the spectrum bandwidth of the Transmitted 4G signal in embms mode is significantly larger

[nenad38111]

Issue Description

The spectrum is definitely wider in this mode comparing to a 'non-embms' mode. For PRB=15 (3MHz), the spectrum in embms mode is about 1-1.5MHz wider.

Have this setup and is basically working, but the shape of the spectrum 'outside the desired bandwidth' (in my case 3MHz) is not what I expected, especially as it looks normal in non-embms mode.

Setup Details

srsmbms srsepc srsenb srsue B210 (TX) ------------------- B210 (RX) UHD driver 3.15LTS ubuntu 22.04 source code compiled for srsran_4G

All the config files matching those outlined here: https://docs.srsran.com/projects/4g/en/latest/app_notes/source/embms/source/index.html

Expected Behavior

Spectrum to be the same bandwidth in non embms as in the embms mode.

Actual Behaviour

Spectrum in embms mode has significantly higher side lobes causing the BW of the spectrum to be much wider.

Steps to reproduce the problem

Just follow the instructions on the https://docs.srsran.com/projects/4g/en/latest/app_notes/source/embms/source/index.html

Additional Information

Have tried with B210, but also BladeRF. It is about the same.

[yagoda]

Hi,

The reference signals are significantly different in eMBMS, they span the entire band whereas the cell reference signals in unicast are more sparse, try full traffic in both modes and compare the spectrum mask in that scenario.

Regards, Justin.

[nenad38111]

Not sure if this picture is going to show up, but in non embms mode, the spectrum is well contained in 3MHz

yellow trace - embms, blue trace embms (max hold) green trace - non embms, red trace non embms (max hold).

[yagoda]

Can you please share the logs & terminal output of the enb for both embms and non-embms mode?

[nenad38111]

Yes of course....and thank you for looking into this.

enb_embms_enabled.log enb_no_embms.log terminal_log_embms_enabled.txt terminal_log_no_embms.txt

[nenad38111]

One more picture.... I have tried everything I could think off, but it is always the same thing...in embms mode the spectrum is significantly wider than it should be.

[nenad38111]

I don't know if related, but eMBMS (for 4G) is not working for PRB=6. It does work for other PRBs (15,25,50).

[nenad38111]

Is there any update on this? In embms mode the spectrum is definitely wider by about 20% and not contain within the specified bandwidth (say 3MHz or 5MHz). I think this is a bug when SIB13 is used.