neers do use other models - such as ray tracing - for the micro-cellular environment. RADIO NETWORK PLANNING AND OPTIMISATION Figure 2.11 W-I model: d: distance in km f: frequency in MHz Lrds: rooftop-street diffraction and scatter loss Lms: multi-screen diffraction loss W: road width b: distance between the centres of two buildings Hbu: height of the building Application of Propagation Models The propagation models are usually not applied directly. The reason is that these models were developed taking particular cities into account, and every city has its own characteristics. Changes made to the propagation models are called correction factors and they are based on drive tests results. If there is no existing cellular network, the radio planning engineers install an omni-antenna at a location which would cover all or most of the types of region - dense urban, urban, rural, etc. A drive test is performed and correction factors for the propagation models are thereby determined. One such table of correction factors is shown in Figure 2.11(a). Category Offset(dB) No data Water -17.00 -17.00 Evergreen -17.00 Deciduous -10.00 Low Density -15.00 Residential High Density -10.00 Residential Commercial/ -15.00 Industrial Urban -3.20 Figure 2.11(a) Correction factors RADIO NETWORK DETAILED PLANNING Planned Coverage Area Based on propagation models, drive tests and correction factors, prediction of coverage areas is done. The sites are located according to the requirements of the network, and the coverage predictions are done as shown in Figure 2.11(b). Usually some radio network planning tools are used for such an exercise. Height (Block) (= Om 1m 30m 31m 60m 61m 90m 91m 120m 121m 150m 151m 180m Water Evergreen High Density Residential Commercial/Industrial Best Server GSM-Default x> -71.5 dBm Urbano denso -71.50=x>>75.5 dBm Urbano 75.50mx>.79.6 dBm Subuibano -79.6>=x>-84.5 dBm Rodovias -84.5>=x>.90.5 dBm Rural AM1042 Figure 2.11(b) Planned coverage area Location Probability As mentioned above, the quality of coverage is d