[srsran-users] Channel state information in TDD

[Mehdi]

Dear all,

I am working on TDD-LTE, using SRS-UE and OAI-eNB. For my research project,
I require the channel state information values (CSIs) which are estimated
at eNB and UE. But I am observing an abnormal behavior that the channel
estimations obtained at the two sides are very different! (I am working on
TDD config. 1, while I select the estimated values with the same frame
number and adjacent subframes 8 and 9 for UL/DL)  Specifically, the channel
estimations at eNB are very different from the values at UE. That is, the
eNB shows much bigger absolute values than that of the UE. This seems to be
in contradiction with the main principles of UL-DL reciprocity in a static
environment. The values which are reported from OAI-eNB do not even follow
the same trend with the channel estimation values reported by SRS-UE!!!

FYI, I am examining ul_ch_estimates as the channel estimations at eNB
<https://gitlab.eurecom.fr/oai/openairinterface5g/-/blob/v1.0.3/openair1/PHY/LTE_ESTIMATION/lte_ul_channel_estimation.c>
side
and ue_dl.chest_res.ce as the channel estimations at UE
<https://github.com/srsran/srsRAN/blob/master/lib/src/phy/ch_estimation/chest_dl.c>.
The corresponding data I get, together with some initial plots of the
values are attached to this email.


This is very critical for my project to find possible reasons for such
surprising behavior. So, I appreciate the community letting me know if
anyone has had any similar experience on inspecting the channel estimations.

Thanks,

Mehdi
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