oai includes a channel simulation feature that any component can use to alter time domain samples of a RF channel by applying pre-defined models as defined, for example, in 3GPP TR 36.873 or TR 38.901
Definition, configuration and run-time modification of a channel model are implemented in common code included in UEs, gNb, eNB and used when running with the rfsimulator or the L1 simulator. Phy simulators are also using channel simulation but configuration is done via dedicated command line options. The rfsimulator is the only option to get access to all the configurations and run-time modifications features of oai channel simulation.
Oai channel simulation is using the [config module](../../../config/config.md) to get its parameters at init time. The [telnet server](../../telnetsrv/DOC/telnetsrv.md) includes a set of commands which can be used to dynamically modify some channel model parameters
All channel simulation parameters are defined in the `channelmod` section. Most parameters are specific to a channel model and are only used by the rfsimulator.
### global parameters
| name | type | default | description |
|:---:|:---:|:---:|:----|
| `max_chan` | integer | `25` | Maximum number of channel model that can be defined in the system. Must be greater than the number of model definitions in the model list loaded at init time. |
| `modellist` | character string | `DefaultChannelList` | Name of the channel models list to load at init time. |
### Model lists
Several model lists can be defined in the oai configuration file. One, defined by the `modellist` parameter is loaded at init time. In the configuration file each model list item describes a channel model using a group of parameters:
| parameter name | type | default | description |
|:---:|:---:|:---:|:----|
| `model name` | character string | mandatory |name of the model, as used in the code to retrieve a model definition|
| `type` | | `AWGN` | name of the channel modelization algorithm applied on rf signal. The list of available model types can be listed via the [telnet server](../../telnetsrv/DOC/telnetsrv.md) or by entering an invalid type name |
| `ploss_dB` | real (float) | | path loss of the channel, in dB |
| `noise_power_dB` | real (double) | | noise of the channel in dB |
| `forgetfact` | real (double) | | |
| `offset` | integer | | |
| `ds_tdl` | real double | | |
Channel simulation parameters can also be specified on the command line:
### Using the telnet server to modify channel simulator parameters
The telnet server includes a `channelmod` command which can be used to dynamically modify some channel model parameters. This command is only available when channel simulation is enabled (via `rfsimulator.options chanmod` option when running the rfsimulator. `channelmod` command has its own help:
```
$ telnet 127.0.0.1 9090
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
softmodem_enb> help
.....................................
module 6 = channelmod:
channelmod help
channelmod show <predef,current>
channelmod modify <channelid> <param> <value>
module 7 = rfsimu:
rfsimu setmodel <model name> <model type>
softmodem_enb> channelmod help
channelmod commands can be used to display or modify channel models parameters
channelmod show predef: display predefined model algorithms available in oai
channelmod show current: display the currently used models in the running executable
channelmod modify <model index> <param name> <param value>: set the specified parameters in a current model to the given value
<model index> specifies the model, the show current model command can be used to list the current models indexes
<param name> can be one of "riceanf", "aoa", "randaoa", "ploss", "noise_power_dB", "offset", "forgetf"
softmodem_enb>
```
The [rfsimulator documentation](../../../../targets/ARCH/rfsimulator/README.md) has also some specific information when using the channel simulation via this tool.
[channel simulation main page](channel_simulation.md)
AssertFatal((channeldesc_p!=NULL),"Could not allocate channel %s type %s \n",*(channelmod_params[pindex_NAME].strptr),*(channelmod_params[pindex_TYPE].strptr));
