. Ineffective attempts also can be caused by low radio signal path gain, an impossibly weak signal. A user terminal tries to set up a call and fails because the paging mes- sages are lost in the radio noise or the user terminal lacks enough power to set up a call. This, too, looks just like a conventional-reuse system not setting up a call because it is in such a weak radio area that a call cannot exist there. Ineffective attempts also can be caused by poor coverage in a manner unique to CDMA. The call would have been fine if it had been closer to the base station, and the call would have been fine if there were fewer users on the CDMA carrier, but the com- bination of the two was enough to keep the call from being started. We can think of these calls as casualties of poor coverage because their signal path is good enough to make a call, but their low radio signal path gain makes them use more CDMA resource than we have available. If we know where the user terminals were located when they failed to start their calls, then we can use propagation maps to evaluate the cause of the ineffective at- tempts. We can think of the system in three parts: Green areas where any call can be set up as long as the CDMA carrier has enough bits left, enough room for the call between its current load and the theoretical CDMA maxi- 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 Turning User Complaints into Useful Data Red areas where no call can be set up no matter what the traffic because the radio path gain is too low Yellow areas where there is some ability to set up a CDMA call, but it requires more CDMA capacity than its bit rate and Eb/No suggest because of low radio signal path gain Even if they do not use this particular color scheme, the radio maps can help us un- derstand which of these three categories should