Monday, 9 January 2017

TD-LTE-eNodeB Handover Failure In NSN IOT Test

 BACKGROUND

In LTE commercial network, sometimes our eNodeB need to connect to other equipment vendor’s core network. In this situation, we need to do a lot of tests to make sure all the functions in our eNodeB can work well. This we can call it IOT. 
   In one IOT, we make the handover test with NSN eNodeB, but it fails. From the signalling caught by EPC side, in the handover failure message, the cause is “Cell Not Available”. So there should be some handover configuration error.

PROBLEM

In one IOT, we make the handover test with NSN eNodeB, but it fails. From the signalling caught by EPC side, in the handover failure message, the cause is “Cell Not Available”. So there should be some handover configuration error.

SOLUTION

For handover, we need to configure the Neighbor cell configuration and Neighbor relation configuration. To let the handover success, we need to know the information of neighbor cell as the following picture. ENB ID, Cell ID, PCI, TAC and so on.

Also, the information of our eNB and the neighbor cell that customer offer are as bellow.
  The information for our eNB:
  The information for neighbor cell:
From the two tables, we can see that the eNB ID, PCI and TAC is clear but except Cell ID. In the first table, we think that “InCelId” is cell id, the same value as PCI and we configure like this. But the handover fails this time. So we have a doubt that “InCellId” is not cell id. In the table there is another item “eutraCelld”, the customer tell us this item is from “eNB ID+ Cell ID”, So we think the real Cell ID should contained in this item, but how can we get it?
The value of eutraCelld is a decimal number, we change it to a hexadecimal number. For example, the cell of PCI 156, eutraCelld is 156429569, change to hexadecimal number is 952ED01, eNB ID is 611053, changes to hexadecimal number is 952ED, so Cell ID of this cell is 01, just is 1. In the same way, Cell ID of PCI 157 is 2, Cell ID of PCI 158 is 3, Cell ID of PCI 177 is 1 and so on. Like this we can get, the 3 cells in each eNB, the cell id is 1,2,3.
    So we modify the cell id in Neighbor cell configuration, and test again. From the signaling we can see, the handover success.

Budi Prasetyo

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