chapter we will look at the internal components of the base station in detail. Those components are listed in Fig. 4.1. 1 4.1 The Antennas Starting at the top, a wireless base station has a set of radio antennas. Typically, there are three antennas per sector, one to transmit the forward signal and two to receive the reverse signal. The two receiving antennas provide microscopic spatial diversity to 1Where there are differences among AMPS, GSM, and CDMA, the CDMA components are il- lustrated. For example, some AMPS systems have multiple amplifiers sharing a combiner rather than one amplifier. These distinctions are discussed in the text. 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. The Base Station Key Radio Concepts Receive Transmit Antennas Antenna Cable Cable External Power Power Communications Receive Power Components Amplifier Amplifier Supply Battery Demodulator Modulator Backup Signaling Link to MSC Base Station Channel Bank Controller (BSC) Packet Switch Voice and Data Link to MSC Figure 4.1 Base-station components. combat the Rayleigh fading described in Sec. 2.1.4. At wireless frequencies, half a me- ter of spacing is enough. In the case of the user terminal, both cost and size are major considerations. The base-station antenna is high atop a tower, and its cost is spread out over hundreds of users SO that we can afford the luxury of putting the right piece of hardware up there. In Sec. 1.8 we discussed how an antenna could have gain by concentrating its focus over a small angle, the radiation pattern of the antenna. 2 The horizontal radiation patterns of the base-station antennas match the sector plan of the cell. We can have an omnidirectional 360-degree pattern, a three-sector 120- degree pattern, or a six-sector 60-degree pattern. For conventional reuse [frequency di- vision multiple access (FDMA) and time division multiple 