Limiting for one sector per MHz sector sector direction carrier 20 MHz per cell TD-SCDMA voice Reverse 198.4 TD-SCDMA data Forward By doing these calculations in just one direction, we have ignored the flexibility of the TDD carrier. If a TD-SCDMA has a total allocation of 20 MHz for both directions, then it can use six-sevenths of that, 17.1 MHz, for just one direction if the subscriber demand in the other direction is light. The frequency division duplex (FDD) carriers not permit this variability on a minute-by-minute basis. 30.8 Conclusion We have now explored and explained the underlying principles that determine capac- ity and quality on CDMA systems. This final chapter of Part 5 gives the equations and estimated values that allow us to move from principles to the application of those prin- ciples. In the next two parts, "Planning for CDMA Capacity" and "Increasing Capacity," we apply these principles to the practical day-to-day work of cellular system planning and growth. In an ideal world, we would be able to model our entire network, optimize the model, and then tweak our systems based on accurate models. Unfortunately, this is not al- ways possible. Sometimes, using algorithms and computer programs, we can work from models that apply these principles. All too often, however, factors that are difficult to quantify, plus time and cost pressures, require us to follow rules of thumb and make our best engineering judgments without the advantage of precise modeling. In such cases, our understanding of the principles we have discussed in this chapter guides our thinking and improves our ability to make good decisions, improving the capacity, reli- ability, and profitability of the systems we design and improve. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Capacity Issues Specific to CDMA Downloaded from Digital Engineering Library @ McG