mplifier power, add CDMA carriers, add sectors, or add repeaters. However, these solutions are not interchangeable. Each solves a different set of problems and works in different sit- uations. We explain when to use each one in this chapter. The primary tool we use to describe the status of a cell in need of added capacity is the system of green, red, and yellow areas described in Sec. 40.2. 41.1 Determining When to Add Capacity Most communication systems offer a clear way to tell when they are getting busy. There are a fixed number of channels, and the system is blocked when those channels are full. Or a packet pipe has a fixed capacity, and the system is too busy when there are more packets than the pipe can carry. We can get a rough estimate of the blocking perfor- mance of the system with 10 percent more traffic than it has by observing how often the system is 90 percent full. The CDMA carrier does not have the same notion of a fixed capacity, so we cannot simply count channels or packet volume. There is no obvi- ous point where a CDMA carrier is 90 percent full, a point where another 10 percent will overload it. We have to look for more subtle signs. The air interface does give some clues of impending traffic overload, however. CDMA systems should have systems in place to measure air-interface performance, and plan- ners should remain vigilant. The CDMA carrier often looks just fine at 95 percent of its capacity, so we may get very little warning before the CDMA channel reaches its limit. As traffic gets denser and cells get smaller, the thermal noise floor of the receiver be- comes less important compared with the interference from our own system. In Figs. 28.1 and 28.2, small cells reach saturation far up along the steep vertical asymptote. This means that the system may be operating at one-third of its power or less when it is 95 percent full. The system may be giving us a warm sense of complacency that everything is just fine when it is only a few percentage points away from carrier saturation. Downloade