Space Communications

The introduction of telecommunication services on commercial flights for passengers and airline crew requires a careful balance in the value chain in order to offer services at reasonable prices, and thereby speed up the market acceptance. Thus, a comprehensive business model is needed that addresses all types of services, licensing, billing, roles of the interested parties, and the relation of the business model to system architecture.

Services like Web browsing and E-mail can be offered without licensing issues. Mobile telephony and short message service (SMS) require licensing, and most likely, both the involvement of mobile operators and roaming agreements, for rapid market expansion. This paper describes the different actors likely to participate in the business model. Of two alternative business models, one is preferred that may simplify system architecture, enabling operators to maintain virtually unchanged networks. The impact of the preferred business model on the billing system is described in some detail.

The objective of the FIFTH Network Project Demonstrator is to study and implement a prototype of a new satellite network skilled in delivery broadband service for fast train travellers. The prototype system will be composed by a satellite terminal and related local area network (LAN) installed on a train, and an access network for support and delivery of suitable services for train users. Following the development phase for the prototype, a validation campaign is foreseen to test services and applications for travellers in a railway environment and scenarios. Towards these ends, two main objectives for the Demonstrator System are: protocol and service validation using a geo-satellite access infrastructure; and channel measurement for radio channel characterisation in the railway context.

In the present paper, the Demonstrator infrastructure and validation strategy under development are described.

The prototype is based on a Ku band satellite access network using the Atlantic Bird 1 positioned at 12.5° W with the DVB-RCS access scheme.

The activity benefits from heritage embodied in several EC frameworks projects, such as SECOMS/ABATE and SUITED.

A number of broadband satellite systems have been proposed in recent years, offering alternative technical solutions. In order to reduce the cost of user equipment and expand the market of satellite services, it should be possible in the future to achieve a high level of commonality of user terminals between different satellite systems, even if different transmission schemes are used.

IP-based transport is an established solution for provisioning of generic services. It is also a means of unifying different underlying networks to provide interworking between them, for example between satellite and terrestrial networks such as the Internet. Nevertheless, special support or adaptation of IP is needed over satellite networks to ensure such features as QoS for multimedia services, fair access to satellite resources, efficient use of radio resources especially for bursty traffic.

Therefore, a generic satellite system (and terminal) architecture based on IP services and incorporating the qualities above was defined to allow flexibility for alternative satellite technologies. This was the main objective of the BRAHMS project, whose results were further developed in the SATIP6 project, both sponsored within the 5th European Research Framework in the area of IST (Information Society and Technology). The BRAHMS project, in particular, greatly contributed to the standardization activity in the field of broadband satellite access especially within the ETSI BSM working group.

It is generally impossible to exchange, repair, or upgrade onboard equipment in orbit, and communications satellites are designed for fifteen or more years of life. Consequently, orbiting communications satellites cannot follow unforeseen changes in terrestrial communications. Moreover, because of long lead times and high costs of satellite development, it is difficult to implement the latest technology at launch. And even if the latest communications technology were implemented at the time of launch, the configuration on orbit has limited capability for configuration change to parallel the endless evolution in terrestrial communications technology.

In this paper, we propose a reconfigurable communication satellite system based on formation flying and inter-satellite communications technology. The satellite is composed of a group of satellites. The functions implemented by each satellite are defined by the OSI (Open Systems Interconnection) reference model. The discussion centers on a three satellite constellation or cluster having relatively close spacing; but the concept may be applied to larger clusters and spacings. Satellites implementing higher OSI layers are small and also on a size reducing trend. Replacing or adding small satellite elements might enable the cluster as a whole to keep pace with frequent paradigm shifts of terrestrial networks.

The provision of multimedia services via a non-geostationary satellite system characterised by highly dynamic conditions requires advanced traffic engineering procedures, including adaptive routing and adaptive forwarding. In this paper we assess traffic class dependent routing in the low earth orbit satellite system with a packet switched intersatellite link network. Traffic class dependent routing is enhanced with adaptive forwarding based on local link load information, which selects the most suitable of the two alternative shortest paths to the destination without any link status distribution between neighbouring nodes. The performance of the proposed forwarding policy is evaluated in two different traffic load scenarios, using a specifically developed simulation model. The simulation results are presented in terms of average packet delay in the network, average normalised data throughput and positions of satellites with critically loaded links. The simulation results indicate that the use of traffic class dependent routing with adaptive forwarding based on local link load information improves the network performance significantly in terms of all performance measures, and that the number of critically loaded links is drastically decreased due to the fast response of the adaptive forwarding policy to congestions on the link.

Resource allocation schemes dedicated to Satellite environment often consider Internet traffic as the superposition of traffic sources without distinguishing between TCP and UDP flows, even if TCP and UDP have different traffic characteristics. In this paper we introduce a system control architecture with three types of flows entering the network, i.e., Constant Bit Rate (CBR), UDP and TCP, and a cost function including an analytical measure of the packet loss for TCP flow. We propose an extension of our previous bandwidth allocation control algorithm Constrained Average Probability–Adaptive Bandwidth Allocation in Satellite Channel (CAP–ABASC) to Extended CAP–ABASC. We provide performance evaluation of the two allocation strategies.

Using advanced Forward Error Correction (FEC) and Adaptive Coding and Modulation (ACM) significant advances have been made to increase the capacity in terms of bits/symbol/Hz for satellite communications. The use of adaptive modems with advanced FEC can increase the capacity for two-way, spot-beam, satellite Internet systems by a factor of three to four over fixed-link based systems using DVB-S on the forward link.

Turbo Product Codes (TPC) and Low Density Parity Check (LPDC) codes permit higher-level modulation (8-ary and above) for providing capacities in the range of 2 to 3 bits/symbol/Hz using power levels that fall within the capability of spot-beam satellite systems. This capacity compares with the typical 1 bit/symbol/Hz for DVB-S using QPSK modulation and a concatenated Reed Solomon outer code with a Convolutional inner code. Gains that can be achieved using TPC and LDPC codes in conjunction with higher level modulations are presented as well as special framing techniques that can be utilized for ACM.

For ground to space radio links, the influence of rainfall on slant path propagation at frequencies above 10 GHz is crucial, especially in tropical and equatorial regions. For the prediction of rainfall attenuation it is necessary to determine the 1-minute rainfall rate distribution. Rainfall rate data acquired from five multiple sites are analyzed to investigate the statistical stability of the cumulative distribution of rainfall rate. The five sites are university research institutions in the Pacific tropical zone. The measured cumulative rainfall rate distributions are compared with the Rice-Holmberg, ITU, Moupfouma, Gamma and Lognormal models. The Moupfouma model was found to be best fit with the measured data.

Apparent antenna gain and polarization effects are dealt with for the case when random scatterers make the received field diffuse. First order multiple scattering and Stokes space concepts are used, respectively, for description of the phenomena. Polarization diversity performance is also dealt with, using a novel approach.