 GSM carriers, 80 channels, serving each cell sector. This means that our GSM system can support about 70 erlangs per sector in 25 MHz each way. 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. Base Station Planning Base Station Planning Let us take one-fifth of this radio spectrum and use it for a wideband CDMA (W-CDMA) carrier. A W-CDMA carrier, 5 MHz in each direction, can handle about 130 voice calls. This is more telephone traffic than the entire GSM system could support. Thus, if we have a significant population of dual-mode user terminals in our GSM pop- ulation, we can serve all of them in a single CDMA carrier and still have 80 percent of the GSM spectrum left over. We do not want to overlap radio spectrum between GSM and CDMA. Even if the CDMA channels are tough enough to withstand some narrowband interference from GSM, the GSM system was never designed to handle CDMA interference. It is certainly best to keep the two technologies in separate radio spectrum allocations. We may decide to convert only the busy area to CDMA. We can share the radio spec- trum between the two technologies if we leave a sufficient geographic buffer zone around the CDMA radio spectrum before reusing it in FDMA or TDMA cells. The buffer zone may be an area two cells wide between the CDMA part of the system and the full- bandwidth FDMA or TDMA section. 33.6.2 Greater traffic efficiency with overflow Neither AMPS nor GSM is designed to hand off calls into a CDMA system. The CDMA system, on the other hand, does have the ability to hand off calls to something else. Thus we will plan on setting up calls on the CDMA spectrum and keeping them there until conditions require them to be handed off to the legacy system. If we plan on setting up calls on CDMA, then we can treat the legacy system as an overflow server for the CDMA system traffic. We start by selling a l