This program computes the EXtrinsic Information Transfer (EXIT) chart for Parallel Concatenated Convolutional Codes (PCCCs) of coding rate 1/3. Actually the Transfer Characteristics (TCs) of the two SISO RSC modules used in the turbo decoder are computed at a given Signal to Noise Ratio (SNR).
Reference: S. ten Brink, ''Convergence behavior of iteratively decoded parallel concatenated codes,`` IEEE Transactions on Communications, vol. 49, pp. 1727-1737, Oct. 2001
using std::cout;
using std::endl;
using std::string;
int main(void)
{
vec sigmaA = "0.01:0.1:7";
double threshold_value = 50;
string map_metric = "maxlogMAP";
ivec gen = "07 05";
int constraint_length = 3;
int nb_blocks_lim = 10;
double EbN0_dB = 0.6;
double R = 1.0 / 3.0;
double Ec = 1.0;
vec sigma2A =
sqr(sigmaA);
int sigma2A_len = sigma2A.length();
int nb_bits = perm_len - (constraint_length - 1);
double sigma2 = (0.5 * Ec / R) *
pow(
inv_dB(EbN0_dB), -1.0);
double Lc = -2 / sigma2;
bvec bits(nb_bits);
bvec tail;
bvec bits_tail(perm_len);
int coded_bits_len = 2 * perm_len;
bvec coded_bits(coded_bits_len);
vec mod_bits(coded_bits_len);
vec rec_sig(coded_bits_len);
vec intrinsic_coded(coded_bits_len);
vec intrinsic_coded_p(2*nb_bits);
intrinsic_coded_p.zeros();
vec apriori_data(perm_len);
vec extrinsic_coded;
vec extrinsic_data;
vec apriori_mutual_info(sigma2A_len);
vec extrinsic_mutual_info(sigma2A_len);
vec extrinsic_mutual_info_p(sigma2A_len);
extrinsic_mutual_info.zeros();
extrinsic_mutual_info_p.zeros();
register int en, n, nb_blocks;
Rec_Syst_Conv_Code rsc;
rsc.set_generator_polynomials(gen, constraint_length);
BPSK bpsk;
AWGN_Channel channel;
channel.set_noise(sigma2);
SISO siso;
siso.set_generators(gen, constraint_length);
siso.set_map_metric(map_metric);
EXIT exit;
for (en = 0;en < sigma2A_len;en++) {
apriori_mutual_info(en) = exit.apriori_mutual_info(sigma2A(en));
cout << "I_A = " << apriori_mutual_info(en) << endl;
for (nb_blocks = 0;nb_blocks < nb_blocks_lim;nb_blocks++) {
rsc.encode_tail(bits, tail, parity_bits);
bits_tail =
concat(bits, tail);
for (n = 0;n < perm_len;n++) {
coded_bits(2*n) = bits_tail(n);
coded_bits(2*n + 1) = parity_bits(n, 0);
}
mod_bits = bpsk.modulate_bits(coded_bits);
rec_sig = channel(mod_bits);
intrinsic_coded = Lc * rec_sig;
apriori_data = exit.generate_apriori_info(bits_tail);
siso.rsc(extrinsic_coded, extrinsic_data, intrinsic_coded, apriori_data, true);
extrinsic_mutual_info(en) += exit.extrinsic_mutual_info(extrinsic_data.left(nb_bits), bits);
for (n = 0;n < nb_bits;n++)
intrinsic_coded_p(2*n + 1) = Lc * rec_sig(2 * n + 1);
apriori_data = exit.generate_apriori_info(bits);
siso.rsc(extrinsic_coded, extrinsic_data, intrinsic_coded_p, apriori_data, false);
extrinsic_mutual_info_p(en) += exit.extrinsic_mutual_info(extrinsic_data, bits);
}
extrinsic_mutual_info(en) /= nb_blocks_lim;
extrinsic_mutual_info_p(en) /= nb_blocks_lim;
}
it_file ff("exit_pccc.it");
ff << Name("IA") << apriori_mutual_info;
ff << Name("IE") << extrinsic_mutual_info;
ff << Name("IE_p") << extrinsic_mutual_info_p;
ff << Name("EbN0_dB") << EbN0_dB;
ff << Name("gen") << gen;
ff << Name("R") << R;
ff << Name("perm_len") << perm_len;
ff << Name("nb_blocks_lim") << nb_blocks_lim;
ff.close();
return 0;
}
static double threshold(const double &x, const double &value)
Functions used to limit values at a given +- threshold.
vec pow(const double x, const vec &y)
Calculates x to the power of y (x^y)
double inv_dB(double x)
Inverse of decibel of x.
double pow10(double x)
Calculate ten to the power of x (10^x)
vec sqr(const cvec &data)
Absolute square of elements.
void RNG_randomize()
Set a random seed for all Random Number Generators in the current thread.
bin randb(void)
Generates a random bit (equally likely 0s and 1s)
Include file for the IT++ communications module.
Mat< bin > bmat
bin matrix
const Array< T > concat(const Array< T > &a, const T &e)
Append element e to the end of the Array a.
When you run this program, the results (mutual a priori and extrinsic information, EbN0_dB, etc.) are saved into exit_pccc.it file. Using the following MATLAB script
the EXIT chart can be displayed.