5G SA UE 5 MHz Bandwidth?

[Clay-Uhing-APL]

Issue Description

The appnote specifies that the 5G SA UE is limited to 10 MHz. Is it only able to support 10 MHz, or can it also support 5 MHz?

Setup Details

Changed working 10 MHz 5G SA gNB Amarisoft configuration to 5 MHz (To do this, I also had to change the n_rb_coreset0 to 24 and the n_symb_coreset0 to 2).

Expected Behavior

srsUE connects to 5 MHz 5G SA gNB

Actual Behaviour

running srsue ue.conf hangs on "Attaching UE..." srsue.log has line RRC-NR [E] Proc "Cell Selection" - Unsupported SSB offset 0 (Amarisoft shows that the SSB still has the same SSB ARFCN of 368410)

Steps to reproduce the problem

Run 5 MHz 5G SA gNB and try to attach srs 5G SA UE

[tecandrew]

wondering and seeing this error as well. Currently testing with a UHD B210 running for 5 Mhz. I had some luck running 10 MHz, but it struggles to keep up.

edit: "it", meaning the machine I'm working with.

[rfquickjr]

I found the error message in https://github.com/srsran/srsRAN/blob/master/srsue/src/stack/rrc_nr/rrc_nr_procedures.cc. The code is certainly interesting (this is the current master branch).

// Check unsupported settings if (mib.cell_barred) { Error("Cell barred"); return proc_outcome_t::error; } if (mib.scs_common != srsran_subcarrier_spacing_15kHz) { Error("Unsupported SCS %s", srsran_subcarrier_spacing_to_str(mib.scs_common)); return proc_outcome_t::error; } // TODO: calculate SSB offset if (mib.ssb_offset != 6) { Error("Unsupported SSB offset %d", mib.ssb_offset); return proc_outcome_t::error; }

The first error is the correct behavior for a barred cell. The second says (surprisingly) that srsUE doesn’t support 30 kHz common scs. The third says only kssb = 6 will work.

With 100 kHz channel spacing, I find no reference frequency that produces kssb = 6 with 15 kHz SSB scs. With 5 MHz bandwidth 30 kHz SSB scs would give only 11 PRBs, not enough to hold SSB (needs 20). Bands with 15 kHz channel raster don't seem to support 5 MHz bandwidth. Conclusion: 5 MHz bandwidth can’t work with the current configuration of srsUE.