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@ -13,6 +13,7 @@
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#include "srsenb/hdr/stack/mac/sched_ue_ctrl/sched_ue_cell.h"
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#include "srsenb/hdr/stack/mac/sched_helpers.h"
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#include "srsenb/hdr/stack/mac/sched_phy_ch/sched_dci.h"
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#include "srsenb/hdr/stack/mac/schedulers/sched_base.h"
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#include <numeric>
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namespace srsenb {
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@ -234,7 +235,7 @@ tbs_info cqi_to_tbs_dl(const sched_ue_cell& cell,
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const rbgmask_t& rbgs,
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uint32_t nof_re,
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srsran_dci_format_t dci_format,
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int req_bytes)
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uint32_t req_bytes)
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{
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bool use_tbs_index_alt = cell.get_ue_cfg()->use_tbs_index_alt and dci_format != SRSRAN_DCI_FORMAT1A;
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uint32_t nof_prbs = count_prb_per_tb(rbgs);
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@ -242,10 +243,10 @@ tbs_info cqi_to_tbs_dl(const sched_ue_cell& cell,
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tbs_info ret;
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if (cell.fixed_mcs_dl < 0 or not cell.dl_cqi().is_cqi_info_received()) {
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// Dynamic MCS configured or first Tx
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uint32_t dl_cqi_avg = cell.dl_cqi().get_grant_avg_cqi(rbgs);
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uint32_t dl_cqi = std::get<1>(find_min_cqi_rbg(rbgs, cell.dl_cqi()));
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ret = compute_min_mcs_and_tbs_from_required_bytes(
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nof_prbs, nof_re, dl_cqi_avg, cell.max_mcs_dl, req_bytes, false, false, use_tbs_index_alt);
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nof_prbs, nof_re, dl_cqi, cell.max_mcs_dl, req_bytes, false, false, use_tbs_index_alt);
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// If coderate > SRSRAN_MIN(max_coderate, 0.932 * Qm) we should set TBS=0. We don't because it's not correctly
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// handled by the scheduler, but we might be scheduling undecodable codewords at very low SNR
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@ -296,7 +297,7 @@ int get_required_prb_dl(const sched_ue_cell& cell,
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auto compute_tbs_approx = [tti_tx_dl, &cell, dci_format](uint32_t nof_prb) {
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uint32_t nof_re = cell.cell_cfg->get_dl_lb_nof_re(tti_tx_dl, nof_prb);
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rbgmask_t min_cqi_rbgs = cell.dl_cqi().get_optim_rbgmask(nof_prb, false);
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tbs_info tb = cqi_to_tbs_dl(cell, min_cqi_rbgs, nof_re, dci_format, -1);
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tbs_info tb = cqi_to_tbs_dl(cell, min_cqi_rbgs, nof_re, dci_format);
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return tb.tbs_bytes;
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};
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@ -340,4 +341,96 @@ uint32_t get_required_prb_ul(const sched_ue_cell& cell, uint32_t req_bytes)
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return req_prbs;
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}
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/// Computes the minimum TBS/MCS achievable for provided UE cell configuration, RBG mask, TTI, DCI format
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tbs_info compute_mcs_and_tbs_lower_bound(const sched_ue_cell& ue_cell,
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tti_point tti_tx_dl,
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const rbgmask_t& rbg_mask,
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srsran_dci_format_t dci_format)
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{
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uint32_t nof_prbs = count_prb_per_tb(rbg_mask);
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if (nof_prbs == 0) {
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return tbs_info{};
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}
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uint32_t nof_re_lb = ue_cell.cell_cfg->get_dl_lb_nof_re(tti_tx_dl, nof_prbs);
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return cqi_to_tbs_dl(ue_cell, rbg_mask, nof_re_lb, dci_format);
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}
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bool find_optimal_rbgmask(const sched_ue_cell& ue_cell,
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tti_point tti_tx_dl,
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const rbgmask_t& dl_mask,
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srsran_dci_format_t dci_format,
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srsran::interval<uint32_t> req_bytes,
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tbs_info& tb,
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rbgmask_t& newtxmask)
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{
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// Find the largest set of available RBGs possible
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newtxmask = find_available_rbgmask(dl_mask.size(), dci_format == SRSRAN_DCI_FORMAT1A, dl_mask);
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// Compute MCS/TBS if all available RBGs were allocated
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tb = compute_mcs_and_tbs_lower_bound(ue_cell, tti_tx_dl, newtxmask, dci_format);
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if (not ue_cell.dl_cqi().subband_cqi_enabled()) {
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// Wideband CQI case
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// NOTE: for wideband CQI, the TBS is directly proportional to the nof_prbs, so we can use an iterative method
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// to compute the best mask given "req_bytes"
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if (tb.tbs_bytes < (int)req_bytes.start()) {
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// the grant is too small. it may lead to srb0 segmentation or not space for headers
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return false;
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}
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if (tb.tbs_bytes <= (int)req_bytes.stop()) {
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// the grant is not sufficiently large to fit max required bytes. Stop search at this point
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return true;
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}
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// Reduce DL grant size to the minimum that can fit the pending DL bytes
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srsran::bounded_vector<tbs_info, MAX_NOF_RBGS> tb_table(newtxmask.count());
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auto compute_tbs_approx = [tti_tx_dl, &ue_cell, dci_format, &tb_table](uint32_t nof_rbgs) {
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rbgmask_t search_mask(ue_cell.cell_cfg->nof_rbgs);
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search_mask.fill(0, nof_rbgs);
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tb_table[nof_rbgs - 1] = compute_mcs_and_tbs_lower_bound(ue_cell, tti_tx_dl, search_mask, dci_format);
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return tb_table[nof_rbgs - 1].tbs_bytes;
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};
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std::tuple<uint32_t, int, uint32_t, int> ret = false_position_method(
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1U, tb_table.size(), (int)req_bytes.stop(), compute_tbs_approx, [](int y) { return y == SRSRAN_ERROR; });
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uint32_t upper_nprb = std::get<2>(ret);
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int upper_tbs = std::get<3>(ret);
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if (upper_tbs >= (int)req_bytes.stop()) {
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tb = tb_table[upper_nprb - 1];
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}
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return true;
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}
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// Subband CQI case
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// NOTE: There is no monotonically increasing guarantee between TBS and nof allocated prbs.
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// One single subband CQI could be dropping the CQI of the whole TB.
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// We start with largest RBG allocation and continue removing RBGs. However, there is no guarantee this is
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// going to be the optimal solution
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// Subtract whole CQI subbands until objective is not met
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// TODO: can be optimized
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rbgmask_t smaller_mask;
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tbs_info tb2;
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do {
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smaller_mask = remove_min_cqi_subband(newtxmask, ue_cell.dl_cqi());
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tb2 = compute_mcs_and_tbs_lower_bound(ue_cell, tti_tx_dl, smaller_mask, dci_format);
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if (tb2.tbs_bytes >= (int)req_bytes.stop() or tb.tbs_bytes <= tb2.tbs_bytes) {
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tb = tb2;
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newtxmask = smaller_mask;
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}
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} while (tb2.tbs_bytes > (int)req_bytes.stop());
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if (tb.tbs_bytes <= (int)req_bytes.stop()) {
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return true;
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}
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do {
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smaller_mask = remove_min_cqi_rbg(newtxmask, ue_cell.dl_cqi());
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tb2 = compute_mcs_and_tbs_lower_bound(ue_cell, tti_tx_dl, smaller_mask, dci_format);
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if (tb2.tbs_bytes >= (int)req_bytes.stop() or tb.tbs_bytes <= tb2.tbs_bytes) {
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tb = tb2;
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newtxmask = smaller_mask;
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}
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} while (tb2.tbs_bytes > (int)req_bytes.stop());
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return true;
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}
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} // namespace srsenb
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Francisco
4 years ago
committed by