The simulation of complex telecommunication systems, such as satellite-based networks, is seldom sufficient to understand fully their real behavior and to evaluate the quality of service (QoS) perceived by their users. The mean opinion score (MOS) method, widely used to evaluate the perceived QoS, requires the use of a working system, and this is usually not the case for satellites, when studying new protocols and/or new system architectures. A simulator able to replicate in real time the behavior of the system under examination would be very useful: we call it an emulator. This paper describes an emulator for IP data traffic on a single beam GEO satellite, with TDM/TDMA radio links and on-board circuit switch. The emulator has been implemented in the CNIT Radio Communication Laboratory at Politecnico di Torino.

The architecture of a high speed packet switch for an ATM system is presented. The switch is based on input electronic modules, where the incoming packets are processed and buffered, and on an optical interconnection network, connecting the inputs to the outputs. During each slot each output can receive a single packet, and each input can transmit up to L packets. A reservation mechanism avoids collisions on the optical network, implementing a series of distributed queues. The switch performance was studied by simulation. The effect of the input switching capacity L on the performance is discussed.>

TOP/PDT, a toolkit for the development and the simulation of communication protocols, is presented. A protocol is described by a high-level language, derived from SDL, and named PDL, short for protocol description language. A compiler translates PDL programs into C programs; these are then compiled and linked using the utilities of the host operating system. TOP/PDT is an open environment: to add functionalities or to optimize a protocol, users can add their own functions, usually written in C, to the existing function library. The validation of the protocol is done by simulation. PDL allows the characterization of the data link(s) used to transmit and provides a set of measurement functions to evaluate the protocol performance. The modular structure of TOP/PDT and the use of the C programming language make it easily portable. The executable program generated using TOP/PDT can also run without a host operating system, since the PDT kernel provides a minimal operating system able to handle an unlimited number of processes and ensures their mutual exclusion in the access to shared data.>

The theoretical aspects of the encoding process are investigated, resulting in a precise definition of linear codes together with theorems that clarify how they can be obtained. A particular subset of linear codes, called superlinear codes, for which the performance analysis is highly simplified is identified. The most relevant performance measures for the analysis of this class of codes are discussed. The minimum Euclidean distance and the event and bit error probabilities are found analytically using the uniform error property (when applicable) or variations on it. This yields accurate upper and lower bounds to the error rate at the price of reasonable computational complexity. The theory is then applied to the search for 'good' codes and to their performance evaluation. The cases of 16- and 32-PSK codes, which are good candidates for use in digital satellite transmission, are considered. Several new results in terms of error event and bit error probabilities are presented, showing considerable gains in terms of SNR with respect to the uncoded case.>

The performance of combined coding and modulation schemes in channels with intersymbol interference and nonlinearities is studied using an analytical approach. The class of possible receivers is presented, and a generalization of the minimum Euclidean distance used for the asymptotic analysis of the performance of combined coding and modulation schemes on AWGN channels is introduced. Numerical results are presented for coded 16-PSK modulation.