rfsimulator: add support to simulate a long propagation delay

Add the option `--rfsimulator.prop_delay` to specify the simulated receive-path (gNB: UL, UE: DL) propagation delay in ms.
This option can be used e.g. to simulate a simple GEO satellite channel by specifying `--rfsimulator.prop_delay 238.74` to both, the gNB and the UE.

This is part of the work developed by Fraunhofer IIS within the ESA-funded project 5G-GOA (https://connectivity.esa.int/projects/5ggoa).

common/config/config_common.c

@@ -141,7 +141,7 @@ int config_setdefault_int64(configmodule_interface_t *cfg, paramdef_t *cfgoption
   config_check_valptr(cfg, cfgoptions, sizeof(*cfgoptions->i64ptr), 1);
 
   if (((cfgoptions->paramflags & PARAMFLAG_MANDATORY) == 0)) {
-    *(cfgoptions->u64ptr) = cfgoptions->defuintval;
+    *(cfgoptions->u64ptr) = cfgoptions->defint64val;
     status=1;
     printf_params(cfg,
                   "[CONFIG] %s.%s set to default value %llu\n",

openair1/SIMULATION/TOOLS/random_channel.c

@@ -76,7 +76,6 @@ static unsigned int max_chan;
 static channel_desc_t **defined_channels;
 static char *modellist_name;
 
-
 void fill_channel_desc(channel_desc_t *chan_desc,
                        uint8_t nb_tx,
                        uint8_t nb_rx,
@@ -92,9 +91,10 @@ void fill_channel_desc(channel_desc_t *chan_desc,
                        double aoa,
                        double forgetting_factor,
                        double max_Doppler,
-                       int32_t channel_offset,
+                       uint64_t channel_offset,
                        double path_loss_dB,
-                       uint8_t random_aoa) {
+                       uint8_t random_aoa)
+{
   uint16_t i,j;
   double delta_tau;
   LOG_I(OCM,"[CHANNEL] Getting new channel descriptor, nb_tx %d, nb_rx %d, nb_taps %d, channel_length %d\n",
@@ -568,7 +568,7 @@ channel_desc_t *new_channel_desc_scm(uint8_t nb_tx,
                                      double maxDoppler,
                                      const corr_level_t corr_level,
                                      double forgetting_factor,
-                                     int32_t channel_offset,
+                                     uint64_t channel_offset,
                                      double path_loss_dB,
                                      float noise_power_dB)
 {
@@ -2063,8 +2063,12 @@ static void display_channelmodel(channel_desc_t *cd,int debug, telnet_printfunc_
   prnt("nb_tx: %i    nb_rx: %i    taps: %i bandwidth: %lf    sampling: %lf\n",cd->nb_tx, cd->nb_rx, cd->nb_taps, cd->channel_bandwidth, cd->sampling_rate);
   prnt("channel length: %i    Max path delay: %lf   ricean fact.: %lf    angle of arrival: %lf (randomized:%s)\n",
        cd->channel_length, cd->Td, cd->ricean_factor, cd->aoa, (cd->random_aoa?"Yes":"No"));
-  prnt("max Doppler: %lf    path loss: %lf  noise: %lf rchannel offset: %i    forget factor; %lf\n",
-       cd->max_Doppler, cd->path_loss_dB, cd->noise_power_dB, cd->channel_offset, cd->forgetting_factor);
+  prnt("max Doppler: %lf    path loss: %lf  noise: %lf rchannel offset: %lu    forget factor; %lf\n",
+       cd->max_Doppler,
+       cd->path_loss_dB,
+       cd->noise_power_dB,
+       cd->channel_offset,
+       cd->forgetting_factor);
   prnt("Initial phase: %lf   nb_path: %i \n",
        cd->ip, cd->nb_paths);
 

openair1/SIMULATION/TOOLS/sim.h

@@ -101,7 +101,7 @@ typedef struct {
   ///path loss including shadow fading in dB
   double path_loss_dB;
   ///additional delay of channel in samples.
-  int32_t channel_offset;
+  uint64_t channel_offset;
   float noise_power_dB;
   ///This parameter (0...1) allows for simple 1st order temporal variation. 0 means a new channel every call, 1 means keep channel constant all the time
   double forgetting_factor;
@@ -307,7 +307,6 @@ typedef struct {
   double ru_amp[NUMBER_OF_RU_MAX];
 } sim_t;
 
-
 channel_desc_t *new_channel_desc_scm(uint8_t nb_tx,
                                      uint8_t nb_rx,
                                      SCM_t channel_model,
@@ -318,7 +317,7 @@ channel_desc_t *new_channel_desc_scm(uint8_t nb_tx,
                                      double maxDoppler,
                                      const corr_level_t corr_level,
                                      double forgetting_factor,
-                                     int32_t channel_offset,
+                                     uint64_t channel_offset,
                                      double path_loss_dB,
                                      float noise_power_dB);
 

radio/rfsimulator/README.md

@@ -73,10 +73,11 @@ The RF simulator is using the configuration module, and its parameters are defin
 |:---------------------           |:-------------------------------------------------------------------------------|----:                   |
 |`--rfsimulator.serveraddr <addr>`| ip address to connect to, or `server` to behave as a tcp server                | 127.0.0.1              |
 |`--rfsimulator.serverport <port>`| port number to connect to or to listen on (eNB, which behaves as a tcp server) | 4043                   |
-| `--rfsimulator.options`         | list of comma separated run-time options, two are supported: `chanmod`, `saviq`| all options disabled   |
-| `--rfsimulator.options saviq`   | store IQs to a file for future replay                                          | disabled               |
+|`--rfsimulator.options`          | list of comma separated run-time options, two are supported: `chanmod`, `saviq`| all options disabled   |
+|`--rfsimulator.options saviq`    | store IQs to a file for future replay                                          | disabled               |
 |`--rfsimulator.options chanmod`  | enable the channel model                                                       | disabled               |
 |`--rfsimulator.IQfile <file>`    | path to a file to store the IQ samples to (only with `saviq`)                  | `/tmp/rfsimulator.iqs` |
+|`--rfsimulator.prop_delay`       | simulated receive-path (gNB: UL, UE: DL) propagation delay in ms               | 0                      |
 |`--rfsimulator.wait_timeout`     | wait timeout when no UE is connected                                           | 1                      |
 
 Please refer to this document [`SIMULATION/TOOLS/DOC/channel_simulation.md`](../../openair1/SIMULATION/TOOLS/DOC/channel_simulation.md) for information about using the RFSimulator options to run the simulator with a channel model.
@@ -152,6 +153,24 @@ The format intends to be compatible with the OAI store/replay feature on USRP.
 
 Please refer to this document [`channel_simulation.md`](../../openair1/SIMULATION/TOOLS/DOC/channel_simulation.md) to get familiar with channel simulation in RFSIM and to see the list of commands for real-time usage with telnet.
 
+## How to simulate a simple GEO satellite channel model
+
+A simple channel model for satellites on a geostationary orbit (GEO) simulates simply one line-of-sight propagation channel.
+
+The most basic version is to simply simulate a constant propagation delay, without any other effects.
+
+In case of a transparent GEO satellite, the minumum one-way propagation delay (DL: gNB -> satellite -> UE, or UL: UE -> satellite -> gNB) is 238.74 ms.
+
+So, additionally to other parameters, this parameter should be given when executing the gNB and the UE executables:
+
+```
+--rfsimulator.prop_delay 238.74
+```
+
+Note:
+
+To successfully establish a connection with such a GEO satellite channel, both gNB and UE need to have the NTN support configured.
+
 # Caveats
 
 There are issues in power control: txgain/rxgain setting is not supported.