The paper discusses co-channel interference as the main interference effect occurring in the user up- and downlink of a multi-beam satellite. Different cluster sizes for the beam pattern are considered, and an optimum cluster size with regard to co-channel interference is discussed in more detail. For the satellite spot beam antenna, a typical tapered antenna is considered. The investigation is based on Monte Carlo simulation of user positions within the beam pattern, resulting in CDFs of SNIR and capacity. Moreover, usage of dual polarisations and the influence of rain fading are investigated.

The paper describes some essential trends in the development of satellite communications and introduces promising future applications. Important developments are the set up of standards based on digital video broadcast (DVB) and the application of on-board switching taking into account quality of service (QoS). Other developments are the application of multiprotocol label switching (MPLS) to satellite networks and the usage of optical inter-satellite and inter-platform links. Seamless interworking with terrestrial wireless access networks and with terrestrial core networks is of paramount importance for the success of satellite networks. Future applications of satellite communications include aeronautical satellite communications, satellite-based air traffic management and personalised land mobile radio broadcasting.

This paper outlines a methodology to estimate the bandwidth demand for a multiservice satellite system. The two basic components of the methodology are (a) an analytical estimation of single-service bandwidth demand for both FDM/TDMA and FDM/CDMA satellite systems, and (b) a general and tractable approach to system capacity dimensioning, essentially based on a new generic multiservice source traffic model. One of the key features of the multiservice model is its scalability, making it a practicable and future-proof tool in the rapidly evolving broadband communication world. Finally, a numerical evaluation of bandwidth requirements for a specified study system is provided.

Currently many efforts are undertaken to develop and install communication networks based on low Earth orbit (LEO) and intermediate circular orbit (ICO) satellites. However, many problems are to be solved before the final operation of such networks. This paper deals with basic design problems of LEO/ICO-based networks. The topology of the satellite network is considered and estimates for the number of satellites necessary, orbits and number of communication channels per satellite are derived. The features and consequences of intersatellite links are discussed. The number of communication channels per link is derived with a more elaborate model. This includes the radio links from the satellites to mobile users and to gateways, as well as intersatellite links and terrestrial lines. We introduce a formal model for LEO/ICO based networks and propose a method for the evaluation of the link capacities, given the network topology and the traffic requirements. As an example, two constellations are investigated in detail. One of these constellations is the Iridium system proposed by Motorola, the other is the LEONET concept developed in an ESA study. Finally, the influence of unequal traffic distribution is discussed.>

Two analytical methods for determining the packet error rate in the non-interleaved Rayleigh fading channel are presented. The first method is an exact evaluation of the packet error rate, whereas the second method is based on a k-state digital channel model. The fading model is a nonfrequency selective Rayleigh fading with a first-order low pass spectrum for the quadrature fading components. The analytical methods are complemented by simulations. The influence of the fading bandwidth on the packet error rate and the packet throughput is discussed. Block codes as well as convolutional codes are considered. The results show that without forward error correction the throughput for slow fading is higher than for fast fading. With forward error correction the packet error rate is sensitive to the fading bandwidth. Furthermore it is shown that the convolutional code with intra packet interleaving is least sensitive to slow fading.>

A concatenated two-stage adaptive error control scheme with automatic repeat request (ARQ) has been developed which is especially suitable for severely fading channels and for a very broad range of signal-to-noise ratios. This new scheme uses two stages of adaptive coding: the inner code is a rate compatible binary block code which due to its short blocklength can be maximum likelihood decoded taking into account soft-decisions and channel state information. For retransmissions code combining can be used. The outer code is a Reed-Solomon code which is maximum-distance separable and can correct error bursts as well as erasures indicated by the inner decoder. No interleaving is necessary and no critical optimization of system parameters is required to adapt to different channels and signal-to-noise ratios. In the paper, the scheme is described in detail and its throughput efficiency is analyzed. Also, simulation results for the throughput in the Gaussian and in the Rayleigh channel are presented. It is shown that the proposed error control scheme offers excellent throughput performance. Compared to other schemes, the new scheme maintains its efficiency over a very broad range of signal-to-noise ratios.>

Towards the year 2000, maritime satellite communications using the INMARSAT system will employ a second and third generation of satellites and new ship earth stations (SES). The new SES standards will use very small antennas with gains between 0 and 15 dBi. At the lower end of SES there will be no antenna stabilization. The communication channel for such small stations is described by a model including multipath fading, Doppler shift, and noise. The results of an extensive measurement program were used to determine the parameters of the channel model, which depend on antenna type and elevation angle. Analytical calculations as well as synthetic and stored channel hardware simulations have been used to determine the performance of several modulation schemes. A complete data link using PSK modems with AFC/Costas loop, interleaving, and FEC codecs at 1.2 kbits/s was built up around a hardware maritime channel simulator, to study the performance of data transmission on the small SES maritime channel. Theoretical and measured results are given for interleaved Viterbi decoding with channel state information and Reed-Solomon codes. The measurements show that with interleaved FEC schemes, the requiredE_{b}/N_{o}for a BER 10-5is in the range of 9-15 dB and the effects of multipath fading are almost compensated for.

Fading in mobile satellite communications severely degrades the performance of data transmission. The channel is modeled with nonfrequency selective Rice and Rayleigh fading. Also, stored channel simulation is used for hardware data transmission. FEC coding with Viterbi decoding of convolutional codes, and Berlekamp-Massey decoding of Reed-Solomon codes, are used to compensate for the fading. In addition to interleaving, channel state and erasure information improve the performance of the decoder. The BER after decoding is calculated for specific codes on several channels and for different transmission schemes. Using very simple channel state and erasure information gives 2-7 dB additional coding gain. These gains have been verified by hardware data transmission on synthetic fading channels and stored mobile satellite channels.