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127 lines
5.4 KiB
C
127 lines
5.4 KiB
C
/**
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* Copyright 2013-2021 Software Radio Systems Limited
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*
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* This file is part of srsLTE.
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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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/******************************************************************************
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* File: npss.h
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*
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* Description: Narrowband Primary synchronization signal (NPSS) generation and detection.
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*
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* The srslte_npss_synch_t object provides functions for fast
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* computation of the crosscorrelation between the NPSS and received
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* signal and CFO estimation. Also, the function srslte_npss_synch_tperiodic()
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* is designed to be called periodically every subframe, taking
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* care of the correct data alignment with respect to the NPSS sequence.
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*
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* The object is designed to work with signals sampled at ?.? Mhz
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* centered at the carrier frequency. Thus, downsampling is required
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* if the signal is sampled at higher frequencies.
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*
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* Reference: 3GPP TS 36.211 version 13.2.0 Release 13 Sec. 10.x.x
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*****************************************************************************/
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#ifndef SRSLTE_NPSS_H
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#define SRSLTE_NPSS_H
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#include <stdbool.h>
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#include <stdint.h>
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#include "srslte/config.h"
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#include "srslte/phy/common/phy_common.h"
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#include "srslte/phy/utils/convolution.h"
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#define CONVOLUTION_FFT
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#define SRSLTE_NPSS_RETURN_PSR
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#define SRSLTE_NPSS_LEN 11
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#define SRSLTE_NPSS_NUM_OFDM_SYMS 11
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#define SRSLTE_NPSS_TOT_LEN (SRSLTE_NPSS_LEN * SRSLTE_NPSS_NUM_OFDM_SYMS)
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#define SRSLTE_NPSS_CORR_FILTER_LEN \
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((SRSLTE_NPSS_NUM_OFDM_SYMS * SRSLTE_NBIOT_FFT_SIZE) + \
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(SRSLTE_NPSS_NUM_OFDM_SYMS - 1) * SRSLTE_CP_LEN_NORM(1, SRSLTE_NBIOT_FFT_SIZE) + \
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SRSLTE_CP_LEN_NORM(0, SRSLTE_NBIOT_FFT_SIZE))
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// The below value corresponds to the time-domain representation of the first
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// three OFDM-symbols plus cyclic prefix that are not transmitted in the sub-frame
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// carrying the NPSS
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#define SRSLTE_NPSS_CORR_OFFSET (SRSLTE_SF_LEN(SRSLTE_NBIOT_FFT_SIZE) - SRSLTE_NPSS_CORR_FILTER_LEN)
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// CFO estimation based on the NPSS is done using the second slot of the sub-frame
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#define SRSLTE_NPSS_CFO_OFFSET (SRSLTE_SF_LEN(SRSLTE_NBIOT_FFT_SIZE) / 2 - SRSLTE_NPSS_CORR_OFFSET)
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#define SRSLTE_NPSS_CFO_NUM_SYMS 6 // number of symbols for CFO estimation
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#define SRSLTE_NPSS_CFO_NUM_SAMPS \
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((SRSLTE_NPSS_CFO_NUM_SYMS * SRSLTE_NBIOT_FFT_SIZE) + \
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(SRSLTE_NPSS_CFO_NUM_SYMS - 1) * SRSLTE_CP_LEN_NORM(1, SRSLTE_NBIOT_FFT_SIZE) + \
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SRSLTE_CP_LEN_NORM(0, SRSLTE_NBIOT_FFT_SIZE)) // resulting number of samples
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// NPSS processing options
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#define SRSLTE_NPSS_ACCUMULATE_ABS // If enabled, accumulates the correlation absolute value on consecutive calls to
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// srslte_pss_synch_find_pss
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#define SRSLTE_NPSS_ABS_SQUARE // If enabled, compute abs square, otherwise computes absolute value only
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#define SRSLTE_NPSS_RETURN_PSR // If enabled returns peak to side-lobe ratio, otherwise returns absolute peak value
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/* Low-level API */
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typedef struct SRSLTE_API {
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#ifdef CONVOLUTION_FFT
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srslte_conv_fft_cc_t conv_fft;
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#endif
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uint32_t frame_size, max_frame_size;
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uint32_t fft_size, max_fft_size;
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cf_t* npss_signal_time;
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cf_t* tmp_input;
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cf_t* conv_output;
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float* conv_output_abs;
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float ema_alpha;
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float* conv_output_avg;
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float peak_value;
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} srslte_npss_synch_t;
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// Basic functionality
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SRSLTE_API int srslte_npss_synch_init(srslte_npss_synch_t* q, uint32_t frame_size, uint32_t fft_size);
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SRSLTE_API void srslte_npss_synch_reset(srslte_npss_synch_t* q);
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SRSLTE_API int srslte_npss_synch_resize(srslte_npss_synch_t* q, uint32_t frame_size, uint32_t fft_size);
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SRSLTE_API void srslte_npss_synch_set_ema_alpha(srslte_npss_synch_t* q, float alpha);
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SRSLTE_API void srslte_npss_synch_free(srslte_npss_synch_t* q);
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SRSLTE_API int srslte_npss_sync_find(srslte_npss_synch_t* q, cf_t* input, float* corr_peak_value);
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// Internal functions
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SRSLTE_API int srslte_npss_corr_init(cf_t* npss_signal_time, uint32_t fft_size, uint32_t frame_size);
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SRSLTE_API int srslte_npss_generate(cf_t* signal);
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SRSLTE_API void srslte_npss_put_subframe(srslte_npss_synch_t* q,
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cf_t* npss_signal,
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cf_t* sf,
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const uint32_t nof_prb,
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const uint32_t nbiot_prb_offset);
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#endif // SRSLTE_NPSS_H
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