Space Communications

It becomes more and more important to integrate satellites with transparent or on‐board switching payload into future Global Broadband Network Infrastructure. This paper presents an overview of the important issues and the recent development of satellite systems for broadband communications. Particularly, it discusses the architecture and performance of broadband network interconnection and terminal access using ATM over satellite. It covers a range of topics including: the major issues on the role of satellites in broadband networks, satellite system structure and architecture with transparent and on‐board switching payload, management and control over satellite, performance and Quality of Service (QoS) of ATM and IP over satellites, bandwidth resource management, future satellite systems and convergence of ATM and Internet.

Processing payload systems are in development now and will soon be part of the satellite communications landscape. This paper shows that processing payload networks can revolutionize the VSAT market. VSAT service providers who recognize the tremendous potential of these systems will be able to offer a dramatically lower‐priced solution to their customers while realizing even greater profits than were possible with transponder‐based networks. The ability to provide full mesh connectivity, dynamic resource allocation, and statistical multiplexing of diverse traffic results in lower costs for existing VSAT networks and an easy migration path for these networks to expand their capacity, connectivity, and range of applications. The results demonstrate that processing payloads represent a superior solution for both today's VSAT networks and for the more sophisticated applications and network topologies inevitable in the future.

In this paper, we investigated the feasibility of providing two‐way broadband access for residential interactive multimedia services such as video‐on‐demand, news on demand, home shopping or webcasting over multibeam satellite systems. We propose new air‐interface protocols and terminal structures for broadband access with special emphasis on the MAC (Medium Access Control) sub‐layer. Functional blocks of the various elements of the broadband satellite access system are presented.

The design of a generic waveform for Ka‐band multimedia satellites with On Board Processing and ATM‐based packet switching is described. Features like service requirements, system architectures, and ground terminal requirements are discussed. Modulation and coding schemes as well as generic frame structures and synchronization procedures are proposed. The impact on payload and equipment architecture is discussed, and a test system for demonstration presented.

This paper discusses relevant architectural trade‐offs performed to design the EuroSkyWay (ESW) satellite system for multimedia communications. The broadband satellite system aims at delivering multimedia services directly to the final users utilizing geostationary satellites. The system is designed to represent a cost effective solution to provide multimedia services throughout Europe, Africa and Middle East with the possibility of integration with the Global Information Infrastructure (GII) platform as well as with other satellite or terrestrial wide area networks.

The overall system architecture is based on the baseline regional system, that will cover Europe and some other countries close to Europe (the ‘extended Europe’), using only one satellite. The satellite network will be progressively increased with more satellites, grouped in clusters, both to extend coverage to other landmasses in the world and to increase the overall sellable capacity on already covered areas. Emphasis is given to the system trade‐offs for satellite performance dimensioning and to the issues relevant to the radio link dimensioning to ensure the needed link quality and data rate for multimedia services provision while keeping as key driver the user terminal low cost and ease of installation.

A code division access and switching method is applied to multibeam satellite for fixed service communications. In this article we present the system architecture, which consists of the Common Air Interface (CAI) and the onboard code switching mechanism. The CAl provides information traffic and Signaling control channels. The traffic channel access and modulation is based on a spectrally efficient CDMA (SE‐CDMA) scheme for which we examined the bit error rate performance. The SE‐CDMA can offer very low bit error rates at low signal to noise ratio while the available spectrum is reused in every beam (frequency reuse one). The onboard code switching mechanism is based on a Code Division Switch (CDS) for which we have evaluated the capacity, speed, and complexity. The CDS is a non‐blocking switch with complexity linearly proportional to its size and can route calls from an uplink to a downlink beam without onboard demodulation and channel decoding. Finally, we present the satellite routing control and optimization mechanism. The system operates with demand assignment control. That is, channel bandwidth and switch connections are only assigned upon user request. The services provided are circuit switched calls for voice data and video and packet switched for data.

Because of their large geographic coverage, inherent broadcast capabilities, and fast deployment features, network operators plan to use satellite‐based networks to supplement existing wire‐line and legacy networks to bring broadband and multimedia services to end‐users. Satellites are multiple access systems with limited transmission capacity compared to terrestrial network nodes. Therefore, end‐to‐end resource management for such systems is key to deliver acceptable Quality of Service (QoS) to services while providing adequate efficiency.

Using simulations, we study in some detail a method integrating Bandwidth on Demand with Call Admission Control in geostationary satellite networks with an on‐board switch. In particular, we describe a set of algorithms and study the impact of different types of bandwidth reservation on the QoS received by the connections and on the network efficiency.

This paper focuses on the performance evaluation of broadband multimedia services in S‐ATM (Satellite Asynchronous Transfer Mode) systems. The investigation includes service mapping and modelling techniques for both Geostationary (GEO) and non‐GEO systems. The queuing performance and the buffer dimensioning of an S‐ATM network model assuming that the network arrivals at the edges of this network are self‐similar processes is also investigated. A new methodology for creating service classes according to the user‐defined performance criteria is developed. Our approach can be used to dynamically regulate the system's call blocking and handoff failure probabilities for different services classes. A new radio resource management scheme, the Adaptive Bandwidth Reservation Scheme (ABRS) is proposed by incorporating two different threshold values for handling the new calls and the handoff requests. Due to the dynamic bandwidth reservation, each service class maintains a Grade of Service (GoS) profile that has been accepted or negotiated during the call set‐up phase and is guaranteed for a predefined service period.

Satellite networks play an indispensable role in providing global Internet access and electronic connectivity. To achieve such global communications, provisioning of quality of service (QoS) within the advanced satellite systems is the main requirement. One of the key mechanisms of implementing the quality of service is traffic management. Traffic management becomes a crucial factor in the case of satellite network because of the limited availability of their resources. Currently, Internet Protocol (IP) only has minimal traffic management capabilities and provides best effort services. In this paper, we presented a broadband satellite network QoS model and simulated performance results. In particular, we discussed the TCP flow aggregates performance for their good behavior in the presence of competing UDP flow aggregates in the same assured forwarding. We identified several factors that affect the performance in the mixed environments and quantified their effects using a full factorial design of experiment methodology.

A high data rate (HDR) satellite communication system is essential for developing the network configuration of a Global Information Infrastructure (GII) because of its features, such as wide area coverage, flexibility of network configuration and multicast connection capability. From this point of view, Communications Research Laboratory (CRL) is conducting research and development of a Gigabit satellite system [1] that has an on‐board ATM switch and gigabit‐class capacity. We have developed a hardware simulator in order to investigate how satellite links influence on‐board ATM switching and network performance, such as a long delay and burst error. In this paper, we describe the simulation results for the TCP layer performance and the SVC connection set‐up performance.

Multimedia spacecraft typically are required to have a high G/T and a high EIRP, at least for communications with user terminals on both the uplink and downlink, to allow for small and low cost user terminals on ground. This explains why the future of multimedia satellites will probably take place at Ka‐band. On‐Board Processing is widely considered for this type of spacecraft in order to efficiently use satellite power and to meet connectivity requirements. It is relatively easy to meet the RF and connectivity requirements if the system includes a single beam on the downlink or on the uplink. As the coverage is enlarged, the RF requirements are met by limiting the size of each spot and consequently, a multi‐spot system is required to cover the full service area. However, meeting the connectivity requirement becomes more complicated.

With Skyplex, EUTELSAT became the pioneer for the commercial exploitation of On‐Board Processing (OBP). From Hot Bird^TM 4 to Hot Bird^TM 6, the evolution of EUTELSAT's Skyplex OBP units has shown a constant improvement in flexibility, number of channels processed and link budget gain. The future of OBPs for multimedia applications could go through the utilisation of standards like the DVB‐RCS and DVB‐S (Direct Video Broadcast – Satellites), respectively for uplink and downlink, that now offer the system designer a tool box to design a system compatible with standard user terminals, and the achievement of connectivity requirements.

A key driver for new telecommunication systems and networks are interactive multimedia services. Satellites will play an important role in these future multimedia applications. A major characteristic of the access traffic is its asymmetry, which typically is very bursty on the inbound direction and consists of a multiplex of burst and stream traffic on the outbound link. One attractive access technology based on advanced satellite communication systems is the use of on‐board processing techniques. With these development in mind, the ARTES‐2 ‘On Board Processing Demonstration Project’ was initiated by ESA in 1994. The objectives were to develop all necessary building blocks to realize a complete satellite communication network.

An overview of the European Space Agency's activities in the field of broadband communication satellite systems is provided. Results for the system design, validation and building block developments of ARTES 2 are provided and the relationship with on‐going ARTES 3 activities is given.

Starting with a short summary of the development status of digital demodulators for on‐board processing applications, the motivation for and scope of the COMED development program is given. The requirements specifications and realisation concepts for advanced multi‐carrier and wide‐band demodulators are presented. Issues of flight hardware implementation are discussed.

The fully digital multi‐carrier demodulator for the SpaceMux™ On‐Board Multimedia Processor implements a focussed subset of the DVB‐RCS transmission standard. This paper describes the design constraints and system considerations influencing the trades‐off, and the ensuing design. Aspects of the ASIC technology chosen for implementation are also addressed, as is the performance in the presence of signal imperfections.

The launch of regional GEO multimedia satellites will initially support an Internet over satellite service in a star network configuration interconnecting users to an ISP. While a star network is ideally suited as an access technology for the bulk of Internet traffic including web browsing and email, the increasing need to support mesh networking for other applications is expected in the future. These applications include conferencing and business to business (B2B) eCommerce.

For a GEO satellite in particular, this requires an on‐board processor to support single hop interconnectivity between small low cost terminals. This approach achieves the following advantages compared to a star configuration, which would require a double hop: (1) it minimises the latency by reducing the roundtrip delay in half; (2) it halves the capacity utilized; and (3) it provides signal regeneration, additional coding gain and switching. In general, some form of switching is required to interconnect beams in a multi‐beam system, typical of regional multimedia satellites which employ high gain spot beams to increase link margin and frequency reuse.

In this paper the architecture and operation of the EMS SpaceMux^TM on‐board processor is described which achieves these objectives for mesh networking. The first generation of SpaceMux^TM supports the DVB‐RCS air interface and will operate as a demonstration of OBP mesh networking technology on the Telesat Anik‐F2 satellite due to be launched in the third quarter of 2002.

Flexible on‐board switching plays an important role in future Ka‐band systems. On‐board switching is required to establish the interconnectivity between the various beams of the satellite and to allow for an efficient use of the limited spectral resources. Due to long duration of the operational phase, on‐board switching must have the flexibility to support an evolving multiservice scenario. In this paper we present architectures for on‐board fast‐packet switches based on label switching technology. An ATM‐based on‐board switch with a shared bus architecture is described. This switch is suitable for a satellite system with medium throughput requirements. The development of components and technologies for high capacity switches with a throughput of 5–10 Gbit/s, within a German technology development programme is presented. Architectural design options are discussed. Both switches support a flexible resource assignment in both the uplink and the downlink and Quality of Service (QoS) by means of suitable DAMA protocols. Special emphasis is laid on flexibility, modularity and fault tolerance.

In the satellites with on board processing, congestion can occur as a result of statistical multiplexing on board the satellite. This would have negative impact on performance and satellite resource utilization. Effective congestion control schemes are required in order to prevent or limit the extent of congestion.

The current paper concentrates on a novel scheme for congestion avoidance in multiple‐beam satellites with on board switching. The scheme is rate‐based and relies on the broadcast nature of the satellite in order to provide efficient support for Available Bit Rate (ABR) services. An important element in achieving efficiency is the synergy obtained by combining the congestion control with the mechanisms of the MAC layer scheduling. The new scheme has a distributed architecture, with algorithms implemented on board the satellite and in the ground terminals. After a detailed description of the scheme, simulation results are provided in order to illustrate its performance.

This paper discusses on‐board dynamic bandwidth allocation for satellite OBP‐based broadband multimedia interactive applications. The paper presents a bandwidth allocation scheme which is oriented towards guaranteeing the Quality of Service (QoS) associated with, but not limited to, the various traffic services/classes as defined by the ATM forum. A novel uplink (UL) access scheme is proposed, based on a Multi‐Frequency Time Division Multiple Access (MF‐TDMA) primary access scheme. The uplink access protocol derived from the proposed scheme can be supported directly on board by the means of the scheduler function. The performance of the uplink access scheme has been evaluated through extensive simulations and sample results are presented and commented. EMS’ heritage on both ground and OBP‐based schedulers is also presented.

In DVB‐RCS systems, Return Channel Satellite Terminals (RCST) receive a stream of Network Clock Reference (NCR) packets from a central Hub station to regenerate their internal clocks and aid network synchronisation. Where the NCR is generated at a ground Hub station the delays between Hub and satellite (and the reverse path) must be measured; an allowance for the measurement error is made in the guard time. The bandwidth efficiency gains of locating the NCR clock on‐board the satellite are evaluated: for high transmission rates the gain may be worthwhile whereas for lower rates a negligible benefit exists. In some applications, on‐board processing may be used to switch packets on the forward link (for routing to different beams). With an on‐ground NCR source, the satellite switching most likely results in NCR delay variance (jumps) beyond acceptable limits for correct RCST frequency regeneration. An on‐board NCR clock aids a system architecture that encompasses forward link switching and can be justified in these circumstances.