Axel Jahn

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. >

Evolution of aeronautical communications for personal and multimedia services

The demand to make air travel more pleasant, secure, and productive for passengers is one of the winning factors for both airlines and the aircraft manufacturing industry for which aeronautical communications is one of the enablers. This article describes current trends in the area of aeronautical passenger communication toward personal and wireless in-cabin communications and multimedia data networks. Technological challenges are summarized as well as market potentials and regulatory issues.

Propagation considerations and fading countermeasures for mobile multimedia services

This paper presents a summary of land mobile satellite (LMS) channel characteristics derived from several measurement campaigns. Narrowband and wideband measurements allow a broad interpretation of the LMS channels. Channel models and its parameters have been derived from the measured data as well. Furthermore, the impact of the LMS channel on the communication service is investigated and possible countermeasures are discussed. Link margins, power control schemes and satellite diversity can compensate the fading on the transmission links. The benefit of adaptive receivers and the dependence on the signal bandwidth are investigated, too. Copyright

Design and validation of QoS aware mobile internet access procedures for heterogeneous networks

In this paper, the requirements for personal environments mobility are addressed from terminal and network perspectives. Practical mobility and Quality of Service (QoS) aware solutions are proposed for a heterogeneous network, comprising of satellite and terrestrial access networks connected to an IP core network. The aim, in adopting a heterogeneous environment, is to provide global, seamless service coverage to a specific area, allowing access to services independently of location. An important assumption is that nomadic user terminals attached to a particular segment should be able to exchange information with any other terminal connected to the network. This is to ensure transparency of device technology. Different communication scenarios are investigated in support of IPv4 and IPv6 operating on user platforms and over access segments. The heterogeneous network necessitates the need to perform handover between access segments to enable coverage extension and seamless connectivity. Handover procedures are analyzed, and an approach is presented that enables various operation and segment specific parameters to be taken into account when deciding upon the need to perform handover and in selecting the optimum access segment. In order to ensure transparency of network technology, the need for end-to-end QoS support is discussed, bearing in mind the deployment of both IntServ and DiffServ enabled routers in the core network. Following this, a new admission control scheme, named Gauge&Gate Reservation with Independent Probing (GRIP), is proposed. The paper concludes with a description of a laboratory testbed, which has been developed in order to verify the presented procedures, together with performance measurements of the handover and the GRIP algorithms.

GSE: A flexible, yet efficient, encapsulation for IP over DVB-S2 continuous generic streams

The second-generation specification for Digital Video Broadcast over Satellite, DVB-S2, defines an improved and adaptive physical layer. A new framing structure at the link layer, known as the generic stream (GS), is introduced offering an alternative to the well-known MPEG transport stream (TS). This paper presents the requirements for and the design of an encapsulation protocol to transport IPv4 and IPv6 datagrams and other network protocol packets directly over DVB-S2 using this GS profile. The resulting generic stream encapsulation (GSE) is a novel method that provides flexible encapsulation with support for fragmentation. A flexible extension header format allows GSE to carry additional header information, suitable for enhanced features, such as link layer encryption and IP header compression. The paper assesses GSE performance by simulation using realistic traffic profiles and attenuation fading. This demonstrates considerable improvement in efficiency compared with the MPE/MPEG-2 TS, especially when used with adaptive coding and modulation (ACM). Although designed for DVB-S2 systems, the new encapsulation is suitable for other second-generation physical layer standards. Copyright

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.

MAC and encapsulation efficiency of satellite DVB using fade mitigation techniques

The paper discusses cross-layer issues of DVB-S2 networks with adaptive coding and modulation (ACM) on the physical layer forward link. Also future return channel via satellite (RCS) systems employing adaptive schemes on the return link are analysed. Cross-layer issues focus on medium access control (MAC) and encapsulation layer effects. Recent work of the S2 encapsulation over generic streams (GS) is described, and the effects on quality of service (QoS) scheduling for the forward link are analysed by means of simulation. A performance comparison between DVB-S and S2, both for transport streams (TS) and GS shows a significant gain by new encapsulation and fragmentation protocols that allow fragmentation across BBFrames. Here, realistic traffic scenarios with a mix of several services as well as rain fading are taken into account. For the return link, an adaptive scheme is discussed, going beyond the current RCS standard. Several approaches for access burst structures are presented and their impact on link efficiency through padding and encapsulation overhead is simulated. Finally, burst segmentation impact on jitter is investigated. Copyright

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.

A versatile propagation channel simulator for land mobile satellite applications

This paper introduces a new channel simulator for land mobile satellite (LMS) systems. The mobiles surroundings are characterized by topographical and land use data, as well as by a statistical description of single roadside objects. The propagation model combines the advantages of deterministic ray tracing algorithms with stochastic models for shadowing and short term fading effects. Thus, in contrast to entirely statistical and empirical approaches, the simulation tool is valid for a wide frequency range and a great variety of operational scenarios. Comparison of calculated results with published LMS measurements show good agreement.

Satellite Based Infrastructure for Emergency Communications

Several recent global disasters have resulted in high losses of lives and massive damage. Both early warning systems and rescue operations would have benefited from improved communications systems providing global coverage and robustness towards the destruction. Katrina wiped out 3 million telephone lines took out 38 emergency 911-call centers and impaired more than 1,000 cellular towers. There were major gaps in communication between different entities operating in the disaster recovery, that resulted in a series of logistical errors and let to a chaotic situation that required massive aid to control. The EU Commission states: “Recent large catastrophes and crisis like Tsunami the Katrina hurricane dramatically showed the importance of communication to prevent the deaths of thousands of people.” And the UN Office for Coordination of Humanitarian Affairs says “A Global Disaster Relief System is desperately needed”. Satellite communications offer a required robustness, global coverage and enables infrastructures to be in place in shorter time then any other technology. Awareness of communication needs in times of disasters is now at a high level worldwide, and satellites can play a key role in creating temporary adhoc infrastructures suitable for both rescue workers and victims during disasters. In order to address this issues, the European Commission is supporting a project called WISECOM; an acronym for Wireless Infrastructure over Satellite for Emergency Communications. This paper presents the WISECOM project, an initiative for outlining global requirements for emergency communications in light of initiatives by the UN, EU, ETSI and others, and discusses the potential impact WISECOM may have for the use of satellites in disaster recovery.