1.1.1.1
Missing Neighboring cells Judgment of missing neighboring cells Neighboring cells refer to cells that may enter the active set, and cells that the UE may reselect as the serving cell or may be handed over to. When the UE is at idle or FACH state, it can read the neighboring cell information from the system information, and it will measure these cells when the conditions are fulfilled. Therefore, missing neighboring cells may cause that the cell reselection cannot be finished in time, which further leads to call setup failure. When the UE is at DCH state, the RNC will deliver the neighboring cell information to the UE through the measurement control command, and instruct the UE to measure all the neighboring cells that it may be handed over to. In this condition, missing neighboring cells may lead to call drops. Generally, the following three methods can be used to judge missing neighboring cells: 1.
Best SC of the UE and Best SC of the Scanner Missing neighboring cells may lead to call drops. If both the UE and the Scanner are used in the test, we can check whether there are any missing neighboring cells by comparing the Ec/Io of the optimal serving cell in the active set of the UE and the Ec/Io of the optimal serving cells measured by the Scanner. If the Ec/Io of the optimal serving cell within the active set of the UE is poor, while that measured by the Scanner is good, and the PSCs of the optimal serving cell recorded by the Scanner is not included in the Measurement Control signaling delivered by the RNC, it is certain that the some neighboring cells are missing. As shown in the figure below, on one road, the Best SC by Ec/Io measured by the UE is poor, lower than -11dB, while that recorded by the Scanner is good, higher than -8 dB. The optimal serving cell recorded by the Scanner is 194 and 409, while that of the UE is 160. Through the Measurement Control signaling received by the UE, we find out that Cell 194 and cell 409 are not included in the neighboring cell list. From this, it is safe to ascertain that some neighboring cells are missing.
Figure Error! No text of specified style in document.-1 Judging missing neighboring cells by Best SC of the UE and the Scanner (1)
Figure Error! No text of specified style in document.-2 Judging missing neighboring cells by Best SC of the UE and the Scanner (2)
2.
Pilot set of the UE If only the UE is used in the test, we can judge whether there are missing neighboring cells by checking the pilot set changes before and after the call drops. It is safe to
ascertain that some neighboring cells are missing when the following three conditions are all met: 1. One cell with strong signals exists in the detective set around the call drop point; 2. The PSC of the cell that the UE accesses after the call drop is different from the one that the UE accessed before the call drop; 3. There is no record about this cell in the last Measurement Control message that the UE received before the call drop. As shown in the figure below, Cell227 with strong pilot strength is included in the detective set. After the call drop, the UE accesses Cell227. However, Cell227 is excluded in the neighboring cell list delivered by the last Measurement Control message. Then, we can ascertain that Cell227 is the missing neighboring cell.
Figure Error! No text of specified style in document.-3 Pilot set of the UE before the call drop
Figure Error! No text of specified style in document.-4 Pilot set of the UE after the call drop
