base station outage. Not only are we serving k cells of traffic with k - 1 base stations, but the missing cell is likely to form a pilot-polluting valley for the other k - 1 cells and perhaps one with poor radio signal paths. After all, if the remaining k - 1 base stations could cover the missing cell with good coverage and low blocking, then we would not have put a base station there in the first place. Subscribers probably will tolerate periods of lower performance as long as they do not happen too often. A system with 5 percent blocking most of the time can easily add percent base station outage to its overall ineffective call rate. However, the essential difference is that the 0.1 percent base station outage is a continuous period of time, several hours during which service will be poor. Even subscribers used to 5 percent blocking will notice when no calls go in or out for hours. The strategy we recommend is to have a large-cell grid of more reliable base stations. In Fig. 33.3 we show a one-in-three grid. (In Sec. 33.6.3 we were using this picture for CDMA migration, but it is the same concept of a large-cell grid overlaid on a small-cell grid.) We could ensure that the large-cell grid has high reliability and adequate coverage so that a failure of one of the other base stations still leaves service over the entire area. If one cell in three is too expensive, we can use every fourth cell, as shown in Fig. 33.5. It is important to make the reliability decisions early. They are part of the system planning process and should not be a reaction to a base station failure. Having broken radio equipment and angry subscribers is not the time to be making decisions about how reliable base stations should be. Decisions made under that kind of duress tend to be short-term patchwork rather than well-thought-out plans. 13 A complete base station plan includes a reliability plan. Each major component of a base station must be quantified as to its failure patterns, rate of failure, and how long it takes to repair it. If fai