We can get a new carrier because a government agency gives us more radio spectrum, but we also can add CDMA carriers as we migrate a frequency division multiple access (FDMA) or time division multiple access (TDMA) system over to CDMA, as described in Sec. 33.6. The second case is when we have a large service area with two distinct population centers. Here in the United States, we have several ser- vice areas with pairs of adjacent cities, for example, Minneapolis and Saint Paul or Dal- las and Fort Worth. If they were separate wireless telephone systems, then we would expect each city to have its own high-density, maximum-carrier zone, as described in Sec. 33.4. And defining one large service area with both cities in it does not change the fact that each city has its own high-traffic area. We expect such a dual city to have two maximum-carrier regions isolated from each other. If traffic increases, then those iso- lated maximum-carrier areas might grow into each other and merge into one large high-traffic CDMA service area. How we add a carrier depends on the base station architecture. Some equipment ven- dors may have us buy a lot of equipment to add a new carrier, and others may have a simpler scheme. If the existing forward transmit amplifier is already close to its maxi- mum power limits, then we will need to add another amplifier as a part of this process. Sometimes the need for a new carrier does not occur in a nice convex-grid cell. It may be necessary to expand carrier coverage by adding the new carrier to transition cells (described in Sec. 33.4) so that the carrier region stays convex as it grows. The alter- native is loss of capacity due to pilot pollution. 41.4 Adding Sectors CDMA sectors are independent servers, SO adding sectors to a cell adds capacity. A three-sector CDMA cell does not divide up the traffic into thirds but instead offers three separate CDMA servers. When a cell runs out of capacity, we can divide it into more sectors by putting more antenna faces at the base station. This is attra