bugfix,scheduler: avoid offset to increase decrease unboundedly when mcs is equal to 0 or max_mcs

srsenb/enb.conf.example

@@ -181,7 +181,7 @@ enable = false
 #policy_args = 2
 #min_aggr_level   = 0
 #max_aggr_level   = 3
-#adaptive_aggr_level = true
+#adaptive_aggr_level = false
 #pdsch_mcs        = -1
 #pdsch_max_mcs    = -1
 #pusch_mcs        = -1

srsenb/hdr/stack/mac/sched_ue_ctrl/sched_harq.h

@@ -36,6 +36,7 @@ public:
   srsran::tti_point get_tti() const;
   bool              get_ndi(uint32_t tb_idx) const;
   uint32_t          max_nof_retx() const;
+  int               get_mcs(uint32_t tb_idx) const { return last_mcs[tb_idx]; }
 
 protected:
   void new_tx_common(uint32_t tb_idx, srsran::tti_point tti, int mcs, int tbs, uint32_t max_retx_);
@@ -147,9 +148,9 @@ public:
    * @param tti_rx tti the DL ACK was received
    * @param tb_idx TB index for the given ACK
    * @param ack true for ACK and false for NACK
-   * @return pair with pid and size of TB of the DL harq that was ACKed
+   * @return tuple with pid, TBS and MCS of the DL harq that was ACKed
    */
-  std::pair<uint32_t, int> set_ack_info(tti_point tti_rx, uint32_t tb_idx, bool ack);
+  std::tuple<uint32_t, int, int> set_ack_info(tti_point tti_rx, uint32_t tb_idx, bool ack);
 
   //! Get UL Harq for a given tti_tx_ul
   ul_harq_proc* get_ul_harq(tti_point tti_tx_ul);

srsenb/hdr/stack/mac/sched_ue_ctrl/sched_ue_cell.h

@@ -91,7 +91,7 @@ private:
   cc_st     cc_state_ = cc_st::idle;
 
   // CQI
-  float delta_down = 0, delta_up = 0;
+  float delta_inc = 0, delta_dec = 0;
   float dl_cqi_coeff = 0, ul_snr_coeff = 0;
   float max_cqi_coeff = -5, max_snr_coeff = 5;
 

srsenb/src/main.cc

@@ -147,7 +147,7 @@ void parse_args(all_args_t* args, int argc, char* argv[])
     ("scheduler.pusch_max_mcs", bpo::value<int>(&args->stack.mac.sched.pusch_max_mcs)->default_value(-1), "Optional PUSCH MCS limit")
     ("scheduler.min_aggr_level", bpo::value<int>(&args->stack.mac.sched.min_aggr_level)->default_value(0), "Optional minimum aggregation level index (l=log2(L)) ")
     ("scheduler.max_aggr_level", bpo::value<int>(&args->stack.mac.sched.max_aggr_level)->default_value(3), "Optional maximum aggregation level index (l=log2(L)) ")
-    ("scheduler.adaptive_aggr_level", bpo::value<bool>(&args->stack.mac.sched.adaptive_aggr_level)->default_value(true), "Boolean flag to enable/disable adaptive aggregation level based on target BLER")
+    ("scheduler.adaptive_aggr_level", bpo::value<bool>(&args->stack.mac.sched.adaptive_aggr_level)->default_value(false), "Boolean flag to enable/disable adaptive aggregation level based on target BLER")
     ("scheduler.max_nof_ctrl_symbols", bpo::value<uint32_t>(&args->stack.mac.sched.max_nof_ctrl_symbols)->default_value(3), "Number of control symbols")
     ("scheduler.min_nof_ctrl_symbols", bpo::value<uint32_t>(&args->stack.mac.sched.min_nof_ctrl_symbols)->default_value(1), "Minimum number of control symbols")
     ("scheduler.pucch_multiplex_enable", bpo::value<bool>(&args->stack.mac.sched.pucch_mux_enabled)->default_value(false), "Enable PUCCH multiplexing")

srsenb/src/stack/mac/sched_ue_ctrl/sched_harq.cc

@@ -366,17 +366,17 @@ dl_harq_proc* harq_entity::get_pending_dl_harq(tti_point tti_tx_dl)
   return get_oldest_dl_harq(tti_tx_dl);
 }
 
-std::pair<uint32_t, int> harq_entity::set_ack_info(tti_point tti_rx, uint32_t tb_idx, bool ack)
+std::tuple<uint32_t, int, int> harq_entity::set_ack_info(tti_point tti_rx, uint32_t tb_idx, bool ack)
 {
   for (auto& h : dl_harqs) {
     if (h.get_tti() + FDD_HARQ_DELAY_DL_MS == tti_rx) {
       if (h.set_ack(tb_idx, ack) == SRSRAN_SUCCESS) {
-        return {h.get_id(), h.get_tbs(tb_idx)};
+        return {h.get_id(), h.get_tbs(tb_idx), h.get_mcs(tb_idx)};
       }
-      return {h.get_id(), -1};
+      return {h.get_id(), -1, -1};
     }
   }
-  return {dl_harqs.size(), -1};
+  return {dl_harqs.size(), -1, -1};
 }
 
 ul_harq_proc* harq_entity::get_ul_harq(tti_point tti_tx_ul)

srsenb/src/stack/mac/sched_ue_ctrl/sched_ue_cell.cc

@@ -49,8 +49,8 @@ sched_ue_cell::sched_ue_cell(uint16_t rnti_, const sched_cell_params_t& cell_cfg
   clear_feedback();
 
   float target_bler = cell_cfg->sched_cfg->target_bler;
-  delta_down        = cell_cfg->sched_cfg->adaptive_link_step_size;
-  delta_up          = (1 - target_bler) * delta_down / target_bler;
+  delta_inc         = cell_cfg->sched_cfg->adaptive_link_step_size; // delta_{down} of OLLA
+  delta_dec         = (1 - target_bler) * delta_inc / target_bler;
   max_cqi_coeff     = cell_cfg->sched_cfg->max_delta_dl_cqi;
   max_snr_coeff     = cell_cfg->sched_cfg->max_delta_ul_snr;
 }
@@ -178,6 +178,24 @@ int sched_ue_cell::set_dl_wb_cqi(tti_point tti_rx, uint32_t dl_cqi_)
 int sched_ue_cell::set_ul_crc(tti_point tti_rx, bool crc_res)
 {
   CHECK_VALID_CC("UL CRC");
+
+  // Adapt UL MCS based on BLER
+  if (cell_cfg->sched_cfg->target_bler > 0 and fixed_mcs_ul < 0) {
+    auto* ul_harq = harq_ent.get_ul_harq(tti_rx);
+    if (ul_harq != nullptr) {
+      int mcs = ul_harq->get_mcs(0);
+      // Note: Avoid keeping increasing the snr delta offset, if MCS is already is at its limit
+      float delta_dec_eff = mcs <= 0 ? 0 : delta_dec;
+      float delta_inc_eff = mcs >= (int)max_mcs_ul ? 0 : delta_inc;
+      ul_snr_coeff += crc_res ? delta_inc_eff : -delta_dec_eff;
+      ul_snr_coeff = std::min(std::max(-max_snr_coeff, ul_snr_coeff), max_snr_coeff);
+      logger.info("SCHED: UL adaptive link: snr_estim=%.2f, last_mcs=%d, snr_offset=%f",
+                  tpc_fsm.get_ul_snr_estim(),
+                  mcs,
+                  ul_snr_coeff);
+    }
+  }
+
   // Update HARQ process
   int pid = harq_ent.set_ul_crc(tti_rx, 0, crc_res);
   if (pid < 0) {
@@ -185,30 +203,30 @@ int sched_ue_cell::set_ul_crc(tti_point tti_rx, bool crc_res)
     return SRSRAN_ERROR;
   }
 
-  if (cell_cfg->sched_cfg->target_bler > 0) {
-    ul_snr_coeff += delta_down - static_cast<float>(not crc_res) * (delta_down + delta_up);
-    ul_snr_coeff = std::min(std::max(-max_snr_coeff, ul_snr_coeff), max_snr_coeff);
-    logger.info("SCHED: UL adaptive link: snr_estim=%f, snr_offset=%f", tpc_fsm.get_ul_snr_estim(), ul_snr_coeff);
-  }
   return pid;
 }
 
 int sched_ue_cell::set_ack_info(tti_point tti_rx, uint32_t tb_idx, bool ack)
 {
   CHECK_VALID_CC("DL ACK Info");
-  std::pair<uint32_t, int> p2        = harq_ent.set_ack_info(tti_rx, tb_idx, ack);
-  int                      tbs_acked = p2.second;
-  if (tbs_acked > 0) {
-    logger.debug(
-        "SCHED: Set DL ACK=%d for rnti=0x%x, pid=%d, tb=%d, tti=%d", ack, rnti, p2.first, tb_idx, tti_rx.to_uint());
-
-    if (cell_cfg->sched_cfg->target_bler > 0) {
-      dl_cqi_coeff += delta_down - static_cast<float>(not ack) * (delta_down + delta_up);
-      dl_cqi_coeff = std::min(std::max(-max_cqi_coeff, dl_cqi_coeff), max_cqi_coeff);
-      logger.info("SCHED: DL adaptive link: cqi=%d, cqi_offset=%f", dl_cqi_ctxt.get_avg_cqi(), dl_cqi_coeff);
-    }
-  } else {
+
+  std::tuple<uint32_t, int, int> p2        = harq_ent.set_ack_info(tti_rx, tb_idx, ack);
+  int                            tbs_acked = std::get<1>(p2);
+  if (tbs_acked <= 0) {
     logger.warning("SCHED: Received ACK info for unknown TTI=%d", tti_rx.to_uint());
+    return tbs_acked;
+  }
+
+  // Adapt DL MCS based on BLER
+  if (cell_cfg->sched_cfg->target_bler > 0 and fixed_mcs_dl < 0) {
+    int mcs = std::get<2>(p2);
+    // Note: Avoid keeping increasing the snr delta offset, if MCS is already is at its limit
+    float delta_dec_eff = mcs <= 0 ? 0 : delta_dec;
+    float delta_inc_eff = mcs >= (int)max_mcs_dl ? 0 : delta_inc;
+    dl_cqi_coeff += ack ? delta_inc_eff : -delta_dec_eff;
+    dl_cqi_coeff = std::min(std::max(-max_cqi_coeff, dl_cqi_coeff), max_cqi_coeff);
+    logger.info(
+        "SCHED: DL adaptive link: cqi=%d, last_mcs=%d, cqi_offset=%f", dl_cqi_ctxt.get_avg_cqi(), mcs, dl_cqi_coeff);
   }
   return tbs_acked;
 }