Introduction to Digital Mobile Communication, 2nd Edition

8EQUIPMENT AND CIRCUITS FOR DIGITAL MOBILE RADIO

This chapter describes equipment and circuit aspects of digital mobile radio systems. The basic structures of the base station and mobile station equipment and some detailed circuit implementations are shown. Some methods and circuits shown here as well as in other parts of this book might be patented. With the evolution of digital signal processing including microcomputers and field programmable gate arrays (FPGAs), many parts of mobile radio systems have been implemented using them. Then the circuit design reduces to programming of them by mathematical expression of operation of the circuit. This topic is not covered in this book. The reader may refer to reference [1].

8.1 BASE STATION

Figure 8.1 shows a simplified block diagram of a base station for the Japanese digital cellular system in the NTT Mobile Communications Network Inc. [2]. A base station covers three sectorized zones (Section 9.1.1). Two-branch diversity reception is used. The antenna gains are 17 and 14 dBi at 800 MHz for antenna aperture lengths of 5.4 and 2.7 m, respectively. A transmit and receive duplexer is connected to one antenna, from which signals are transmitted. In order to achieve a low-noise figure, an outdoor common receive low-noise amplifier is used, whose noise figure is less than 3 dB and gain 40 dB. The beam can be tilted by 0–5 or 3–11 degrees in the vertical plane by phase shifting the feeder circuits for the vertical array antenna (