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codec2/src/interldpc.c

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/*---------------------------------------------------------------------------*\
FILE........: interldpc.c
AUTHOR......: David Rowe
DATE CREATED: April 2018
Helper functions for LDPC-based waveforms.
\*---------------------------------------------------------------------------*/
/*
Copyright (C) 2018 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/>.
*/
#include "interldpc.h"
#include <assert.h>
#include <math.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "gp_interleaver.h"
#include "mpdecode_core.h"
#include "ofdm_internal.h"
void freedv_pack(unsigned char *bytes, unsigned char *bits, int nbits);
void freedv_unpack(unsigned char *bits, unsigned char *bytes, int nbits);
unsigned short freedv_crc16_unpacked(unsigned char *bits, int nbits);
void set_up_ldpc_constants(struct LDPC *ldpc, int code_length,
int parity_bits) {
/* following provided for convenience and to match Octave variable names */
/* these remain fixed */
ldpc->ldpc_data_bits_per_frame = code_length - parity_bits;
ldpc->ldpc_coded_bits_per_frame = code_length;
/* in the case there are some unused data bits, these may be
modified to be less that ldpc->ldpc_xxx versions above. We
place known bits in the unused data bit positions, which make
the code stronger, and allow us to mess with different speech
codec bit allocations without designing new LDPC codes. */
ldpc->data_bits_per_frame = ldpc->ldpc_data_bits_per_frame;
ldpc->coded_bits_per_frame = ldpc->ldpc_coded_bits_per_frame;
ldpc->protection_mode = LDPC_PROT_2020;
}
void set_data_bits_per_frame(struct LDPC *ldpc, int new_data_bits_per_frame) {
ldpc->data_bits_per_frame = new_data_bits_per_frame;
ldpc->coded_bits_per_frame =
ldpc->data_bits_per_frame + ldpc->NumberParityBits;
}
/* 1' stuffing (code rate reduction) - tweak LDPC code setup for selected modes
*/
void ldpc_mode_specific_setup(struct OFDM *ofdm, struct LDPC *ldpc) {
/* mode specific set up */
if (!strcmp(ofdm->mode, "2020")) set_data_bits_per_frame(ldpc, 312);
if (!strcmp(ofdm->mode, "2020B")) {
set_data_bits_per_frame(ldpc, 156);
ldpc->protection_mode = LDPC_PROT_2020B;
}
if (!strcmp(ofdm->mode, "datac4")) set_data_bits_per_frame(ldpc, 448);
if (!strcmp(ofdm->mode, "datac13")) set_data_bits_per_frame(ldpc, 128);
}
/* LDPC encode frame - generate parity bits and a codeword, applying the
selected FEC protection scheme */
void ldpc_encode_frame(struct LDPC *ldpc, int codeword[],
unsigned char tx_bits_char[]) {
unsigned char pbits[ldpc->NumberParityBits];
int codec_frame;
int i, j;
unsigned char tx_bits_char_padded[ldpc->ldpc_data_bits_per_frame];
switch (ldpc->protection_mode) {
case LDPC_PROT_EQUAL:
assert(ldpc->data_bits_per_frame == ldpc->ldpc_data_bits_per_frame);
/* we have enough data bits to fill the codeword */
encode(ldpc, tx_bits_char, pbits);
break;
case LDPC_PROT_2020:
/* not all data bits in codeword used, so set them to known values */
memcpy(tx_bits_char_padded, tx_bits_char, ldpc->data_bits_per_frame);
for (i = ldpc->data_bits_per_frame; i < ldpc->ldpc_data_bits_per_frame;
i++)
tx_bits_char_padded[i] = 1;
encode(ldpc, tx_bits_char_padded, pbits);
break;
case LDPC_PROT_2020B:
/* We only want to protect the stage 1 VQ data bits, 0..10 in
each 52 bit codec frame. There are 3 codec frames 3x52=156
bits, and 56 parity bits. We only use 11*3 = 33 bits of
the LDPC codeword data bits, the rest are set to known
values.
*/
for (j = 0, codec_frame = 0; codec_frame < 3; codec_frame++)
for (i = 0; i < 11; i++, j++)
tx_bits_char_padded[j] = tx_bits_char[codec_frame * 52 + i];
assert(j == 33);
for (i = 33; i < ldpc->ldpc_data_bits_per_frame; i++)
tx_bits_char_padded[i] = 1;
encode(ldpc, tx_bits_char_padded, pbits);
break;
default:
assert(0);
}
/* output codeword is concatenation of (used) data bits and parity
bits, we don't bother sending unused (known) data bits */
for (i = 0; i < ldpc->data_bits_per_frame; i++) codeword[i] = tx_bits_char[i];
for (j = 0; j < ldpc->NumberParityBits; i++, j++) codeword[i] = pbits[j];
}
void qpsk_modulate_frame(COMP tx_symbols[], int codeword[], int n) {
int s, i;
int dibit[2];
complex float qpsk_symb;
for (s = 0, i = 0; i < n; s += 2, i++) {
dibit[0] = codeword[s + 1] & 0x1;
dibit[1] = codeword[s] & 0x1;
qpsk_symb = qpsk_mod(dibit);
tx_symbols[i].real = crealf(qpsk_symb);
tx_symbols[i].imag = cimagf(qpsk_symb);
}
}
/* run LDPC decoder, taking into account the FEC protection scheme */
void ldpc_decode_frame(struct LDPC *ldpc, int *parityCheckCount, int *iter,
uint8_t out_char[], float llr[]) {
float llr_full_codeword[ldpc->ldpc_coded_bits_per_frame];
int unused_data_bits =
ldpc->ldpc_data_bits_per_frame - ldpc->data_bits_per_frame;
uint8_t out_char_ldpc[ldpc->coded_bits_per_frame];
int i, j;
int codec_frame;
switch (ldpc->protection_mode) {
case LDPC_PROT_EQUAL:
/* Equal protection all data bits in codeword
(e.g. 700D/700E), works well with rate 0.5 codes */
assert(ldpc->data_bits_per_frame == ldpc->ldpc_data_bits_per_frame);
*iter = run_ldpc_decoder(ldpc, out_char, llr, parityCheckCount);
break;
case LDPC_PROT_2020:
/* some data bits in codeword unused, effectively
decreasing code rate and making FEC more powerful
(without having to design a new code) */
for (i = 0; i < ldpc->data_bits_per_frame; i++)
llr_full_codeword[i] = llr[i];
// known bits ... so really likely
for (i = ldpc->data_bits_per_frame; i < ldpc->ldpc_data_bits_per_frame;
i++)
llr_full_codeword[i] = -100.0f;
// parity bits at end
for (i = ldpc->ldpc_data_bits_per_frame;
i < ldpc->ldpc_coded_bits_per_frame; i++)
llr_full_codeword[i] = llr[i - unused_data_bits];
*iter =
run_ldpc_decoder(ldpc, out_char, llr_full_codeword, parityCheckCount);
break;
case LDPC_PROT_2020B:
/* 2020B waveform, with unequal error protection. Only the
stage1 VQ index of each LPCNet vocoder frames is
protected. In this case the FEC codeword is much smaller
than the payload data. */
// set up LDPC codeword
for (j = 0, codec_frame = 0; codec_frame < 3; codec_frame++)
for (i = 0; i < 11; i++, j++)
llr_full_codeword[j] = llr[codec_frame * 52 + i];
// set known LDPC codeword data bits
for (i = 33; i < ldpc->ldpc_data_bits_per_frame; i++)
llr_full_codeword[i] = -100;
// parity bits at end
for (i = 0; i < ldpc->NumberParityBits; i++)
llr_full_codeword[ldpc->ldpc_data_bits_per_frame + i] =
llr[ldpc->data_bits_per_frame + i];
*iter = run_ldpc_decoder(ldpc, out_char_ldpc, llr_full_codeword,
parityCheckCount);
// pass through received data bits, replacing only decoded bits
for (i = 0; i < ldpc->data_bits_per_frame; i++) {
out_char[i] = llr[i] < 0;
}
for (j = 0, codec_frame = 0; codec_frame < 3; codec_frame++)
for (i = 0; i < 11; i++, j++)
out_char[codec_frame * 52 + i] = out_char_ldpc[j];
break;
default:
assert(0);
}
}
/* Count uncoded (raw) bit errors over frame, note we don't include UW
of txt bits as this is done after we dissassemmble the frame */
int count_uncoded_errors(struct LDPC *ldpc, struct OFDM_CONFIG *config,
COMP codeword_symbols_de[], int crc16) {
int i, Nerrs;
int coded_syms_per_frame = ldpc->coded_bits_per_frame / config->bps;
int coded_bits_per_frame = ldpc->coded_bits_per_frame;
int data_bits_per_frame = ldpc->data_bits_per_frame;
int rx_bits_raw[coded_bits_per_frame];
/* generate test codeword from known payload data bits */
int test_codeword[coded_bits_per_frame];
uint16_t r[data_bits_per_frame];
uint8_t tx_bits[data_bits_per_frame];
ofdm_rand(r, data_bits_per_frame);
for (i = 0; i < data_bits_per_frame; i++) {
tx_bits[i] = r[i] > 16384;
}
if (crc16) {
uint16_t tx_crc16 =
freedv_crc16_unpacked(tx_bits, data_bits_per_frame - 16);
uint8_t tx_crc16_bytes[] = {tx_crc16 >> 8, tx_crc16 & 0xff};
freedv_unpack(tx_bits + data_bits_per_frame - 16, tx_crc16_bytes, 16);
}
ldpc_encode_frame(ldpc, test_codeword, tx_bits);
for (i = 0; i < coded_syms_per_frame; i++) {
int bits[2];
complex float s =
codeword_symbols_de[i].real + I * codeword_symbols_de[i].imag;
qpsk_demod(s, bits);
rx_bits_raw[config->bps * i] = bits[1];
rx_bits_raw[config->bps * i + 1] = bits[0];
}
Nerrs = 0;
for (i = 0; i < coded_bits_per_frame; i++) {
if (test_codeword[i] != rx_bits_raw[i]) Nerrs++;
}
return Nerrs;
}
int count_errors(uint8_t tx_bits[], uint8_t rx_bits[], int n) {
int i;
int Nerrs = 0;
for (i = 0; i < n; i++)
if (tx_bits[i] != rx_bits[i]) Nerrs++;
return Nerrs;
}
/* for unequal protection modes, count coded errors only in those bits that have
* been protected */
void count_errors_protection_mode(int protection_mode, int *pNerrs,
int *pNcoded, uint8_t tx_bits[],
uint8_t rx_bits[], int n) {
int i;
int Nerrs = 0;
int Ncoded = 0;
switch (protection_mode) {
case LDPC_PROT_EQUAL:
case LDPC_PROT_2020:
for (i = 0; i < n; i++) {
if (tx_bits[i] != rx_bits[i]) Nerrs++;
Ncoded++;
}
break;
case LDPC_PROT_2020B:
/* We only protect bits 0..10 in each 52 bit LPCNet codec
frame. There are 3 codec frames 3x52=156 data bits, of
which only 11*3 = 33 bits are protected.
*/
for (int codec_frame = 0; codec_frame < 3; codec_frame++) {
for (i = 0; i < 11; i++) {
if (tx_bits[codec_frame * 52 + i] != rx_bits[codec_frame * 52 + i])
Nerrs++;
Ncoded++;
}
}
break;
default:
assert(0);
}
*pNerrs = Nerrs;
*pNcoded = Ncoded;
}
/*
Given an array of tx_bits, LDPC encodes, interleaves, and OFDM modulates
*/
void ofdm_ldpc_interleave_tx(struct OFDM *ofdm, struct LDPC *ldpc,
complex float tx_sams[], uint8_t tx_bits[],
uint8_t txt_bits[]) {
int Npayloadsymsperpacket = ldpc->coded_bits_per_frame / ofdm->bps;
int Npayloadbitsperpacket = ldpc->coded_bits_per_frame;
int Nbitsperpacket = ofdm_get_bits_per_packet(ofdm);
int codeword[Npayloadbitsperpacket];
COMP payload_symbols[Npayloadsymsperpacket];
COMP payload_symbols_inter[Npayloadsymsperpacket];
complex float tx_symbols[Nbitsperpacket / ofdm->bps];
ldpc_encode_frame(ldpc, codeword, tx_bits);
qpsk_modulate_frame(payload_symbols, codeword, Npayloadsymsperpacket);
gp_interleave_comp(payload_symbols_inter, payload_symbols,
Npayloadsymsperpacket);
ofdm_assemble_qpsk_modem_packet_symbols(ofdm, tx_symbols,
payload_symbols_inter, txt_bits);
ofdm_txframe(ofdm, tx_sams, tx_symbols);
}
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