Hi Experts,
We are currently working with an ORAN 7.2x and FlexRAN 23.07 setup, integrating a Benetel ORU (Category A).
The system is operating correctly with the default configuration:
dl.numTxAntennaPorts = 4
ul.numRxAntennaPorts = 2
numDlLayers = 2
numUlLayers = 1
With this configuration, the setup functions as expected. Upon reviewing the QXDM logs, we observe that the SIB1 message decoding is using 2x2 MIMO, while other messages are utilizing 4x4 MIMO.
We aim to explicitly verify and operate the setup in 2x2 MIMO mode across all signaling and data paths in the FlexRAN + ORU environment.
To force a 2x2 MIMO configuration, we modified the DU parameters on the Intel platform as follows:
Configuration 1:
dl.numTxAntennaPorts = 2
ul.numRxAntennaPorts = 2
numDlLayers = 2
numUlLayers = 2
Configuration 2:
dl.numTxAntennaPorts = 2
ul.numRxAntennaPorts = 2
numDlLayers = 2
numUlLayers = 1
Additionally, we tested Transmission Enabled (2x2) using 1T3R and 2T4R antenna port configurations in the Benetel ORU.
However, in these scenarios, the UE fails to register, with RACH failure observed in QXDM logs.
Could you please provide your expert insights on the following:
Are there specific constraints or prerequisites in the Benetel ORU or FlexRAN 23.07 stack for supporting 2x2 MIMO operation in a 7.2x split setup?
Are additional configuration changes (e.g., beamforming or mapping adjustments) required to align the antenna port settings across the DU and ORU?
Any recommended debug steps or log points (DU/ORU side) to further investigate the RACH failure when operating in 2x2 MIMO?
Your support in enabling 2x2 MIMO in this setup would be greatly appreciated.
There is eAxC ID mapping. When you change the number of antennas, then this ID also changes. This should be correct between DU and RU.
Normally, for the 4TR system, it is 0,1,2,3 for data and 4,5,6,7 for PRACH.
If this is incorrect, RU may not receive FH packets properly. If this is correct only for data, then DU may not receive packets properly on all antenna ports.
There are some fundamental questions. When you say SIB1 with 2x2 and data with 4x4, are you using any precoder? Is this precoder different for SIB1 and different for PDSCH and PDCCH? This raises questions about the working configuration itself. If there is no precoder fed, then the physical layer can’t differentiate between SIb1 and other data.
When you say you are testing 2x2 with 1T3R and 2T4R, you might not have checked the fundamental condition in the 1T3R case. The number of layers should always be greater than or equal to the number of antennas. You can configure 2 DL layers with 2x4TR system.
My suggestion is as follows:
First, check the Benetel RU data sheet if it supports 2T4R or not. If it doesn’t then you better do 2x2 or 4x4 antenna configuration.
Now, whatever antenna configuration you set in step 1, you make sure the right eAxC IDs are used, if they are manually assigned in DU and RU, if not manually assigned, then ignore.
If the above 2 are correct, then you will see RU receiving FH C and U plane packets on time and DU receiving FH UL U plane resources on time. if you don’t see it then first 2 steps are wrong.
If the above 3 are correct, then check if your UE is decoding MIB/SIB1. If yes, then it means the DL path is correct.
If the above 4 are ok, then see if UE is sending PRACH and gNB is receiving it. If the Preable ID transmitted by UE doesn’t match with the decoded preamble ID at gNB, then check with the Benetel RU support if there is any timing/frequency offset, which can be corrected.
If both preamble IDs match, then make sure the gNB sends Msg2 and check at the UE side if the UE decodes it. If yes then you say your RACH is working fine.