Equipment and Circuits for Digital Mobile Radio

This chapter describes equipment and circuit aspects of digital mobile radio systems. It shows the basic structures of the base station and mobile station equipment and some detailed circuit implementations. The two‐receiver postdemodulation diversity system is adopted for the car‐mounted and the shoulder‐type mobile stations. The principle of demodulation for the direct conversion signal is based on the zero IF complex or quadrature representation of modulated signals. The center frequencies of the band‐pass filters are chosen at the transmit and receive frequency bands, respectively. Compactness, low power consumption, low noise, frequency stability, and fast channel switching are major technical issues for frequency synthesizers in mobile radio equipment. An AGC (automatic gain control) circuit is needed to cope with the wide dynamic range of the received signal in a mobile radio channel. DC blocking or ac coupling is desirable for preventing baseband signals from the dc offsets of the circuits.