[srslte-users] Cell ports, downlink decoding

[Merlin Chlosta]

Hi all,

for testing purposes I'd like to observe network entry procedures in downlink, starting from Random Access Response until Security Mode Command. I use data processing from the pdsch_ue example, but modified it to listen to the correct RA-RNTI and C-RNTI. UE talks to eNB, srsLTE listens in downlink.

This works on some cells, and I can observe the regular net entry in downlink, i.e. RAR, RRC Connection Setup / Reject, NAS Auth request and Security Mode Command and following encrypted traffic.

On other cells however, this fails. I can observe RAR, RRC Connection Setup and some Timing Advance commands. But most other DL-SCH packets that I expect are missing. I've had a look if srsLTE detects any DCI, but fails to decode the data. That does not seem to be the case, I do not get many failed pdsch_decodes.

One difference in cell configuration is nof_ports. It seems to work with nof_ports=1, and misses lot's of data with nof_ports=2. I'm using srsLTE @ 12603e4da258e180a5dbb98dc906fccf2273e71f from August 2nd. Since I have not fully understood the concept of those ports, and there has been a lot of progress on srsLTE with recent release, I'd like to ask if the number of ports could make srsLTE miss DCI information. Or if you have sth. else in mind why I'm missing packets in DL-SCH, after RRC Connection Setup passed through.

I'm new to both LTE and srsLTE; maybe I've understood sth. fundamentally wrong about this low-level data detection and decoding. Looking forward to any comments on this.

Thank you.
Merlin Chlosta