feature, scheduler: Add configuration parameter to set minimum TTI interval between TPCs

lib/include/srsran/interfaces/sched_interface.h

@@ -61,6 +61,7 @@ public:
     float       max_delta_dl_cqi        = 5;
     float       max_delta_ul_snr        = 5;
     float       adaptive_link_step_size = 0.001;
+    uint32_t    min_tpc_tti_interval    = 1;
   };
 
   struct cell_cfg_t {

srsenb/enb.conf.example

@@ -173,6 +173,7 @@ enable = false
 # max_delta_dl_cqi:  Maximum shift in CQI for adaptive DL link
 # max_delta_ul_snr:  Maximum shift in UL SNR for adaptive UL link
 # adaptive_link_step_size: Step size or learning rate used in adaptive link
+# min_tpc_tti_interval: Minimum TTI interval between TPCs different than 1
 #
 #####################################################################
 [scheduler]
@@ -192,6 +193,7 @@ enable = false
 #max_delta_dl_cqi = 5
 #max_delta_ul_snr = 5
 #adaptive_link_step_size = 0.001
+#min_tpc_tti_interval = 1
 
 #####################################################################
 # eMBMS configuration options

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

@@ -38,15 +38,17 @@ public:
   explicit tpc(uint32_t cell_nof_prb,
                float    target_pucch_snr_dB_  = -1.0,
                float    target_pusch_sn_dB_   = -1.0,
-               bool     phr_handling_flag_   = false) :
+               bool     phr_handling_flag_    = false,
+               uint32_t min_tpc_tti_interval_ = 1) :
     nof_prb(cell_nof_prb),
     target_pucch_snr_dB(target_pucch_snr_dB_),
     target_pusch_snr_dB(target_pusch_sn_dB_),
     snr_estim_list({ul_ch_snr_estim{target_pusch_snr_dB}, ul_ch_snr_estim{target_pucch_snr_dB}}),
-    phr_handling_flag(phr_handling_flag_)
+    phr_handling_flag(phr_handling_flag_),
-  {
+    max_prbs_cached(nof_prb),
-    max_prbs_cached = nof_prb;
+    min_tpc_tti_interval(min_tpc_tti_interval_),
-  }
+    logger(srslog::fetch_basic_logger("MAC"))
+  {}
   void set_cfg(float target_pusch_snr_dB_, float target_pucch_snr_dB_)
   {
     target_pucch_snr_dB = target_pucch_snr_dB_;
@@ -85,7 +87,8 @@ public:
 
   void new_tti()
   {
-    for (size_t chidx = 0; chidx < 2; ++chidx) {
+    tti_count++;
+    for (size_t chidx = 0; chidx < nof_ul_ch_code; ++chidx) {
       float target_snr_dB = chidx == PUSCH_CODE ? target_pusch_snr_dB : target_pucch_snr_dB;
       auto& ch_snr        = snr_estim_list[chidx];
 
@@ -139,39 +142,50 @@ private:
       case 3:
         return 3;
       default:
-        srslog::fetch_basic_logger("MAC").warning("Invalid TPC delta value=%d", delta);
+        logger.warning("Invalid TPC delta value=%d", delta);
         return 1;
     }
   }
   uint8_t encode_tpc(uint32_t cc)
   {
-    float target_snr_dB = cc == PUSCH_CODE ? target_pusch_snr_dB : target_pucch_snr_dB;
     auto& ch_snr = snr_estim_list[cc];
     assert(ch_snr.pending_delta == 0); // ensure called once per {cc,tti}
-    if (target_snr_dB < 0) {
+
-      // undefined target sinr case.
+    float target_snr_dB = cc == PUSCH_CODE ? target_pusch_snr_dB : target_pucch_snr_dB;
-      ch_snr.pending_delta = 0;
+    if (target_snr_dB < 0 or last_phr == 0) {
-    } else {
+      // undefined target sinr case, or no more PHR
+      return encode_tpc_delta(0);
+    }
+    if (last_phr < 0) {
+      // negative PHR
+      encode_tpc_delta(-1);
+    }
+    if ((tti_count - ch_snr.last_tpc_tti_count) < min_tpc_tti_interval) {
+      // more time required before sending next TPC
+      return encode_tpc_delta(0);
+    }
+
     // target SINR is finite and there is power headroom
     float diff = target_snr_dB - ch_snr.snr_avg.value();
     diff -= ch_snr.win_tpc_values.value() + ch_snr.acc_tpc_values;
-      int8_t diff_round = roundf(diff);
+    if (diff >= 1) {
-      if (diff_round >= 1) {
+      ch_snr.pending_delta      = diff > 3 ? 3 : 1;
-        ch_snr.pending_delta = diff_round > 3 ? 3 : 1;
+      ch_snr.last_tpc_tti_count = tti_count;
-      } else if (diff_round <= -1) {
+    } else if (diff <= -1) {
       ch_snr.pending_delta      = -1;
-      }
+      ch_snr.last_tpc_tti_count = tti_count;
-      if (last_phr <= 0) {
-        // In case there is no headroom, forbid power increases
-        ch_snr.pending_delta = std::min(ch_snr.pending_delta, 0);
-      }
     }
     return encode_tpc_delta(ch_snr.pending_delta);
   }
 
   uint32_t              nof_prb;
+  uint32_t              min_tpc_tti_interval = 1;
   float                 target_pucch_snr_dB, target_pusch_snr_dB;
   bool                  phr_handling_flag;
+  srslog::basic_logger& logger;
+
+  // state
+  uint32_t tti_count = 0;
 
   // PHR-related variables
   int      last_phr        = undefined_phr;
@@ -188,8 +202,9 @@ private:
     srsran::exp_average_irreg_sampling<float> snr_avg;
     // Accumulation of past TPC commands
     srsran::sliding_sum<int> win_tpc_values;
-    int                      pending_delta  = 0;
+    int8_t                   pending_delta      = 0;
     int                      acc_tpc_values     = 0;
+    uint32_t                 last_tpc_tti_count = 0;
 
     explicit ul_ch_snr_estim(float initial_snr) :
       snr_avg(0.1, initial_snr < 0 ? 5 : initial_snr), win_tpc_values(FDD_HARQ_DELAY_UL_MS + FDD_HARQ_DELAY_DL_MS)

srsenb/src/main.cc

@@ -155,6 +155,7 @@ void parse_args(all_args_t* args, int argc, char* argv[])
     ("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")
+    ("scheduler.min_tpc_tti_interval", bpo::value<uint32_t>(&args->stack.mac.sched.min_tpc_tti_interval)->default_value(1), "Minimum TTI interval between positive or negative TPCs")
 
 
     /* Downlink Channel emulator section */

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

@@ -38,7 +38,8 @@ sched_ue_cell::sched_ue_cell(uint16_t rnti_, const sched_cell_params_t& cell_cfg
   tpc_fsm(cell_cfg->nof_prb(),
           cell_cfg->cfg.target_pucch_ul_sinr,
           cell_cfg->cfg.target_pusch_ul_sinr,
-          cell_cfg->cfg.enable_phr_handling),
+          cell_cfg->cfg.enable_phr_handling,
+          cell_cfg->sched_cfg->min_tpc_tti_interval),
   fixed_mcs_dl(cell_cfg_.sched_cfg->pdsch_mcs),
   fixed_mcs_ul(cell_cfg_.sched_cfg->pusch_mcs),
   current_tti(current_tti_),