[LENA] Link layer losses reason?

[Xing Xu]

Dear all,

I have a high-level question about link layer retx. In general, I want to know the root cause of link layer losses (which leads to retx), is it due to CQI is not good, or CQI is OK but my packet unfortunately collide with some interfering packet?

In my experiment, when using AM mode, I found that inter-cell interference can lead to a lot of link layer retx at DL (I know this from printed log information at lte-rlc-am.cc). I wonder whether this is normal? As I thought because there is inter-cell interference, CQI would be lower and it should make the AMC chooses a modulation that would not generate so many losses, which wastes bandwidth resources.

Another question is, in my experiment, I think this packet loss at DL is due to UL packet of neighboring base stations. So, please correct my below statement, I think when I'm sending my DL packet, if at the same time, there is an UL packet to my neighboring base station, my packet would be interfered and dropped; however, if my packet was not colliding with neighboring base station's UL packet, it would not be dropped. I also wonder whether such "collide or not" will be reflected by CQI report?

Details about my experiment:

I'm using ns3::FriisPropagationLossModel which has a pretty obvious backlobe effect, so UEs of neighboring base station but sits within that backlobe would generate severe interference to UEs of my focused base station.

Thanks,

Xing