e addition of base stations while meeting capacity requirements for growing demand. However, it is not an instanta- neous solution to any existing problem on the wireless network because cellular providers cannot force customers to abandon their current phones immediately. In fact, the need to support existing phones is often a major constraint in the devel- opment of cellular networks. Two particular examples come to mind. As AMPS use lessens, part of the AMPS frequency has been reallocated to support CDMA transmis- sion. CDMA is much more effective in its use of bandwidth, SO the preferred solution would be to abandon analog systems and convert everyone to CDMA, but this is sim- ply not feasible. Instead, as AMPS users replace their older mobile telephones, providers are converting AMPS bandwidth to CDMA use and reducing the number of available AMPS channels, as described in Chap. 33.6. The second example involves the design of cdma2000 and how it will replace cdmaOne in the United States. Although support for the higher capacity cdma2000 will arrive within the next few years, the systems will continue to support cdmaOne mobile units for perhaps a decade or more. This capability for legacy support was built into the cdma2000 specification. However, many individual elements that may seem trivial to engineers drive the cel- lular market as well. In addition to personal preferences such as style and color, there are health concerns related to radiation, perceptions of brand quality, and other factors. These are nontrivial. Radiation shields that protect the brain from cell phone trans- missions are already on the accessories market. It is fair to say that if a smart array antenna is developed for cell phones, it is likely to undergo evaluation as a potential health hazard and that no matter what the research findings, some customers will not want to put these units next to their heads. Other user terminal features create engineering challenges and may change not only the cell phone but also other components of the