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UMTS Network Planning Basics!
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Link Budget and Coverage

The WCDMA link budget calculations start from the uplink (reverse link) direction. Uplink interference (noise from other mobiles) is usually the limiting factor in cdma systems.

1 The starting point of a link budget calculation is to define the required data rate(s) in each network areas and Eb/No (Energy per Bit to Noise power density ratio) targets. Usually the operator predefines these, but simulation tools can be used to tailor the Eb/No. Simulation can be done by creating a uniform base station and a mobile distribution plan with defined service profiles. Almost every UMTS vendor has a simulation tool for operators to test their network plan models.

2 The next step is to gather vendor specific data like a BTS output power and a receiver noise figure, defined and used cable systems (thicker the cable, more expensive it is to install), used antenna types, usage of intelligent antenna systems in specific areas, possible additional line amplifiers, used diversities (like antenna, polarisation, receiver) etc.

3 For each geographical areas network operator has to define Eb/No, data services, a system loading factor, estimated mobile speeds, different penetration losses, coverage reliability and a used fade margin. Soft handover area sizes will be addressed later.

4 Mobile power levels, the chip rate and the process gains are defined by the UMTS standards. Soft handover gain and the thermal noise density are the same in every UMTS system. Both parties also have to agree on propagation models after drive tests.

The link budget gives a cell range and from that cell coverage area can be calculated. Cell coverage overlap parameter is usually missing from the calculation as it increases the cell count dramatically. Most network planners agree that overlap should be 20-30 percent, but that relates directly to build cost. After all that, the base station requirements for the each type of areas can to be calculated.

UMTS link budget

Cell coverage calculation using link budget.
This link budget is for an example only. The values for the real network may vary a lot!

Notice how sensitive the site count is to variations of the propagation model and cell overlap values. High speed 3G network needs a lot of base stations!

Next: Calculating the capacity requirements

3G Network Planning Basics
     1. Planning  5. Radio Access Network Design
     2. Coverage Planning  6. Core Network Design
     3. Capacity Planning  7. Transmission Design
     4. General Guidelines  8. The Summary

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