SRSue Large Number of HARQ NACKs in Presence of Other UEs

[davidlwhite]

Issue Description

I am seeing SRSue receive an unusually large number of HARQ NACKs from the eNB whenever a commercial UE is attached and actively transmitting/receiving on the same cell...

I ran tests with two different commercial UEs (a Pixel4 and a OnePlus N200) with similar results.

Is this a known issue / limitation? Any ideas how to fix/get around this?

Setup Details

I used the latest in the master branch (commit sha: eea87b1d893ae58e0b08bc381730c502024ae71f). SRSue is running on Ubuntu 22.04.3 LTS, using a USRP B210, and UHD_4.1.0.5-3. eNB is a commercial eNB. Other details are in the logs attached.

Expected Behavior

Few to no MAC NACKs.

Actual Behaviour

Large number of HARQ NACKs from eNB to SRSue.

Steps to reproduce the problem

• I used the latest in the master branch (commit sha: eea87b1d893ae58e0b08bc381730c502024ae71f)
• Attach the commercial UE to commercial eNB, get UE's IP.
• Ping commercial UE.
• Run SRSue, attach and get its IP.
• Ping SRSue.
• Watch NACK count in ue.log rack up.

Additional Information

Attached are two sets of debug level logs and pcap files:

• oneUE_lotsOfNACKs: Setup as above, shows issue. Grepping for keyword "Adapt" (printed whenever a NACK is received) shows 13345 NACKs.

>> grep -c "Adapt" oneUE_lotsOfNACKs/ue.log
13345

• noUEs_noNACKs: Similar setup as above, but commercial UE is kept in Airplane mode. Grepping for keyword "Adapt" shows 0 NACKs.

>> grep -c "Adapt" noUEs_noNACKs/ue.log
0

  SRSue config file is also attached.

noUEs_noNACKs.tar.gz oneUE_lotsOfNACKs.tar.gz