23-02-2013, 10:07 AM
WCDMA Introduction and Overview
WCDMA Introduction.pptx (Size: 713.01 KB / Downloads: 42)
WCDMA Spreading process
Spreading:- This is used to increase the B.W of the signal beyond the bandwidth normally required to accommodate information.
For Spreading OVSF code are used which is known as Orthogonal variable spreading factor code .
Spreading factor=chip rate/symbol rate .
Scrambling – Scrambling is used on top of the spreading so , it does not change the signal bandwidth but only makes the signal from different source separable from each other.
Process gain = 10 log (chip rate/bit rate)
As bit rate increase process gain decrease .
Cell breathing is situation where cell foot print decrease due to large amount of user access the network beyond the capacity of that particular cell.
Use full Plots
Server Plot – Useful to find out Swap or Overshooting.
UE Plot - To Check Neighbour Relation.
RSCP Plot- Coverage holes
Ec /No- for good Throughput and removing pilot pollution.
4th best Server – Echno should be > -10db
5th best Server – Echno should be > -10db
SCFT-Single Cell Functional Test
Before the single site verification, we should only ensure the following conditions have been met.
Alarm Check
Cell Status Check
Parameter Check
Alarm Check / Cell Status Check
The product support engineer will be responsible for checking and resolving all the alarms. It is important for the optimization engineer prior to any field test to check with product support engineer regarding any alarms especially intermittent alarms.
Parameter Check
The optimization engineer need to ensure the radio part parameters configuration list has been achieved. In the list the radio part parameters includes: the scrambling code, power setting, neighbor cell list, handover parameter etc.
Problem and Solution
In the site verification, following problems have been found
Scrambling Code Setting is wrong: The scrambling code from scanner and mobile is different from the planning
After feeder swapped, the CPICH RSCP is 20dB lower than before.
Scrambling Code Setting is wrong
The Scrambling Code may be wrong in RNC, check the datasheet in RNC.
If the Scrambling Code from scanner is the same as that of another sector in same site planned, maybe the TX/RX feeder is crossed to the another sector.
After feeder swapped, the CPICH RSCP is 20dB lower than before:
The RX feeder is crossed to the antenna of another sector. In this case, the CPICH RSCP will be high in the coverage area of the other antenna. Check the connection between the feeder and the antenna.