Erich Lutz

Integration of satellite and terrestrial systems in future multimedia communications

In this article we examine the role of satellite communications in future telecommunication networks and service provision. Lessons from the past indicate that satellites are successful as a result of their wide area coverage or speed to market for new services. Niche areas such as coverage of air and sea will persist, but for land masses convergence of fixed, mobile, and broadcasting will dictate that the only way forward for satellites is in an integrated format with terrestrial systems. We outline future ways forward for satellites, and discuss the research challenges and technology advances needed to facilitate this integrated approach.

Analysis of system parameters for LEO/ICO-satellite communication networks

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. >

A Markov model for correlated land mobile satellite channels.

Some of the planned new satellite communication systems will use satellite diversity, i.e. simultaneous transmission via two or more satellites, in order to enhance the quality of service. Starting from two-state Markov models for two separate land mobile satellite channels, a combined model for two channels is developed, which takes into account their statistical interdependence. The parameters of this model as well as the resulting service quality are analytically derived; they depend on the statistics of the separate channels and on their correlation coefficient. Numerical examples for the unavailability of service illustrate the influence of the correlation coefficient on the benefit of satellite diversity and give some insight into the possible range of improvement.

Packet error rate in the non-interleaved Rayleigh channel

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 (CTSA) error control scheme for data transmission in time-varying channels

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. >

Channel Characterization for Mobile Satellite Communications

This paper concentrates on channel modelling for mobile personal satellite systems. A single-environment channel model is introduced suitable to quasi-stationary flat-flat channels. The model is compared with results taken from the literature. Also a two-state generative channel model with parameters fitted from measurements is presented. Finally, the structure of a wideband channel model is proposed. In order to derive its parameters, DLR currently performs a measurement campaign for channel effects related to non-geostationary satellite systems. The programme comprises narrowband and wideband propagation measurements as well as interference measurements.

ATM-based multimedia communication via satellite

Within the next years, a large number of new satellite systems for broadband multimedia communications will be developed, mainly for fixed terminals, but to a lesser degree also for portable and mobile terminals. The most important systems will be based on low earth orbit (LEO) satellite constellations with inter satellite links (ISLs), and will be seamlessly integrated into the environment of terrestrial broadband networks. Since most of the terrestrial broadband networks will be based on the Asynchronous Transfer Mode ATM, it is advantageous for the satellite networks to adopt the ATM transmission scheme and implement ATM switches on board the satellites. However, compared to communication in fixed networks, satellite communication is characterised by special constraints (limited bandwidth, propagation delay, transmission errors, dynamic network topology) requiring the development of a new ATM-based communication technology. In the paper, an ISL-based LEO satellite network for multimedia communication will be considered. Several relevant aspects will be discussed, such as the system architecture, the system requirements, and the protocol architecture. Since the users access the satellite network via a radio interface, an error control scheme and a multiple access scheme suitable for multimedia communication must be implemented. The aspects of TDMA- and CDMA-based medium access control are discussed. Further issues are ATM resource management, radio resource management, and ISL routing. Finally, methods for terminal antenna steering are addressed, and the demonstration of aeronautical multimedia communication via the ITALSAT satellite is described.

Towards the Terabit/s satellite – interference issues in the user link

Present high-capacity geostationary satellites provide throughput in the range of 70 Gb/s (Ka-Sat) up to 140 Gb/s (ViaSat-1, EchoStar 17). In order to keep up with the quickly increasing bit rate requirements of new services and applications, future communication satellites must increase their capacity by an order of magnitude, thus reaching the terabit/s throughput range. The challenge of achieving a terabit/s satellite system requires investigation of a multitude of issues, limitations and problems. This paper discusses the main interference effects occurring in the user uplinks and downlinks of a multi-beam satellite: co-channel interference, adjacent-channel interference and cross-polarisation interference. Different cluster sizes for the beam pattern and use of dual polarisations are considered, and an optimum cluster scheme with regard to throughput is discussed in more detail. Moreover, the influence of beam spacing, interference cancellation for the user uplink as well as rain fading for the uplink and downlink are discussed. For the satellite spot beam antenna, a typical tapered antenna characteristic with side lobes is considered. The investigation is based on Monte Carlo simulation of user positions within the beam pattern, resulting in CDFs of signal-to-noise-plus-interference power ratio and capacity. Besides Shannon capacity, the achievable throughput of Digital Video Broadcasting - Return Channel over Satellite, 2nd Generation (DVB-RCS2), Digital Video Broadcasting over Satellite, 2nd Generation (DVB-S2) and Digital Video Broadcasting over Satellite, 2nd Generation, Extension (DVB-S2X) is evaluated. Considering 200 beams and 1 GHz of bandwidth, it is shown that with efficient uplink and downlink schemes, a total throughput of 1 Tb/s can be approached.

SatNEx - the European satellite communications network of excellence

Summary form only given. This paper outlines the primary goal of SatNEx which is to achieve long-lasting integration of the European research in satellite communications and to develop a common base of knowledge. Networks of excellence have been introduced as a new instrument within the 6/sup th/ IST framework program, and SatNEx is one of the first consortia to implement the new ideas and to overcome the fragmentation of European research. Through co-operation of outstanding universities and research organizations with excellent expertise in satellite communications, SatNEx will build a European virtual centre of excellence in satellite communications and contribute to the realization of the European Research Area (ERA) SatNEx will include an advisory board incorporating representatives of the European space industry, satellite service providers, and standardization and regulation organizations. SatNEx will collaborate with these players and put together a critical mass of resources and expertise needed for making Europe a world force in the field of satellite communications.

Co-channel interference in high-throughput multibeam satellite systems

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.