Common Design Guidelines
After calculating the coverage and capacity requirements in each geographical area, the greater one of those two values has to be chosen. Ideally requirements match in each geographical area, but normally that does not happen. To optimise the used resources some readjustments should be made.
If a geographical area is coverage limited, the load on each sector can be reduced until coverage and capacity requirements match. Reducing the load will cut the link budget interference margin and increase Node B count. If area is capacity limited, transmitter diversity can be added or amount of transceivers can be increased.
Operators are normally forced to co-locate their 3G base stations with existing sites or select new site locations only on buildings known to be owned by friendly site owners. This limits the cell planning options and may sacrifice the network quality, but it helps to build networks faster. Forced co-location should be taken in to account in initial capacity and coverage planning. All variation to standard configuration may need pilot power, handover, antenna, cable and base station power level modifications.
Some network areas need special attention. Very dense urban area (CBD), open spaces, in-building areas, water surroundings, hot spots and other special coverage areas need well planned approach. Out-of-Cell Interference versus soft-handover cell overlap has also to be considered. Hierarchical systems work with multi-frequency networks, but not with single-frequency systems (like cdma). If multi-layered is planned, separate frequencies are needed for different layers.
There is no need for plan channelisation codes as those are managed by the RNC. Unlike the channelisation codes, the scrambling codes need to be planned. The number of scrambling codes is so great that the planning is a quite trivial task.
The uplink scrambling code for each user is allocated by the RNC. Every RNC has a pool of codes that are unique to it. Allocation of uplink scrambling codes to RNCs is a simple task, due to the huge number of available codes.
Downlink scrambling codes planning is an important issue in the border areas between countries. There is a minimum separation that should be used between cells using the same scrambling code, but in practice the maximum separation will be planned.
| Codes |
Scrambling codes |
Channelisation codes |
| Uplink |
Different users |
Channels from the same user |
| Downlink |
Different Node B's |
Different users |
UMTS code usages
Next: RAN design
|
3G Network Planning Basics
|
|
|
|
|
