Case19: Handover failure between M4370 & T5000+EU+picoRRU (SFN value)

1. Production:

M4370 (V3.7SP05)

T5000+EU+picoRRU (V676)

2. Issue Description:

Handover fails between M4370 & T5000+EU+picoRRU. 

3. Test Scenario:

1. Serving cell -> Picocell
2. Target cell -> M4370
3. RF power is 250mw for both of them
4. traced the radio using “tcpdump” command

On both traces, there a “XnUAddressIndication” that we’ve never seen so far.

4. Issue Troubleshooting:

By comparing the mirror environment in BTI lab, we found that the UE did not trigger A3 events (signaling log), and captured FAPI3 log, which shows that the SFN on both gNbs are out of sync, one system frame differ.

5. Root Cause:
The value of the 730 registers in the calling script for the accelerate card is different, there is a difference of one SFN: 

6. Solution:

Modified the SFN value to 10ms in the T5000BBU(which connect to EU+ PICO cell) (as below): in order to compensate for the 1 SFN.

 

After modifying this parameter, “HORequired” message was properly triggered and rest of the procedure has been successfully performed. 

HO WORKS between pico (BBU+EU+RRU) and M4370.

7. WARNING:

This fix will be included in next releases, we need to keep in mind that whenever we’re going to upgrade a picocell, on which we had performed this fix like in this case, we must change the “Frame offset” value back to 0ms.