr_max = corr;
b_max = b;
}
}
float foff = (b_max-Ndft/2)*Fs/Ndft;
//fprintf(stderr, "fsk->fs_tx: %d\n",fsk->fs_tx);
for (int m=0; m<M; m++)
fsk->f2_est[m] = foff + m*fsk->fs_tx;
#ifdef MODEMPROBE_ENABLE
modem_probe_samp_f("t_f2_est",fsk->f2_est,M);
#endif
#ifndef DEMOD_ALLOC_STACK
free(fftin);
free(fftout);
#endif
}
/* core demodulator function */
void fsk_demod_core(struct FSK *fsk, uint8_t rx_bits[], float rx_sd[], COMP fsk_in[]){
int N = fsk->N;
int Ts = fsk->Ts;
int Rs = fsk->Rs;
int Fs = fsk->Fs;
int nsym = fsk->Nsym;
int nin = fsk->nin;
int P = fsk->P;
int Nmem = fsk->Nmem;
int M = fsk->mode;
size_t i,j,m;
float ft1;
COMP t[M]; /* complex number temps */
COMP t_c; /* another complex temp */
COMP *phi_c = fsk->phi_c;
COMP *f_dc = fsk->f_dc;
COMP phi_ft;
int nold = Nmem-nin;
COMP dphift;
float rx_timing,norm_rx_timing,old_norm_rx_timing,d_norm_rx_timing,appm;
float fc_avg,fc_tx;
float meanebno,stdebno,eye_max;
int neyesamp,neyeoffset;
#ifdef MODEMPROBE_ENABLE
#define NMP_NAME 26
char mp_name_tmp[NMP_NAME+1]; /* Temporary string for modem probe trace names */
#endif
/* Estimate tone frequencies */
fsk_demod_freq_est(fsk,fsk_in,fsk->f_est,M);
#ifdef MODEMPROBE_ENABLE
modem_probe_samp_f("t_f_est",fsk->f_est,M);
#endif
float *f_est;
if (fsk->freq_est_type){
f_est = fsk->f2_est;
}else{
f_est = fsk->f_est;
}
/* update filter (integrator) memory by shifting in nin samples */
for(m=0; m<M; m++) {
for(i=0,j=Nmem-nold; i<nold; i++,j++)
f_dc[m*Nmem+i] = f_dc[m*Nmem+j];
}
/* freq shift down to around DC, ensuring continuous phase from last frame */
COMP dphi_m;
for(m=0; m<M; m++) {
dphi_m = comp_exp_j(2*M_PI*((f_est[m])/(float)(Fs)));
for(i=nold,j=0; i<Nmem; i++,j++) {
phi_c[m] = cmult(phi_c[m],dphi_m);
f_dc[m*Nmem+i] = cmult(fsk_in[j],cconj(phi_c[m]));
//f_dc[m*Nmem+i] = cconj(phi_c[m]);
}
phi_c[m] = comp_normalize(phi_c[m]);
#ifdef MODEMPROBE_ENABLE
snprintf(mp_name_tmp,NMP_NAME,"t_f%zd_dc",m+1);
modem_probe_samp_c(mp_name_tmp,&f_dc[m*Nmem],Nmem);
#endif
}
/* integrate over symbol period at a variety of offsets */
COMP f_int[M][(nsym+1)*P];
for(i=0; i<(nsym+1)*P; i++) {
int st = i*Ts/P;
int en = st+Ts-1;
for(m=0; m<M; m++) {
f_int[m][i] = comp0();
for(j=st; j<=en; j++)
f_int[m][i] = cadd(f_int[m][i], f_dc[m*Nmem+j]);
}
}
#ifdef MODEMPROBE_ENABLE
for(m=0; m<M; m++) {
snprintf(mp_name_tmp,NMP_NAME,"t_f%zd_int",m+1);
modem_probe_samp_c(mp_name_tmp,&f_int[m][0],(nsym+1)*P);
}
#endif
/* Fine Timing Estimation */
/* Apply magic nonlinearity to f1_int and f2_int, shift down to 0,
* extract angle */
/* Figure out how much to spin the oscillator to extract magic spectral line */
dphift = comp_exp_j(2*M_PI*((float)(Rs)/(float)(P*Rs)));
phi_ft.real = 1;
phi_ft.imag = 0;
t_c=comp0();
for(i=0; i<(nsym+1)*P; i++){
/* Get abs^2 of fx_int[i], and add 'em */
ft1 = 0;
for( m=0; m<M; m++){
ft1 += (f_int[m][i].real*f_int[m][i].real) + (f_int[m][i].imag*f_int[m][i].imag);
}
/* Down shift and accumulate magic line */
t_c = cadd(t_c,fcmult(ft1,phi_ft));
/* Spin the oscillator for the magic line shift */
phi_ft = cmult(phi_ft,dphift);
}
/* Check for NaNs in the fine timing estimate, return if found */
/* otherwise segfaults happen */
if( isnan(t_c.real) || isnan(t_c.imag)){
return;
}
/* Get the magic angle */
norm_rx_timing = atan2f(t_c.imag,t_c.real)/(2*M_PI);
rx_timing = norm_rx_timing*(float)P;
old_norm_rx_timing = fsk->norm_rx_timing;
fsk->norm_rx_timing = norm_rx_timing;
/* Estimate sample clock offset */
d_norm_rx_timing = norm_rx_timing - old_norm_rx_timing;
/* Filter out big jumps in due to nin change */
if(fabsf(d_norm_rx_timing) < .2){
appm = 1e6*d_norm_rx_timing/(float)nsym;
fsk->ppm = .9*fsk->ppm + .1*appm;
}
/* Figure out how many samples are needed the next modem cycle */
/* Unless we're in burst mode or nin locked */
if(!fsk->burst_mode && !fsk->lock_nin) {
if(norm_rx_timing > 0.25)
fsk->nin = N+Ts/2;
else if(norm_rx_timing < -0.25)
fsk->nin = N-Ts/2;
else
fsk->nin = N;
}
modem_probe_samp_f("t_norm_rx_timing",&(norm_rx_timing),1);
modem_probe_samp_i("t_nin",&(fsk->nin),1);
/* Re-sample the integrators with linear interpolation magic */
int low_sample = (int)floorf(rx_timing);
float fract = rx_timing - (float)low_sample;
int high_sample = (int)ceilf(rx_timing);
/* Vars for finding the max-of-4 for each bit */
float tmax[M];
#ifdef EST_EBNO
meanebno = 0;
stdebno = 0;
#endif
/* FINALLY, THE BITS */
/* also, resample fx_int */
for(i=0; i<nsym; i++){
int st = (i+1)*P;
for( m=0; m<M; m++){
t[m] = fcmult(1-fract,f_int[m][st+ low_sample]);
t[m] = cadd(t[m],fcmult( fract,f_int[m][st+high_sample]));
/* Figure mag^2 of each resampled fx_int */
tmax[m] = (t[m].real*t[m].real) + (t[m].imag*t[m].imag);
}
float max = tmax[0]; /* Maximum for figuring correct symbol */
float min = tmax[0];
int sym = 0; /* Index of maximum */
for( m=0; m<M; m++){
if(tmax[m]>max){
max = tmax[m];
sym = m;
}
if(tmax[m]<min){
min = tmax[m];
}
}
/* Get the actual bit */
if(rx_bits != NULL){
/* Get bits for 2FSK and 4FSK */
/* TODO: Replace this with something more generic maybe */
if(M==2){
rx_bits[i] = sym==1; /* 2FSK. 1 bit per symbol */
}else if(M==4){
rx_bits[(i*2)+1] = (sym&0x1); /* 4FSK. 2 bits per symbol */
rx_bits[(i*2) ] = (sym&0x2)>>1;
}
}
/* Produce soft decision symbols */
if(rx_sd != NULL){
/* Convert symbols from max^2 into max */
for( m=0; m<M; m++)
tmax[m] = sqrtf(tmax[m]);
if(M==2){
rx_sd[i] = tmax[0] - tmax[1];
}else if(M==4){
/* TODO: Find a soft-decision mode that works for 4FSK */
min = sqrtf(min);
rx_sd[(i*2)+1] = - tmax[0] ; /* Bits=00 */
rx_sd[(i*2) ] = - tmax[0] ;
rx_sd[(i*2)+1]+= tmax[1] ; /* Bits=01 */
rx_sd[(i*2) ]+= - tmax[1] ;
rx_sd[(i*2)+1]+= - tmax[2] ; /* Bits=10 */
rx_sd[(i*2) ]+= tmax[2] ;
rx_sd[(i*2)+1]+= tmax[3] ; /* Bits=11 */
rx_sd[(i*2) ]+= tmax[3] ;
}
}
/* Accumulate resampled int magnitude for EbNodB estimation */
/* Standard deviation is calculated by algorithm devised by crafty soviets */
#ifdef EST_EBNO
/* Accumulate the square of the sampled value */
ft1 = max;
stdebno += ft1;
/* Figure the abs value of the max tone */
meanebno += sqrtf(ft1);
#endif
/* Soft output goes here */
}
#ifdef EST_EBNO
/* Calculate mean for EbNodB estimation */
meanebno = meanebno/(float)nsym;
/* Calculate the std. dev for EbNodB estimate */
stdebno = (stdebno/(float)nsym) - (meanebno*meanebno);
/* trap any negative numbers to avoid NANs flowing through */
if (stdebno > 0.0) {
stdebno = sqrt(stdebno);
} else {
stdebno = 0.0;
}
fsk->EbNodB = -6+(20*log10f((1e-6+meanebno)/(1e-6+stdebno)));
#else
fsk->EbNodB = 1;
#endif
/* Write some statistics to the stats struct */
/* Save clock offset in ppm */
fsk->stats->clock_offset = fsk->ppm;
/* Calculate and save SNR from EbNodB estimate */
fsk->stats->snr_est = .5*fsk->stats->snr_est + .5*fsk->EbNodB;//+ 10*log10f(((float)Rs)/((float)Rs*M));
/* Save rx timing */
fsk->stats->rx_timing = (float)rx_timing;
/* Estimate and save frequency offset */
fc_avg = fc_tx = 0.0;
for(int m=0; m<M; m++) {
fc_avg += f_est[m]/M;
fc_tx += (fsk->f1_tx + m*fsk->fs_tx)/M;
}
fsk->stats->foff = fc_tx-fc_avg;
/* Take a sample for the eye diagrams ---------------------------------- */
/* due to oversample rate P, we have too many samples for eye
trace. So lets output a decimated version. We use 2P
as we want two symbols worth of samples in trace */
int neyesamp_dec = ceil(((float)P*2)/MODEM_STATS_EYE_IND_MAX);
neyesamp = (P*2)/neyesamp_dec;
assert(neyesamp <= MODEM_STATS_EYE_IND_MAX);
fsk->stats->neyesamp = neyesamp;
neyeoffset = high_sample+1;
int eye_traces = MODEM_STATS_ET_MAX/M;
int ind;
fsk->stats->neyetr = fsk->mode*eye_traces;
for( i=0; i<eye_traces; i++){
for ( m=0; m<M; m++){
for(j=0; j<neyesamp; j++) {
/*
2*P*i...........: advance two symbols for next trace
neyeoffset......: centre trace on ideal timing offset, peak eye opening
j*neweyesamp_dec: For 2*P>MODEM_STATS_EYE_IND_MAX advance through integrated
samples newamp_dec at a time so we dont overflow rx_eye[][]
*/
ind = 2*P*i + neyeoffset + j*neyesamp_dec;
assert((i*M+m) < MODEM_STATS_ET_MAX);
assert(ind < (nsym+1)*P);
fsk->stats->rx_eye[i*M+m][j] = cabsolute(f_int[m][ind]);
}
}
}
if (fsk->normalise_eye) {
eye_max = 0;
/* Normalize eye to +/- 1 */
for(i=0; i<M*eye_traces; i++)
for(j=0; j<neyesamp; j++)
if(fabsf(fsk->stats->rx_eye[i][j])>eye_max)
eye_max = fabsf(fsk->stats->rx_eye[i][j]);
for(i=0; i<M*eye_traces; i++)
for(j=0; j<neyesamp; j++)
fsk->stats->rx_eye[i][j] = fsk->stats->rx_eye[i][j]/eye_max;
}
fsk->stats->nr = 0;
fsk->stats->Nc = 0;
for(i=0; i<M; i++)
fsk->stats->f_est[i] = f_est[i];
/* Dump some internal samples */
modem_probe_samp_f("t_EbNodB",&(fsk->EbNodB),1);
modem_probe_samp_f("t_ppm",&(fsk->ppm),1);
modem_probe_samp_f("t_rx_timing",&(rx_timing),1);
}
/*---------------------------------------------------------------------------*\
FUNCTION....: fsk_demod/fsk_demod_sd
AUTHOR......: Brady O'Brien
DATE CREATED: 11 February 2016
FSK demodulator functions:
fsk_demod...: complex samples in, bits out
fsk_demos_sd: complex samples in, soft decision symbols out
\*---------------------------------------------------------------------------*/
void fsk_demod(struct FSK *fsk, uint8_t rx_bits[], COMP fsk_in[]){
fsk_demod_core(fsk,rx_bits,NULL,fsk_in);
}
void fsk_demod_sd(struct FSK *fsk, float rx_sd[], COMP fsk_in[]){
fsk_demod_core(fsk,NULL,rx_sd,fsk_in);
}
/* make sure stats have known values in case monitoring process reads stats before they are set */
static void stats_init(struct FSK *fsk) {
/* Take a sample for the eye diagrams */
int i,j,m;
int P = fsk->P;
int M = fsk->mode;
/* due to oversample rate P, we have too many samples for eye
trace. So lets output a decimated version */
/* asserts below as we found some problems over-running eye matrix */
/* TODO: refactor eye tracing code here and in fsk_demod */
int neyesamp_dec = ceil(((float)P*2)/MODEM_STATS_EYE_IND_MAX);
int neyesamp = (P*2)/neyesamp_dec;
assert(neyesamp <= MODEM_STATS_EYE_IND_MAX);
fsk->stats->neyesamp = neyesamp;
int eye_traces = MODEM_STATS_ET_MAX/M;
fsk->stats->neyetr = fsk->mode*eye_traces;
for(i=0; i<eye_traces; i++) {
for (m=0; m<M; m++){
for(j=0; j<neyesamp; j++) {
assert((i*M+m) < MODEM_STATS_ET_MAX);
fsk->stats->rx_eye[i*M+m][j] = 0;
}
}
}
fsk->stats->rx_timing = fsk->stats->snr_est = 0;
}
/* Set the FSK modem into burst demod mode */
void fsk_enable_burst_mode(struct FSK *fsk){
fsk->nin = fsk->N;
fsk->burst_mode = 1;
}
void fsk_clear_estimators(struct FSK *fsk){
int i;
/* Clear freq estimator state */
for(i=0; i < (fsk->Ndft); i++){
fsk->Sf[i] = 0;
}
/* Reset timing diff correction */
fsk->nin = fsk->N;
}
void fsk_get_demod_stats(struct FSK *fsk, struct MODEM_STATS *stats){
/* copy from internal stats, note we can't overwrite stats completely
as it has other states rqd by caller, also we want a consistent
interface across modem types for the freedv_api.
*/
stats->clock_offset = fsk->stats->clock_offset;
stats->snr_est = fsk->stats->snr_est; // TODO: make this SNR not Eb/No
stats->rx_timing = fsk->stats->rx_timing;
stats->foff = fsk->stats->foff;
stats->neyesamp = fsk->stats->neyesamp;
stats->neyetr = fsk->stats->neyetr;
memcpy(stats->rx_eye, fsk->stats->rx_eye, sizeof(stats->rx_eye));
memcpy(stats->f_est, fsk->stats->f_est, fsk->mode*sizeof(float));
/* these fields not used for FSK so set to something sensible */
stats->sync = 0;
stats->nr = fsk->stats->nr;
stats->Nc = fsk->stats->Nc;
}
/*
* Set the minimum and maximum frequencies at which the freq. estimator can find tones
*/
void fsk_set_freq_est_limits(struct FSK *fsk, int est_min, int est_max){
assert(fsk != NULL);
assert(est_min >= -fsk->Fs/2);
assert(est_max <= fsk->Fs/2);
assert(est_max > est_min);
fsk->est_min = est_min;
fsk->est_max = est_max;
}
void fsk_stats_normalise_eye(struct FSK *fsk, int normalise_enable) {
assert(fsk != NULL);
fsk->normalise_eye = normalise_enable;
}
void fsk_set_freq_est_alg(struct FSK *fsk, int est_type) {
assert(fsk != NULL);
fsk->freq_est_type = est_type;
}
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