 higher value for L(v) at 1650 MHz was attributed to a reduced antenna aperture at this frequency compared to 900 MHz. For a 100-dB path loss, the base station and mobile terminal distance exceeded 70 m on the same floor, was 30 m for the floor above, and was 20 m for the floor above that, when the propagation frequency was 1650 MHz. The corresponding distances at 900 MHz were 70 m, 55 m, and 30 m. Results will vary from building to building, depending on the type of construction of the building, the furniture and equipment it houses, and the number and deployment of the people who populate it. 18.4 IMPAIRMENTS: FADING IN THE MOBILE ENVIRONMENT 18.4.1 Introduction Fading in the mobile situation is quite different from the static line-of-sight (LOS) microwave situation discussed in Section 9.2.4. In this case radio paths are not opti- mized as in the LOS environment. The mobile terminal may be fixed throughout a 18.4 IMPAIRMENTS: FADING IN THE MOBILE ENVIRONMENT DIRECTION TO ELEVATED BASE STATION building mobile Figure 18.4 Mobile terminal in an urban setting. R, reflection; D, diffraction. telephone or data call, but is more apt to be in motion. Even the hand-held terminal may well have micromotion. When a terminal is in motion, the path characteristics are constantly changing. Multipath propagation is the rule. Consider the simplified pictorial model in Figure 18.4. Commonly, multiple rays reach the receive antenna, each with its own delay. The construc- tive and destructive fading can become quite complex. We must deal with both reflection and diffraction 3 Energy will arrive at the receive antenna reflected off sides of build- ings, towers, streets, and SO on. Energy will also arrive diffracted from knife edges (e.g., building corners) and rounded obstacles (e.g., water tanks, hill tops). Because the same signal arrives over several paths, each with a different electrical length, the phases of each path will be different, resulting in constructive and destructive amplitude fading. Fades of 20 dB are common, an