mirror of https://github.com/PentHertz/srsLTE.git
273 lines
7.8 KiB
C
273 lines
7.8 KiB
C
/**
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*
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* \section COPYRIGHT
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*
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* Copyright 2013-2015 Software Radio Systems Limited
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*
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* \section LICENSE
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*
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* This file is part of the srsLTE library.
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*
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* srsLTE is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as
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* published by the Free Software Foundation, either version 3 of
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* the License, or (at your option) any later version.
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*
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* srsLTE is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* A copy of the GNU Affero General Public License can be found in
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* the LICENSE file in the top-level directory of this distribution
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* and at http://www.gnu.org/licenses/.
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*
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*/
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#include <stdint.h>
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#include <stdio.h>
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#include <string.h>
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#include <strings.h>
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#include <stdlib.h>
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#include <stdbool.h>
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#include <assert.h>
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#include <math.h>
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#include "srslte/phch/regs.h"
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#include "srslte/phch/pcfich.h"
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#include "srslte/common/phy_common.h"
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#include "srslte/utils/bit.h"
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#include "srslte/utils/vector.h"
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#include "srslte/utils/debug.h"
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// Table 5.3.4-1
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static uint8_t cfi_table[4][PCFICH_CFI_LEN] = {
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{ 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1,
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1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1 },
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{ 1, 0, 1,
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1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,
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0, 1, 1, 0 },
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{ 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1,
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0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1 },
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{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } // reserved
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};
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bool srslte_pcfich_exists(int nframe, int nslot) {
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return true;
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}
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/** Initializes the pcfich channel receiver.
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* On error, returns -1 and frees the structrure
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*/
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int srslte_pcfich_init(srslte_pcfich_t *q, srslte_regs_t *regs, srslte_cell_t cell) {
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int ret = SRSLTE_ERROR_INVALID_INPUTS;
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if (q != NULL &&
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regs != NULL &&
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srslte_cell_isvalid(&cell))
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{
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ret = SRSLTE_ERROR;
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bzero(q, sizeof(srslte_pcfich_t));
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q->cell = cell;
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q->regs = regs;
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q->nof_symbols = PCFICH_RE;
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if (srslte_modem_table_lte(&q->mod, SRSLTE_MOD_QPSK)) {
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goto clean;
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}
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for (int nsf = 0; nsf < SRSLTE_NSUBFRAMES_X_FRAME; nsf++) {
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if (srslte_sequence_pcfich(&q->seq[nsf], 2 * nsf, q->cell.id)) {
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goto clean;
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}
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}
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/* convert cfi bit tables to floats for demodulation */
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for (int i=0;i<3;i++) {
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for (int j=0;j<PCFICH_CFI_LEN;j++) {
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q->cfi_table_float[i][j] = (float) 2.0*cfi_table[i][j]-1.0;
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}
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}
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ret = SRSLTE_SUCCESS;
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}
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clean:
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if (ret == SRSLTE_ERROR) {
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srslte_pcfich_free(q);
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}
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return ret;
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}
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void srslte_pcfich_free(srslte_pcfich_t *q) {
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for (int ns = 0; ns < SRSLTE_NSUBFRAMES_X_FRAME; ns++) {
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srslte_sequence_free(&q->seq[ns]);
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}
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srslte_modem_table_free(&q->mod);
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bzero(q, sizeof(srslte_pcfich_t));
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}
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/** Finds the CFI with minimum distance with the vector of received 32 bits.
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* Saves the CFI value in the cfi pointer and returns the distance.
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*/
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float srslte_pcfich_cfi_decode(srslte_pcfich_t *q, uint32_t *cfi) {
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int i;
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int index = 0;
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float max_corr = 0;
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float corr[3];
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for (i = 0; i < 3; i++) {
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corr[i] = srslte_vec_dot_prod_fff(q->cfi_table_float[i], q->data_f, PCFICH_CFI_LEN);
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if (corr[i] > max_corr) {
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max_corr = corr[i];
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index = i;
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}
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}
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if (cfi) {
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*cfi = index + 1;
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}
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return max_corr;
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}
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/** Encodes the CFI producing a vector of 32 bits.
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* 36.211 10.3 section 5.3.4
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*/
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int srslte_pcfich_cfi_encode(uint32_t cfi, uint8_t bits[PCFICH_CFI_LEN]) {
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if (cfi < 1 || cfi > 3) {
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return SRSLTE_ERROR_INVALID_INPUTS;
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} else{
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memcpy(bits, cfi_table[cfi - 1], PCFICH_CFI_LEN * sizeof(uint8_t));
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return SRSLTE_SUCCESS;
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}
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}
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/* Decodes the PCFICH channel and saves the CFI in the cfi pointer.
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*
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* Returns 1 if successfully decoded the CFI, 0 if not and -1 on error
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*/
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int srslte_pcfich_decode(srslte_pcfich_t *q, cf_t *slot_symbols, cf_t *ce[SRSLTE_MAX_PORTS], float noise_estimate,
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uint32_t nsubframe, uint32_t *cfi, float *corr_result)
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{
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/* Set pointers for layermapping & precoding */
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int i;
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cf_t *x[SRSLTE_MAX_LAYERS];
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cf_t *ce_precoding[SRSLTE_MAX_PORTS];
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if (q != NULL &&
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slot_symbols != NULL &&
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nsubframe < SRSLTE_NSUBFRAMES_X_FRAME)
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{
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/* number of layers equals number of ports */
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for (i = 0; i < SRSLTE_MAX_PORTS; i++) {
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x[i] = q->x[i];
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}
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for (i = 0; i < SRSLTE_MAX_PORTS; i++) {
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ce_precoding[i] = q->ce[i];
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}
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/* extract symbols */
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if (q->nof_symbols
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!= srslte_regs_pcfich_get(q->regs, slot_symbols, q->symbols[0])) {
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fprintf(stderr, "There was an error getting the PCFICH symbols\n");
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return SRSLTE_ERROR;
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}
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/* extract channel estimates */
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for (i = 0; i < q->cell.nof_ports; i++) {
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if (q->nof_symbols != srslte_regs_pcfich_get(q->regs, ce[i], q->ce[i])) {
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fprintf(stderr, "There was an error getting the PCFICH symbols\n");
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return SRSLTE_ERROR;
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}
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}
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/* in control channels, only diversity is supported */
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if (q->cell.nof_ports == 1) {
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/* no need for layer demapping */
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srslte_predecoding_single(q->symbols[0], q->ce[0], q->d, q->nof_symbols, noise_estimate);
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} else {
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srslte_predecoding_diversity(q->symbols[0], ce_precoding, x,
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q->cell.nof_ports, q->nof_symbols);
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srslte_layerdemap_diversity(x, q->d, q->cell.nof_ports,
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q->nof_symbols / q->cell.nof_ports);
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}
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/* demodulate symbols */
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srslte_demod_soft_demodulate(SRSLTE_MOD_QPSK, q->d, q->data_f, q->nof_symbols);
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/* Scramble with the sequence for slot nslot */
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srslte_scrambling_f(&q->seq[nsubframe], q->data_f);
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/* decode CFI */
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float corr = srslte_pcfich_cfi_decode(q, cfi);
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if (corr_result) {
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*corr_result = corr;
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}
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return 1;
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} else {
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return SRSLTE_ERROR_INVALID_INPUTS;
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}
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}
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/** Encodes CFI and maps symbols to the slot
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*/
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int srslte_pcfich_encode(srslte_pcfich_t *q, uint32_t cfi, cf_t *slot_symbols[SRSLTE_MAX_PORTS],
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uint32_t subframe) {
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int i;
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if (q != NULL &&
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cfi <= 3 &&
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slot_symbols != NULL &&
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subframe < SRSLTE_NSUBFRAMES_X_FRAME)
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{
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/* Set pointers for layermapping & precoding */
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cf_t *x[SRSLTE_MAX_LAYERS];
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cf_t *symbols_precoding[SRSLTE_MAX_PORTS];
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/* number of layers equals number of ports */
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for (i = 0; i < q->cell.nof_ports; i++) {
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x[i] = q->x[i];
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}
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for (i = 0; i < SRSLTE_MAX_PORTS; i++) {
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symbols_precoding[i] = q->symbols[i];
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}
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/* pack CFI */
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srslte_pcfich_cfi_encode(cfi, q->data);
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/* scramble for slot sequence nslot */
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srslte_scrambling_b(&q->seq[subframe], q->data);
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srslte_mod_modulate(&q->mod, q->data, q->d, PCFICH_CFI_LEN);
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/* layer mapping & precoding */
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if (q->cell.nof_ports > 1) {
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srslte_layermap_diversity(q->d, x, q->cell.nof_ports, q->nof_symbols);
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srslte_precoding_diversity(x, symbols_precoding, q->cell.nof_ports,
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q->nof_symbols / q->cell.nof_ports);
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} else {
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memcpy(q->symbols[0], q->d, q->nof_symbols * sizeof(cf_t));
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}
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/* mapping to resource elements */
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for (i = 0; i < q->cell.nof_ports; i++) {
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if (srslte_regs_pcfich_put(q->regs, q->symbols[i], slot_symbols[i]) < 0) {
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fprintf(stderr, "Error putting PCHICH resource elements\n");
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return SRSLTE_ERROR;
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}
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}
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return SRSLTE_SUCCESS;
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} else {
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return SRSLTE_ERROR_INVALID_INPUTS;
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}
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}
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