Digital Modulation/Demodulation for Mobile Radio Communication

This chapter describes some digital modulation methods in order of appearance: digital modulation for analog FM systems, spectrum‐efficient digital FM, linear modulation, spread spectrum system, multicarrier transmission, and single‐carrier frequency‐division modulation. Special requirements for digital mobile radio communication are stable performance of bit error rate in fast‐fading channels and cochannel interfering environments, low power consumption, as well as size and cost‐effectiveness of equipment. The chapter also describes linear modulation/demodulation systems. The spectrum of linearly modulated signals is given by translating the modulating baseband signal spectrum into the carrier frequency. In spread‐spectrum systems the spectrum is spread by introducing additional modulation with SS codes. In this system, digital signals are transmitted in parallel using multiple carriers with different frequencies. The single‐carrier frequency‐division modulated signal recently shows a spectrum that is divided into several separated frequency regions and spreads by putting null spaces in the frequency domain.