[srsran-users] Channel state information in TDD

[Mehlhose, Matthias]

Hi Mehdi,


nice question.


Please take into account, that your channel is not only the wireless one from one antenna to another.


It's also all RF components, like cable, plugs, filters, splitters, switches, circulators, and amplifiers or attenuators.

-> All the things between your antennas and the RF Transceiver chip ADC/DAC.


In most cases, it will not be the same path! And therefore, you will not see the same channel, because each RF component will add an individual response.


I hope you find a way to calibrate and measure the hopefully static differences on TX and RX sides, for your project.


BR Matthias

________________________________
Von: srsran-users <srsran-users-bounces at lists.srsran.com> im Auftrag von Mehdi <studentatsharif at gmail.com>
Gesendet: Sonntag, 5. Dezember 2021 16:55:53
An: srsran-users at lists.srsran.com
Betreff: [srsran-users] Channel state information in TDD

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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