grid superimposed on the FDMA or TDMA system. In Fig. 33.3 we show every third cell being marked for CDMA service. The resulting one-in-three grid is shown in Fig. 33.4. Even with only one-third of the cells using CDMA, the radio-efficiency advantage still favors using it. Thus we start with a large-cell CDMA grid and let the revenue from that investment pay for the conversion of more cells to CDMA. It is expensive to reoutfit hundreds of cells, and we certainly would rather let the CDMA revenue stream pay for the change as the system continues to migrate to CDMA. Spreading the introduction out over more cells means that it will take longer, but the initial outlay of cash will be much smaller. If the cells are not too large, then we may decide to start with every fourth cell marked for CDMA service, as shown in Fig. 33.5. Several options are available for ini- tial CDMA introduction, and the best choice depends on how much a service provider wants to invest initially, how quickly a service provider wants to switch to CDMA, and how great the pressure for radio efficiency is in the market. The coordination of cell conversion and frequency conversion is guided by a desire to make better use of radio bandwidth and a desire not to spend too much money up front. The migration plan is ready to go when it takes into account market penetration of dual-mode user terminals, introduction of CDMA carriers to specified cells, increasing the CDMA presence to more cells, and increasing the CDMA spectrum to realize the gains in efficiency. Figure 33.3 Every third cell marked for CDMA service. Downloaded from Digital Engineering Library @ McGraw-Hil (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hil Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Base Station Planning Base Station Planning Figure 33.4 Resulting one-in-three CDMA grid. Figure 33.5 Every fourth cell marked for CDMA grid. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringl