 service range of about 50 miles. This FM system was fully interconnected with AT&T's wireline telephone network. The service was not cheap. There was a basic $15 monthly charge, and usage was billed at a flat $0.15 per minute. In spite of the cost, the ser- vice was quite popular; a fact that led to its undoing. System engineers based their design on existing radio systems, which were primarily designed for dispatch applications. The traffic patterns of 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. Access Technologies Access Technologies radio dispatches are different than telephony: A dispatch occupies sev- eral seconds of airtime, while a telephone call typically lasts several min- utes. Almost immediately, blocking became a serious problem. In fact, in New York City, where the service quickly became popular, AT&T had 543 active subscribers in 1976 and a waiting list of nearly 4,000 anxious-to- be-connected customers that the system's limited capacity could not accommodate. Radio design played a role in improving spectrum utilization. The first systems-such as the one in St. Louis-used a scheme called nontrunked radio. In nontrunked radio systems, the available spectrum was divided into channels and groups of users were assigned to those channels. The advantage of this technique is that nontrunked radios were relatively inexpensive. The downside was that certain channels could become severely overloaded, while others remained virtually unused. The invention of trunked radio relieved this problem immensely. Trunked radios were frequency agile, meaning that all radios could access all channels. When a user placed a call, the radio unit would search for an available channel and use it. With the arrival of this capability, blocking became a nonissue. The downside, of course, was that frequency-agile radios, because of their more complex cir