etransmitters, as described in Sec. 4.6. Without any telephone transport of their own, they enhance radio communication by breaking a single radio path into two hops. When a weak radio area is supported by a repeater to a base sta- tion, the cell changes shape to include that weak area. Coverage is increased when subscribers in red areas can get service that was hard to get at any time without the repeater. Capacity is increased when subscribers in yellow areas can get service using less CDMA radio resource with higher effective radio path gain because of the repeater. The best candidates for coverage repeaters are places with poor radio access to base stations that have convenient electrical power but no convenient telephone transport. This is how we discussed repeaters in Sec. 32.4. The candidates for capacity-enhancing repeaters are areas of significant subscriber density where there is acceptable CDMA service when the system is lightly loaded. This indicates that the radio path gain is low, and calls from this area cannot compete in transmit power with calls in better areas. A base station might not be cost-effective or it might be hard to get telephone transport, so we use a repeater. Also, if our system has a four- or five-way zone of pilot pollution, then a repeater might be a cost-effective way to break the tie and have one dominant server in that geographic area. 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. Increasing Capacity of a Base Station Increasing Capacity Repeaters are not base stations. They do not do as much as base stations, but they do not cost as much either. We can use repeaters as cost-effective ways to add capacity as well as coverage. 41.6 Conclusion When we add capacity to the air interface of a base station, we need to monitor the backhaul from the base station to the mobile switching center (MSC) to make sure