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/* GMR-1 RACH channel coding */
/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.5 */
/* (C) 2011-2016 by Sylvain Munaut <tnt@246tNt.com>
* All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*! \addtogroup rach
* @{
*/
/*! \file l1/rach.c
* \brief Osmocom GMR-1 RACH channel coding implementation
*/
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <osmocom/core/bits.h>
#include <osmocom/core/conv.h>
#include <osmocom/core/crcgen.h>
#include <osmocom/gmr1/l1/conv.h>
#include <osmocom/gmr1/l1/crc.h>
#include <osmocom/gmr1/l1/interleave.h>
#include <osmocom/gmr1/l1/scramb.h>
static struct osmo_conv_code gmr1_conv_rach;
static void __attribute__ ((constructor))
gmr1_rach_init(void)
{
int i, *p;
/* Init convolutional coder */
memcpy(&gmr1_conv_rach, &gmr1_conv_14, sizeof(struct osmo_conv_code));
gmr1_conv_rach.len = 159;
/* Generate puncturer (only b[0] .. b[539] punctured) */
p = malloc((135*2 + 1) * sizeof(int));
if (!p)
abort();
for (i=0; i<135; i++) {
p[(i<<1) ] = (i << 2) + 2;
p[(i<<1)+1] = (i << 2) + 3;
}
p[270] = -1;
gmr1_conv_rach.puncture = p;
}
/*! \brief Stateless GMR-1 RACH channel coder
* \param[out] bits_e Data bits of a burst
* \param[in] rach RACH packet data (2 class-1 bytes, 16 class-2 bytes)
* \param[in] sb_mask RACH SB Mask value (see GMR-1 04.008)
*
* RACH data is 18 bytes long (2 class-1, 16 class-2), and bits_e is a
* 494 hard bits array to be mapped on a RACH burst.
*/
void
gmr1_rach_encode(ubit_t *bits_e, const uint8_t *rach, uint8_t sb_mask)
{
ubit_t bits_u[159], *bits_u1, *bits_u2;
ubit_t bits_c[382];
ubit_t bits_e1p[112], bits_e2p[270];
ubit_t bits_ep[494];
ubit_t bits_x[494];
int i;
/* rach -> d : unpacking */
bits_u1 = bits_u + 135;
bits_u2 = bits_u;
osmo_pbit2ubit_ext(bits_u1, 0, rach, 0, 16, 1);
osmo_pbit2ubit_ext(bits_u2, 0, rach, 16, 123, 1);
/* d -> u : CRC addition */
osmo_crc8gen_set_bits (&gmr1_crc8, bits_u1, 16, bits_u1+16);
osmo_crc16gen_set_bits(&gmr1_crc12, bits_u2, 123, bits_u2+123);
/* u -> u' : masking */
for (i=0; i<8; i++)
bits_u1[16+i] ^= (sb_mask >> (7-i)) & 1;
/* u' -> c : convolutional coding */
osmo_conv_encode(&gmr1_conv_rach, bits_u, bits_c);
/* c -> e' : interleaving */
gmr1_interleave_intra(bits_e1p, bits_c+270, 14);
gmr1_interleave_intra(bits_e2p, bits_c, 33);
memcpy(bits_e2p+264, bits_c+264, 6);
memcpy(bits_ep, bits_e1p, 112);
memcpy(bits_ep+112, bits_e2p, 270);
memcpy(bits_ep+382, bits_e1p, 112);
/* e' -> x : scrambling */
gmr1_scramble_ubit(bits_x, bits_ep, 494);
/* x -> e=m : multiplex */
memcpy(bits_e, bits_x+112, 136);
memcpy(bits_e+136, bits_x, 112);
memcpy(bits_e+248, bits_x+382, 112);
memcpy(bits_e+360, bits_x+248, 134);
}
/*! \brief Stateless GMR-1 RACH channel decoder
* \param[out] rach RACH packet data (2 class-1 bytes, 16 class-2 bytes)
* \param[in] bits_e Data bits of a burst
* \param[in] sb_mask RACH SB Mask value (see GMR-1 04.008)
* \param[out] conv_rv Return of the convolutional decode (can be NULL)
* \param[out] crc_rv Return array of the 2 CRC checks (can be NULL)
* \return 0 if all CRC check pass, any other value for fail.
*
* RACH data is 18 bytes long (2 class-1, 16 class-2), and bits_e is a
* 494 soft bits array unmapped from a RACH burst.
*/
int
gmr1_rach_decode(uint8_t *rach, const sbit_t *bits_e, uint8_t sb_mask,
int *conv_rv, int *crc_rv)
{
sbit_t bits_x[494];
sbit_t bits_ep[494];
sbit_t bits_e1p[112], bits_e2p[270];
sbit_t bits_c[382];
ubit_t bits_u[159], *bits_u1, *bits_u2;
int i, rv, crc[2];
/* e=m -> x : de-multiplex */
memcpy(bits_x, bits_e+136, 112);
memcpy(bits_x+112, bits_e, 136);
memcpy(bits_x+248, bits_e+360, 134);
memcpy(bits_x+382, bits_e+248, 112);
/* x -> e' : de-scrambling */
gmr1_scramble_sbit(bits_ep, bits_x, 494);
/* e' -> c : de-interleaving */
memcpy(bits_e2p, bits_ep+112, 270);
for (i=0; i<112; i++)
bits_e1p[i] = (sbit_t)(((int)bits_ep[i] + (int)bits_ep[i+382]) >> 1);
gmr1_deinterleave_intra(bits_c+270, bits_e1p, 14);
gmr1_deinterleave_intra(bits_c, bits_e2p, 33);
memcpy(bits_c+264, bits_e2p+264, 6);
/* c -> u' / u : convolutional decoding */
rv = osmo_conv_decode(&gmr1_conv_rach, bits_c, bits_u);
if (conv_rv)
*conv_rv = rv;
bits_u1 = bits_u + 135;
bits_u2 = bits_u;
/* CRC checks */
crc[0] = osmo_crc8gen_check_bits (&gmr1_crc8, bits_u1, 16, bits_u1+16);
crc[1] = osmo_crc16gen_check_bits(&gmr1_crc12, bits_u2, 123, bits_u2+123);
if (crc[0]) {
for (i=0; i<8; i++)
bits_u1[16+i] ^= (sb_mask >> (7-i)) & 1;
crc[0] = osmo_crc8gen_check_bits (&gmr1_crc8, bits_u1, 16, bits_u1+16);
}
if (crc_rv) {
crc_rv[0] = crc[0];
crc_rv[1] = crc[1];
}
/* CRC removal & packing */
rach[17] = 0x00;
osmo_ubit2pbit_ext(rach, 0, bits_u1, 0, 16, 1);
osmo_ubit2pbit_ext(rach, 16, bits_u2, 0, 123, 1);
return crc[0] || crc[1];
}
/*! @} */
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