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Commit 4cfba89e authored by Guido Casati's avatar Guido Casati :speech_balloon:
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Updated and enhanced channel simulation documentation 

- centralized channel simulation documentation in channel_simulation.md
- removed redundant documentation repeated in multipled .md files
- updated links
- removed obsolete information
- introduced mermaid flowchart for rfsim
- added missing information about available options and usage
- deleted:    ../../../openair1/SIMULATION/TOOLS/DOC/devusage.md
- deleted:    ../../../openair1/SIMULATION/TOOLS/DOC/rtusage.md
- deleted:    ../../../openair1/SIMULATION/TOOLS/DOC/arch.md

related to issue #739
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2 merge requests!2593Integration: 2024.w09,!2576RFSIM: cleanup and documentation
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common/utils/telnetsrv/DOC/telnetarch.md
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......@@ -21,11 +21,11 @@ The telnet server provides an API which can be used by any oai component to add
telnet server source files are located in [common/utils/telnetsrv](https://gitlab.eurecom.fr/oai/openairinterface5g/tree/develop/common/utils/telnetsrv)
1. [telnetsrv.c](https://gitlab.eurecom.fr/oai/openairinterface5g/tree/develop/common/utils/telnetsrv/telnetsrv.c) contains the telnet server implementation, including the implementation of the `telnet` CLI command. This implementation is compatible with all softmodem executables and is in charge of loading any additional `libtelnetsrv_<app> .so` containing code specific to the running executables.
1. [telnetsrv.h](https://gitlab.eurecom.fr/oai/openairinterface5g/tree/develop/common/utils/telnetsrv/telnetsrv.h) is the telnet server include file containing both private and public data type definitions. It also contains API prototypes for functions that are used to register a new command in the server.
1. [telnetsrv.c](../telnetsrv.c) contains the telnet server implementation, including the implementation of the `telnet` CLI command. This implementation is compatible with all softmodem executables and is in charge of loading any additional `libtelnetsrv_<app> .so` containing code specific to the running executables.
1. [telnetsrv.h](../telnetsrv.h) is the telnet server include file containing both private and public data type definitions. It also contains API prototypes for functions that are used to register a new command in the server.
1. `telnetsrv_<XXX\>.c`: implementation of \<XXX\> CLI command which are delivered with the telnet server and are common to all softmodem executables.
1. `telnetsrv_<XXX\>.h`: include file for the implementation of XXX CLI command. Usually included only in the corresponding `.c`file
1. `telnetsrv_<app>_<XXX>.c`: implementation of \<XXX\> CLI command specific to the executable identified by \<app\>.These sources are used to create `libtelnetsrv_<app>.so` at build time.
1. [telnetsrv_CMakeLists.txt](https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/common/utils/telnetsrv/telnetsrv_CMakeLists.txt): CMakelists file containing the cmake instructions to build the telnet server. this file is included in the [global oai CMakelists](https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/cmake_targets/CMakeLists.txt).
1. [telnetsrv_CMakeLists.txt](../CMakeLists.txt): CMakelists file containing the cmake instructions to build the telnet server. this file is included in the [global oai CMakelists](../../../../cmake_targets/CMakeLists.txt).
[oai telnet server home](telnetsrv.md)
common/utils/telnetsrv/DOC/telnetusage.md
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* [measur command](telnetmeasur.md)
# telnet server parameters
The telnet server is using the [oai configuration module](Config/Rtusage). Telnet parameters must be specified in the `telnetsrv` section. Some parameters can be modified via the telnet telnet server command, as specified in the last column of the following table.
The telnet server is using the [oai configuration module](../../../../common/config/DOC/config/rtusage.md). Telnet parameters must be specified in the `telnetsrv` section. Some parameters can be modified via the telnet telnet server command, as specified in the last column of the following table.
| name | type | default | description | dynamic |
|:---:|:---:|:---:|:----|:----:|
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doc/README.md
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- [How to run a 5G-NSA setup](./TESTING_GNB_W_COTS_UE.md)
- [How to run a 4G setup using L1 simulator](./L1SIM.md) _Note: we recommend the RFsimulator_
- [How to use the L2 simulator](./L2NFAPI.md)
- [How to use the OAI channel simulator](../openair1/SIMULATION/TOOLS/DOC/channel_simulation.md)
- [How to use multiple BWPs](./RUN_NR_multiple_BWPs.md)
- [How to run OAI-VNF and OAI-PNF](./RUN_NR_NFAPI.md) _Note: does not work currently_
- [How to use the positioning reference signal (PRS)](./RUN_NR_PRS.md)
......
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# Channel simulation source files
1. [random_channel.c](../random_channel.c)
1. [sim.h](../sim.h)
[channel simulation main page](channel_simulation.md)
[oai Wikis home](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/home)
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[[_TOC_]]
# OAI channel simulation feature
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
OpenAirInterface RFSimulator incorporates a channel simulation feature. This feature allows any component to modify the time domain samples of a RF channel. It achieves this by applying predefined models, such as those defined in 3GPP TR 36.873 or TR 38.901.
The definition, configuration, and real-time modification of a channel model are implemented in a common code. This code is included in UE, gNB and eNB. It is utilized when operating with the RFSimulator or the L1 simulator. PHY simulators also employ channel simulation, but their configuration is accomplished via dedicated command-line options.
The RFSimulator is the exclusive option that provides access to all the configuration and real-time modification features of OAI's channel simulation. This makes it a comprehensive tool for managing and manipulating channel simulations in OAI.
# Implementation
OAI channel simulation is using the [config module](../../../../common/config/DOC/config.md) to get its parameters at init time. The [telnet server](../../../../common/utils/telnetsrv/DOC/telnetsrv.md) includes a set of commands which can be used to dynamically modify some channel model parameters.
The relevant source files are:
1. [`radio/rfsimulator/simulator.c`](../../../../radio/rfsimulator/simulator.c)
2. [`radio/rfsimulator/apply_channelmod.c`](../../../../radio/rfsimulator/apply_channelmod.c)
3. [`random_channel.c`](../random_channel.c)
4. [`sim.h`](../sim.h)
All channel parameters are set depending on the model name via a call to:
```bash
channel_desc_t *new_channel_desc_scm(uint8_t nb_tx,
uint8_t nb_rx,
SCM_t channel_model,
double sampling_rate,
uint64_t center_freq,
double channel_bandwidth,
double DS_TDL,
double maxDoppler,
const corr_level_t corr_level,
double forgetting_factor,
int32_t channel_offset,
double path_loss_dB,
float noise_power_dB);
```
# Channel Model configuration file
To define and use a channel model for uplink, the gNB configuration file needs to include a channel configuration file. To do this, add `@include "channelmod_rfsimu.conf"` at the end of the gNB configuration file, and place the channel configuration file in the same directory. The same shall be done for downlink by including the channel model configuration file at the end of UE configuration file (e.g. [`ci-scripts/conf_files/nrue.uicc.conf`](../../../../ci-scripts/conf_files/nrue.uicc.conf)).
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. An example of the configuration file can be found here:
* [`ci-scripts/conf_files/channelmod_rfsimu.conf`](../../../../ci-scripts/conf_files/channelmod_rfsimu.conf)
e.g.:
```bash
channelmod = {
max_chan = 10;
modellist = "modellist_rfsimu_1";
modellist_rfsimu_1 = (
{
model_name = "rfsimu_channel_enB0"
type = "AWGN";
ploss_dB = 20;
noise_power_dB = -4;
forgetfact = 0;
offset = 0;
ds_tdl = 0;
},
{
model_name = "rfsimu_channel_ue0"
type = "AWGN";
ploss_dB = 20;
noise_power_dB = -2;
forgetfact = 0;
offset = 0;
ds_tdl = 0;
}
);
};
```
where `rfsimu_channel_ue0` will be activated on server side (i.e. eNB/gNB) for uplink and `rfsimu_channel_enB0` will be activated on client side (i.e. UE) for downlink.
# Run OAI with a channel model
When the `chanmod` option is enabled, the RF channel simulator with a channel modeling function is called. Add the following options to the command line to enable the channel model:
```bash
--rfsimulator.options chanmod
```
Example run of OAI RFSIM on the same machine with activation of the channel model via command line:
gNB:
```bash
sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band78.fr1.106PRB.usrpb210.conf --gNBs.[0].min_rxtxtime 6 --rfsim --sa --rfsimulator.options chanmod --telnetsrv
```
UE:
```bash
sudo ./nr-uesoftmodem -r 106 --numerology 1 --band 78 -C 3619200000 --rfsim --sa --rfsimulator.serveraddr 127.0.0.1 --uicc0.imsi 001010000000001 -O ../../../ci-scripts/conf_files/nrue.uicc.conf --rfsimulator.options chanmod
```
where `@include "channelmod_rfsimu.conf"` has been added at the end of `ci-scripts/conf_files/channelmod_rfsimu.conf` which has been copied to `targets/PROJECTS/GENERIC-LTE-EPC/CONF/`.
## Set channel simulation parameters via CL:
Channel simulation parameters can also be specified on the command line by using the `--channelmod` option:
### Global parameters
| CL option |type |default | description |
|:--- |:---- |:---- |:----|
|`modellist` |char string |`DefaultChannelList`|select and load the `modellist` from the config file.|
|`max_chan` |integer |10 |set the maximum number of channel models that can be defined in the system. Must be greater than the number of model definitions in the model list loaded at init time.|
Example usage:
```bash
--channelmod.modellist modellist_rfsimu_2
```
### Model lists
Several model lists can be defined in the OAI channel simulation 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` |char string | mandatory |name of the model, as used in the code to retrieve a model definition.|
| `type` |char string | `AWGN` |name of the channel modelization algorithm applied on RF signal. The list of available models is defined in [`sim.h`](../sim.h]|
| `ploss_dB` |real (float) | 0|total path loss of the channel including shadow fading, in dB |
| `noise_power_dB`|real (double)| -50|Noise power in dB, used to compute the SNR. Its value is proportional to the noise added.|
| `forgetfact` |real (double)| 0|Forgetting factor, allows for simple 1st order temporal variation. 0 means a new channel every call, 1 means keep channel constant all the time|
| `offset` |integer | 0|channel offset for accessing the input signal, in samples|
| `ds_tdl` |real double | 0|delay spread for TDL models|
`ploss_dB` and `noise_power_dB` are applied to each IQ sample in order to scale the received signal.
Example usage, set the offset for the selected model of the selected `modellist`:
```bash
--channelmod.<modellist>.[<model ID>].offset
```
e.g. with the softmodem:
```bash
sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-NR-5GC/CONF/gnb.sa.band78.fr1.106PRB.usrpb210.conf --gNBs.[0].min_rxtxtime 6 --rfsim --sa --rfsimulator.options chanmod --telnetsrv --channelmod.modellist modellist_rfsimu_2 --channelmod.modellist_rfsimu_2.[1].offset 120
```
## Real time control and monitoring with telnet server
Add the `--telnetsrv` option to the command line. Then in a new shell, connect to the telnet server, e.g.:
```bash
$ telnet 127.0.0.1 9090
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'
```
to enter the command and control of the simulator press any key: `softmodem_enb` will be displayed for the eNB/gNB and `softmodem_5Gue` will be displayed for the UE. Select a different port in order to use both servers on the same machine.
The telnet server includes two modules to change the RF channel simulation in real-time:
1. `channelmod` to dynamically modify the channel model configuration parameters
2. `rfsimu` to set a different channel model
They both have their own help:
```bash
softmodem_enb> help
.....................................
module 4 = channelmod:
channelmod help
channelmod show <predef,current>
channelmod modify <channelid> <param> <value>
channelmod show params <channelid> <param> <value>
module 5 = rfsimu:
rfsimu setmodel <model name> <model type>
rfsimu setdistance <model name> <distance>
rfsimu getdistance <model name>
rfsimu vtime
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>
```
### channelmod module
Example usage:
| Command |Description |
|:--- |:---- |
|`channelmod show current` |Monitor the current status |
|`channelmod show predef` |See the available channel modelss|
|`channelmod modify <channelid> <param> <value>`|Set parameters specific to the channel model, e.g. pathloss, Ricean factor|
Where `<param>` in the `channelmod modify` command can be:
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.
|Parameter |Type |Range |Description |
|:--- |:---: |:---: |:---- |
|`riceanf` |double|0 to 1 |Ricean factor, of first tap w.r.t. other taps (where 0 means AWGN and 1 means Rayleigh channel)|
|`aoa` |double|0 to 2*Pi|Angle of arrival of wavefront (in radians). For Ricean channel only. This assumes that both RX and TX have linear antenna arrays with lambda/2 antenna spacing. Also it is assumed that the arrays are parallel to each other and that they are far enough apart so that we can safely assume plane wave propagation. |
|`randaoa` |bool |0 or 1 |randomized angle of arrival according to a uniform random distribution|
|`ploss` |double|- |same as ploss_dB in [Model lists](#model-lists)|
|`noise_power_dB`|int |- |same as noise_power_dB in [Model lists](#model-lists)|
|`forgetf` |double|0 to 1 |same as forgetfact in [Model lists](#model-lists)|
## Documentation
Example usage:
```bash
channelmod modify 0 ploss 12
channelmod modify 0 noise_power_dB 3
```
* [runtime usage](rtusage.md)
* [developer usage](devusage.md)
* [module architecture](arch.md)
### rfsimu module
This module can be used to set a different channel model, e.g. `rfsimu setmodel AWGN`.
[oai Wikis home](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/home)
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### channel simulation developer usage
[Configuring the channel simulation](rtusage.md)
[channel simulation main page](channel_simulation.md)
[oai Wikis home](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/home)
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## configuring the 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:
```bash
./lte-softmodem -O ../../../ci-scripts/conf_files/enb.band7.tm1.50prb.usrpb210.conf --noS1 --rfsim --rfsimulator.options chanmod --rfsimulator.serveraddr enb --telnetsrv --channelmod.modellist modellist_rfsimu_2 --channelmod.modellist_rfsimu_2.[1].offset 120
```
### 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](../../../../radio/rfsimulator/README.md ) has also some specific information when using the channel simulation via this tool.
[channel simulation main page](channel_simulation.md)
[oai Wikis home](https://gitlab.eurecom.fr/oai/openairinterface5g/wikis/home)
radio/rfsimulator/README.md
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......@@ -12,6 +12,29 @@ As much as possible, it works like an RF board, but not in real-time: It can
run faster than real-time if there is enough CPU, or slower (it is CPU-bound
instead of real-time RF sampling-bound).
# Architecture
High-level flowchart of the RF Simulator, including the channel simulation feature:
```mermaid
flowchart TD
subgraph ide1 [RX]
RU[ru_thread]-->|FH southbound|FH[rx_rf]
FH-->read
read -->|apply channel model|rxAddInput
end
subgraph ide2 [RFSim initialization]
A[load_lib] -->|load RFSIM lib| B[device_init]
B[device_init] -.-> |set trx_read_func|read[rfsimulator_read]
rxAddInput --> FH
B -->cfg[rfsimulator_readconfig]
cfg -->|read RFSIM CL options|C{rfsimu_params}
C -->|chanmod|loadchannel[load_channellist]
C -->|saviq|E[saveIQfile]
loadchannel-->|new SCM|scm[new_channel_desc_scm]
end
```
# Build
## From [build_oai](../../../doc/BUILD.md) script
......@@ -44,46 +67,19 @@ default the RF simulator device will try to connect to host 127.0.0.1, port
have to pass `--rfsimulator.serveraddr server` on the command line, or specify
the corresponding section in the configuration file.
The RF simulator is using the configuration module, and its parameters are defined in a specific section called "rfsimulator".
| parameter | usage | default |
|:---------------------|:------------------------------------------------------------------------------------------------------------------|----:|
| serveraddr | ip address to connect to, or `server` to behave as a tcp server | 127.0.0.1 |
| serverport | port number to connect to or to listen on (eNB, which behaves as a tcp server) | 4043 |
| options | list of comma separated run-time options, two are supported: `chanmod` to enable channel modeling and `saviq` to write transmitted iqs to a file | all options disabled |
| modelname | Name of the channel model to apply on received iqs when the `chanmod` option is enabled | AWGN |
| IQfile | Path to the file to be used to store iqs, when the `saviq` option is enabled | /tmp/rfsimulator.iqs |
The RF simulator is using the configuration module, and its parameters are defined in a specific section called "rfsimulator". Add the following options to the command line in order to enable different RFSim features:
## How to use the RF simulator options
| CL option | usage | default |
|:--------------------- |:-------------------------------------------------------------------------------|----: |
|`--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 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.wait_timeout` | wait timeout when no UE is connected | 1 |
To define and use a channel model, the configuration file needs to include a
channel configuration file. To do this, add `@include "channelmod_rfsimu.conf"`
to the end of the configuration file, and place the channel configuration file
in the same directory. An example channel configuration file is
[`ci-scripts/conf_files/channelmod_rfsimu.conf`](../../ci-scripts/conf_files/channelmod_rfsimu.conf).
Add the following options to the command line to enable the channel model and the IQ samples saving for future replay:
```bash
--rfsimulator.options chanmod,saviq
```
or just:
```bash
--rfsimulator.options chanmod
```
to enable the channel model.
set the model with:
```bash
--rfsimulator.modelname AWGN
```
Example run:
```bash
sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-LTE-EPC/CONF/gnb.band78.tm1.106PRB.usrpn300.conf --parallel-config PARALLEL_SINGLE_THREAD --rfsim --phy-test --rfsimulator.options chanmod --rfsimulator.modelname AWGN
```
where `@include "channelmod_rfsimu.conf"` has been added at the end of the file, and `ci-scripts/conf_files/channelmod_rfsimu.conf` copied to `targets/PROJECTS/GENERIC-LTE-EPC/CONF/`.
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.
## 4G case
......@@ -133,9 +129,9 @@ sudo ./nr-uesoftmodem --rfsim --phy-test --rfsimulator.serveraddr <TARGET_GNB_IP
Notes:
1. This starts the gNB and UE in the `phy-test` UP-only mode where the gNB is started as if a UE had already connected. See [RUNMODEM.md](../../doc/RUNMODEM.md) for more details.
1. This starts the gNB and UE in the `phy-test` UP-only mode where the gNB is started as if a UE had already connected. See [`RUNMODEM.md`](../../doc/RUNMODEM.md) for more details.
2. `<TARGET_GNB_IP_ADDRESS>` should be the IP interface address of the remote host running the gNB executable, if the gNB and nrUE run on separate hosts, or be omitted if they are on the same host.
3. To enable the noS1 mode, `--noS1` option should be added to the command line, see again [RUNMODEM.md](../../doc/RUNMODEM.md).
3. To enable the noS1 mode, `--noS1` option should be added to the command line, see again [`RUNMODEM.md`](../../doc/RUNMODEM.md).
4. To operate the gNB/UE with a 5GC, start them using the `--sa` option. More information can be found [here](../../../doc/NR_SA_Tutorial_OAI_CN5G.md).
## Store and replay
......@@ -152,65 +148,9 @@ The file format is successive blocks of a header followed by the I/Q array. If y
The format intends to be compatible with the OAI store/replay feature on USRP.
## Channel simulation
When the `chanmod` option is enabled, the RF channel simulator is called.
In the current version all channel parameters are set depending on the model name via a call to:
```bash
new_channel_desc_scm(bridge->tx_num_channels,
bridge->rx_num_channels,
<model name>,
bridge->sample_rate,
bridge->tx_bw,
0.0, // forgetting_factor
0, // maybe used for TA
0); // path_loss in dB
```
Only the input noise can be changed on command line with the `-s` parameter.
With path loss = 0 set `-s 5` to see a little noise. `-s` is a shortcut to `channelmod.s`. It is expected to enhance the channel modelization flexibility by the addition of more parameters in the channelmod section.
## How to use OAI RFSIM with a channel model
Example to add a very small noise:
```bash
-s 30
```
to add a lot of noise:
```bash
-s 5
```
Example run commands:
```bash
sudo ./nr-softmodem -O ../../../targets/PROJECTS/GENERIC-LTE-EPC/CONF/gnb.band78.tm1.106PRB.usrpn300.conf --parallel-config PARALLEL_SINGLE_THREAD --rfsim --phy-test --rfsimulator.options chanmod --rfsimulator.modelname AWGN
```
# Real time control and monitoring
Add the `--telnetsrv` option to the command line. Then in a new shell, connect to the telnet server, example:
```bash
telnet 127.0.0.1 9090
```
once connected it is possible to monitor the current status:
```bash
channelmod show current
```
see the available channel models:
```bash
channelmod show predef
```
or modify the channel model, for example setting a new model:
```bash
rfsimu setmodel AWGN
```
setting the pathloss, etc...:
```bash
channelmod modify <channelid> <param> <value>
channelmod modify 0 ploss 15
```
where `<param>` can be one of `riceanf`, `aoa`, `randaoa`, `ploss`, `offset`, `forgetf`.
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.
# Caveats
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