Dynamic PDCCH aggregation level

The aggregation level search order for PDCCH candidates is modified:
 - the search starts from desired_agg_level_index, which is a value from 0 to 4
   proportial to pdcch_cl_adjust.
 - pdcch_cl_adjust is a value between 0 and 1 that indicates PDCCH channel quality
   by averaging HARQ DTX rate. A value of 0 means perfect channel, a value o 1 means
   impaired channel.

doc/MAC/mac-usage.md

@@ -38,6 +38,28 @@ The actual scheduler implementation can be found in functions `pf_dl()` and
 [`gNB_scheduler_ulsch.c`](../../openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_ulsch.c)
 (for UL), respectively.
 
+## PDDCH aggregation level
+
+PDCCH aggregation level is selected using closed loop controller, where DL HARQ
+feedback is the controller feedback signal. It is used to increment `pdcch_cl_adjust`
+variable if no feedback is detected and decrement the variable when feedback is detected.
+`pdcch_cl_adjust` is later mapped PDCCH aggregation level range.
+
+The value of `pdcch_cl_adjust` is clamped to range <0,1>, the increment value is 0.05 while
+the decrement value is 0.01.
+
+### Examples:
+#### Example 1:
+Say we have 90% PDCCH success rate at aggregation level 1, `pdcch_cl_adjust` will stay at 0
+for most of the time. 2 consecutive PDCCH failures will not result in increasing the aggregation
+level (because (0.05 + 0.05) * 4 = 0.4 which is closer to 0 than to 1). If PDCCH fails 3 times
+in a row the aggregation level will change to 2 and hopefully back to 1 once more PDDCH successes
+happen.
+
+### Example 2
+Say we have 0% PDCCH success rate (radio link failure scenario) but `pdcch_cl_adjust` is 0 indicating
+perfect PDCCH channel. it would take ~18 PDCCH failures to reach maximum aggregation level.
+
 # Periodic output and interpretation
 
 The scheduler periodically outputs statistics that can help you judge the radio

openair1/PHY/NR_TRANSPORT/nr_dci.c

@@ -99,7 +99,7 @@ static void nr_generate_dci(PHY_VARS_gNB *gNB,
     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\n",
+            "reg_mapping %d), Scrambling_Id %d, ScramblingRNTI %x, PayloadSizeBits %d AggregationLevel %d\n",
             rb_offset,
             n_rb,
             dmrs_length,
@@ -108,7 +108,8 @@ static void nr_generate_dci(PHY_VARS_gNB *gNB,
             pdcch_pdu_rel15->CceRegMappingType,
             dci_pdu->ScramblingId,
             dci_pdu->ScramblingRNTI,
-            dci_pdu->PayloadSizeBits);
+            dci_pdu->PayloadSizeBits,
+            dci_pdu->AggregationLevel);
     dmrs_length += rb_offset*6; // To accommodate more DMRS symbols in case of rb offset
       
     /// DMRS QPSK modulation

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_RA.c

@@ -874,7 +874,8 @@ static void nr_generate_Msg3_retransmission(module_id_t module_idP,
                                  ss,
                                  coreset,
                                  &ra->sched_pdcch,
-                                 true);
+                                 true,
+                                 0);
     if (CCEIndex < 0) {
       LOG_E(NR_MAC, "UE %04x cannot find free CCE!\n", ra->rnti);
       return;
@@ -1484,7 +1485,7 @@ static void nr_generate_Msg2(module_id_t module_idP,
   }
 
   uint8_t aggregation_level;
-  int CCEIndex = get_cce_index(nr_mac, CC_id, slotP, 0, &aggregation_level, beam.idx, ss, coreset, &ra->sched_pdcch, true);
+  int CCEIndex = get_cce_index(nr_mac, CC_id, slotP, 0, &aggregation_level, beam.idx, ss, coreset, &ra->sched_pdcch, true, 0);
 
   if (CCEIndex < 0) {
     LOG_W(NR_MAC, "UE %04x: %d.%d cannot find free CCE for Msg2!\n", ra->rnti, frameP, slotP);
@@ -2006,7 +2007,8 @@ static void nr_generate_Msg4_MsgB(module_id_t module_idP,
                                  ss,
                                  coreset,
                                  &ra->sched_pdcch,
-                                 true);
+                                 true,
+                                 0);
 
     if (CCEIndex < 0) {
       LOG_E(NR_MAC, "Cannot find free CCE for RA RNTI 0x%04x!\n", ra->rnti);

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_dlsch.c

@@ -553,7 +553,8 @@ static bool allocate_dl_retransmission(module_id_t module_id,
                                sched_ctrl->search_space,
                                sched_ctrl->coreset,
                                &sched_ctrl->sched_pdcch,
-                               false);
+                               false,
+                               sched_ctrl->pdcch_cl_adjust);
   if (CCEIndex<0) {
     LOG_D(NR_MAC, "[UE %04x][%4d.%2d] could not find free CCE for DL DCI retransmission\n", UE->rnti, frame, slot);
     return false;
@@ -817,7 +818,8 @@ static void pf_dl(module_id_t module_id,
                                  sched_ctrl->search_space,
                                  sched_ctrl->coreset,
                                  &sched_ctrl->sched_pdcch,
-                                 false);
+                                 false,
+                                 sched_ctrl->pdcch_cl_adjust);
     if (CCEIndex < 0) {
       LOG_D(NR_MAC, "[UE %04x][%4d.%2d] could not find free CCE for DL DCI\n", rnti, frame, slot);
       reset_beam_status(&mac->beam_info,

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_phytest.c

@@ -148,7 +148,8 @@ void nr_preprocessor_phytest(module_id_t module_id, frame_t frame, sub_frame_t s
                                sched_ctrl->search_space,
                                sched_ctrl->coreset,
                                &sched_ctrl->sched_pdcch,
-                               false);
+                               false,
+                               0);
   AssertFatal(CCEIndex >= 0, "Could not find CCE for UE %04x\n", UE->rnti);
 
   NR_sched_pdsch_t *sched_pdsch = &sched_ctrl->sched_pdsch;
@@ -312,7 +313,8 @@ bool nr_ul_preprocessor_phytest(module_id_t module_id, frame_t frame, sub_frame_
                                sched_ctrl->search_space,
                                sched_ctrl->coreset,
                                &sched_ctrl->sched_pdcch,
-                               false);
+                               false,
+                               0);
   if (CCEIndex < 0) {
     LOG_E(MAC, "%s(): CCE list not empty, couldn't schedule PUSCH\n", __func__);
     return false;

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_primitives.c

@@ -119,6 +119,9 @@ static const uint16_t cqi_table3[16][2] = {{0, 0},
                                            {6, 6660},
                                            {6, 7720}};
 
+static void determine_aggregation_level_search_order(int agg_level_search_order[NUM_PDCCH_AGG_LEVELS],
+                                                     float pdcch_cl_adjust);
+
 uint8_t get_dl_nrOfLayers(const NR_UE_sched_ctrl_t *sched_ctrl,
                           const nr_dci_format_t dci_format) {
 
@@ -550,15 +553,18 @@ int get_cce_index(const gNB_MAC_INST *nrmac,
                   const NR_SearchSpace_t *ss,
                   const NR_ControlResourceSet_t *coreset,
                   NR_sched_pdcch_t *sched_pdcch,
-                  bool is_common)
+                  bool is_common,
+                  float pdcch_cl_adjust)
 {
-
   const uint32_t Y = is_common ? 0 : get_Y(ss, slot, rnti);
   uint8_t nr_of_candidates;
-  for (int i = 0; i < 5; i++) {
-    // for now taking the lowest value among the available aggregation levels
-    find_aggregation_candidates(aggregation_level, &nr_of_candidates, ss, 1 << i);
-    if(nr_of_candidates > 0)
+
+  int agg_level_search_order[NUM_PDCCH_AGG_LEVELS];
+  determine_aggregation_level_search_order(agg_level_search_order, pdcch_cl_adjust);
+
+  for (int i = 0; i < NUM_PDCCH_AGG_LEVELS; i++) {
+    find_aggregation_candidates(aggregation_level, &nr_of_candidates, ss, 1 << agg_level_search_order[i]);
+    if (nr_of_candidates > 0)
       break;
   }
   int CCEIndex = find_pdcch_candidate(nrmac, CC_id, *aggregation_level, nr_of_candidates, beam_idx, sched_pdcch, coreset, Y);
@@ -2516,6 +2522,7 @@ NR_UE_info_t *add_new_nr_ue(gNB_MAC_INST *nr_mac, rnti_t rntiP, NR_CellGroupConf
   sched_ctrl->ta_update = 31;
   sched_ctrl->sched_srs.frame = -1;
   sched_ctrl->sched_srs.slot = -1;
+  sched_ctrl->pdcch_cl_adjust = 0;
 
   // initialize LCID structure
   seq_arr_init(&sched_ctrl->lc_config, sizeof(nr_lc_config_t));
@@ -3524,3 +3531,31 @@ bool nr_mac_get_new_rnti(NR_UEs_t *UEs, const NR_RA_t *ra_base, int ra_count, rn
   } while (loop < 100 && (exist_connected_ue || exist_in_pending_ra_ue));
   return loop < 100; // nothing found: loop count 100
 }
+
+/// @brief Orders PDCCH aggregation levels so that we first check desired aggregation level according to
+///        pdcch_cl_adjust
+/// @param agg_level_search_order in/out 5-element array of aggregation levels from 0 to 4
+/// @param pdcch_cl_adjust value from 0 to 1 indication channel impariments (0 - good channel, 1 - bad channel)
+static void determine_aggregation_level_search_order(int agg_level_search_order[NUM_PDCCH_AGG_LEVELS], float pdcch_cl_adjust)
+{
+  int desired_agg_level_index = round(4 * pdcch_cl_adjust);
+  int agg_level_search_index = 0;
+  for (int i = desired_agg_level_index; i < NUM_PDCCH_AGG_LEVELS; i++) {
+    agg_level_search_order[agg_level_search_index++] = i;
+  }
+  for (int i = desired_agg_level_index - 1; i >= 0; i--) {
+    agg_level_search_order[agg_level_search_index++] = i;
+  }
+}
+
+/// @brief Update PDCCH closed loop adjust for UE depending on detection of feedback.
+/// @param sched_ctrl UE scheduling control info
+/// @param feedback_not_detected Whether feedback (PUSCH or HARQ) was detected
+void nr_mac_update_pdcch_closed_loop_adjust(NR_UE_sched_ctrl_t *sched_ctrl, bool feedback_not_detected)
+{
+  if (feedback_not_detected) {
+    sched_ctrl->pdcch_cl_adjust = min(1, sched_ctrl->pdcch_cl_adjust + 0.05);
+  } else {
+    sched_ctrl->pdcch_cl_adjust = max(0, sched_ctrl->pdcch_cl_adjust - 0.01);
+  }
+}

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_uci.c

@@ -787,6 +787,7 @@ void handle_nr_uci_pucch_0_1(module_id_t mod_id,
       const int8_t pid = sched_ctrl->feedback_dl_harq.head;
       remove_front_nr_list(&sched_ctrl->feedback_dl_harq);
       LOG_D(NR_MAC,"%4d.%2d bit %d pid %d ack/nack %d\n",frame, slot, harq_bit,pid,harq_value);
+      nr_mac_update_pdcch_closed_loop_adjust(sched_ctrl, harq_confidence != 0);
       handle_dl_harq(UE, pid, harq_value == 0 && harq_confidence == 0, nrmac->dl_bler.harq_round_max);
       if (!UE->Msg4_MsgB_ACKed && harq_value == 0 && harq_confidence == 0)
         UE->Msg4_MsgB_ACKed = true;

openair2/LAYER2/NR_MAC_gNB/gNB_scheduler_ulsch.c

@@ -1742,7 +1742,8 @@ static bool allocate_ul_retransmission(gNB_MAC_INST *nrmac,
                                sched_ctrl->search_space,
                                sched_ctrl->coreset,
                                &sched_ctrl->sched_pdcch,
-                               false);
+                               false,
+                               sched_ctrl->pdcch_cl_adjust);
   if (CCEIndex<0) {
     LOG_D(NR_MAC, "[UE %04x][%4d.%2d] no free CCE for retransmission UL DCI UE\n", UE->rnti, frame, slot);
     return false;
@@ -1926,7 +1927,8 @@ static void pf_ul(module_id_t module_id,
                                    sched_ctrl->search_space,
                                    sched_ctrl->coreset,
                                    &sched_ctrl->sched_pdcch,
-                                   false);
+                                   false,
+                                   sched_ctrl->pdcch_cl_adjust);
       if (CCEIndex < 0) {
         LOG_D(NR_MAC, "[UE %04x][%4d.%2d] no free CCE for UL DCI (BSR 0)\n", UE->rnti, frame, slot);
         reset_beam_status(&nrmac->beam_info, sched_frame, sched_slot, UE->UE_beam_index, n, beam.new_beam);
@@ -2073,7 +2075,8 @@ static void pf_ul(module_id_t module_id,
                                  sched_ctrl->search_space,
                                  sched_ctrl->coreset,
                                  &sched_ctrl->sched_pdcch,
-                                 false);
+                                 false,
+                                 sched_ctrl->pdcch_cl_adjust);
 
     if (CCEIndex < 0) {
       reset_beam_status(&nrmac->beam_info, frame, slot, iterator->UE->UE_beam_index, n_dl, dci_beam.new_beam);

openair2/LAYER2/NR_MAC_gNB/mac_proto.h

@@ -433,7 +433,8 @@ int get_cce_index(const gNB_MAC_INST *nrmac,
                   const NR_SearchSpace_t *ss,
                   const NR_ControlResourceSet_t *coreset,
                   NR_sched_pdcch_t *sched_pdcch,
-                  bool is_common);
+                  bool is_common,
+                  float pdcch_cl_adjust);
 
 bool nr_find_nb_rb(uint16_t Qm,
                    uint16_t R,
@@ -493,5 +494,6 @@ bool nr_mac_add_lcid(NR_UE_sched_ctrl_t *sched_ctrl, const nr_lc_config_t *c);
 bool nr_mac_remove_lcid(NR_UE_sched_ctrl_t *sched_ctrl, long lcid);
 
 bool nr_mac_get_new_rnti(NR_UEs_t *UEs, const NR_RA_t *ra_base, int ra_count, rnti_t *rnti);
+void nr_mac_update_pdcch_closed_loop_adjust(NR_UE_sched_ctrl_t *sched_ctrl, bool feedback_not_detected);
 
 #endif /*__LAYER2_NR_MAC_PROTO_H__*/

openair2/LAYER2/NR_MAC_gNB/nr_mac_gNB.h

@@ -125,6 +125,15 @@ typedef enum {
   nrRA_WAIT_Msg4_MsgB_ACK,
 } RA_gNB_state_t;
 
+typedef enum {
+  PDCCH_AGG_LEVEL1 = 0,
+  PDCCH_AGG_LEVEL2,
+  PDCCH_AGG_LEVEL4,
+  PDCCH_AGG_LEVEL8,
+  PDCCH_AGG_LEVEL16,
+  NUM_PDCCH_AGG_LEVELS
+} Pdcch_Aggregation_Level_t;
+
 static const char *const nrra_text[] =
     {"IDLE", "Msg2", "WAIT_MsgA_PUSCH", "WAIT_Msg3", "Msg3_retransmission", "Msg3_dcch_dtch", "Msg4", "MsgB", "WAIT_Msg4_ACK"};
 
@@ -675,6 +684,10 @@ typedef struct {
 
   /// per-LC configuration
   seq_arr_t lc_config;
+
+  // pdcch closed loop adjust for PDCCH aggregation level, range <0, 1>
+  // 0 - good channel, 1 - bad channel
+  float pdcch_cl_adjust;
 } NR_UE_sched_ctrl_t;
 
 typedef struct {