131 lines
4.4 KiB
C
131 lines
4.4 KiB
C
/*
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* Licensed to the OpenAirInterface (OAI) Software Alliance under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The OpenAirInterface Software Alliance licenses this file to You under
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* the OAI Public License, Version 1.1 (the "License"); you may not use this file
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* except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.openairinterface.org/?page_id=698
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*-------------------------------------------------------------------------------
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* For more information about the OpenAirInterface (OAI) Software Alliance:
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* contact@openairinterface.org
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*/
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/*! \file PHY/LTE_TRANSPORT/prach_common.c
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* \brief Common routines for NR UE/gNB PRACH physical channel V15.4 2019-03
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* \author R. Knopp
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* \date 2019
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* \version 0.1
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* \company Eurecom
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* \email: knopp@eurecom.fr
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* \note
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* \warning
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*/
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#include "PHY/sse_intrin.h"
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#include "PHY/impl_defs_nr.h"
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#include "PHY/defs_nr_UE.h"
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#include "PHY/NR_TRANSPORT/nr_prach.h"
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#include "PHY/NR_TRANSPORT/nr_transport_common_proto.h"
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#include "common/utils/LOG/log.h"
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#include "T.h"
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/* Extended Euclidean Algorithm to compute modulo inverse */
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static int modulo_multiplicative_inverse(const int a, const int m)
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{
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DevAssert(a < m);
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int t = 0;
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int newt = 1;
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int r = m;
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int newr = a;
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while (newr != 0) {
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const int q = r / newr;
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int tmp = t;
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t = newt;
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newt = tmp - q * newt;
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tmp = r;
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r = newr;
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newr = tmp - q * newr;
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}
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AssertFatal(r <= 1, "Modulo inverse doesn't exist for a %d, m %d\n", a, m);
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t = (t < 0) ? t + m : t;
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LOG_D(PHY, "Modulo %d inverse of %d is %d\n", m, a, t);
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return t;
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}
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// This function computes the du
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void nr_fill_du(uint16_t N_ZC, const uint16_t* prach_root_sequence_map, uint16_t nr_du[NR_PRACH_SEQ_LEN_L - 1])
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{
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uint16_t iu,u,p;
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for (iu=0; iu<(N_ZC-1); iu++) {
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u=prach_root_sequence_map[iu];
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p=1;
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while (((u*p)%N_ZC)!=1)
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p++;
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nr_du[u] = ((p<(N_ZC>>1)) ? p : (N_ZC-p));
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}
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}
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void compute_nr_prach_seq(uint8_t short_sequence, uint8_t num_sequences, uint8_t rootSequenceIndex, c16_t X_u[64][839])
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{
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// Compute DFT of x_u => X_u[k] = x_u(inv(u)*k)^* X_u[k] = exp(j\pi u*inv(u)*k*(inv(u)*k+1)/N_ZC)
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int N_ZC;
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const uint16_t* prach_root_sequence_map;
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LOG_D(PHY,"compute_prach_seq: prach short sequence %x, num_sequences %d, rootSequenceIndex %d\n", short_sequence, num_sequences, rootSequenceIndex);
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N_ZC = (short_sequence) ? NR_PRACH_SEQ_LEN_S : NR_PRACH_SEQ_LEN_L;
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if (short_sequence) {
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// FIXME cannot be reached
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prach_root_sequence_map = prach_root_sequence_map_abc;
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} else {
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prach_root_sequence_map = prach_root_sequence_map_0_3;
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}
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LOG_D( PHY, "compute_prach_seq: done init prach_tables\n" );
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for (int i = 0; i < num_sequences; i++) {
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int index = (rootSequenceIndex+i) % (N_ZC-1);
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if (short_sequence) {
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// prach_root_sequence_map points to prach_root_sequence_map4
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DevAssert( index < sizeof(prach_root_sequence_map_abc) / sizeof(prach_root_sequence_map_abc[0]) );
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} else {
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// prach_root_sequence_map points to prach_root_sequence_map0_3
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DevAssert( index < sizeof(prach_root_sequence_map_0_3) / sizeof(prach_root_sequence_map_0_3[0]) );
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}
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const uint16_t u = prach_root_sequence_map[index];
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LOG_D(PHY,"prach index %d => u=%d\n",index,u);
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const int inv_u = modulo_multiplicative_inverse(u, N_ZC); // multiplicative inverse of u
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// X_u[0] stores the first ZC sequence where the root u has a non-zero number of shifts
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// for the unrestricted case X_u[0] is the first root indicated by the rootSequenceIndex
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const int zc_inv_2 = modulo_multiplicative_inverse(2, N_ZC);
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for (int k = 0; k < N_ZC; k++) {
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const unsigned int j = (((k * (1 + (inv_u * k))) % N_ZC) * zc_inv_2) % N_ZC;
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const double w = 2 * M_PI * (double)j / N_ZC;
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const c16_t ru = {.r = (int16_t)(floor(32767.0 * cos(w))), .i = (int16_t)(floor(32767.0 * sin(w)))};
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// multiply by inverse of 2 (required since ru is exp[j 2\pi n])
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X_u[i][k] = ru;
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}
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}
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}
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