Digital modulation has been used for a long time in analog FM mobile radio communication systems. The role of digital transmission in the analog FM mobile radio system is to send low-speed data signals to control the system, for example, paging a called mobile terminal and setting up and releasing of a dedicated channel. Spectrum efficiency of the digital modulation was not a key issue for such systems, since the data transmission rate is low: from several hundreds to thousands of bits per second.
The history of research and development of spectrum-efficient digital modulation techniques for mobile radio communication is not so long. It started in 1978 with the invention of spectrum-efficient digital FM by de Jager and Dekker. After their invention, many digital modulation methods were proposed in a very short period, described later in detail. The motivation for efficient digital modulation was digital voice communications.
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. Research and development in digital modulation techniques for mobile radio communications are still in progress at the time of the writing of this book.
Special requirements for digital mobile radio communication are stable performance ...