feature - implement adaptive link adaptation in DL and UL

lib/include/srsran/interfaces/sched_interface.h

@@ -55,6 +55,10 @@ public:
     uint32_t    max_nof_ctrl_symbols    = 3;
     int         max_aggr_level          = 3;
     bool        pucch_mux_enabled       = false;
+    float       target_bler             = 0.05;
+    float       max_delta_dl_cqi        = 5;
+    float       max_delta_ul_snr        = 5;
+    float       adaptive_link_step_size = 0.001;
   };
 
   struct cell_cfg_t {

srsenb/enb.conf.example

@@ -167,6 +167,10 @@ enable = false
 # pusch_max_mcs:     Optional PUSCH MCS limit 
 # min_nof_ctrl_symbols: Minimum number of control symbols 
 # max_nof_ctrl_symbols: Maximum number of control symbols 
+# target_bler:       Target BLER (in decimal) to achieve via adaptive link 
+# max_delta_dl_cqi:  Maximum shift in CQI for adaptive DL link 
+# max_delta_ul_cqi:  Maximum shift in UL SNR for adaptive UL link 
+# target_bler:       Step size or learning rate used in adaptive link 
 #
 #####################################################################
 [scheduler]
@@ -180,6 +184,10 @@ enable = false
 #min_nof_ctrl_symbols = 1
 #max_nof_ctrl_symbols = 3
 #pucch_multiplex_enable = false
+#target_bler = 0.05
+#max_delta_dl_cqi = 5
+#max_delta_ul_snr = 5
+#adaptive_link_step_size = 0.001
 
 #####################################################################
 # eMBMS configuration options

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

@@ -33,7 +33,7 @@ struct sched_ue_cell {
   void clear_feedback();
   void finish_tti(tti_point tti_rx);
 
-  void set_dl_wb_cqi(tti_point tti_rx, uint32_t dl_cqi_);
+  int set_dl_wb_cqi(tti_point tti_rx, uint32_t dl_cqi_);
 
   bool             configured() const { return ue_cc_idx >= 0; }
   int              get_ue_cc_idx() const { return ue_cc_idx; }
@@ -43,6 +43,11 @@ struct sched_ue_cell {
   const sched_interface::ue_cfg_t* get_ue_cfg() const { return configured() ? ue_cfg : nullptr; }
   cc_st                            cc_state() const { return cc_state_; }
 
+  int get_dl_cqi() const;
+  int get_dl_cqi(const rbgmask_t& rbgs) const;
+  int get_ul_cqi() const;
+
+  int set_ack_info(tti_point tti_rx, uint32_t tb_idx, bool ack);
   int set_ul_crc(tti_point tti_rx, bool crc_res);
   int set_ul_snr(tti_point tti_rx, float ul_snr, uint32_t ul_ch_code);
 
@@ -66,7 +71,6 @@ struct sched_ue_cell {
   tti_point           dl_ri_tti_rx{};
   uint32_t            dl_pmi = 0;
   tti_point           dl_pmi_tti_rx{};
-  uint32_t            ul_cqi = 1;
   tti_point           ul_cqi_tti_rx{};
 
   uint32_t max_mcs_dl = 28, max_mcs_ul = 28;
@@ -84,6 +88,11 @@ private:
   tti_point current_tti;
   cc_st     cc_state_ = cc_st::idle;
 
+  // CQI
+  float delta_down = 0, delta_up = 0;
+  float dl_cqi_coeff = 0, ul_snr_coeff = 0;
+  float max_cqi_coeff = -5, max_snr_coeff = 5;
+
   sched_dl_cqi dl_cqi_ctxt;
 };
 

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

@@ -88,10 +88,6 @@ public:
     for (size_t chidx = 0; chidx < 2; ++chidx) {
       float target_snr_dB = chidx == PUSCH_CODE ? target_pusch_snr_dB : target_pucch_snr_dB;
       auto& ch_snr        = snr_estim_list[chidx];
-      if (target_snr_dB < 0) {
-        ch_snr.pending_delta = 0;
-        continue;
-      }
 
       // Enqueue pending UL Channel SNR measurement
       if (ch_snr.pending_snr == null_snr) {
@@ -105,7 +101,9 @@ public:
       ch_snr.pending_snr = null_snr;
 
       // Enqueue PUSCH/PUCCH TPC sent in last TTI (zero for both Delta_PUSCH/Delta_PUCCH=0 and TPC not sent)
+      if (target_snr_dB >= 0) {
         ch_snr.win_tpc_values.push(ch_snr.pending_delta);
+      }
       ch_snr.pending_delta = 0;
     }
   }
@@ -126,6 +124,8 @@ public:
 
   uint32_t max_ul_prbs() const { return max_prbs_cached; }
 
+  float get_ul_snr_estim(uint32_t ul_ch_code = PUSCH_CODE) const { return snr_estim_list[ul_ch_code].snr_avg.value(); }
+
 private:
   uint8_t encode_tpc_delta(int8_t delta)
   {

srsenb/src/main.cc

@@ -149,6 +149,10 @@ void parse_args(all_args_t* args, int argc, char* argv[])
     ("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")
+    ("scheduler.target_bler", bpo::value<float>(&args->stack.mac.sched.target_bler)->default_value(0.05), "Target BLER (in decimal) to achieve via adaptive link")
+    ("scheduler.max_delta_dl_cqi", bpo::value<float>(&args->stack.mac.sched.max_delta_dl_cqi)->default_value(5.0), "Maximum shift in CQI for adaptive DL link")
+    ("scheduler.max_delta_ul_snr", bpo::value<float>(&args->stack.mac.sched.max_delta_ul_snr)->default_value(5.0), "Maximum shift in UL SNR for adaptive UL link")
+    ("scheduler.adaptive_link_step_size", bpo::value<float>(&args->stack.mac.sched.max_delta_ul_snr)->default_value(0.001), "Step size or learning rate used in adaptive link")
 
 
     /* Downlink Channel emulator section */

srsenb/src/stack/mac/sched_ue.cc

@@ -227,20 +227,7 @@ bool sched_ue::pusch_enabled(tti_point tti_rx, uint32_t enb_cc_idx, bool needs_p
 
 int sched_ue::set_ack_info(tti_point tti_rx, uint32_t enb_cc_idx, uint32_t tb_idx, bool ack)
 {
-  int tbs_acked = -1;
+  return cells[enb_cc_idx].set_ack_info(tti_rx, tb_idx, ack);
-  if (cells[enb_cc_idx].cc_state() != cc_st::idle) {
-    std::pair<uint32_t, int> p2 = cells[enb_cc_idx].harq_ent.set_ack_info(tti_rx, tb_idx, ack);
-    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());
-    } else {
-      logger.warning("SCHED: Received ACK info for unknown TTI=%d", tti_rx.to_uint());
-    }
-  } else {
-    logger.warning("Received DL ACK for invalid cell index %d", enb_cc_idx);
-  }
-  return tbs_acked;
 }
 
 void sched_ue::set_ul_crc(tti_point tti_rx, uint32_t enb_cc_idx, bool crc_res)
@@ -815,7 +802,7 @@ uint32_t sched_ue::get_expected_dl_bitrate(uint32_t enb_cc_idx, int nof_rbgs) co
   auto&    cc = cells[enb_cc_idx];
   uint32_t nof_re =
       cc.cell_cfg->get_dl_lb_nof_re(to_tx_dl(current_tti), count_prb_per_tb_approx(nof_rbgs, cc.cell_cfg->nof_prb()));
-  float max_coderate = srsran_cqi_to_coderate(std::min(cc.dl_cqi().get_avg_cqi() + 1u, 15u), cfg.use_tbs_index_alt);
+  float max_coderate = srsran_cqi_to_coderate(std::min(cc.get_dl_cqi() + 1u, 15u), cfg.use_tbs_index_alt);
 
   // Inverse of srsran_coderate(tbs, nof_re)
   uint32_t tbs = max_coderate * nof_re - 24;
@@ -829,7 +816,7 @@ uint32_t sched_ue::get_expected_ul_bitrate(uint32_t enb_cc_idx, int nof_prbs) co
   uint32_t N_srs        = 0;
   uint32_t nof_symb     = 2 * (SRSRAN_CP_NSYMB(cell.cp) - 1) - N_srs;
   uint32_t nof_re       = nof_symb * nof_prbs_alloc * SRSRAN_NRE;
-  float    max_coderate = srsran_cqi_to_coderate(std::min(cells[enb_cc_idx].ul_cqi + 1u, 15u), false);
+  float    max_coderate = srsran_cqi_to_coderate(std::min(cells[enb_cc_idx].get_ul_cqi() + 1u, 15u), false);
 
   // Inverse of srsran_coderate(tbs, nof_re)
   uint32_t tbs = max_coderate * nof_re - 24;
@@ -884,7 +871,7 @@ uint32_t sched_ue::get_pending_ul_data_total(tti_point tti_tx_ul, int this_enb_c
       uint32_t max_cqi = 0, max_cc_idx = 0;
       for (uint32_t cc = 0; cc < cells.size(); ++cc) {
         if (cells[cc].configured()) {
-          uint32_t sum_cqi = cells[cc].dl_cqi().get_avg_cqi() + cells[cc].ul_cqi;
+          uint32_t sum_cqi = cells[cc].get_dl_cqi() + cells[cc].get_ul_cqi();
           if (cells[cc].cc_state() == cc_st::active and sum_cqi > max_cqi) {
             max_cqi    = sum_cqi;
             max_cc_idx = cc;
@@ -978,7 +965,7 @@ uint32_t sched_ue::get_aggr_level(uint32_t enb_cc_idx, uint32_t nof_bits)
 {
   const auto& cc = cells[enb_cc_idx];
   return srsenb::get_aggr_level(
-      nof_bits, cc.dl_cqi().get_avg_cqi(), cc.max_aggr_level, cc.cell_cfg->nof_prb(), cfg.use_tbs_index_alt);
+      nof_bits, cc.get_dl_cqi(), cc.max_aggr_level, cc.cell_cfg->nof_prb(), cfg.use_tbs_index_alt);
 }
 
 void sched_ue::finish_tti(tti_point tti_rx, uint32_t enb_cc_idx)

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

@@ -13,10 +13,9 @@
 #include "srsenb/hdr/stack/mac/sched_ue_ctrl/sched_ue_cell.h"
 #include "srsenb/hdr/stack/mac/sched_helpers.h"
 #include "srsenb/hdr/stack/mac/sched_phy_ch/sched_dci.h"
-#include "srsenb/hdr/stack/mac/schedulers/sched_base.h"
 #include <numeric>
 
-#define CHECK_INVALID_FEEDBACK(feedback_type)                                                                          \
+#define CHECK_VALID_CC(feedback_type)                                                                                  \
   do {                                                                                                                 \
     if (cc_state() == cc_st::idle) {                                                                                   \
       logger.warning("SCHED: rnti=0x%x received " feedback_type " for idle cc=%d", cell_cfg->enb_cc_idx);              \
@@ -47,6 +46,12 @@ sched_ue_cell::sched_ue_cell(uint16_t rnti_, const sched_cell_params_t& cell_cfg
   dl_cqi_ctxt(cell_cfg_.nof_prb(), 0, 1)
 {
   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;
+  max_cqi_coeff     = cell_cfg->sched_cfg->max_delta_dl_cqi;
+  max_snr_coeff     = cell_cfg->sched_cfg->max_delta_ul_snr;
 }
 
 void sched_ue_cell::set_ue_cfg(const sched_interface::ue_cfg_t& ue_cfg_)
@@ -148,7 +153,6 @@ void sched_ue_cell::clear_feedback()
   dl_pmi        = 0;
   dl_pmi_tti_rx = tti_point{};
   dl_cqi_ctxt.reset_cqi(ue_cc_idx == 0 ? cell_cfg->cfg.initial_dl_cqi : 1);
-  ul_cqi        = 1;
   ul_cqi_tti_rx = tti_point{};
 }
 
@@ -158,39 +162,84 @@ void sched_ue_cell::finish_tti(tti_point tti_rx)
   harq_ent.reset_pending_data(tti_rx);
 }
 
-void sched_ue_cell::set_dl_wb_cqi(tti_point tti_rx, uint32_t dl_cqi_)
+int sched_ue_cell::set_dl_wb_cqi(tti_point tti_rx, uint32_t dl_cqi_)
 {
+  CHECK_VALID_CC("DL CQI");
   dl_cqi_ctxt.cqi_wb_info(tti_rx, dl_cqi_);
   if (ue_cc_idx > 0 and cc_state_ == cc_st::activating and dl_cqi_ > 0) {
     // Wait for SCell to receive a positive CQI before activating it
     cc_state_ = cc_st::active;
     logger.info("SCHED: SCell index=%d is now active", ue_cc_idx);
   }
+  return SRSRAN_SUCCESS;
 }
 
 int sched_ue_cell::set_ul_crc(tti_point tti_rx, bool crc_res)
 {
-  CHECK_INVALID_FEEDBACK("UL CRC");
+  CHECK_VALID_CC("UL CRC");
   // Update HARQ process
   int pid = harq_ent.set_ul_crc(tti_rx, 0, crc_res);
   if (pid < 0) {
     logger.warning("SCHED: rnti=0x%x received UL CRC for invalid tti_rx=%d", (int)tti_rx.to_uint());
     return SRSRAN_ERROR;
   }
+
+  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: adjusting UL SNR by %f", 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());
+
+    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: adjusting DL CQI by %f", dl_cqi_coeff);
+  } else {
+    logger.warning("SCHED: Received ACK info for unknown TTI=%d", tti_rx.to_uint());
+  }
+  return tbs_acked;
+}
+
 int sched_ue_cell::set_ul_snr(tti_point tti_rx, float ul_snr, uint32_t ul_ch_code)
 {
-  CHECK_INVALID_FEEDBACK("UL SNR estimate");
+  CHECK_VALID_CC("UL SNR estimate");
   tpc_fsm.set_snr(ul_snr, ul_ch_code);
   if (ul_ch_code == tpc::PUSCH_CODE) {
-    ul_cqi        = srsran_cqi_from_snr(ul_snr);
     ul_cqi_tti_rx = tti_rx;
   }
   return SRSRAN_SUCCESS;
 }
 
+int sched_ue_cell::get_ul_cqi() const
+{
+  if (not ul_cqi_tti_rx.is_valid()) {
+    return 1;
+  }
+  float snr = tpc_fsm.get_ul_snr_estim();
+  return srsran_cqi_from_snr(snr + ul_snr_coeff);
+}
+
+int sched_ue_cell::get_dl_cqi(const rbgmask_t& rbgs) const
+{
+  float dl_cqi = std::get<1>(find_min_cqi_rbg(rbgs, dl_cqi_ctxt));
+  return std::max(0, (int)std::min(dl_cqi + dl_cqi_coeff, 15.0f));
+}
+
+int sched_ue_cell::get_dl_cqi() const
+{
+  rbgmask_t rbgmask(cell_cfg->nof_rbgs);
+  rbgmask.fill(0, rbgmask.size());
+  return get_dl_cqi(rbgmask);
+}
+
 /*************************************************************
  *                    TBS/MCS derivation
  ************************************************************/
@@ -280,7 +329,7 @@ tbs_info cqi_to_tbs_dl(const sched_ue_cell& cell,
   tbs_info ret;
   if (cell.fixed_mcs_dl < 0 or not cell.dl_cqi().is_cqi_info_received()) {
     // Dynamic MCS configured or first Tx
-    uint32_t dl_cqi = std::get<1>(find_min_cqi_rbg(rbgs, cell.dl_cqi()));
+    uint32_t dl_cqi = cell.get_dl_cqi(rbgs);
 
     ret = compute_min_mcs_and_tbs_from_required_bytes(
         nof_prbs, nof_re, dl_cqi, cell.max_mcs_dl, req_bytes, false, false, use_tbs_index_alt);
@@ -309,7 +358,7 @@ tbs_info cqi_to_tbs_ul(const sched_ue_cell& cell, uint32_t nof_prb, uint32_t nof
   if (mcs < 0) {
     // Dynamic MCS
     ret = compute_min_mcs_and_tbs_from_required_bytes(
-        nof_prb, nof_re, cell.ul_cqi, cell.max_mcs_ul, req_bytes, true, ulqam64_enabled, false);
+        nof_prb, nof_re, cell.get_ul_cqi(), cell.max_mcs_ul, req_bytes, true, ulqam64_enabled, false);
 
     // If coderate > SRSRAN_MIN(max_coderate, 0.932 * Qm) we should set TBS=0. We don't because it's not correctly
     // handled by the scheduler, but we might be scheduling undecodable codewords at very low SNR

srsenb/test/mac/sched_ue_cell_test.cc

@@ -38,9 +38,8 @@ void test_neg_phr_scenario()
   ue_cc.set_ue_cfg(ue_cfg);
 
   float snr = 0;
-  ue_cc.tpc_fsm.set_snr(snr, 0);
+  ue_cc.set_ul_snr(tti_point(0), snr, 0);
-  ue_cc.tpc_fsm.set_snr(snr, 1);
+  ue_cc.set_ul_snr(tti_point(0), snr, 1);
-  ue_cc.ul_cqi = srsran_cqi_from_snr(snr);
   ue_cc.tpc_fsm.set_phr(-5);
   ue_cc.new_tti(tti_point(0));