SC Plan Verification

1.1.1 RF Analysis

1.1.1.1 SC Plan Verification

Scanner measurements can be used to verify the Scrambling Code plan. Ideally, each cell should have an area where in all samples it is the best SC, and it should not be the best SC in any other area. The scrambling code plan is preferably analyzed in MapInfo/MCOM. Displaying best serving SC in MapInfo/MCOM is very useful to clarify cell coverage and that all cells in the cluster have been assigned the correct SC according to plan. This could give an indication of possible co-SC-clashes, swapped feeders, cell not transmitting, or overshooting cell. Other installation faults will not be able to be discovered during cluster analysis. An example of the best serving SC plot in MCOM is shown in Figure 7.

Figure 7, Example of SC plot in MCOM

The process can be summarized in the flowchart as shown in Figure 8.

Figure 8, Scrambling Code Plan Analysis Process

A good SC planning should reuse the code as far away as possible in terms of geographical location. This is to facilitate identifying interfering cells and neighbour cell check. Tight re-use of the SC is a very common problem as planners will try to maximise the code usage as efficient as possible. This will create a potential co-SC issue in the network if not planned cautiously.

All of the 1^st, 2^nd and 3^rd tier cell neighbour relation should not share the same SC so as to avoid co-SC problems. Potential co-SC issue can be identified by analyzing the coverage of one single SC in MapInfo/MCOM. If the SC is repeated within a short distance there is a risk that two identical SC from two different cells will be present in the Monitored Set. This can occur when there are two active set and the two neighbour cell lists are merged as shown in Figure 9. The RNC will not be able to identify which SC belongs to the correct cell. This will cause the RNC to release the connection when UE request to add the SC (in this example SC7) into the active set. This is because the RNC cannot differentiate between two cells having the same scrambling code.

Figure 9, Co-SC Problem

It is recommended to allocate a spare SC group for indoor cells and new site additions. The benefit of this arrangement will be to avoid co-SC problem and also eliminate the need to review the SC plan every time when new sites are added. An example of the SC group usage is shown in Figure 10.

Figure 10, Example of SC Group Usage