MODEMS FOR EMERGING DIGITAL CELLULAR-MOBILE RADIO SYSTEM

Digital MODEM (modulation-demodulation) techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed in this paper. In particular, theoretical performance, experimental results, principles of operation and various architectures of "pi/4-QPSK" (pi/4-shifted coherent or differential QPSK) modems for second generation U.S. digital cellular radio system applications are presented. The spectral/power efficiency and performance of the pi/4-QPSK modems (American and Japanese digital cellular emerging standards) is studied and briefly compared to GMSK modems (proposed for European DECT and GSM cellular standards). Improved filtering strategies and digital pilot aided (digital channel sounding) techniques are also considered for pi/4-QPSK and for other digital modems. These techniques could significantly improve the performance of digital cellular and of other digital land mobile and satellite mobile radio systems. Research results and publications of members of the Digital Communications Research Laboratory (DCRL) cellular/mobile radio group, University of California, Davis have been used in most of the performance prediction and review (tutorial) sections of this paper. More spectrally efficient modem trends for future cellular/mobile (land mobile) and satellite communication systems applications are also highlighted.