rted territory. We must not let our lack of market experience keep us from formulating forecasts and deriving decisions from those forecasts. The decision to proceed with a 3G CDMA system should be based on firm data service forecasts, and we should use these fore- casts in forming our estimates of data service requirements. As with voice, we start by estimating the subscriber count for wireless data services. There are several candidate data services with different bit rates and different quality- of-service (QoS) requirements. For each of these, we need some estimate of the sub- scriber count, and we need a more detailed forecast than the voice telephony estimate. In data services forecasting, we need to form a more detailed picture with less histori- cal experience. The interactive data services take priority in their use of air-interface resources. Subscribers browsing the Internet do not like to wait too long for their Web pages and images to download. The demand for these low-delay services at peak times determines the required capacity for wireless data service. Other data services are less time-critical. E-mail and nightly database downloads can accept delays that interactive subscribers would not tolerate. Even though these data can tolerate longer delays, they still have to get to their destination, and the CDMA air interface has to have enough capacity for the total data service demand. Thus we should form an estimate of these higher-delay service subscribers as well, 1There are a variety of measures we can use for CDMA capacity. The gross chip rate used here is our own way of calibrating all these CDMA 3G services with a common measure of capacity uti- lization. These are not actual chip rates but an equivalent chip rate. 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. Estimating Wireless Telephone Demand Estimating Wireless Tele