[srslte-users] Pi 4 srsLTE

[Kenneth Barlee]

Hey guys

I have been having a play with a Pi 4B /4GB rev 1.2 running the new 
Ubuntu Pi Server 20.04 x64 image, and trying to get srsLTE working. I 
know several others have been talking about trying this, but haven't 
noticed my issue coming up elsewhere.

I started with the latest versions of UHD, SoapySDR, LimeSuite, srsLTE 
(commit ID e3e38482100f5bf13f15af3bc09df882e937bc60). Everything 
compiles happily (no need to change those lines in CMakeLists.txt), and 
the srsenb/srsepc software runs successfully (after an initial wait of 
~5 mins after first launch for any change in n_prb). However, no phone 
is able to fully connect when using a USRP B210/ LimeSDR-USB/ 
LimeSDR-Mini. It seems to start the attach, and there is a core 
handshake, but the core reports that the "UE is not ECM connected" and 
the UE never shows the signal bars.

Decided to roll the Pi back to srsLTE v19.12, commit ID 
d045213fb9cbf98c83c06d7c17197a9dcbfddacf, as I have been running this on 
my desktop for a while now, and know it is stable. Again, this compiles 
without issue. With this version, a phone will join a USRP B210 (not the 
LimeSDRs, but that is probably another issue). It seems relatively 
stable, and can continue running for several hours with a phone attached 
running internet ping tests.

I have attached logs and PCAPs for the two setups.

A potentially related sidenote, with both srsenb versions, and all 
radios, "SCHED: Could not transmit RAR within the window (RA TTI=2591, 
Window=10, Now=2608)" type messages appear repeatedly in the terminal. 
Running cellmapper on the phone, the LTE timing advance is estimated to 
be '~250m' when using the USRP, but over '3.5km' with the LimeSDRs. This 
is likely one of the reasons the LimeSDRs do not work with srsLTE v19.12.

For reference, the UE used was a Samsung S20 Ultra 5G; LTE B3 earfcn 
1934, n_prb=15, SISO tm=1 nof_ports = 1.

Has anybody experienced similar? Happy to do more testing if it helps 
with debugging!

Thanks


Kenny Barlee | Research Associate
Software Defined Radio Research Laboratory
Department of Electronic and Electrical Engineering
University of Strathclyde
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