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Update vrtsim documentation

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This commit is contained in:
Bartosz Podrygajlo
2025-08-08 17:55:12 +02:00
parent ea3a4b991c
commit 74fc56813f
1 changed files with 75 additions and 5 deletions
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radio/vrtsim/README.md
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@@ -4,12 +4,24 @@ This implements a shared memory realtime and near-realtime radio interface.
This is performed using `shm_td_iq_channel` which handles the shared memory
interface.
# Architecture
The `vrtsim` architecture follows a server-client model:
- **Server (gNB)**: On startup, the server writes a file, default location is
`/tmp/vrtsim_connection`. This file contains information required by the client
to establish communication.
- **Client (UE)**: The client reads this file from, verifies its contents, and uses
the provided information to open and connect to the shared memory channel.
- **Shared Memory Channel**: Both server and client use the `shm_td_iq_channel` to
exchange IQ samples and control data in real time or near-real time.
## Channel modelling:
# Limitations
- Only 1gNB to 1nrUE: gNB as a server, UE as a client.
- Server only accepts connections during device bringup. This means that
restarting the client will not make it reconnect, the server has to be
restarted as well.
# Usage
@@ -21,5 +33,63 @@ is the default and means realtime.
Channel modelling can be enabled by adding `vrtsim.chanmod 1` to the
command line and should work the same as channel modelling in rfsimulator,
see rfsimulator [documentation](../rfsimulator/README.md), provided that your
CPU is fast enough.
see rfsimulator [documentation](../rfsimulator/README.md) with a slight difference:
channel modelling is done on transmission instead of reception. To refect this,
the model names are slightly different: the server expects a model named
`server_tx_channel_model` while the client expects a model named `client_tx_channel_model`
Additionally, `taps_client` is available in vrtsim. This allows to connect to
channel emulation server and receive external taps (or channel impulse responses).
To use external taps, use `--taps-socket` and provide a nanomsg PUB socket address
that will publish the taps.
# Debugging
## Realtime issues
Realtime issues can prevent the UE from connecting to the gNB, especially with
channel modelling enabled. Consider adjusting `timescale` parameter until
the UE can connect reliably.
On exit, vrtsim will output a histogram of the measured transmission budget, which
is defined as the number of microseconds before the transmitted samples could be
read by peer.
Example:
```
[HW] VRTSIM: Average TX budget 939.210 uS (more is better)
[HW] VRTSIM: TX budget histogram: 216 samples
[HW] Bin 0 [0.0 - 100.0uS]: 0
[HW] Bin 1 [100.0 - 200.0uS]: 0
[HW] Bin 2 [200.0 - 300.0uS]: 0
[HW] Bin 3 [300.0 - 400.0uS]: 0
[HW] Bin 4 [400.0 - 500.0uS]: 0
[HW] Bin 5 [500.0 - 600.0uS]: 0
[HW] Bin 6 [600.0 - 700.0uS]: 0
[HW] Bin 7 [700.0 - 800.0uS]: 0
[HW] Bin 8 [800.0 - 900.0uS]: 0
[HW] Bin 9 [900.0 - 1000.0uS]: 117
[HW] Bin 10 [1000.0 - 1100.0uS]: 0
[HW] Bin 11 [1100.0 - 1200.0uS]: 0
[HW] Bin 12 [1200.0 - 1300.0uS]: 0
[HW] Bin 13 [1300.0 - 1400.0uS]: 0
[HW] Bin 14 [1400.0 - 1500.0uS]: 0
[HW] Bin 15 [1500.0 - 1600.0uS]: 0
[HW] Bin 16 [1600.0 - 1700.0uS]: 0
[HW] Bin 17 [1700.0 - 1800.0uS]: 0
[HW] Bin 18 [1800.0 - 1900.0uS]: 0
[HW] Bin 19 [1900.0 - 2000.0uS]: 0
[HW] Bin 20 [2000.0 - 2100.0uS]: 0
[HW] Bin 21 [2100.0 - 2200.0uS]: 0
[HW] Bin 22 [2200.0 - 2300.0uS]: 0
[HW] Bin 23 [2300.0 - 2400.0uS]: 0
[HW] Bin 24 [2400.0 - 2500.0uS]: 0
[HW] Bin 25 [2500.0 - 2600.0uS]: 0
[HW] Bin 26 [2600.0 - 2700.0uS]: 0
[HW] Bin 27 [2700.0 - 2800.0uS]: 0
[HW] Bin 28 [2800.0 - 2900.0uS]: 0
[HW] Bin 29 [2900.0 - 3000.0uS]: 0
```
Samples in bin 0 indicate realtime issues.