disable mcs>20 if eNB supports UL 64QAM but UE doesn't

lib/include/srslte/interfaces/sched_interface.h

@@ -84,6 +84,7 @@ public:
     uint32_t maxharq_msg3tx;
     uint32_t n1pucch_an;
     uint32_t delta_pucch_shift;
+    bool     enable_64qam;
 
     // If non-negative, statically allocate N prbs at the edges of the uplink for PUCCH
     int nrb_pucch;

srsenb/src/stack/mac/scheduler_ue.cc

@@ -1242,9 +1242,10 @@ int cc_sched_ue::cqi_to_tbs(uint32_t nof_prb, uint32_t nof_re, bool use_tbs_inde
   uint32_t cqi, max_mcs, max_Qm;
   float    max_coderate;
   if (is_ul) {
-    cqi          = ul_cqi;
-    max_mcs      = cfg->support_ul_64qam ? max_mcs_ul : std::min(max_mcs_ul, 20u);
-    max_Qm       = cfg->support_ul_64qam ? 6 : 4;
+    cqi = ul_cqi;
+    // if cell supports UL 64QAM but the UE does not support it, cap the mcs to avoid Qm == 6
+    max_mcs = (not cfg->support_ul_64qam and cell_params->cfg.enable_64qam) ? std::min(max_mcs_ul, 20u) : max_mcs_ul;
+    max_Qm  = cfg->support_ul_64qam ? 6 : 4;
     max_coderate = srslte_cqi_to_coderate(std::min(cqi + 1u, 15u), false);
   } else {
     cqi          = dl_cqi;

srsenb/src/stack/rrc/rrc.cc

@@ -597,6 +597,7 @@ void rrc::config_mac()
         cfg.sibs[1].sib2().rr_cfg_common.rach_cfg_common.ra_supervision_info.ra_resp_win_size.to_number();
     item.prach_freq_offset = cfg.sibs[1].sib2().rr_cfg_common.prach_cfg.prach_cfg_info.prach_freq_offset;
     item.maxharq_msg3tx    = cfg.sibs[1].sib2().rr_cfg_common.rach_cfg_common.max_harq_msg3_tx;
+    item.enable_64qam      = cfg.sibs[1].sib2().rr_cfg_common.pusch_cfg_common.pusch_cfg_basic.enable64_qam;
     item.initial_dl_cqi    = cfg.cell_list[ccidx].initial_dl_cqi;
 
     item.nrb_pucch = SRSLTE_MAX(cfg.sr_cfg.nof_prb, cfg.cqi_cfg.nof_prb);