ls are in soft handoff, each using two channels, then those 20 calls are using 40 chan- nels. Each cell has an additional 10 channels for calls not in soft handoff. As a result, the two cells with a capacity of 30 calls each have a total shared capacity of only 40 calls. The capacity loss due to the need for soft handoff when a subscriber is near the border of a cell is one-third the total ca- pacity of the two cells. 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. Capacity Issues Specific to CDMA Capacity Issues Specific to CDMA soft handoff maintains a continuous state of near-optimal communication between user terminals and antenna faces. There are thresholds for starting and stopping the soft-handoff process in a CDMA system. Adjusting these thresholds tunes the tradeoff between suboptimal radio links and the cell-capacity reduction created by the up-front cost of soft handoff. 30.3 Multipath As we discussed in Sec. 8.4, the multipath radio environment is another challenge in CDMA design. The broad bandwidth of CDMA and the yet broader bandwidth of 3G CDMA free us from the severe Rayleigh fading of narrowband radio links, but the higher chip rates increase the amount of intersymbol interference, which is dealt with by the rake filter. As a result, multipath is more of a capacity issue in CDMA and more of a call-quality issue in conventional reuse. The capacity cost of multipath is highly dependent on the radio environment, which determines the amount of intersymbol interference. It is an unfortunate fact of nature that the regions with high demand densities are the same urban environments that have a lot of big buildings that generate multiple radio paths. The rake filter does a better job of filtering out same-sector interferers on the reverse link where the radio paths are different for each user terminal. In the forward direc- tion, t