Interference on satcom up-links and its suppression

Most of the current communication systems are based on copper or fibre-optic links which provide coverage only where cables are available. To overcome this limitation, an increasing number of communication systems are being based either on terrestrial radio or on satellite communication (SATCOM) links. The latter is focused on in this paper. There the transmitted signals are relayed over a satellite transponder. Most current systems cover broad geographical regions; future systems will provide global coverage with from ten to several hundred satellites (F. Abrishamkar and Z. Siveski, ‘PCS global mobile satellites’,IEEE Commun. Mag. , 34(9), 132–136 (1996)). At the end of this century there will be two or three worldwide operating satellite systems competing with each other. As a consequence, the chance of mutual interference is augmented, since the number of transmitters radiating their signals towards the sky is multiplied. In the case of transparent transponders, used here, all received signals are retransmitted back to the earth. Each extra signal reduces the energy available to the user signal. Owing to the non-linearity of the transponder, operated relatively close to saturation, intermodulation (IM) products are created that influence the user signal quality. The effects of interference from a single interfering signal on the uplink are investigated in this paper with the aid of a simulation model for 20–30 GHz SATCOM links (M. Kohl, Simulationsmodelle fu ̈r die Bewertung von Satellitenu ̈bertragungsstrecken im 20/30 GHz Bereich, Forschungsberichte aus dem Institut fu ̈r Nachrichtentechnik der Universita ̈t Karlsruhe (TH), Band 1, 1997). First the influence of different interferers and their effects on the transmission of the user signal are evaluated. Subsequently the user signal is modulated by a bandwidth-spreading waveform to examine its interference suppression capabilities. Two techniques, frequency hopping (FH) and direct sequence spread spectrum (DSSS), are considered. As far as the authors know, no investigations equivalent to the work described in this paper concerning the interference on SATCOM links are reported in the literature.  1998 John Wiley & Sons, Ltd.