). We will refer to a radio path gain of 130 dB or a higher radio path gain of 110 dB. In this way, we do not have to remember which number to subtract, a mistake far easier to make in a spreadsheet than on a piece paper. The notion of path gain rather than path loss also avoids the constant hassle of remembering that greater path loss means less radio signal. Life gets more complicated, however. The 40 dB per decade is an average over vary- ing terrain and surface clutter. Rolling hills make the radio path gain higher on the side near the antenna and lower on the far side. Wooded areas have lower path gain than clear areas, and this difference is greater in the summer when the trees have leaves. Buildings not only reduce the path gain on average, but they also greatly in- crease the signal variability as one moves from one place to another nearby place. Sig- nal variability is the variation in received signal strength from a fixed transmitter as a mobile unit is moved around a relatively small area. While the earth's surface is almost always curved, it is not necessarily curved the same way in all places. Los Angeles and Salt Lake City are two U.S. cities built in val- leys, so their ground curves up instead of down. This means that cellular interference in these cities, and others with similar topography, is going to be different and very likely more difficult to manage than elsewhere. Bodies of water also affect propagation. Radio waves that would be absorbed or dif- fused by shrubbery can bounce off a water surface. This can form local radio "hot spots" near lakes and rivers. Because of the multiplicative nature of path gain reductions from terrain, buildings, and shrubbery, the statistical effect is a log-normal signal distribution, as described in Sec. 1.6. Typical standard deviations are about 10 dB. 9 Understanding radio propagation is essen- tial to CDMA capacity and quality planning. Chapter 47 goes into the subject in depth. 1.8 Antenna Gain We see the term antenna gain, and we have to wonder: How can 