Space Communications

Broadband satellite systems will need specific functions and interfaces in order to fit seamlessly into an end-to-end Next Generation Network (NGN) Quality of Service (QoS) architecture. This paper will define NGN overall architecture, showing how the coupling between Application/session layers and Network/transport layers can achieve end-to-end QoS support. Possible integration scenarios of satellite access into such architectures will be depicted, with a special emphasis on transparent and regenerative satellite architectures based on DVB-RCS [ETSI EN 301 790 v1.1.2 (2003)] type of access.

Detailed architectures proposed by two recent research projects, IST Satellite Broadband Multimedia System for IPv6 (SATIP6) [http://satip6.tilab.com] and ESA Integrated Resources and QoS Management in DVB-RCS networks (QoSforRCS) [22nd AIAA Int. Communications Satellite Systems Conference; http://telecom.estec.esa.nl], will be presented. On the one hand, we will develop a “QoS assured” architecture proposed in the frame of QoSforRCS that provides dynamic Service Level Agreement (SLA) management and strict QoS control. The Admission Control (AC) function is located in the satellite Hub which allows fine control and billing by the Service Providers. On the other hand, a “QoS enabled” architecture proposed in the frame of SATIP6 is presented: it allows simple QoS differentiation between applications based on configuration by the end user or the subscriber's network administrator. This architecture may include AC function and is designed for Virtual Private Network (VPN) deployment.

In recent years, demand for broadband wireless IP networks which support mobility has increased tremendously. Satellite Internet could play a key role, provided that performance problems TCP protocol encounters on mobile satellite channels can be solved. In fact, in such a scenario TCP tends to perform poorly because of high delay-bandwidth product, high bit error rate (BER) and burst errors due to shadowing and multipath fading. With the aim of enabling mobile users to access Web service by a satellite terminal, a simulation campaign has been carried out to compare two different approaches that may improve TCP performance and, thus, HTTP and all other TCP-based application-level protocols performance in a mobile satellite-terrestrial integrated network. The former approach adopts TCP Reno and a reliable data link protocol on the satellite channel, the latter one exploits TCP Reno with the SACK option and an unreliable data link protocol on the satellite channel. The simulation results have shown that in sub-urban and rural environments recovering wireless losses at link layer can improve HTTP performance more than using an enhanced version of TCP.

Each object in an MPEG (Moving Picture Experts Group)-4 video data stream can be managed independently by using object-oriented coding. An object is composed of an ES (Elementary Stream) and transmitted through a DMIF (Delivery Multimedia Integration Framework) layer.

Digital Video Broadcasting (DVB) can be improved or enhanced in reliability, usability and compatibility by cyclic retransmission to a Data Carousel Return Channel via Satellite. This paper describes a cooperative system of MPEG-4 and DVB-data carousel that uses descriptors. The cooperative system works on two-way satellite environments. MPEG-4 clients can receive the data of DVB-data carousel, with the greater flexibility in representation of information inherent in MPEG-4. Further performance enhancement is achieved through use of a PEP (Performance Enhancing Proxy) server. Experimental results show significant improvement in data throughput.

The IP ConferEncing with Broadband multimedia over Geostationary Satellites (ICEBERGS) project investigated the provision of IP-based multi-party videoconference services through a communication infrastructure where Next Generation Satellite Systems (NGSS) are fully integrated with the Internet. GEO satellite platform features regenerative payloads with On-Board Processing (OBP) and Bandwidth on-Demand (BoD) capabilities, as well as multi spot-beams coverage. Many issues pertinent to multicast communications (e.g., QoS and users dispersion) can be easily overcome by possible solutions. The ICEBERGS scenario assumes a seamless interoperation of a Connection Oriented (CO) GEO satellite network with Internet multicast domains. This entails that, whenever a satellite transport service is required, connections must be dynamically set-up among different spot-beams bandwidth, depending on both the mutual position of sources and receivers of multicast groups in the satellite footprint area. In addition, fair bandwidth and the QoS requirements of multicast traffic must be met. This paper describes the main features of the interworking function defined between signalling protocols of the Internet multicast domains and the signalling protocol of the satellite network.

This paper presents a novel approach called VSP (Variable Size Packets) for satellite access lower layers. The VSP solution aims at optimizing the transport of packets issued from network layers with highly variable sizes. Therefore, VSP relies on the definition of multiple encapsulation sizes associated to a waveform, and an access adapted to the transport of variable size packets. We recall the VSP concept, insisting on its impact at the physical and access layers, and present an efficient coding and modulation scheme for the VSP solution, resources allocation constraints and packet sizes and slot sizes definition strategies.

This paper proposes a new rate based congestion control algorithm that significantly improves the utilization of planetary links with respect to classic TCP congestion control. Ns-2 simulation results have shown that the proposed algorithm provides significant goodput improvements with respect to New Reno, Reno Sack, Reno Fack, Vegas, and Westwood+ TCP in the presence of RTTs larger than 1 s and smaller than 2000 s and packet loss probability ranging from 0.0001 to 0.01.

The continuous growth of subscribers and the large variety of requested services in cellular communication networks are driving the telecommunication industry to provide ubiquitous information access and diversified services by requiring different bandwidth and Quality of Service (QoS). Proposals being pursued in several studies and field implementations address these needs using hierarchical architectures integrating satellite and terrestrial networks in a single advanced infrastructure.

In this paper a two levels hierarchical cellular communication network has been analyzed, integrating Low Earth Orbit (LEO) satellite and terrestrial layers. DS/CDMA multiple access is employed in both layers of this integrated telecommunication infrastructure. An original analytical model, based on queueing networks, has been developed for analysis of traffic. Analytical results evaluate the main system performance parameters in terms of new calls blocking probability and forced termination probability, for two classes of users.

The paper proposes enhanced algorithms for two of the three basic steps in Low Earth Orbit (LEO) satellite network routing: the downlink routing and the inter-satellite links (ISLs) routing. In this study we refer to polar/near-polar constellations and to connectionless routing protocols such as the ones based on the Internet Protocol (IP).

In particular a downlink routing procedure is proposed that does not exploit any external localization system to identify the position of the destination mobile terminal. In addition, an ISL routing algorithm is proposed that improves the one based on the minimization of the number of hops, by reducing the overall path length of the connection and, hence, the end-to-end delay.

The improved algorithms are evaluated in terms of system performance and computational burden. At the price of a neglectable increase in the computational complexity, a significant improvement in the end-to-end delay is achieved by using the proposed algorithm, when the source and the destination interface are largely spaced in latitude and longitude, with a consequent benefit on the overall LEO network efficiency.