sched,nr: add function that schedule SSB

Notes:
- NOT YET TESTED
- Requires rebase on commit with PHY changes to work

Signed-off-by: Carlo Galiotto <carlo@srs.io>

srsenb/hdr/stack/mac/nr/sched_nr_grant_allocator.h

@@ -41,6 +41,8 @@ struct harq_ack_t {
 };
 using harq_ack_list_t = srsran::bounded_vector<harq_ack_t, MAX_GRANTS>;
 
+// save data for scheduler to keep track of previous allocations
+// This only contains information about a given slot
 struct bwp_slot_grid {
   uint32_t          slot_idx = 0;
   const bwp_params* cfg      = nullptr;
@@ -79,6 +81,7 @@ struct bwp_res_grid {
   const bwp_params* cfg = nullptr;
 
 private:
+  // TTIMOD_SZ is the longest allocation in the future
   srsran::bounded_vector<bwp_slot_grid, TTIMOD_SZ> slots;
 };
 

srsenb/hdr/stack/mac/nr/sched_nr_signalling.h

@@ -24,6 +24,8 @@ void sched_nzp_csi_rs(srsran::const_span<srsran_csi_rs_nzp_set_t> nzp_csi_rs_set
                       const srsran_slot_cfg_t&                    slot_cfg,
                       nzp_csi_rs_list&                            csi_rs_list);
 
+void sched_ssb_basic(const slot_point&  sl_point, uint32_t ssb_periodicity, ssb_list& ssb_list);
+
 /// For a given BWP and slot, schedule SSB, NZP CSI RS and SIBs
 void sched_dl_signalling(const bwp_params& bwp_params,
                          slot_point        sl_pdcch,

srsenb/src/stack/mac/nr/sched_nr_grant_allocator.cc

@@ -182,6 +182,8 @@ alloc_result bwp_slot_allocator::alloc_rar_and_msg3(uint16_t
   return alloc_result::success;
 }
 
+// ue is the UE (1 only) that will be allocated
+// func computes the grant allocation for this UE
 alloc_result bwp_slot_allocator::alloc_pdsch(slot_ue& ue, const prb_grant& dl_grant)
 {
   if (ue.cfg->active_bwp().bwp_id != bwp_grid.cfg->bwp_id) {
@@ -195,12 +197,12 @@ alloc_result bwp_slot_allocator::alloc_pdsch(slot_ue& ue, const prb_grant& dl_gr
   }
   bwp_slot_grid& bwp_pdcch_slot = bwp_grid[ue.pdcch_slot];
   bwp_slot_grid& bwp_pdsch_slot = bwp_grid[ue.pdsch_slot];
-  bwp_slot_grid& bwp_uci_slot   = bwp_grid[ue.uci_slot];
+  bwp_slot_grid& bwp_uci_slot   = bwp_grid[ue.uci_slot];  // UCI : UL control info
   alloc_result   result         = verify_pdsch_space(bwp_pdsch_slot, bwp_pdcch_slot);
   if (result != alloc_result::success) {
     return result;
   }
-  if (bwp_pdcch_slot.dl_prbs.collides(dl_grant)) {
+  if (bwp_pdsch_slot.dl_prbs.collides(dl_grant)) {
     return alloc_result::sch_collision;
   }
 

srsenb/src/stack/mac/nr/sched_nr_signalling.cc

@@ -12,6 +12,11 @@
 
 #include "srsenb/hdr/stack/mac/nr/sched_nr_signalling.h"
 
+#define POS_IN_BURST_FIRST_BIT_IDX  0
+#define POS_IN_BURST_SECOND_BIT_IDX 1
+#define POS_IN_BURST_THIRD_BIT_IDX  2
+#define POS_IN_BURST_FOURTH_BIT_IDX  3
+
 namespace srsenb {
 namespace sched_nr_impl {
 
@@ -33,6 +38,83 @@ void sched_nzp_csi_rs(srsran::const_span<srsran_csi_rs_nzp_set_t> nzp_csi_rs_set
   }
 }
 
+void sched_ssb_basic(const slot_point&  sl_point, uint32_t ssb_periodicity, ssb_list& ssb_list)
+{
+  /* This function is extremely simplified.
+   * It works based on the following assumptions (hard-coded parameters)
+   * 1) 15kHz subcarrier spacing
+   * 2) Below 3GHz
+   * 3) Position in Burst 1000
+   * */
+
+  uint32_t sl_idx = sl_point.to_uint();
+  uint32_t ssb_sf_idx = sl_point.to_uint() % ssb_periodicity;
+
+  // code below is simplified
+  if (ssb_sf_idx == 0)
+  {
+    ssb_t ssb_msg = {};
+    srsran_mib_nr_t  mib_msg = {};
+    mib_msg.sfn = sl_point.sfn();
+    mib_msg.hrf = (sl_idx % SRSRAN_NSLOTS_PER_FRAME_NR(srsran_subcarrier_spacing_15kHz) < SRSRAN_NSLOTS_PER_FRAME_NR(srsran_subcarrier_spacing_15kHz) / 2);
+    mib_msg.ssb_idx = 0;  // This corresponds to "Position in Burst" = 1000
+    srsran_pbch_msg_nr_mib_pack(&mib_msg, &ssb_msg.pbch_msg);
+    ssb_list.push_back(ssb_msg);
+  }
+
+}
+
+#if 0
+void sched_ssb(int slot_idx, int ssb_periodicity, srsran::bounded_bitset<4>& pos_in_burst)
+{
+  /* Input needed:
+   * - slot_idx: slot index
+   * - ssb_periodicity: Periodicity of SSB in ms
+   * - pos_in_burst: position in Burst (bit map indicating in which SSB opportunities gNB needs to tx
+   *
+   * Parameters that could be passed but are currently hard-coded
+   * - Subcarrier spacing: 15kHz
+   * - Frequency (info on whether carrier is above or below 3GHz)
+   *
+   * NOTE: this function is hard coded for frequency < 3GHz,
+   * and SubCarrierSpacing 15kHz. Therefore, we assume
+   * 1 slot = 1ms
+   * */
+
+  // NOTE: This
+  // This function only implements SSB for frequency < 3GHz, and SubCarrierSpacing 15kHz
+  // In this case, 1 slot = 1ms
+  int ssb_sf_idx = slot_idx % ssb_periodicity;
+
+  // if slot falls into the correct periodicity, continue with further checks
+  // check if slot is
+
+  // code below will be simplified, depending on struct used
+  if (ssb_sf_idx == 0)
+  {
+    // check first two bit in bitmap (position in burst)
+    // and pack corresponding SSB for slot 0
+    if ( pos_in_burst.test(POS_IN_BURST_FIRST_BIT_IDX) )
+      printf("Pack first SSB in slot 0 ");
+    if ( pos_in_burst.test(POS_IN_BURST_SECOND_BIT_IDX) )
+      printf("Pack second SSB in slot 0 ");
+  }
+  else if (ssb_sf_idx == 1)
+  {
+    // check second two bit in bitmap (position in burst)
+    // and pack corresponding SSB for slot 1
+    if ( pos_in_burst.test(POS_IN_BURST_FIRST_BIT_IDX) )
+      printf("Pack first SSB in slot 1 ");
+    if ( pos_in_burst.test(POS_IN_BURST_SECOND_BIT_IDX) )
+      printf("Pack second SSB in slot 1 ");
+  }
+  else
+    // nothing to do here
+    return;
+
+}
+#endif
+
 void sched_dl_signalling(const bwp_params& bwp_params,
                          slot_point        sl_pdcch,
                          ssb_list&         ssb_list,
@@ -42,7 +124,7 @@ void sched_dl_signalling(const bwp_params& bwp_params,
   cfg.idx = sl_pdcch.to_uint();
 
   // Schedule SSB
-  // TODO
+  sched_ssb_basic(sl_pdcch, bwp_params.cell_cfg.ssb.periodicity_ms, ssb_list);
 
   // Schedule NZP-CSI-RS
   sched_nzp_csi_rs(bwp_params.cfg.pdsch.nzp_csi_rs_sets, cfg, nzp_csi_rs);

srsenb/src/stack/mac/nr/sched_nr_worker.cc

@@ -68,10 +68,10 @@ void slot_cc_worker::run(slot_point pdcch_slot, ue_map_t& ue_db)
   srsran_assert(not running(), "scheduler worker::start() called for active worker");
   slot_rx = pdcch_slot - TX_ENB_DELAY;
 
-  // Run pending cell feedback
+  // Run pending cell feedback (process feedback)
   run_feedback(ue_db);
 
-  // Reserve UEs for this worker slot
+  // Reserve UEs for this worker slot (select candidate UEs)
   for (auto& ue_pair : ue_db) {
     uint16_t rnti = ue_pair.first;
     ue&      u    = *ue_pair.second;
@@ -79,6 +79,7 @@ void slot_cc_worker::run(slot_point pdcch_slot, ue_map_t& ue_db)
       continue;
     }
 
+    // info for a given UE on a slot to be process
     slot_ues.insert(rnti, u.try_reserve(pdcch_slot, cfg.cc));
     if (slot_ues[rnti].empty()) {
       // Failed to generate slot UE because UE has no conditions for DL/UL tx