Jaroslava Fiedlerova
e1a327ca4f
NR UE: add support for multiple RF frontends
This MR adds basic support for multiple RF-frontends at the UE.
There are multiple reasons why we might want this:
1. There might be different antennas needed for different bands (e.g. NTN or
TN antennas). These antennas might be connected to different RF-frontends.
In case of Handover, the UE needs to dynamically switch between these
RF-frontends.
2. Each rf-simulator connection carries baseband I/Q samples. To be able to
perform a handover between two cells at different frequencies, there must
be two rf-simulator connections, as the baseband channels should not
interfere and thus cannot simply be added.
3. When we want to support multiple UE simulation within one instance of
nr-uesoftmodem, and allow multiple cells and probably even handover between
these cells, we need either:
1. dedicated RF-frontends for each simulated UE, or
2. dedicated RF-frontends for each connected cell and dynamically assign
simulated UEs accordingly.
This MR implements what is needed for 1., 2. and 3.1.
Overview
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_channelto 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.
Usage
On the UE and gNB: use device.name vrtsim command line argument.
Additionally on gNB use vrtsim.role server and optionally
vrtsim.timescale <timescale> to set the timescale. Timescale 1.0
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 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.