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// This example demonstrates the performance of the qpacket modem
// object to combine forward error-correction and modulation in one
// simple interface.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <getopt.h>
#include <assert.h>
#include "liquid.h"
#define OUTPUT_FILENAME "qpacketmodem_performance_example.m"
void usage()
{
printf("qpacketmodem_performance_example [options]\n");
printf(" -h : print usage\n");
printf(" -p : payload length [bytes], default: 400\n");
printf(" -m : modulation scheme (qpsk default)\n");
liquid_print_modulation_schemes();
printf(" -v : data integrity check: crc32 default\n");
liquid_print_crc_schemes();
printf(" -c : coding scheme (inner): g2412 default\n");
printf(" -k : coding scheme (outer): none default\n");
liquid_print_fec_schemes();
printf(" -s : SNR start [dB], default: -5\n");
printf(" -x : SNR max [dB], default: 20\n");
printf(" -d : SNR step [dB], default: 0.5\n");
printf(" -e : minimum number of packet errors per step, default: 50\n");
printf(" -t : minimum number of packet trials per step, default: 2000\n");
printf(" -T : maximum number of packet trials per step, default: 40000\n");
}
int main(int argc, char *argv[])
{
// options (defaults to frame64 parameters)
modulation_scheme ms = LIQUID_MODEM_QPSK; // mod. scheme
crc_scheme check = LIQUID_CRC_24; // data validity check
fec_scheme fec0 = LIQUID_FEC_NONE; // fec (inner)
fec_scheme fec1 = LIQUID_FEC_GOLAY2412; // fec (outer)
unsigned int payload_len = 72; // payload length
float SNRdB_min = -5.0f; // signal-to-noise ratio (minimum)
float SNRdB_max = 20.0f; // signal-to-noise ratio (maximum)
float SNRdB_step = 0.5f; // signal-to-noise ratio (maximum)
unsigned int min_packet_errors = 50; // minimum errors to observe for each step
unsigned int min_packet_trials = 2000; // minimum number of packets for each step
unsigned int max_packet_trials =40000; // maximum number of packets for each step
// get options
int dopt;
while((dopt = getopt(argc,argv,"hp:m:v:c:k:s:x:d:e:t:T:")) != EOF){
switch (dopt) {
case 'h': usage(); return 0;
case 'p': payload_len = atol(optarg); break;
case 'm': ms = liquid_getopt_str2mod(optarg); break;
case 'v': check = liquid_getopt_str2crc(optarg); break;
case 'c': fec0 = liquid_getopt_str2fec(optarg); break;
case 'k': fec1 = liquid_getopt_str2fec(optarg); break;
case 's': SNRdB_min = atof(optarg); break;
case 'x': SNRdB_max = atof(optarg); break;
case 'd': SNRdB_step = atof(optarg); break;
case 'e': min_packet_errors = atoi(optarg); break;
case 't': min_packet_trials = atoi(optarg); break;
case 'T': max_packet_trials = atoi(optarg); break;
default:
exit(-1);
}
}
unsigned int i;
// create and configure packet encoder/decoder object
qpacketmodem q = qpacketmodem_create();
qpacketmodem_configure(q, payload_len, check, fec0, fec1, ms);
qpacketmodem_print(q);
// get frame length
unsigned int frame_len = qpacketmodem_get_frame_len(q);
// initialize payload
unsigned char payload_tx [payload_len]; // payload (transmitted)
unsigned char payload_rx [payload_len]; // payload (received)
float complex frame_tx [frame_len]; // frame samples (transmitted)
float complex frame_rx [frame_len]; // frame samples (received)
// output file
FILE* fid = fopen(OUTPUT_FILENAME, "w");
fprintf(fid,"%% %s: auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all; close all; SNR=[]; ber=[]; per=[];\n");
printf(" %8s %8s %8s %12s %8s %8s %6s\n",
"SNR [dB]", "errors", "bits", "BER", "errors", "packets", "PER");
float SNRdB = SNRdB_min;
while (SNRdB < SNRdB_max) {
// reset counters
float nstd = powf(10.0f, -SNRdB/20.0f); // noise standard deviation
unsigned int num_packet_trials = 0, num_packet_errors = 0;
unsigned int num_bit_trials = 0, num_bit_errors = 0;
while (1) {
// initialize payload
for (i=0; i<payload_len; i++) {
payload_tx[i] = rand() & 0xff;
payload_rx[i] = 0x00;
}
// encode frame
qpacketmodem_encode(q, payload_tx, frame_tx);
// add noise
for (i=0; i<frame_len; i++)
frame_rx[i] = frame_tx[i] + nstd*(randnf() + _Complex_I*randnf())*M_SQRT1_2;
// decode frame
int crc_pass = qpacketmodem_decode(q, frame_rx, payload_rx);
// accumulate errors
num_bit_errors += count_bit_errors_array(payload_tx, payload_rx, payload_len);
num_packet_errors += crc_pass ? 0 : 1;
num_packet_trials += 1;
num_bit_trials += 8*payload_len;
if (num_packet_trials < min_packet_trials)
continue;
if (num_packet_errors >= min_packet_errors)
break;
if (num_packet_trials >= max_packet_trials)
break;
}
float BER = (float)num_bit_errors / (float)num_bit_trials;
float PER = (float)num_packet_errors / (float)num_packet_trials;
printf(" %8.2f %8u %8u %12.4e %8u %8u %6.2f%%\n",
SNRdB,
num_bit_errors, num_bit_trials, BER,
num_packet_errors, num_packet_trials, PER*100.0f);
fprintf(fid,"SNR(end+1)=%g; ber(end+1)=%g; per(end+1)=%g;\n", SNRdB, BER, PER);
if (num_packet_errors < min_packet_errors)
break;
SNRdB += SNRdB_step;
}
// destroy allocated objects
qpacketmodem_destroy(q);
fprintf(fid,"figure('position',[100 100 500 720]);\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," gamma = 10.^(SNR/10);\n");
fprintf(fid," ber_qpsk = 0.5*(1 - erf(sqrt(gamma)/sqrt(2)));\n");
fprintf(fid," hold on;\n");
fprintf(fid," semilogy(SNR, ber, '-o', 'LineWidth',2, 'MarkerSize',2);\n");
fprintf(fid," semilogy(SNR, ber_qpsk,'-o', 'LineWidth',2, 'MarkerSize',2);\n");
fprintf(fid," hold off;\n");
fprintf(fid," xlabel('SNR [dB]');\n");
fprintf(fid," ylabel('Bit Error Rate');\n");
fprintf(fid," axis([%f SNR(end)+5 1e-6 1]);\n", SNRdB_min);
fprintf(fid," grid on;\n");
fprintf(fid," legend('Measured','Uncoded QPSK','location','southwest');\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," semilogy(SNR, per,'-o', 'LineWidth',2, 'MarkerSize',2);\n");
fprintf(fid," xlabel('SNR [dB]');\n");
fprintf(fid," ylabel('Packet Error Rate');\n");
fprintf(fid," axis([%f SNR(end)+5 1e-3 1]);\n", SNRdB_min);
fprintf(fid," grid on;\n");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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