anning Figure D.9 Prediction of radio coverage offered by a radio base station suburban areas, etc.). Knowing the cell area for the desired type of service and the area to be covered, the number of base stations can easily be estimated. In a next step, to obtain more accurate results, a software tool for radio coverage predictions using a digital map can be used (Figure D.9). This method gives more reliable results than the previous one because the terrain height and the actual distribution of the various terrain types are taken into consideration. In the tool, the base stations for each site should be properly configured with the EIRP and antenna radiation pattern information. The software tool will calculate the radio coverage map and will show using different colour codes the different levels of the received signal level for each point on the geographical map. D.5.2 Traffic Capacity Planning At the end of the previous step the total number of required base stations to meet the customer requirements has been calculated. As a next step the number of carriers for each radio base station can be requested. This item can be calculated by estimating the required traffic offered by each cell and then the number of traffic channels per cell. As already explained, the TETRA is a trunking system, which means that a large number of users can share the relatively small number of channels in a cell by providing access to each user on demand from pool of available channels. Upon termination of a call the channel is immediately returned to the pool of available channels. When all traffic channels are busy a further channel request is blocked. The calls TETRA Network Planning User Traffic Total Profile traffic Erlang Traffic channel definition formula numbers per cell per cell Number of users per cell Grade of service Figure D.10 Traffic channel estimation process can be rejected or delayed. The TETRA standard, in the case of blocking at the air interface, can insert further requests of traffic channels in a queue and they wil