a common antenna on a radio tower, usually between 50 ft and 300 ft (15 m and 92 m) high. Com- panion receivers use a separate antenna system mounted on the same tower. The receive antennas are often arranged in a space diversity configuration. To telephone network Figure 18.1 Conceptual layout of a cellular radio system. 1 CGSA is a term coined by the U.S. FCC. We do not believe it is used in other countries. 2Care must be taken with terminology. In this instance, ERP and EIRP are not the same. The reference antenna in this case is the dipole, which has a 2.15-dBi gain. CELLULAR AND PCS RADIO SYSTEMS The MTSO provides switching and control functions for a group of cell sites. A method of connectivity is required between the MTSO and the cell site facilities. The MTSO is an electronic switch and carries out a fairly complex group of processing functions to control communications to and from mobile units as they move between cells as well as to make connections with the PSTN. Besides making connectivity with the public network, the MTSO controls cell site activities and mobile actions through command-and-control data channels. The connectivity between cell sites and the MTSO is often via DS1 on wire pairs or on microwave facilities, the latter being the most common. A typical cellular mobile unit consists of a control unit, a radio transceiver, and an antenna. The control unit has a telephone handset, a push-button keypad to enter com- mands into the cellular/telephone network, and audio and visual indications for customer alerting and call progress. The transceiver permits full-duplex transmission and reception between a mobile and cell sites. Its ERP is nominally 6 W. Hand-held terminals combine all functions into one small package that can easily be held in one hand. The ERP of a hand-held is a nominal 0.6 W. In North America, cellular communication is assigned a 25-MHz band between 824 MHz and 849 MHz for mobile unit-to-base transmission and a similar band between 869 MHz and 894 MHz for transmission from base