mirror of https://github.com/pvnis/srsRAN_4G.git
Initial NR-PBCH-DMRS integration
Xavier Arteaga
4 years ago
committed by
Andre Puschmann
parent
997f7db23a
commit
a245039cf3
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/**
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*
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* \section COPYRIGHT
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*
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* Copyright 2013-2021 Software Radio Systems Limited
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*
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* By using this file, you agree to the terms and conditions set
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* forth in the LICENSE file which can be found at the top level of
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* the distribution.
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*
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*/
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#ifndef SRSRAN_DMRS_PBCH_H
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#define SRSRAN_DMRS_PBCH_H
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#include "srsran/phy/common/phy_common_nr.h"
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/**
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* @brief Describes the DeModulation Reference Signals (DMRS) for NR PBCH configuration
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*/
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typedef struct SRSRAN_API {
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uint32_t N_id; ///< Physical cell identifier
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uint32_t n_hf; ///< Number of half radio frame, 0 or 1
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uint32_t ssb_idx; ///< SSB candidate index
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uint32_t L_max; ///< Number of SSB opportunities in half radio frame
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float beta; ///< Power allocation specified in TS 38.213
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srsran_subcarrier_spacing_t scs; ///< SSB configured subcarrier spacing
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} srsran_dmrs_pbch_cfg_t;
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/**
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* @brief Describes an NR PBCH DMRS based measurement
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*/
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typedef struct SRSRAN_API {
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float corr; ///< Normalised correlation
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float epre; ///< Linear energy per resource element
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float rsrp; ///< Linear RSRP
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float cfo_hz; ///< CFO in Hz
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float avg_delay_us; ///< Average delay in us
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} srsran_dmrs_pbch_meas_t;
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/**
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* @brief Put NR PBCH DMRS in the SSB resource grid
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* @param cfg PBCH DMRS configuration
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* @param[out] ssb_grid SSB resource grid
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* @return SRSRAN_SUCCESS if the inputs and configuration are valid, SRSRAN_ERROR code otherwise
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*/
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SRSRAN_API int srsran_dmrs_pbch_put(const srsran_dmrs_pbch_cfg_t* cfg, cf_t ssb_grid[SRSRAN_SSB_NOF_RE]);
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/**
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* @brief Estimates NR PBCH DMRS
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* @param cfg PBCH DMRS configuration
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* @param ssb_grid Demodulated SSB resource grid
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* @param[out] ce Estimated channel
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* @param[out] meas Estimated channel measurements
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* @return SRSRAN_SUCCESS if the inputs and configuration are valid, SRSRAN_ERROR code otherwise
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*/
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SRSRAN_API int srsran_dmrs_pbch_estimate(const srsran_dmrs_pbch_cfg_t* cfg,
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const cf_t ssb_grid[SRSRAN_SSB_NOF_RE],
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cf_t ce[SRSRAN_SSB_NOF_RE],
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srsran_dmrs_pbch_meas_t* meas);
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#endif // SRSRAN_DMRS_PBCH_H
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@ -0,0 +1,218 @@
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/**
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*
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* \section COPYRIGHT
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*
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* Copyright 2013-2021 Software Radio Systems Limited
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*
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* By using this file, you agree to the terms and conditions set
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* forth in the LICENSE file which can be found at the top level of
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* the distribution.
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*
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*/
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#include "srsran/phy/ch_estimation/dmrs_pbch.h"
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#include "srsran/phy/common/sequence.h"
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#include "srsran/phy/utils/debug.h"
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#include "srsran/phy/utils/vector.h"
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#include <complex.h>
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#include <math.h>
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/*
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* Number of NR PBCH DMRS resource elements present in an SSB resource grid
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*/
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#define DMRS_PBCH_NOF_RE 144
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static uint32_t dmrs_pbch_cinit(const srsran_dmrs_pbch_cfg_t* cfg)
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{
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// Default values for L_max == 4
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uint64_t i_ssb = (cfg->ssb_idx & 0b11U) + 4UL * cfg->n_hf; // Least 2 significant bits
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if (cfg->L_max == 8 || cfg->L_max == 64) {
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i_ssb = cfg->ssb_idx & 0b111U; // Least 3 significant bits
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}
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return SRSRAN_SEQUENCE_MOD(((i_ssb + 1UL) * (SRSRAN_FLOOR(cfg->N_id, 4UL) + 1UL) << 11UL) + ((i_ssb + 1UL) << 6UL) +
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(cfg->N_id % 4));
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}
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int srsran_dmrs_pbch_put(const srsran_dmrs_pbch_cfg_t* cfg, cf_t ssb_grid[SRSRAN_SSB_NOF_RE])
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{
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// Validate inputs
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if (cfg == NULL || ssb_grid == NULL) {
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return SRSRAN_ERROR_INVALID_INPUTS;
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}
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// Calculate index shift
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uint32_t v = cfg->N_id % 4;
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// Calculate power allocation
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float beta = M_SQRT1_2;
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if (isnormal(cfg->beta)) {
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beta = cfg->beta;
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}
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// Initialise sequence
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uint32_t cinit = dmrs_pbch_cinit(cfg);
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srsran_sequence_state_t sequence_state = {};
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srsran_sequence_state_init(&sequence_state, cinit);
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// Generate sequence
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cf_t r[DMRS_PBCH_NOF_RE];
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srsran_sequence_state_gen_f(&sequence_state, beta, (float*)r, DMRS_PBCH_NOF_RE * 2);
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// r sequence read index
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uint32_t r_idx = 0;
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// Put sequence in symbol 1
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for (uint32_t k = v; k < SRSRAN_SSB_BW_SUBC; k += 4) {
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ssb_grid[SRSRAN_SSB_BW_SUBC * 1 + k] = r[r_idx++];
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}
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// Put sequence in symbol 2, lower section
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for (uint32_t k = v; k < 48; k += 4) {
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ssb_grid[SRSRAN_SSB_BW_SUBC * 2 + k] = r[r_idx++];
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}
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// Put sequence in symbol 2, upper section
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for (uint32_t k = 192 + v; k < SRSRAN_SSB_BW_SUBC; k += 4) {
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ssb_grid[SRSRAN_SSB_BW_SUBC * 2 + k] = r[r_idx++];
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}
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// Put sequence in symbol 3
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for (uint32_t k = v; k < SRSRAN_SSB_BW_SUBC; k += 4) {
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ssb_grid[SRSRAN_SSB_BW_SUBC * 3 + k] = r[r_idx++];
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}
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return SRSRAN_SUCCESS;
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}
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int dmrs_pbch_extract_lse(const srsran_dmrs_pbch_cfg_t* cfg,
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const cf_t ssb_grid[SRSRAN_SSB_NOF_RE],
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cf_t lse[DMRS_PBCH_NOF_RE])
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{
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// Calculate index shift
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uint32_t v = cfg->N_id % 4;
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// Calculate power allocation
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float beta = M_SQRT1_2;
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if (isnormal(cfg->beta)) {
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beta = cfg->beta;
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}
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// Initialise sequence
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uint32_t cinit = dmrs_pbch_cinit(cfg);
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srsran_sequence_state_t sequence_state = {};
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srsran_sequence_state_init(&sequence_state, cinit);
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// Generate sequence
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cf_t r[DMRS_PBCH_NOF_RE];
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srsran_sequence_state_gen_f(&sequence_state, beta, (float*)r, DMRS_PBCH_NOF_RE * 2);
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// r sequence read index
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uint32_t r_idx = 0;
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// Put sequence in symbol 1
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for (uint32_t k = v; k < SRSRAN_SSB_BW_SUBC; k += 4) {
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lse[r_idx++] = ssb_grid[SRSRAN_SSB_BW_SUBC * 1 + k];
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}
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// Put sequence in symbol 2, lower section
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for (uint32_t k = v; k < 48; k += 4) {
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lse[r_idx++] = ssb_grid[SRSRAN_SSB_BW_SUBC * 2 + k];
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}
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// Put sequence in symbol 2, upper section
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for (uint32_t k = 192 + v; k < SRSRAN_SSB_BW_SUBC; k += 4) {
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lse[r_idx++] = ssb_grid[SRSRAN_SSB_BW_SUBC * 2 + k];
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}
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// Put sequence in symbol 3
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for (uint32_t k = v; k < SRSRAN_SSB_BW_SUBC; k += 4) {
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lse[r_idx++] = ssb_grid[SRSRAN_SSB_BW_SUBC * 3 + k];
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}
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// Calculate actual least square estimates
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srsran_vec_prod_conj_ccc(lse, r, lse, DMRS_PBCH_NOF_RE);
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return SRSRAN_SUCCESS;
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}
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int srsran_dmrs_pbch_estimate(const srsran_dmrs_pbch_cfg_t* cfg,
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const cf_t ssb_grid[SRSRAN_SSB_NOF_RE],
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cf_t ce[SRSRAN_SSB_NOF_RE],
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srsran_dmrs_pbch_meas_t* meas)
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{
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// Validate inputs
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if (cfg == NULL || ssb_grid == NULL || ce == NULL || meas == NULL) {
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return SRSRAN_ERROR_INVALID_INPUTS;
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}
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// Extract least square estimates
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cf_t lse[DMRS_PBCH_NOF_RE];
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if (dmrs_pbch_extract_lse(cfg, ssb_grid, lse) < SRSRAN_SUCCESS) {
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return SRSRAN_ERROR;
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}
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float scs_hz = SRSRAN_SUBC_SPACING_NR(cfg->scs);
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if (!isnormal(scs_hz)) {
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ERROR("Invalid SCS");
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return SRSRAN_ERROR;
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}
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// Compute average delay in microseconds from the symbols 1 and 3 (symbol 2 does not carry PBCH in all the grid)
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float avg_delay1_norm = srsran_vec_estimate_frequency(&lse[0], 60) / 4.0f;
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float avg_delay3_norm = srsran_vec_estimate_frequency(&lse[84], 60) / 4.0f;
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float avg_delay_norm = (avg_delay1_norm + avg_delay3_norm) / 2.0f;
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float avg_delay_us = avg_delay_norm / scs_hz;
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// Generate a second SSB grid with the corrected average delay
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cf_t ssb_grid_corrected[SRSRAN_SSB_NOF_RE];
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for (uint32_t l = 0; l < SRSRAN_SSB_DURATION_NSYMB; l++) {
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srsran_vec_apply_cfo(&ssb_grid[SRSRAN_SSB_BW_SUBC * l],
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avg_delay_norm,
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&ssb_grid_corrected[SRSRAN_SSB_BW_SUBC * l],
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SRSRAN_SSB_BW_SUBC);
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}
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// Extract LSE from corrected grid
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if (dmrs_pbch_extract_lse(cfg, ssb_grid_corrected, lse) < SRSRAN_SUCCESS) {
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return SRSRAN_ERROR;
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}
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// Compute correlation of symbols 1 and 3
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cf_t corr1 = srsran_vec_acc_cc(&lse[0], 60) / 60.0f;
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cf_t corr3 = srsran_vec_acc_cc(&lse[84], 60) / 60.0f;
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// Estimate CFO from correlation
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float distance_s = srsran_symbol_distance_s(1, 3, cfg->scs);
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float cfo_hz = 0.0f;
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if (isnormal(distance_s)) {
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cfo_hz = cargf(corr1 * conjf(corr3)) / (2.0f * (float)M_PI * distance_s);
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}
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// Estimate wideband gain at symbol 0
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cf_t wideband_gain = (srsran_vec_acc_cc(lse, DMRS_PBCH_NOF_RE) / DMRS_PBCH_NOF_RE) *
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cexpf(I * 2.0f * M_PI * srsran_symbol_offset_s(2, cfg->scs) * cfo_hz);
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// Compute RSRP from correlation
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float rsrp = SRSRAN_CSQABS((corr1 + corr3) / 2.0f);
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// Compute EPRE
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float epre = srsran_vec_avg_power_cf(lse, DMRS_PBCH_NOF_RE);
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// Write measurements
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meas->corr = rsrp / epre;
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meas->epre = epre;
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meas->rsrp = rsrp;
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meas->cfo_hz = cfo_hz;
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meas->avg_delay_us = avg_delay_us;
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// Compute channel estimates
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for (uint32_t l = 0; l < SRSRAN_SSB_DURATION_NSYMB; l++) {
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float t_s = srsran_symbol_offset_s(l, cfg->scs);
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cf_t symbol_wideband_gain = cexpf(-I * 2.0f * M_PI * cfo_hz * t_s) * wideband_gain;
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srsran_vec_gen_sine(symbol_wideband_gain, -avg_delay_norm, &ce[l * SRSRAN_SSB_BW_SUBC], SRSRAN_SSB_BW_SUBC);
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}
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return SRSRAN_SUCCESS;
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}
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