diff --git a/executables/nr-uesoftmodem.c b/executables/nr-uesoftmodem.c
index 262f0b1631..047ef6c557 100644
--- a/executables/nr-uesoftmodem.c
+++ b/executables/nr-uesoftmodem.c
@@ -159,6 +159,9 @@ int           oaisim_flag = 0;
 int            emulate_rf = 0;
 uint32_t       N_RB_DL    = 106;
 
+// NTN cellSpecificKoffset-r17, but in slots for DL SCS
+unsigned int NTN_UE_Koffset = 0;
+
 /* see file openair2/LAYER2/MAC/main.c for why abstraction_flag is needed
  * this is very hackish - find a proper solution
  */
@@ -591,6 +594,9 @@ int main(int argc, char **argv)
       }
     }
 
+    // NTN cellSpecificKoffset-r17, but in slots for DL SCS
+    NTN_UE_Koffset = nrUE_params.ntn_koffset << PHY_vars_UE_g[0][0]->frame_parms.numerology_index;
+
     init_openair0();
     lock_memory_to_ram();
 
diff --git a/openair1/PHY/INIT/nr_parms.c b/openair1/PHY/INIT/nr_parms.c
index 4fc91037b8..6a2c300b72 100644
--- a/openair1/PHY/INIT/nr_parms.c
+++ b/openair1/PHY/INIT/nr_parms.c
@@ -262,15 +262,15 @@ uint32_t get_slot_from_timestamp(openair0_timestamp timestamp_rx, const NR_DL_FR
    return slot_idx; 
 }
 
-uint32_t get_samples_slot_timestamp(int slot, const NR_DL_FRAME_PARMS *fp, uint8_t sl_ahead)
+uint32_t get_samples_slot_timestamp(int slot, const NR_DL_FRAME_PARMS *fp, unsigned int sl_ahead)
 {
   uint32_t samp_count = 0;
 
   if(!sl_ahead) {
-    for(uint8_t idx_slot = 0; idx_slot < slot; idx_slot++)
+    for(unsigned int idx_slot = 0; idx_slot < slot; idx_slot++)
       samp_count += fp->get_samples_per_slot(idx_slot, fp);
   } else {
-    for(uint8_t idx_slot = slot; idx_slot < slot+sl_ahead; idx_slot++)
+    for(unsigned int idx_slot = slot; idx_slot < slot+sl_ahead; idx_slot++)
       samp_count += fp->get_samples_per_slot(idx_slot, fp);
   }
   return samp_count;
diff --git a/openair1/PHY/defs_nr_common.h b/openair1/PHY/defs_nr_common.h
index 3d0f2efa88..9c2dff22b8 100644
--- a/openair1/PHY/defs_nr_common.h
+++ b/openair1/PHY/defs_nr_common.h
@@ -135,7 +135,7 @@ typedef struct NR_DL_FRAME_PARMS NR_DL_FRAME_PARMS;
 typedef uint32_t (*get_samples_per_slot_t)(int slot, const NR_DL_FRAME_PARMS *fp);
 typedef uint32_t (*get_slot_from_timestamp_t)(openair0_timestamp timestamp_rx, const NR_DL_FRAME_PARMS *fp);
 
-typedef uint32_t (*get_samples_slot_timestamp_t)(int slot, const NR_DL_FRAME_PARMS *fp, uint8_t sl_ahead);
+typedef uint32_t (*get_samples_slot_timestamp_t)(int slot, const NR_DL_FRAME_PARMS *fp, unsigned int sl_ahead);
 
 struct NR_DL_FRAME_PARMS {
   /// frequency range
diff --git a/openair1/PHY/impl_defs_top.h b/openair1/PHY/impl_defs_top.h
index c06cd13ff7..618a7e6c58 100644
--- a/openair1/PHY/impl_defs_top.h
+++ b/openair1/PHY/impl_defs_top.h
@@ -268,13 +268,24 @@
 #define TDD_CONFIG_NB_FRAMES                     (2)
 #define NR_MAX_SLOTS_PER_FRAME                   (160)                    /* number of slots per frame */
 
-/* FFS_NR_TODO it defines ue capability which is the number of slots     */
-/* - between reception of pdsch and tarnsmission of its acknowlegment    */
-/* - between reception of un uplink grant and its related transmission   */
-// should be 2 as per NR standard, but current UE is not able to perform this value
+/* FFS_NR_TODO it defines ue capability which is the number of slots        */
+/* - between reception of pdsch and transmission of its acknowlegment  (k1) */
+/* - between reception of un uplink grant and its related transmission (k2) */
 #define NR_UE_CAPABILITY_SLOT_RX_TO_TX (3)
 
-#define DURATION_RX_TO_TX (NR_UE_CAPABILITY_SLOT_RX_TO_TX)
+/* When the OAI UE receives RX slot N, it starts sending TX slot N+DURATION_RX_TO_TX.
+ * Therefore DURATION_RX_TO_TX must not be larger than the minimum k1 and k2 values (NR_UE_CAPABILITY_SLOT_RX_TO_TX).
+ * In case of NTN, the propagation delay is so large, that the TX slot needs to be transmitted far in advance.
+ * Therefore, the NTN_UE_Koffset is added to DURATION_RX_TO_TX.
+ *
+ * Note: currently, the UE requires this to be a constant.
+ * But in case of NTN, Koffset is only known after receiving SIB19.
+ * Therefore, support should be added to allow changing DURATION_RX_TO_TX on reception of SIB19 (via FAPI-like interface).
+ * E.g. no transmission before successful reception of SIB19, and re-sync with disabled transmission if Koffset changes.
+ * When this has been implemented, the global variable NTN_UE_Koffset should be removed, too.
+ */
+extern unsigned int NTN_UE_Koffset;
+#define DURATION_RX_TO_TX (NR_UE_CAPABILITY_SLOT_RX_TO_TX + NTN_UE_Koffset)
 
 #define NR_MAX_ULSCH_HARQ_PROCESSES              (NR_MAX_HARQ_PROCESSES)  /* cf 38.214 6.1 UE procedure for receiving the physical uplink shared channel */
 #define NR_MAX_DLSCH_HARQ_PROCESSES              (NR_MAX_HARQ_PROCESSES)  /* cf 38.214 5.1 UE procedure for receiving the physical downlink shared channel */
diff --git a/openair1/SIMULATION/NR_PHY/dlsim.c b/openair1/SIMULATION/NR_PHY/dlsim.c
index 728163e049..d6be222a9b 100644
--- a/openair1/SIMULATION/NR_PHY/dlsim.c
+++ b/openair1/SIMULATION/NR_PHY/dlsim.c
@@ -95,6 +95,9 @@ nfapi_ue_release_request_body_t release_rntis;
 instance_t DUuniqInstance=0;
 instance_t CUuniqInstance=0;
 
+// NTN cellSpecificKoffset-r17, but in slots for DL SCS
+unsigned int NTN_UE_Koffset = 0;
+
 void nr_derive_key_ng_ran_star(uint16_t pci, uint64_t nr_arfcn_dl, const uint8_t key[32], uint8_t *key_ng_ran_star)
 {
 }
diff --git a/openair1/SIMULATION/NR_PHY/ulsim.c b/openair1/SIMULATION/NR_PHY/ulsim.c
index 822153fd14..e0cf501e96 100644
--- a/openair1/SIMULATION/NR_PHY/ulsim.c
+++ b/openair1/SIMULATION/NR_PHY/ulsim.c
@@ -93,6 +93,9 @@ nfapi_ue_release_request_body_t release_rntis;
 instance_t DUuniqInstance=0;
 instance_t CUuniqInstance=0;
 
+// NTN cellSpecificKoffset-r17, but in slots for DL SCS
+unsigned int NTN_UE_Koffset = 0;
+
 void nr_derive_key_ng_ran_star(uint16_t pci, uint64_t nr_arfcn_dl, const uint8_t key[32], uint8_t *key_ng_ran_star)
 {
 }