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receive.cpp
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receive.cpp
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/**********************************************************************************/
/* Copyright © 2011, Kumar Appaiah, Radha Krishna Ganti, Kannan Srinivasan */
/* The University of Texas at Austin */
/* */
/* This file is part of Simple OFDM Modem. */
/* */
/* Simple OFDM Modem 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. */
/* */
/* Simple OFDM Modem 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 Simple OFDM Modem. If not, see */
/* <http://www.gnu.org/licenses/>. */
/* */
/**********************************************************************************/
#include "parameters.hpp"
#include "receive.hpp"
#include "unwrap.hpp"
void
channel_equalize_and_demodulate(OFDM &ofdm, const cvec &channel_estimate_subcarriers, const cvec &received_symbols, cvec &received_symbols_equalized)
{
cvec received_symbols_subcarriers, received_symbols_subcarriers_n;
received_symbols_equalized = "";
for (int i = 0; i < received_symbols.length() / (NFFT + NCP); ++i) {
received_symbols_subcarriers = ofdm.demodulate(received_symbols.mid(i * (NFFT + NCP), NFFT + NCP));
received_symbols_subcarriers_n = elem_div(received_symbols_subcarriers, channel_estimate_subcarriers);
received_symbols_equalized = concat(received_symbols_equalized, received_symbols_subcarriers_n);
}
}
#define MAX_ROTATIONS 6
int
coarse_frequency_offset_estimate(const cvec &single_ofdm_symbol, const cvec &pilots_freq_ref)
{
cvec rotated_pilots;
double metric_max = -1.0, metric;
double energy = 1.0;
int max_offset;
ivec correlation_locations = "1:63";
ivec offset_vec(pilots_freq_ref.length());
for (int i = -MAX_ROTATIONS; i < MAX_ROTATIONS + 1; ++i) {
offset_vec = correlation_locations + i;
for (int j = 0; j < pilots_freq_ref.length(); ++j) {
offset_vec[j] = (offset_vec[j] < 0) ? offset_vec[j] + NFFT : ((offset_vec[j] >= NFFT) ? offset_vec[j] - NFFT : offset_vec[j]);
}
rotated_pilots = single_ofdm_symbol(offset_vec);
energy = sum(sqr(rotated_pilots));
metric = abs(sum(elem_mult(rotated_pilots, conj(pilots_freq_ref(correlation_locations))))) / sqrt(energy);
if (metric > metric_max) {
max_offset = i;
metric_max = metric;
}
}
return max_offset;
}
int
channel_coarse_frequency_estimate(OFDM &ofdm, const cvec &pilots_time, const cvec &pilots_freq_ref, cvec &estimate)
{
cvec pilots_freq = ofdm.demodulate(pilots_time);
estimate = zeros_c(NFFT);
for (int i = 0; i < pilots_freq.length() / NFFT; ++i) {
estimate = estimate + elem_div(pilots_freq.mid(i * NFFT, NFFT), pilots_freq_ref);
}
estimate = estimate / NREP_ESTIMATION_SYMBOL;
return coarse_frequency_offset_estimate(pilots_freq.left(NFFT), pilots_freq_ref);
}
void
spc_timing_freq_recovery_wrap(const cvec& databuffer, int l_databuffer, int l_preambletones, int nreps_preamble, double metric_tol, int *pos, double *cfo_hat, int *pd)
{
int corrlength = l_preambletones;
vec auto_corr(l_databuffer - 2 * corrlength + 1);
int i;
int k;
auto_corr[0] = 0;
cvec cross_corr(l_databuffer - (2 * corrlength) + 1);
vec metric(l_databuffer - (2 * corrlength) + 1);
*pos = -1;
*pd=0;
for (i = 0; i < corrlength; i++) {
cross_corr[0] = cross_corr[0] + conj(databuffer[i]) * databuffer[i + corrlength];
auto_corr[0] += 0.5*(sqr(databuffer[i]) + sqr(databuffer[i+corrlength]));
}
metric[0] = abs(cross_corr[0]) / auto_corr[0];
complex<double> temp1;
complex<double> temp2;
for ( k = 1; k < l_databuffer - 2 * corrlength + 1; k++) {
temp1 = conj(databuffer[k-1])* databuffer[k+corrlength-1];
temp2 = conj(databuffer[k+corrlength-1])*databuffer[k+2*corrlength-1];
cross_corr[k] = cross_corr[k-1]- temp1 + temp2;
auto_corr[k] = auto_corr[k - 1] - 0.5 * sqr(databuffer[k - 1])
+ 0.5 * sqr(databuffer[k + 2* corrlength - 1]);
metric[k] = abs(cross_corr[k]) / abs(auto_corr[k]);
}
int sync_point = 0;
float sync_value = -std::numeric_limits<float>::infinity();
float tmp;
for (i = 0; i < l_databuffer - (2 * corrlength); i++) {
tmp = abs(cross_corr[i]);
if (sync_value < tmp) {
sync_value = tmp;
sync_point = i;
}
}
// printf(" The sync point is %d \n", sync_point);
// double phase = imag(log(cross_corr[sync_point]));
double phase = arg(cross_corr[sync_point]);
float absmetric =abs(metric[sync_point]);
if ((absmetric <= (1 + metric_tol)) && (absmetric >= (1 - metric_tol))
&& (sync_point != (l_databuffer - 2* corrlength - 1))) {
*pos = sync_point + 1;
phase = phase > 0 ? fmod(phase, M_PI) : fmod(phase, -M_PI);
*cfo_hat = phase / corrlength;
*pd=1;
}
}
void
introduce_frequency_offset(cvec &c, double offset)
{
for (int i = 0; i < c.length(); ++i) {
c[i] = c[i] * std::exp(complex<double>(0, 1) * offset * double(i));
}
}
void
estimate_ofdm_symbol(cvec &ofdm_subcarriers)
{
cvec pilot_val = zeros_c(64);
for (int i = -7; i < 7; ++i) {
pilot_val[(i + 64) % 64] = ofdm_subcarriers[57] * double(7 - i) / 14.0 + ofdm_subcarriers[7] * double(14 - 7 + i) / 14.0;
}
for (int i = 7; i < 21; ++i) {
pilot_val[i] = ofdm_subcarriers[7] * double(7 - i) / 14.0 + ofdm_subcarriers[21] * double(14 - 7 + i) / 14.0;
}
for (int i = 21; i < 43; ++i) {
pilot_val[i] = ofdm_subcarriers[21] * double(7 - i) / 14.0 + ofdm_subcarriers[43] * double(14 - 7 + i) / 14.0;
}
for (int i = 43; i < 57; ++i) {
pilot_val[i] = ofdm_subcarriers[43] * double(7 - i) / 14.0 + ofdm_subcarriers[57] * double(14 - 7 + i) / 14.0;
}
ofdm_subcarriers = elem_div(ofdm_subcarriers, pilot_val / complex<double>(1,1) * sqrt(2) + ALPHA);
}
void
extract_ofdm_symbol(const cvec &ofdm_symbol_subcarriers, cvec &pilots, cvec &symbols, bool awgn)
{
pilots = zeros_c(4);
int pilot_index = 0;
symbols = zeros_c(SYMBOLS_PER_ODFM);
int symbol_index = 0;
cvec ofdm_symbol_subcarriers_modified = ofdm_symbol_subcarriers;
// if (!awgn) { estimate_ofdm_symbol(ofdm_symbol_subcarriers_modified); }
for (int i = 0; i < NFFT; ++i) {
switch(mask[i]) {
case PILOT_SUBC:
pilots[pilot_index++] = ofdm_symbol_subcarriers_modified[i];
break;
case DATA_SUBC:
symbols[symbol_index++] = ofdm_symbol_subcarriers_modified[i];
break;
default:
break;
}
}
}
#define Ns 16
double
estimate_frequency_offset(const cvec &c, int n_fft)
{
vec fft_vals = zeros(n_fft);
int index;
double v = 0;
cvec ys = zeros_c(Ns);
for (int n = 0; n < Ns; ++n) {
for (int j = 0; j < 9; ++j) {
ys[j] = c(j * 16 + n);
}
fft_vals = fft_vals + sqr(fft(ys, n_fft));
}
max(fft_vals, index);
index = (index > n_fft / 2) ? index - n_fft : index;
v = double(index) / 16.0 / double(n_fft);
return v;
}
cvec
fourth_power_derotate(const cvec &symbols)
{
cvec fixed_vector = "";
cvec subvector;
cvec fourth_pow;
vec angles;
double average_phi;
for (int i = 0; i < symbols.length() / FOURTH_POWER_WINDOW; ++i) {
subvector = symbols.mid(FOURTH_POWER_WINDOW * i, FOURTH_POWER_WINDOW);
fourth_pow = elem_mult(subvector, subvector);
fourth_pow = -elem_mult(fourth_pow, fourth_pow);
angles = arg(fourth_pow);
// unwrap(arg(fourth_pow), angles);
average_phi = sum(angles) / FOURTH_POWER_WINDOW / 4.0;
fixed_vector = concat(fixed_vector, subvector * exp(complex<double>(0,-1.0) * average_phi));
}
return fixed_vector;
}
void
apply_bonus(cvec &received_syms, int bonus)
{
if (NCP < bonus) {
cerr << "Bonus must be within cyclic prefix" << endl;
}
if (bonus == 0) return;
for (int i = 0; i < received_syms.length() / (NFFT + NCP); ++i) {
for (int j = NCP - bonus; j < NCP; ++j) {
received_syms[i * (NFFT + NCP) + j + NFFT] = 0.5 * (received_syms[i * (NFFT + NCP) + j + NFFT] + received_syms[i * (NFFT + NCP) + j]);
}
}
}