Modems for emerging digital cellular-mobile radio system

摘要

Digital modem techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed. 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 US digital cellular radio system applications are presented. The spectral/power efficiency and performance of the pi /4-QPSK modems (emerging American and Japanese digital cellular standards) are studied and briefly compared to GMSK (Gaussian minimum-shift keying) 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 other digital modems. More spectrally efficient modem trends for future cellular mobile (land mobile) and satellite communication system applications are also highlighted.