Interference on SATCOM up-links and its suppression

Most of the current communication systems are based on copper or fibre-opti c links which provide coverage only where cables are available. To overcome this limitation, an increasing number of communication systems are being b ased either on terrestrial radio or on satellite communication (SATCOM) lin ks. The latter is focused on in this paper. There the transmitted signals a re relayed over a satellite transponder. Most current systems cover broad g eographical regions; future systems will provide global coverage with from ten to several hundred satellites (F. Abrishamkar and Z. Siveski, 'PCS glob al mobile satellites', IEEE Commun. Mag., 34(9), 132-136 (1996)). At the en d of this century there will be two or three worldwide operating satellite systems competing with each other. As a consequence, the chance of mutual i nterference is augmented, since the number of transmitters radiating their signals towards the sky is multiplied. In the case of transparent transpond ers, used here, all received signals are retransmitted back to the earth. E ach extra signal reduces the energy available to the user signal. Owing to the non-linearity of the transponder, operated relatively close to saturati on, intermodulation (IM) products are created that influence the user signa l quality. The effects of interference from a single interfering signal on the uplink are investigated in this paper with the aid of a simulation mode l for 20-30 GHz SATCOM links (M. Kohl, Simulationsmodelle fur die Bewertung von Satellitenubertragungsstrecken im 20/30GHz Bereich, Forschungsberichte aus dem Institut fur Nachrichtentechnik der Universitat Karlsruhe (TH), Ba nd 1, 1997). First the influence of different interferers and their effects on the transmission of the user signal are evaluated. Subsequently the use r signal is modulated by a bandwidth-spreading waveform so examine its inte rference suppression capabilities. Two techniques, frequency hopping (FH) a nd direct sequence spread spectrum (DSSS), are considered. As far as the au thors know, no investigations equivalent to the work described in this pape r concerning the interference on SATCOM links are reported in the literatur e. (C) 1998 John Wiley & Sons, Ltd.