An asynchronous transfer mode (ATM)-based concept for the routing of information in a low Earth orbit/medium Earth orbit (LEO/MEO) satellite system including intersatellite links (ISLs) is proposed. Specific emphasis is laid on the design of an ATM-based routing scheme for the ISL part of the system. The approach is to prepare a virtual topology by means of virtual path connections (VPCs) connecting all pairs of end nodes in the ISL subnetwork for a complete period in advance, similar to implementing a set of (time dependent) routing tables. The search for available end-to-end routes within the ISL network is based on a modified Dijkstra (1959) shortest path algorithm (M-DSPA) capable of coping with the time-variant topology. With respect to the deterministic time variance of the considered ISL topologies, an analysis of optimization aspects for the selection of a path at call setup time is presented. The performance of the path search in combination with a specific optimization procedure is-by means of extensive simulations-evaluated for example LEO and MEO ISL topologies, respectively.

A top-down design methodology for LEO systems is illustrated by an example. The considered service is data messaging over local areas. The design method is based on a three-level approach: mission objectives, constellation selection and network design, and technical studies. It is shown that many alternatives are to be explored, and this requires a set of consistent and efficient simulation tools. The tools considered in the paper are a rapid computation algorithm for in-view period determination, and a discrete event simulation module. These tools are shown to provide the designer with means to rapidly select the appropriate constellation and evaluate the network performance.>

The authors present modeling of an integrated terrestrial-satellite network using very small aperture terminals (VSATs), for transaction-oriented computer applications. They address the analytical and simulation modeling techniques used to study the network performance. More specifically, these models are used to obtain network response times for an integrated terrestrial-VSAT network for inquiry-response applications under various load conditions at the cluster controller units. The major result obtained through this analytical and simulation modeling suggests that communications satellite channels can be used efficiently for the interactive inquiry-response traffic at an acceptable response time, provided that the system parameters including the link transmission rates are chosen appropriately.>

Data derived synchronization is plagued by self-noise arising from the randomness of the data stream. Experimental spectrum plots of the in-phase and quadrature self-noise components are given for various channel bandwidth and prefiltering conditions and different types of nonlinear devices. Results bring up features not covered by available theoretical analysis.

This paper presents a theoretical analysis supported by practical measurements of a digital self-bit synchronizer and detector. This synchronizer is based on the generation of spectral line components by nonlinear filtering of the received bit stream, and extracting the line by a digital phase-locked loop (PLL). Data detection is realized by a digital matched filter (DMF). The interesting features of this realization are the short acquisition time and the all-digital structure.