In this paper we discuss multidimensional signaling for transmission over the satellite channel, i.e., a bandlimited radio channel with nonlinearities. We derive a set of basis signals that are orthogonal and whose bandwidth occupancy is minimal, in the sense that they maximize the power inside a fixed frequency interval (/spl minus/B, B). Since we remove the assumption that the signals be confined in one symbol interval, the concept of orthogonality must be revisited. We design basis signals that satisfy the following requirements: (a) When passed through their matched filter, the sample sequence has no intersymbol interference; (b) when passed through the filter matched to another basis signal, the sample sequence has no interchannel interference, and (c) their bandwidth occupancy is minimum. The performance of four-dimensional signals designed according to this criterion is evaluated in terms of bandwidth occupancy and error probability over nonlinear satellite channels. Comparisons with two-dimensional modulation schemes (in particular QPSK) are also made.>

TOPSIM III is a flexible, easy to use, stand-alone Fortran package for the digital simulation of communication systems in the time domain. TOPSIM III provides a simple high-level language for the description of the system. Programs can be written following the same structure used in drawing the system block diagram. The paper discusses the time domain simulation approach used in the design of the package and describes its capabilities. The contents of the subprogram libraries are presented, describing some of the building blocks that can be used in the simulation as well as the performance evaluation facilities available in the package. Some simple examples illustrate the use of TOPSIM III as a tool for analysis and design of digital communication systems.

A mixed analytic and simulation method is described for the study of a DCPSK up-link used in a regenerative satellite transmission system. A great variety of impairments is considered and their effects on error probability are evaluated, thus emphasizing the performance evaluation in a "real situation." A case study is worked out in detail to stress the design-oriented approach.

An expression for the error probability of multilevel coherent phase-shift-keyed (CPSK) systems in the presence of intersymbol, interchannel, and co-channel interferences and additive Gaussian noise is derived. An exact expression is given for the binary CPSK system, whereas upper and lower bounds are presented for the multilevel systems. The approach proposed in this paper overcomes the difficulties of the exhaustive methods and allows accurate and fast evaluation of the character error probability. Only the impulse responses of the overall channels are needed, and the computational labor is reduced to the numerical evaluation of one particular type of integral, whose computation is based upon nonclassical Gaussian quadrature rules. The model of the system is general enough to allow the choice of a rectangular or otherwise-shaped modulating pulse and a constant or shaped envelope of the modulating carrier. Phase incoherence between adjacent carriers is also assumed, and a random misalignment among the modulating bit streams can be taken into account, if necessary. Extensive numerical results are presented for 2- and 4-level systems. The presentation of the results stresses a possible utilization of them in system design problems.