. Unfortunately, a single symptom, such as static or a dropped call, may have many different causes. The cause of the event could be an area of poor coverage, a cell operating at capacity, or an event outside our control, such as a failing user terminal. We need to gather all the in- formation we can about each complaint and look at each complaint both individually and as part of a larger pattern of complaints and performance statistics to understand what is really going on and what, if anything, we can do about it. The journey from symptom to problem comes first, and it is followed by the journey from problem to solution. In this chapter we will look at how to turn user complaints about voice and data service into useful information that helps us identify problems. We also will look at how changes in subscriber usage patterns can be monitored so that we can provide the best mix of voice, data, and video services. 40.1 Symptoms and Causes Diagnosing technical problems from user experience is sometimes easy but at other times can be very difficult. When a user terminal experiences a rising bit error rate (BER) because of interference from a neighboring cell, the subscriber is only going to complain that the call was lost. The serving sector, the carrier, and the interfering cell are not going to be mentioned in the user complaint. If we are lucky, then the sub- scriber will remember when and where the call was made. If we know the mobile telephone number and the time, then we can often track location because third-generation (3G) code division multiple access (CDMA) user ter- minals use the assisted Global Positioning System (GPS) to determine their position. 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. Turning User Complaints into Useful Data Increasing Capacity The combination of position and time can give engineers critical information 