O the reverse capacity goes up to 29 channels when stationary and up to 22 channels when moving 20 km/h. 29.4.2 High data rates The high data rates around 2 Mbps of cdma2000 EV-DO and W-CDMA depend on close- range service from microcells or picocells. These services use high-order constellations with several bits per symbol, so having interference from other cell sectors would spoil the party. We expect these high-rate wireless data services to be offered in office buildings or other specific targeted areas. Large-scale service at these levels would require an enor- mous number of serving base stations. These services do not support handoffs or even rapidly moving user terminals, so there is no obvious need for seamless service over a large area. 4The same arithmetic applies in our TD-SCDMA example. Thus 11 kbps times 3 is 33 kbps on a 1.28-megachip-per-second carrier. 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. CDMA Data Capacity Principles Capacity and Quality Principles The capacity of a 2-Mbps 3G CDMA carrier is one forward channel. This does not re- strict the service to just one user, however, because that channel can be shared among several user terminals. A community of subscribers can all share high-speed, graphic Web access from the same carrier, although if multiple downloads are requested at the same time, service may be slow or somebody will have to wait. 29.5 Conclusion In this chapter we derived the rates of data services offered to CDMA subscribers and showed the relationship between E/No and BER. We also discussed the capacity of a server providing a particular data rate. In the next chapter we look at a number of is- sues affecting CDMA capacity and then derive equations that approximate real-world capacity values for each direction for each of the CDMA standards. Downloaded from Digital Engineering Library @ McGraw-Hil