Two classes of turbo codes constructed on high-order finite fields are introduced. The codes are derived from a particular protograph sub-ensemble of the (2,3) regular low-density parity-check (LDPC) code ensemble. The first construction results in a parallel concatenation of two non-binary, time-variant accumulators. The second construction consists of the serial concatenation of a non-binary time-variant differentiator with a non-binary time-variant accumulator, and provides a highly structured flexible encoding scheme for (2,4) LDPC codes. A cycle graph representation is also provided. The proposed codes can be decoded efficiently either as LDPC codes (via belief propagation decoding on their bipartite graphs) or as turbo codes (via the forward-backward algorithm applied to the component code trellises) by means of the fast Fourier transform. The proposed codes provide remarkable coding gains (more than 1 dB at a codeword error rate 10-4) over binary LDPC and turbo codes in the moderate-short block length regime.

This paper presents a radio interface recently standardised by ETSI under the name of S-MIM (S-band Mobile Interactive Multimedia) and especially designed to provide messaging services over GEO satellites using low-power terminals.

SafeTRIP is a project in progress partially financed by the Seventh Framework Programme's (FP7) European research and development activities in the subtheme of Sustainable Surface Transportation. SafeTRIP intends to implement a demonstrator of an integrated system, from data collection to service provision, that aims at optimising the use of road transport infrastructures. In this paper a general overview of the SafeTRIP architecture is presented. A detailed analysis and description of the functionalities characterizing the main elements of the system and a brief description of infomobility services such as alerting, disaster recovery and dynamic traffic data is given. A relevant part of this architecture is the Satellite Communication System which operates through the W2A Geostationary Satellite. To have an idea of the potentialities of the proposed system, a summary of functional requirements and performances relating to different types of services implemented is reported.

Two classes of turbo codes over high-order finite fields are introduced. The codes are derived from a particular protograph sub-ensemble of the (dv=2,dc=3) low-density parity-check code ensemble. A first construction is derived as a parallel concatenation of two non-binary, time-variant accumulators. The second construction is based on the serial concatenation of a non-binary, time-variant differentiator and of a non-binary, time-variant accumulator, and provides a highly-structured flexible encoding scheme for (dv=2,dc=4) ensemble codes. A cycle graph representation is provided. The proposed codes can be decoded efficiently either as low-density parity-check codes (via belief propagation decoding over the codes bipartite graph) or as turbo codes (via the forward-backward algorithm applied to the component codes trellis). The forward-backward algorithm for symbol maximum a posteriori decoding of the component codes is developed and simplified by means of the fast Fourier transform. The proposed codes provide remarkable gains (~1 dB) over binary low-density parity-check and turbo codes in the moderate-short block regimes.

In this paper, the current trends and the most recent advancements in the utilization of aerospace communications for emergency rescue applications will be discussed, with a special focus on the integration of the aerospace segment with terrestrial backbones and ad hoc terrestrial networks for both data connections and assisted localization (information about position is essential in emergency relief).

Satellite radio for vehicles is normally hampered by the problem of the shadowing of the line-of-sight between satellite and receiver. One possible way to overcome this challenge is to provide a new type of radio service, hereafter referred to as personalized satellite radio, in alternative to the streaming approach used for traditional radio: individual audio and multimedia files are broadcasted instead of transmitting a number of distinct continuous streams. The received files are stored in a large cache located in the receiver of each mobile terminal and are sequentially played to generate a service similar to traditional radio/entertainment programmes. The resulting file-based radio approach makes use of higher-layer coding on transport level, to ensure a sufficient file transfer reliability even when some packets are lost due to the shadowing of the line-of-sight path, and of smart techniques to build up an audible programme with no interruptions and full audio quality based upon the available files. The paper presents this novel radio concept and the results of extensive trials which were conducted with a system test-bed developed in the framework of an ESA funded project.

In this paper, we study the provision of broadband interactive services to passengers of Korean high-speed train in the ISM 2.4 GHz band. We address in particular the design of tunnel gap-fillers (GFs) able to provide bi-directional connectivity to train-based terminals. The work has been developed in the broader context of interactive services provision for high-speed trains through satellite networks. First, a channel model for the in-tunnel propagation is derived. Taking into account the results of the propagation analysis, a comparison between commercial technologies (belonging to both the IEEE and the DVB standard families) is provided, showing the possible strengths and weaknesses of the proposed solutions with respect to architectural and performance point of views.

The railroad satellite channel is characterized by frequent signal outages due to tunnels, bridges and electrical trellises. While for medium/long tunnels the main option to offer reliable and uninterrupted connectivity deals with the adoption of gap-filling techniques, signal outages due to small bridges/tunnels or electrical trellises can be faced with ad-hoc recovery techniques. In this paper, we face the problem from a link layer perspective, showing how a proper design of an erasure correcting code operating at link layer represents a valuable countermeasure against short outage events. The performance evaluation is developed in comparison with a more traditional technique based on physical layer coding in combination with a long channel interleaver. Advantages of the link layer coding scheme will be shown.

A key issue in the design of a mobile satellite communication system is an adequate knowledge of the statistical behavior of the propagation channel. To achieve this goal, the development of very accurate models plays a very important role. In contrast to traditional multi-state Markov chain based models, the novel approach proposed in this paper makes no prior assumptions on the number of states or on the statistical distributions characterizing each state. The sequence of channel states is blindly estimated using a Reversible Jump Monte Carlo Markov Chain algorithm.

A key issue in the design of a mobile satellite communication system is an adequate knowledge of the statistical behavior of the propagation channel. To achieve this goal, the development of very accurate models plays a very important role. In contrast to traditional multi-state Markov chain based models, the novel approach proposed in this paper makes no prior assumptions on the number of states or on the statistical distributions characterizing each state. The sequence of channel states is blindly estimated using a reversible jump Monte Carlo Markov chain algorithm.

Linear periodically time-varying systems are the basis of many practical systems, ranging from electrical networks with periodically time-varying components to filters which incorporate modulators in the signal path. Despite the pervasive use of digital systems, the study of analog time-varying systems can be considered an important branch of applied mathematics and control, with applications to' signal processing and communications. Given the well-known modulators filter bank description of a linear periodically time-varying system the spectral transformation between the input and the output would follow readily. This paper shows a simple way to find such a description for a continuous-time linear periodically time-varying system within a feedback loop, motivated by applications such as gated phase-locked loops.

Coding at the sample level in still image watermarking takes advantage of avoiding a non-optimum initial diversity stage, used in many watermarking systems for tailoring Gaussian channels with desired properties. Nevertheless, the low signal-to-noise ratio (SNR) encountered, due to the perceptual constraints imposed to the watermark, makes necessary the use of very powerful coding techniques as it happens in deep-space communications.We study the application of turbo coding to sample-level discrete cosine transform (DCT) domain watermarking. This near-optimum codification strategy is possible thanks to the existence of statistical models in the DCT domain, that also permit the computation of theoretical bounds for performance.

This paper studies the performance of the clock transfer scheme for burst-mode communication systems for which data are received during short, equally spaced intervals. Its main focus is on satellite-based time-division multiple-access (TDMA) communication systems with data regeneration and switching onboard the satellite, although the results apply to other TDMA systems as well. The system reference clock is generated onboard from an incoming, very stable ground source, based on a burst-mode demodulator that extracts the clock from a discontinuous modulated carrier due to the bursty nature of TDMA signals. If good enough, this onboard regenerated clock avoids the use of bulky and expensive clocks in the satellite payload and can act as the master clock of the TDMA system.