he network planning objectives are not met. This could mean that there is a need to go back to the previous step where, for example, new radio base station positions must be selected or the offered traffic capacity must be modified. Therefore the whole process could be iterative. Introduction to TETRA Network Planning Network Planning Requirements Radio Capacity Transmission Net work Network Frequency Final and Core Planning Planning Planning Network Planning Network Figure D.7 Network planning process Radio network planning consists basically of the definition of the quantity and position of the radio base stations in order to meet radio coverage requirements. This objective can be met by properly choosing the antenna system and selecting the best available sites. The customer wants to use the minimum number of sites; therefore very often sites on the top of mountain or hill are preferred. This choice can often produce problems in the traffic capacity and frequency planning phases. In other cases, the TETRA system is used to replace an existing old PMR system and therefore the customers want to re-use as much as possible of the existing infrastructure. This places constraints on site selection, with the result that the number of sites will probably not be optimised. Traffic capacity planning is a very important step in the process because the cells must be dimensioned avoiding at the same time the saturation of the traffic resource and waste of frequency carriers. In a PS&S network the traffic resources must be dimensioned very carefully since in the case of an accident or other situations requiring police force intervention, the network can suffer from an anomalous concentration of users under the same cell and the peak traffic could reach unexpected values. When the traffic capacity resources are defined for each cell, frequency planning can be carried out with the scope to re-use the same frequency as much as possible while minimising the probability of co-channel and adjacent channel interference. At the end