Several fixes in UL scheduler

- Limit minimum UL grant size to accommodate both BSR and RLC headers
- Limit UL CQI update to PUSCH SNR reports
- Avoid TPC commands when target PUSCH and PUCCH SNR are not specified

srsenb/hdr/stack/mac/sched_ue.h

@@ -90,8 +90,10 @@ public:
 
   uint32_t get_required_prb_ul(uint32_t enb_cc_idx, uint32_t req_bytes);
 
+  /// Get total pending bytes to be transmitted in DL.
+  /// The amount of CEs to transmit depends on whether enb_cc_idx is UE's PCell
+  uint32_t     get_pending_dl_bytes(uint32_t enb_cc_idx);
   rbg_interval get_required_dl_rbgs(uint32_t enb_cc_idx);
-  srsran::interval<uint32_t> get_requested_dl_bytes(uint32_t enb_cc_idx);
   uint32_t     get_pending_dl_rlc_data() const;
   uint32_t     get_expected_dl_bitrate(uint32_t enb_cc_idx, int nof_rbgs = -1) const;
 
@@ -147,6 +149,8 @@ public:
   bool pusch_enabled(tti_point tti_rx, uint32_t enb_cc_idx, bool needs_pdcch) const;
 
 private:
+  srsran::interval<uint32_t> get_requested_dl_bytes(uint32_t enb_cc_idx);
+
   bool is_sr_triggered();
 
   tbs_info allocate_new_dl_mac_pdu(sched_interface::dl_sched_data_t* data,

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

@@ -119,14 +119,14 @@ public:
    * @remark See TS 36.213 Section 5.1.1
    * @return accumulated TPC value {-1, 0, 1, 3}
    */
-  uint8_t encode_pusch_tpc() { return enconde_tpc(PUSCH_CODE); }
+  uint8_t encode_pusch_tpc() { return encode_tpc(PUSCH_CODE); }
 
   /**
    * Called during DCI format1/2A/A encoding to set PUCCH TPC command
    * @remark See TS 36.213 Section 5.1.2
    * @return accumulated TPC value {-1, 0, 1, 3}
    */
-  uint8_t encode_pucch_tpc() { return enconde_tpc(PUCCH_CODE); }
+  uint8_t encode_pucch_tpc() { return encode_tpc(PUCCH_CODE); }
 
   uint32_t max_ul_prbs() const { return max_prbs_cached; }
 
@@ -147,18 +147,14 @@ private:
         return 1;
     }
   }
-  uint8_t enconde_tpc(uint32_t cc)
+  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. Increase Tx power once per PHR, considering the number of allocable PRBs remains
-      // unchanged
-      if (not ch_snr.phr_flag) {
-        ch_snr.pending_delta = (max_prbs_cached == nof_prb) ? 1 : (last_phr < 0 ? -1 : 0);
-        ch_snr.phr_flag      = true;
-      }
+      // undefined target sinr case.
+      ch_snr.pending_delta = 0;
     } else {
       // target SINR is finite and there is power headroom
       float diff = target_snr_dB - ch_snr.snr_avg.value();

srsenb/src/stack/mac/sched_grid.cc

@@ -671,7 +671,7 @@ void sf_sched::set_dl_data_sched_result(const sf_cch_allocator::alloc_result_t&
       continue;
     }
     sched_ue*           user        = ue_it->second.get();
-    uint32_t            data_before = user->get_requested_dl_bytes(cc_cfg->enb_cc_idx).stop();
+    uint32_t            data_before = user->get_pending_dl_bytes(cc_cfg->enb_cc_idx);
     const dl_harq_proc& dl_harq     = user->get_dl_harq(data_alloc.pid, cc_cfg->enb_cc_idx);
     bool                is_newtx    = dl_harq.is_empty();
 
@@ -687,7 +687,7 @@ void sf_sched::set_dl_data_sched_result(const sf_cch_allocator::alloc_result_t&
                      data_alloc.pid,
                      data_alloc.user_mask,
                      tbs,
-                     user->get_requested_dl_bytes(cc_cfg->enb_cc_idx).stop());
+                     user->get_pending_dl_bytes(cc_cfg->enb_cc_idx));
       logger.warning("%s", srsran::to_c_str(str_buffer));
       continue;
     }
@@ -707,7 +707,7 @@ void sf_sched::set_dl_data_sched_result(const sf_cch_allocator::alloc_result_t&
                    dl_harq.nof_retx(0) + dl_harq.nof_retx(1),
                    tbs,
                    data_before,
-                   user->get_requested_dl_bytes(cc_cfg->enb_cc_idx).stop(),
+                   user->get_pending_dl_bytes(cc_cfg->enb_cc_idx),
                    get_tti_tx_dl());
     logger.info("%s", srsran::to_c_str(str_buffer));
   }

srsenb/src/stack/mac/sched_ue.cc

@@ -311,8 +311,10 @@ void sched_ue::set_ul_snr(tti_point tti_rx, uint32_t enb_cc_idx, float snr, uint
 {
   if (cells[enb_cc_idx].cc_state() != cc_st::idle) {
     cells[enb_cc_idx].tpc_fsm.set_snr(snr, ul_ch_code);
+    if (ul_ch_code == tpc::PUSCH_CODE) {
       cells[enb_cc_idx].ul_cqi        = srsran_cqi_from_snr(snr);
       cells[enb_cc_idx].ul_cqi_tti_rx = tti_rx;
+    }
   } else {
     logger.warning("Received SNR info for invalid cell index %d", enb_cc_idx);
   }
@@ -776,6 +778,11 @@ rbg_interval sched_ue::get_required_dl_rbgs(uint32_t enb_cc_idx)
   return {min_pending_rbg, max_pending_rbg};
 }
 
+uint32_t sched_ue::get_pending_dl_bytes(uint32_t enb_cc_idx)
+{
+  return get_requested_dl_bytes(enb_cc_idx).stop();
+}
+
 /**
  * Returns the range (min,max) of possible MAC PDU sizes.
  * - the lower boundary value is set based on the following conditions:

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

@@ -307,6 +307,7 @@ int get_required_prb_dl(const sched_ue_cell& cell,
 
 uint32_t get_required_prb_ul(const sched_ue_cell& cell, uint32_t req_bytes)
 {
+  const static int MIN_ALLOC_BYTES = 10;
   if (req_bytes == 0) {
     return 0;
   }
@@ -317,11 +318,20 @@ uint32_t get_required_prb_ul(const sched_ue_cell& cell, uint32_t req_bytes)
   };
 
   // find nof prbs that lead to a tbs just above req_bytes
-  int                                      target_tbs = static_cast<int>(req_bytes) + 4;
+  int                                      target_tbs = std::max(static_cast<int>(req_bytes) + 4, MIN_ALLOC_BYTES);
   uint32_t                                 max_prbs   = std::min(cell.tpc_fsm.max_ul_prbs(), cell.cell_cfg->nof_prb());
   std::tuple<uint32_t, int, uint32_t, int> ret =
       false_position_method(1U, max_prbs, target_tbs, compute_tbs_approx, [](int y) { return y == SRSRAN_ERROR; });
   uint32_t req_prbs  = std::get<2>(ret);
+  uint32_t final_tbs = std::get<3>(ret);
+  while (final_tbs < MIN_ALLOC_BYTES and req_prbs < cell.cell_cfg->nof_prb()) {
+    // Note: If PHR<0 is limiting the max nof PRBs per UL grant, the UL grant may become too small to fit any
+    //       data other than headers + BSR. Besides, forcing unnecessary segmentation, it may additionally
+    //       forbid the UE from fitting small RRC messages (e.g. RRCReconfComplete) in the UL grants.
+    //       To avoid TBS<10, we force an increase the nof required PRBs.
+    req_prbs++;
+    final_tbs = compute_tbs_approx(req_prbs);
+  }
   while (!srsran_dft_precoding_valid_prb(req_prbs) && req_prbs < cell.cell_cfg->nof_prb()) {
     req_prbs++;
   }

srsenb/test/mac/sched_tpc_test.cc

@@ -109,7 +109,7 @@ int test_undefined_target_snr()
   TESTASSERT(sum_pusch == 0);
   TESTASSERT(sum_pucch == 0);
 
-  // TEST: If the PHR allows full utilization of available PRBs, the TPC slightly increments UL Tx power
+  // TEST: Check that high PHR allows full utilization of available PRBs, TPC remains at zero (no target SINR)
   int phr = 30;
   tpcfsm.set_phr(phr);
   TESTASSERT(tpcfsm.max_ul_prbs() == 50);
@@ -120,8 +120,7 @@ int test_undefined_target_snr()
     sum_pusch += decode_tpc(tpcfsm.encode_pusch_tpc());
     sum_pucch += decode_tpc(tpcfsm.encode_pucch_tpc());
   }
-  TESTASSERT(sum_pusch > 0 and sum_pusch <= 3);
-  TESTASSERT(sum_pucch > 0 and sum_pucch <= 3);
+  TESTASSERT(sum_pusch == 0 and sum_pucch == 0);
 
   // TEST: PHR is too low to allow all PRBs to be allocated. This event should not affect TPC commands
   phr = 5;
@@ -144,8 +143,8 @@ int test_undefined_target_snr()
     sum_pusch += decode_tpc(tpcfsm.encode_pusch_tpc());
     sum_pucch += decode_tpc(tpcfsm.encode_pucch_tpc());
   }
-  TESTASSERT(sum_pusch <= 0 and sum_pusch >= -1);
-  TESTASSERT(sum_pucch <= 0 and sum_pucch >= -1);
+  TESTASSERT(sum_pusch == 0);
+  TESTASSERT(sum_pucch == 0);
 
   return SRSRAN_SUCCESS;
 }