9-6.55loghb)logd + Lother (2.7) where f is the frequency (MHz), h is the BTS antenna height (m), a(h) is a function of the MS antenna height, d is the distance between the BS and MS (km), Lother is the attenuation due to land usage classes, and a(hm) is given by: a(hm) = (1.1log.fc-0.7)hm - (1.56logfc -0.8). For a small or medium-sized city: a(hm) 8.25(log1.54hm)2 - 1.1, for fc </ 200 MHz (2.8) For a large city: a(hm) 3.2(log11.75hm)2 - 4.97, for fc > 400 MHz (2.9) The value of the constants A and B varies with frequencies as shown below: A = 69.55 and B = 26.16 for 150-1000 MH2 A = 46.3 and B = 33.9 for 1000-2000 MHz. The attenuation will vary with the type of terrain. This may include losses in an urban environment where small cells are predominant. Then there are foliage losses when forests are present in the landscape. Similarly, the effects of other natural aspects such as water bodies, hills, mountains, glaciers, etc., and the change in behaviour in different seasons have to be taken into account. A Micro-cell Propagation Model The most commonly used micro-cellular propagation model is the Walfish-Ikegami model. This is basically used for micro-cells in urban environments. It can be used for the frequency range 800-2000 MHz, for heights up to 50 m (i.e. the height of building + height of the BTS antenna) for a distance of up to 5 km. This model talks about two conditions: line-of-sight (LOS) and no-line-of-sight (NLOS). The path loss formula for the LOS condition is: P = 42.6 + 26 log d + 20log f. (2.10) For the NLOS condition, the path loss is given as: P = 32.4 + 20 log f + 20 log d + Ltds + Lms. (2.11) The parameters in the equations above for the model can be understood from Figure 2.11. The values of the rooftop-to-street diffraction loss are dependent upon the street orienta- tion, street width and the frequency of operation. The multi-screen diffraction losses are dependent upon the distance and frequency. Note: Walfish-Ikegami model can be used also for macro-cells. However, some radio planning engi