 wireless system. The voice messaging feature requires memory storage capacity on the cellular network available to users. Similar storage can be used to store user data, such as autodial lists and the sound clips needed for voice recognition on the cellular system, rather than in the cell phone. This could increase the demand for electronic memory on the cellular system and also increase usage of the network's signaling channels. 9The subscriber-to-base-station ratio depends on the subscribers and how much they use their mobile telephones. If people tend to spend a lot of time using their cell phones, then the system will have a lower ratio of user terminals to base stations. 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. The User Terminal Key Radio Concepts 3.2 Other User Terminals As electronic technology becomes more pervasive, more and more different types of user terminals will interact with the cellular network. In this section we will discuss the possibility of cellular systems replacing land lines for the local loop to the cus- tomer's residence or place of business, various types of wireless data terminals, and terminals without a human interface. In addition to describing current technology, we also will risk a bit of prediction regarding what will come. 3.2.1 Wireless local loop (WLL) The local loop, the landline link between each customer phone and the local branch ex- change, is an expensive component of the public switched telephone network (PSTN). Engineers sometimes call the local loop just a loop. In the United States, Europe, and other developed areas, this infrastructure is in place and is unlikely to be changed any time soon. Over the last 20 years, there have been discussions of replacing copper twisted-pair cable with coaxial or fiberoptic cable to get higher transmission rates. The reality has been that, instead, we 