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openairinterface5g/openair1/PHY/NR_TRANSPORT/nr_dci.c
T
Sakthivel Velumani 044ca835d6 phy: use fftshift'ed buffer for txdataF 
So far txdataF buffer has DC RE as the first element. This was prefered
most likely to avoid memcpy before iFFT but comes with a small
complexity in RE mapping functions.

Instead, we use a flat buffer that holds freq domain data starting from
first negative SC. After resource mapping is done on all channels, each
OFDM symbol is shifted before iFFT so that the buffer start with DC RE.

This reduces complexity in mapping functions and later on when passing
beam IDs to 7.2 split RU especially when a beam is associated to
interleaved RB and/or REs.

There is already a memcpy in place to copy txdataF from gNB stuct to RU
struct. So this change does not introduce new memcpy.
2026-03-09 18:27:27 +00:00

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/*
* Licensed to the OpenAirInterface (OAI) Software Alliance under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The OpenAirInterface Software Alliance licenses this file to You under
* the OAI Public License, Version 1.1 (the "License"); you may not use this file
* except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.openairinterface.org/?page_id=698
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*-------------------------------------------------------------------------------
* For more information about the OpenAirInterface (OAI) Software Alliance:
* contact@openairinterface.org
*/
/*! \file PHY/NR_TRANSPORT/nr_dci.c
* \brief Implements DCI encoding and PDCCH TX procedures (38.212/38.213/38.214). V15.4.0 2019-01.
* \author Guy De Souza
* \date 2018
* \version 0.1
* \company Eurecom
* \email: desouza@eurecom.fr
* \note
* \warning
*/
#include "nr_dci.h"
#include "nr_dlsch.h"
#include "nr_sch_dmrs.h"
#include "PHY/MODULATION/nr_modulation.h"
#include "common/utils/nr/nr_common.h"
#include "SCHED_NR/sched_nr.h"
//#define DEBUG_PDCCH_DMRS
//#define DEBUG_DCI
//#define DEBUG_CHANNEL_CODING
static void nr_pdcch_scrambling(uint32_t *in, uint32_t size, uint32_t Nid, uint32_t scrambling_RNTI, uint32_t *out)
{
int roundedSz = ((size + 31) / 32);
uint32_t *seq = gold_cache((scrambling_RNTI << 16) + Nid, roundedSz);
LOG_D(NR_PHY_DCI, "PDCCH scrambling_RNTI %x \n", scrambling_RNTI);
for (int i = 0; i < roundedSz; i++)
out[i] = in[i] ^ seq[i];
}
void nr_generate_dci(PHY_VARS_gNB *gNB,
const nfapi_nr_dl_tti_pdcch_pdu_rel15_t *pdcch_pdu_rel15,
NR_DL_FRAME_PARMS *frame_parms,
int slot)
{
// fill reg list per symbol
int reg_list[MAX_DCI_CORESET][NR_MAX_PDCCH_AGG_LEVEL * NR_NB_REG_PER_CCE];
nr_fill_reg_list(reg_list, pdcch_pdu_rel15);
// compute rb_offset and n_prb based on frequency allocation
int n_rb, cset_start;
get_coreset_rballoc(pdcch_pdu_rel15->FreqDomainResource, &n_rb, &cset_start);
int additional_offset = 0;
// first common RB of the first group of 6 PRBs has common RB index equal to 6 * ⌈BWP_start / 6⌉
if (pdcch_pdu_rel15->CoreSetType == 1)
additional_offset = (pdcch_pdu_rel15->BWPStart + 5) / 6 * 6 - pdcch_pdu_rel15->BWPStart;
int rb_offset = cset_start + additional_offset;
uint16_t cset_start_sc = (pdcch_pdu_rel15->BWPStart + rb_offset) * NR_NB_SC_PER_RB;
int idx1 = pdcch_pdu_rel15->StartSymbolIndex+pdcch_pdu_rel15->DurationSymbols;
int idx2 = (((n_rb + rb_offset + pdcch_pdu_rel15->BWPStart) * 3) + 15) & ~15;
c16_t mod_dmrs[idx1][idx2] __attribute__((aligned(16)));
for (int d = 0; d < pdcch_pdu_rel15->numDlDci; d++) {
/*The coreset is initialised
* in frequency: the first subcarrier is obtained by adding the first CRB overlapping the SSB and the rb_offset for coreset 0
* or the rb_offset for other coresets
* in time: by its first slot and its first symbol*/
const nfapi_nr_dl_dci_pdu_t *dci_pdu = &pdcch_pdu_rel15->dci_pdu[d];
uint32_t cset_start_symb = pdcch_pdu_rel15->StartSymbolIndex;
uint32_t cset_nsymb = pdcch_pdu_rel15->DurationSymbols;
int dci_idx = 0;
// multi-beam number (for concurrent beams)
int bitmap = SL_to_bitmap(cset_start_symb, pdcch_pdu_rel15->DurationSymbols);
int beam_nb = beam_index_allocation(gNB->enable_analog_das,
dci_pdu->precodingAndBeamforming.prgs_list[0].dig_bf_interface_list[0].beam_idx,
&gNB->common_vars,
slot,
frame_parms->symbols_per_slot,
bitmap);
LOG_D(NR_PHY_DCI, "pdcch: Coreset rb_offset %d, nb_rb %d BWP Start %d\n", rb_offset, n_rb, pdcch_pdu_rel15->BWPStart);
LOG_D(NR_PHY_DCI,
"pdcch: Coreset starting subcarrier %d on symbol %d (%d symbols)\n",
cset_start_sc,
cset_start_symb,
cset_nsymb);
// DMRS length is per OFDM symbol
uint32_t dmrs_length = (n_rb+pdcch_pdu_rel15->BWPStart)*6; //2(QPSK)*3(per RB)*6(REG per CCE)
uint32_t encoded_length = dci_pdu->AggregationLevel*108; //2(QPSK)*9(per RB)*6(REG per CCE)
if (dci_pdu->RNTI != 0xFFFF)
LOG_D(NR_PHY_DCI,
"DL_DCI : rb_offset %d, nb_rb %d, DMRS length per symbol %d\t DCI encoded length %d (precoder_granularity %d, "
"reg_mapping %d), Scrambling_Id %d, ScramblingRNTI %x, PayloadSizeBits %d AggregationLevel %d\n",
rb_offset,
n_rb,
dmrs_length,
encoded_length,
pdcch_pdu_rel15->precoderGranularity,
pdcch_pdu_rel15->CceRegMappingType,
dci_pdu->ScramblingId,
dci_pdu->ScramblingRNTI,
dci_pdu->PayloadSizeBits,
dci_pdu->AggregationLevel);
dmrs_length += rb_offset*6; // To accommodate more DMRS symbols in case of rb offset
/// DMRS QPSK modulation
for (int symb = cset_start_symb; symb < cset_start_symb + pdcch_pdu_rel15->DurationSymbols; symb++) {
const uint32_t *gold = nr_gold_pdcch(frame_parms->N_RB_DL, frame_parms->symbols_per_slot, dci_pdu->ScramblingId, slot, symb);
nr_modulation(gold, dmrs_length, DMRS_MOD_ORDER, (int16_t *)mod_dmrs[symb]); // Qm = 2 as DMRS is QPSK modulated
#ifdef DEBUG_PDCCH_DMRS
if(dci_pdu->RNTI!=0xFFFF) {
for (int i=0; i<dmrs_length>>1; i++)
printf("symb %d i %d %p gold seq 0x%08x mod_dmrs %d %d\n",
symb,
i,
&gold_pdcch_dmrs[symb][i >> 5],
gold_pdcch_dmrs[symb][i >> 5],
mod_dmrs[symb][i].r,
mod_dmrs[symb][i].i);
}
#endif
}
/// DCI payload processing
// CRC attachment + Scrambling + Channel coding + Rate matching
uint32_t encoder_output[NR_MAX_DCI_SIZE_DWORD];
uint16_t n_RNTI = dci_pdu->RNTI;
uint16_t Nid = dci_pdu->ScramblingId;
uint16_t scrambling_RNTI = dci_pdu->ScramblingRNTI;
polar_encoder_fast((uint64_t*)dci_pdu->Payload, (void*)encoder_output, n_RNTI, 1,
NR_POLAR_DCI_MESSAGE_TYPE, dci_pdu->PayloadSizeBits, dci_pdu->AggregationLevel);
#ifdef DEBUG_CHANNEL_CODING
//debug dump dci
printf("polar rnti %x,length %d, L %d\n",n_RNTI, dci_pdu->PayloadSizeBits,pdcch_pdu_rel15->dci_pdu->AggregationLevel);
printf("DCI PDU: [0]->0x%lx \t [1]->0x%lx\n",
((uint64_t*)dci_pdu->Payload)[0], ((uint64_t*)dci_pdu->Payload)[1]);
printf("Encoded Payload (length:%u dwords):\n", encoded_length>>5);
for (int i=0; i<encoded_length>>5; i++)
printf("[%d]->0x%08x \t", i,encoder_output[i]);
printf("\n");
#endif
/// Scrambling
uint32_t scrambled_output[NR_MAX_DCI_SIZE_DWORD]= {0};
nr_pdcch_scrambling(encoder_output, encoded_length, Nid, scrambling_RNTI, scrambled_output);
#ifdef DEBUG_CHANNEL_CODING
printf("scrambled output: [0]->0x%08x \t [1]->0x%08x \t [2]->0x%08x \t [3]->0x%08x\t [4]->0x%08x\t [5]->0x%08x\t \
[6]->0x%08x \t [7]->0x%08x \t [8]->0x%08x \t [9]->0x%08x\t [10]->0x%08x\t [11]->0x%08x\n",
scrambled_output[0], scrambled_output[1], scrambled_output[2], scrambled_output[3], scrambled_output[4],scrambled_output[5],
scrambled_output[6], scrambled_output[7], scrambled_output[8], scrambled_output[9], scrambled_output[10],scrambled_output[11] );
#endif
/// QPSK modulation
c16_t mod_dci[NR_MAX_DCI_SIZE / 2] __attribute__((aligned(16)));
nr_modulation(scrambled_output, encoded_length, DMRS_MOD_ORDER, (int16_t *)mod_dci); // Qm = 2 as DMRS is QPSK modulated
#ifdef DEBUG_DCI
for (int i=0; i<encoded_length>>1; i++)
printf("i %d mod_dci %d %d\n", i, mod_dci[i].r, mod_dci[i].i);
#endif
/// Resource mapping
uint16_t amp = gNB->TX_AMP;
c16_t *txdataF = gNB->common_vars.txdataF[beam_nb][0];
int num_regs = dci_pdu->AggregationLevel * NR_NB_REG_PER_CCE / pdcch_pdu_rel15->DurationSymbols;
/*Mapping the encoded DCI along with the DMRS */
for(int symbol_idx = 0; symbol_idx < pdcch_pdu_rel15->DurationSymbols; symbol_idx++) {
// allocating rbs per symbol
for (int reg_count = 0; reg_count < num_regs; reg_count++) {
int k = cset_start_sc + reg_list[d][reg_count] * NR_NB_SC_PER_RB;
LOG_D(NR_PHY_DCI, "REG %d k %d\n", reg_list[d][reg_count], k);
int l = cset_start_symb + symbol_idx;
// dmrs index depends on reference point for k according to 38.211 7.4.1.3.2
int dmrs_idx;
if (pdcch_pdu_rel15->CoreSetType == NFAPI_NR_CSET_CONFIG_PDCCH_CONFIG)
dmrs_idx = (reg_list[d][reg_count] + pdcch_pdu_rel15->BWPStart + rb_offset) * 3;
else
dmrs_idx = (reg_list[d][reg_count] + rb_offset) * 3;
int k_prime = 0;
for (int m = 0; m < NR_NB_SC_PER_RB; m++) {
if (m == (k_prime << 2) + 1) { // DMRS if not already mapped
txdataF[l * frame_parms->ofdm_symbol_size + k] = c16mulRealShift(mod_dmrs[l][dmrs_idx], amp, 15);
#ifdef DEBUG_PDCCH_DMRS
LOG_I(NR_PHY_DCI,
"PDCCH DMRS %d: l %d position %d => (%d,%d)\n",
dmrs_idx,
l,
k,
txdataF[l * frame_parms->ofdm_symbol_size + k].r,
txdataF[l * frame_parms->ofdm_symbol_size + k].i);
#endif
dmrs_idx++;
k_prime++;
} else { // DCI payload
txdataF[l * frame_parms->ofdm_symbol_size + k] = c16mulRealShift(mod_dci[dci_idx], amp, 15);
dci_idx++;
}
k++;
} // m
} // reg_count
} // symbol_idx
LOG_D(NR_PHY_DCI,
"DCI: payloadSize = %d | payload = %llx\n",
dci_pdu->PayloadSizeBits,
*(unsigned long long *)dci_pdu->Payload);
} // for (int d=0;d<pdcch_pdu_rel15->numDlDci;d++)
}
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