Digital phase modulation methods giving a band-limited spectrum for satellite communications

Abstract

SUMMARY This paper highlights a new class of digital phase m odulation methods which are designed to obtain very low out-of-band radiation of a hard-limiting radio transmitter without the use of output filtering. After enu~erating the main requirements of a digital modulation method for satellite communication in a multiple FDMA mode, usable in small and simple ground ter~inals, known digital modulation methods such as QPSK and MSK are scrutinized regarding these requirements. It appears that there is a need for spectrum control to reduce the out-of-band radiation to a l ower level. A general outline of the measures necessary to achieve this is given, and these are illustrated by two practical examples, TFM and COR-PSK (4-51, which were invented at the Philips Research and Advanced Developpent laboratories. Calculations and measurements of the output spectra indicate a monotonic decreasing sideband level at a rate of about 80 dB per fbit frequency change. The phase trajectories are compared with t hose of some known digital phase m odulation methods. Good phase control is essential for exact spectrum control, t herefore new types of phase modulators which perform this function are described. Finally, the obtainable channel separation with TFM is indicated and some details of the receiver circuitry application in small ground terminals are discussed.