Simulation of SISO demappers using ST codes in ideal MIMO channels

This program shows the usage of Soft-Input Soft-Output (SISO) demappers with Space Time (ST) codes in Multiple-Input Multiple-Output (MIMO) channels. The ST codes are generated using the STC class, the MIMO channels are ideal (no multi-antenna interferrence and no noise) and the receiver is implemented by the demapper method of the SISO class.

#include "itpp/itcomm.h"
using namespace itpp;
using std::cout;
using std::endl;
using std::string;
void print_help(char *prog_name)
{
cout << "Usage: " << prog_name << " [options]\n"
<< "Available options:\n"
<< "-d demapper_method: sets the demapper method. Available demapper "
"methods: Hassibi_maxlogMAP, GA, sGA, mmsePIC, zfPIC and Alamouti_maxlogMAP.\n"
<< "-s code_name: sets the ST code name. Available code names: Golden_2x2, "
"V-BLAST_MxN, Damen_2x2, Alamouti_2xN.\n"
<< "-c const_size: sets the constellation size\n"
<< "-e nb_errors_lim: sets the limit for the number of bit errors\n"
<< "-b nb_bits_lim: sets the limit for the number of bits to send\n"
<< "-p perm_len: sets the length of the permutation\n"
<< "-i nb_iter: sets the number of iterations\n"
<< "-t em_antennas: sets the number of emission antenna\n"
<< "-r rec_antennas: sets the number of reception antenna\n"
<< "-u channel_uses: sets the number of channel uses\n"
<< "-g: enables the ideal Gaussian MIMO channel (no MAI). Available only "
"if em_antennas == rec_antennas.\n"
<< "-n EbN0_dB_min: sets the lower limit for the SNR [dB]\n"
<< "-m EbN0_dB_max: sets the upper limit for the SNR [dB]\n"
<< "-l EbN0_dB_step: step for the SNR vector [dB]\n"
<< "-h: displays this help message" << endl;
}
int get_opts(int argc, char *argv[], std::string &demapper_method, int &const_size,
int &nb_errors_lim, int &nb_bits_lim, int &perm_len, int &nb_iter,
int &rec_antennas, int &em_antennas, int &channel_uses, std::string &code_name,
bool &ideal_channel, bool &to_file, vec &EbN0_dB)
{
int opt;
double EbN0_dB_min = EbN0_dB[0];
double EbN0_dB_max = EbN0_dB[length(EbN0_dB)-1];
double EbN0_dB_step = 1.0;
while (-1 != (opt = getopt(argc, argv, "hgfd:c:e:b:p:i:r:t:u:s:n:m:l:")))
{
switch (opt)
{
case 'h':
return EXIT_FAILURE;//print help and exit
case 'd':
demapper_method = optarg;
break;
case 'c':
const_size = atoi(optarg);
break;
case 'e':
nb_errors_lim = atoi(optarg);
break;
case 'b':
nb_bits_lim = atoi(optarg);
break;
case 'p':
perm_len = atoi(optarg);
break;
case 'i':
nb_iter = atoi(optarg);
break;
case 'r':
rec_antennas = atoi(optarg);
break;
case 't':
em_antennas = atoi(optarg);
break;
case 'u':
channel_uses = atoi(optarg);
break;
case 's':
code_name = optarg;
break;
case 'g':
ideal_channel = true;
break;
case 'f':
to_file = true;
break;
case 'n':
EbN0_dB_min = atof(optarg);
break;
case 'm':
EbN0_dB_max = atof(optarg);
break;
case 'l':
EbN0_dB_step = atof(optarg);
break;
default:
return EXIT_FAILURE;
}
}
/* update SNR if needed */
if ((EbN0_dB_min <= EbN0_dB_max) && (0 < EbN0_dB_step) &&
((EbN0_dB[0] != EbN0_dB_min) || (EbN0_dB[length(EbN0_dB)-1] != EbN0_dB_max)))
{
int size = int((EbN0_dB_max-EbN0_dB_min)/EbN0_dB_step)+1;
EbN0_dB.set_size(size);
EbN0_dB[0] = EbN0_dB_min;
for (int n = 1; n < size; ++n)
{
EbN0_dB[n] = EbN0_dB[n-1]+EbN0_dB_step;
}
}
return EXIT_SUCCESS;
}
int main(int argc, char *argv[])
{
//receiver parameters
ivec gen = "0133 0171";
int constraint_length = 7;
int const_size = 16;//constellation size
int coherence_time = 512;//expressed in symbol durations, multiple of T, T<=coherence_time<=tx_duration, T is the ST code duration
double threshold_value = 50;
string map_metric="maxlogMAP";
string demapper_method = "mmsePIC";//Hassibi_maxlogMAP or GA or sGA or mmsePIC or zfPIC or Alamouti_maxlogMAP
int nb_errors_lim = 1500;
int nb_bits_lim = int(1e6);
int perm_len = pow2i(14);//permutation length
int nb_iter = 5;//number of iterations in the turbo decoder
int rec_antennas = 2;//number of reception antennas
vec EbN0_dB = "0:20";
double Es = 1.0;//mean symbol energy
int em_antennas = 2;//number of emission antennas
int channel_uses = 1;//ST code duration
string code_name = "V-BLAST_MxN";//V-BLAST_MxN, Golden_2x2, Damen_2x2, Alamouti_2xN
bool ideal_channel = false;
bool to_file = false;
//get parameters if any
if (EXIT_FAILURE == get_opts(argc, argv, demapper_method, const_size,
nb_errors_lim, nb_bits_lim, perm_len, nb_iter, rec_antennas, em_antennas,
channel_uses, code_name, ideal_channel, to_file, EbN0_dB))
{
print_help(argv[0]);
return EXIT_FAILURE;
}
//convolutional code generator polynomials
Convolutional_Code nsc;
nsc.set_generator_polynomials(gen, constraint_length);
double coding_rate = 1.0/2.0;
//QAM modulator class
QAM mod(const_size);
//Space-Time code parameters
STC st_block_code(code_name, const_size, em_antennas, channel_uses);//generate matrices for LD code (following Hassibi's approach)
int symb_block = st_block_code.get_nb_symbols_per_block();
em_antennas = st_block_code.get_nb_emission_antenna();//these parameters could by changed depending on the selected code
channel_uses = st_block_code.get_channel_uses();
//recompute interleaver length
int G = coherence_time*mod.bits_per_symbol()*symb_block;
perm_len = G*(perm_len/G);//recompute interleaver length
int block_len = int(coding_rate*perm_len);//informational block length
int nb_symb = perm_len/mod.bits_per_symbol();//number of symbols at the modulator output
int nb_subblocks = nb_symb/symb_block;//number of blocks of ST code emitted in an interleaver period
int tx_duration = channel_uses*nb_subblocks;//transmission duration expressed in number of symbol periods
//show configuration parameters
std::cout << "const_size = " << const_size
<< "\ndemapper_method = " << demapper_method
<< "\nnb_errors_lim = " << nb_errors_lim
<< "\nnb_bits_lim = " << nb_bits_lim
<< "\nperm_len = " << perm_len
<< "\ncode_name = " << code_name
<< "\nem_antennas = " << em_antennas
<< "\nchannel_uses = " << channel_uses
<< "\nnb_iter = " << nb_iter
<< "\nrec_antennas = " << rec_antennas
<< "\nEbN0_dB = " << EbN0_dB << std::endl;
if (true == ideal_channel)
{
if (em_antennas == rec_antennas)
{
std::cout << "Using ideal AWGN MIMO channel (no MAI)" << std::endl;
} else
{
std::cout << "Warning: cannot use ideal AWGN MIMO channel" << std::endl;
ideal_channel = false;
}
} else
{
std::cout << "Using random MIMO channel (with MAI)" << std::endl;
}
//fading channel parameters
if (coherence_time%channel_uses)//check if the coherence time is a multiple of channel_uses
{
coherence_time = channel_uses*(coherence_time/channel_uses);
std::cout << "Warning! The coherence time must be a multiple of T. Choosing coherence_time=channel_uses*floor(coherence_time/channel_uses) = "\
<< coherence_time << std::endl;
}
if (coherence_time>tx_duration)
{
coherence_time = channel_uses*(tx_duration/channel_uses);
std::cout << "Warning! The coherence time must be <= tx_duration. Choosing coherence_time = channel_uses*floor(tx_duration/channel_uses) = "\
<< coherence_time << std::endl;
}
cmat fading_pattern = ones_c(1, coherence_time/channel_uses);
//other parameters
string filename = "STBICM_"+map_metric+"_"+demapper_method+".it";
if (true == to_file)
{
std::cout << "Saving results to " << filename << std::endl;
}
double R = coding_rate*double(mod.bits_per_symbol()*symb_block)/double(channel_uses);//ST code rate in (info.) bits/channel use
vec sigma2 = (0.5*Es/(R*double(mod.bits_per_symbol())))*pow(inv_dB(EbN0_dB), -1.0);//N0/2
int nb_blocks;//number of blocks
int nb_errors;
bvec bits(block_len);//data bits
bvec coded_bits(perm_len);//no tail
cvec em(nb_symb);
ivec perm(perm_len);
ivec inv_perm(perm_len);
//SISO demapper
vec demapper_apriori_data(perm_len);
vec demapper_extrinsic_data(perm_len);
//SISO NSC
vec nsc_intrinsic_coded(perm_len);
vec nsc_apriori_data(block_len);
nsc_apriori_data.zeros();//always zero
vec nsc_extrinsic_coded(perm_len);
vec nsc_extrinsic_data(block_len);
//decision
bvec rec_bits(block_len);
int snr_len = EbN0_dB.length();
mat ber(nb_iter,snr_len);
ber.zeros();
register int en,n,ns;
cmat S(tx_duration, em_antennas);
cmat rec(tx_duration,rec_antennas);
//Rayleigh fading
cmat ch_attenuations(em_antennas*rec_antennas,tx_duration/channel_uses);
//SISO blocks
SISO siso;
siso.set_map_metric(map_metric);
siso.set_generators(gen, constraint_length);
siso.set_demapper_method(demapper_method);
siso.set_constellation(mod.bits_per_symbol(), mod.get_symbols()/sqrt(em_antennas), mod.get_bits2symbols());
siso.set_st_block_code(st_block_code.get_nb_symbols_per_block(), st_block_code.get_1st_gen_matrix(), st_block_code.get_2nd_gen_matrix(), rec_antennas);
//decision
BPSK bpsk;
//BER
BERC berc;
//Randomize generators
RNG_randomize();
//main loop
std::cout << std::endl;
for (en=0;en<snr_len;en++)
{
std::cout << "EbN0_dB = " << EbN0_dB[en] << std::endl;
siso.set_noise(sigma2(en));
nb_errors = 0;
nb_blocks = 0;
while ((nb_errors<nb_errors_lim) && (nb_blocks*block_len<nb_bits_lim))//if at the last iteration the nb. of errors is inferior to lim, then process another block
{
//permutation
perm = sort_index(randu(perm_len));
//inverse permutation
inv_perm = sort_index(perm);
//bits generation
bits = randb(block_len);
//convolutional code
nsc.encode(bits, coded_bits);//no tail
//permutation+QAM modulation
em = mod.modulate_bits(coded_bits(perm))/sqrt(em_antennas);//normalize emitted symbols
//ST code
S = st_block_code.encode(em);
/* channel matrices (there are tx_duration/tau_c different channel matrices MxN)
* a channel matrix is represented as a M*Nx1 vector (first M elements are the first column of the channel matrix)
* the channel matrix is constant over tau_c symbol periods (a multiple of T symbol durations)
* the channel matrix is the transpose of the true channel matrix
*/
if (false == ideal_channel)
{
ch_attenuations = kron(randn_c(em_antennas*rec_antennas, tx_duration/coherence_time), fading_pattern);
} else
{
cmat mimo_channel = kron(reshape(eye_c(em_antennas),
em_antennas*rec_antennas, 1), ones_c(1, tx_duration/coherence_time));
ch_attenuations = kron(mimo_channel, fading_pattern);
}
//flat-fading MIMO channel
for (ns=0;ns<nb_subblocks;ns++)
rec.set_submatrix(ns*channel_uses, 0, \
S(ns*channel_uses, (ns+1)*channel_uses-1, 0, em_antennas-1)*reshape(ch_attenuations.get_col(ns), em_antennas, rec_antennas));
rec += sqrt(2*sigma2(en))*randn_c(tx_duration,rec_antennas);//sigma2 is the variance on each dimension
//turbo receiver
demapper_apriori_data.zeros();//a priori information of emitted bits
siso.set_impulse_response(ch_attenuations);
for (n=0;n<nb_iter;n++)
{
//first decoder
siso.demapper(demapper_extrinsic_data, rec, demapper_apriori_data);
//deinterleave+threshold
nsc_intrinsic_coded = SISO::threshold(demapper_extrinsic_data(inv_perm), threshold_value);
//second decoder
siso.nsc(nsc_extrinsic_coded, nsc_extrinsic_data, nsc_intrinsic_coded, nsc_apriori_data, false);
//decision
rec_bits = bpsk.demodulate_bits(-nsc_extrinsic_data);//suppose that a priori info is zero
//count errors
berc.clear();
berc.count(bits, rec_bits);
ber(n,en) += berc.get_errorrate();
//interleave
demapper_apriori_data = nsc_extrinsic_coded(perm);
}//end iterations
nb_errors += int(berc.get_errors());//get number of errors at the last iteration
nb_blocks++;
}//end blocks (while loop)
//compute BER over all tx blocks
ber.set_col(en, ber.get_col(en)/nb_blocks);
}
if (true == to_file)
{
//save results to file
it_file ff(filename);
ff << Name("BER") << ber;
ff << Name("EbN0_dB") << EbN0_dB;
ff << Name("gen") << gen;
ff << Name("coding_rate") << coding_rate;
ff << Name("nb_iter") << nb_iter;
ff << Name("block_len") << block_len;
ff << Name("nb_errors_lim") << nb_errors_lim;
ff << Name("nb_bits_lim") << nb_bits_lim;
ff << Name("const_size") << const_size;
ff.close();
} else
{
//show BER
cout << "BER = " << ber << endl;
}
return 0;
}

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