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Digital Satellite Communications focuses on the study and design of efficient and flexible physical layers for broadband mobile and fixed satellite links. The chapters address long-term developments for advanced physical layer techniques in broadband communications, fixed and mobile terminals, and 4G evolutions with a potential convergence between different technologies. A general description of satellite systems and services is provided which organizes the material into a generalized and readable framework. The approach is both analytical and descriptive. The book provides a unified view of essential topics, including: - fundamental theories - channel coding and modulation - synchronization and parameter estimation - distortions and countermeasures - diversity techniques - multiplexing and multiple access schemes - software radio Digital Satellite Communications is ideal for researchers and students in the fields of communication and signal processing.

For a long time, mainstream psychological research on cognitive pro- cesses has been focused on the investigation of externally-oriented cognition, namely deliberate processes generated in response to cues provided by the experi- menter and associated with specific experimental paradigms. During the last two decades, there has been a surge of interest in both psychology and neuroscience toward the investigation of internally-oriented cognition, and, among the different kinds, a growing interest has been devoted to mind wandering (MW), which repre- sents a shift in the contents of thought away from an ongoing task and/or from events in the external environment, toward internal mental contents. By definition, MW is characterized by a flow of thought, and it occurs without a fixed course or a drive to reach a specific goal. Creative thinking also involves dynamic shifts between different information and mental states. Does mind wandering contribute to creativ- ity? Here we briefly review mixed findings on the association between MW and creativity and we outline a new multidimensional dynamic approach, in which the associations between different kinds of MW (i.e. spontaneous and deliberate) and different forms of creativity are considered. Practical implications of this approach are discussed.

International audience; The problem of fast code acquisition in dual-band Galileo receivers is tackled. The proposed techniques exploit the Galileo E1 and E5 Open Service signals structure, implementing a cross-band aiding approach that yields mutual assistance in code synchronization adopting a master/slave configuration. The schemes are analyzed in terms of mean acquisition time (MAT) introducing the procedure flow-graph and overall mean acquisition time (OMAT). Numerical evaluation shows enhanced OMAT performance w.r.t. autonomous dual-band acquisition, guaranteeing complexity reduction.

We consider a windowed decoding scheme for LDPC convolutional codes that is based on the belief-propagation (BP) algorithm. We discuss the advantages of this decoding scheme and identify certain characteristics of LDPC convolutional code ensembles that exhibit good performance with the windowed decoder. We will consider the performance of these ensembles and codes over erasure channels with and without memory. We show that the structure of LDPC convolutional code ensembles is suitable to obtain performance close to the theoretical limits over the memoryless erasure channel, both for the BP decoder and windowed decoding. However, the same structure imposes limitations on the performance over erasure channels with memory., 18 pages, 9 figures, accepted for publication in the IEEE Transactions on Information Theory

This paper takes a broad view on the history and the present status of satellite communications and broadcasting. The necessary starting point of this overview is the visionary papers produced by Sir Arthur C. Clarke and John Pierce. This was the real dawn of the satellite communication era. This paper attempts to explain the “fil rouge” of the evolution of satellite technologies across six decades, analyzing successes and failures of past satellite missions, and concluding with a picture of future satellite communications.

This paper addresses the problem of robust frame synchronization for TDM/TDMA systems in the presence of frequency errors, accomplished through data-aided recognition of the Unique Word (UW) preamble in the transmission flow. Robust detection design is performed applying, through approximations, the Maximum Likelihood (ML) criterion coupled to Post Detection Integration (PDI), to obtain a novel detector identified as Balanced-GPDI (B-GPDI). This new approach considerably outperforms other schemes available in the literature, at the cost of a moderate complexity increase. This is possible thanks to an optimized use of coherent accumulation, which enhances the correlation term in the decision variable, along with highly accurate modeling of the energy correction factor. To limit complexity increase and memory requirements, several approximations of the exact B-GPDI are proposed and discussed in the paper, to provide the designer with practical solutions that are still able to outperform other approaches in specific application scenarios. In particular, approximations for low and high Signal-to-Noise Ratio (SNR) are presented. Different application scenarios are considered in the paper for numerical analysis. In particular, the cases of forward link Continuous Transmission (CTX) and return link Burst Transmission (BTX) are addressed.

5G communications will enable new paradigms architectures and services, and the integration of satellite and terrestrial networks can play a key role. Cognitive radios are seen as the most promising solution to dynamically cooperate, in order to exploit advanced frequency sharing techniques. To this end, efficient sensing techniques for spectrum awareness are a must. In this paper, we provide preliminary results on energy detection (ED) and cyclostationary feature detection (CFD) algorithms applied to a downlink Ka-band scenario. These results show that coexistence between satellite and terrestrial networks is possible and cognitive radios can ease their integration in future 5G communications.

This paper describes the origins of the Advanced Satellite Mobile Systems Task Force (ASMS-TF), its structure and its membership. The paper also discusses the overall vision of the Task Force for the short and for the long term, and the objectives which the Task Force is pursuing. What the Task Force has achieved so far in its existence is listed, together with its future plans and priorities.

This paper deals with the analysis of the code-acquisition process performed by a mobile terminal in a code-division multiple-access cellular system. The fundamental contribution is the setting of a theoretical framework for code-acquisition analysis, accounting for the presence of fading and shadowing with specified coherence time. A multidwell architecture is considered, accounting for different verification strategies. The MAX/TC detection criterion is used, and the acquisition performance is analyzed, following both the direct and flow-graph approaches. Expressions for the acquisition time probability density function under different assumptions are given, as well as closed-form expressions for the mean and variance of the acquisition time. Practical applications and numerical results are reported in the Part II companion paper.

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Metodo per la riduzione del rapporto tra la potenza di picco e la potenza media di un segnale modulato in divisione di frequenza ortogonale mediante mappatura di simboli in luoghi geometrici, e relativo sistema

Existing approaches for fine-grained access control for RDF data suffer from high overhead, making them ill-suited for mobile devices. This makes it difficult to develop mobile applications that manage personal RDF data in a privacy preserving manner. In this paper we propose a new approach to realise fine-grained access control for mobile devices. We show how fine-grained privacy settings for personal information stored in mobile devices can be described using the Privacy Preference Ontology (PPO) - a light-weight vocabulary for defining fine-grained privacy preferences. Moreover, we introduce a two stage privacy preservation approach for efficient filtering of personal information on mobile devices. Our approach combines (1) an efficient query-based analysis stage with (2) a result filtering stage based on the privacy preferences described using PPO. © 2013 Springer-Verlag.

In the last years we are seeing the increasing presence of multimedia applications together with a wide variety of terminals, from the PCs to the notebooks, from the smartphones to the tablets. In order to exploit such advanced services, ubiquitous and broadband connections are required. While urban or suburban areas can be covered by using terrestrial wireless broadband networks, there are several rural or low populated areas with narrowband access. To this aim, satellite community has developed in the last years two communications standards specifically suited for mobile communications, i.e., DVB-SH and DVB-RCS NG. Among others they consider adaptive waveforms techniques for increasing the system reliability and throughput aiming to exploit the variable channel behavior. Adaptive coding and modulation (ACM) belongs to this family of algorithms, by adapting the modulation and coding scheme based on the channel behavior. In this paper we focus on a state adaptive algorithm suited for mobile applications.

Emergency management is one of the most important areas where technology innovation has direct impact on social well-being and sustainability. In the past few years, Information and Communication Technology (ICT) has proved to be instrumental to improve emergency management with particular focus on resilience, rapidity of response, adaptability to situations. To these ends, joint optimization of communication and computing is a promising cross-layer approach. Indeed, this paper is focused on the consideration of both cognitive and autonomic networking approaches when deploying an emergency management system. The cognitive approach was initially considered specifically for wireless communications, while the autonomic approach was initially introduced for managing complex computing systems; however, they share several similarities in dealing with fully reconfigurable systems. The future trend is to expand their influence toward the global optimization of the ICT infrastructure, as the authors show in this paper for the specific case of emergency management systems.

This paper presents a new deterministic closed-loop phase-alignment algorithm based on quantized feedback from the receiver for distributed beamforming. In contrast with previously proposed methods, which entailed repeated transmissions from all the nodes in the network, this new algorithm requires each node to transmit only once during the synchronization cycle. This drastically reduces the amount of power consumed to achieve phase alignment, yet the new algorithm converges at least as fast as all other existing schemes. In contrast with previous analyses of distributed beamforming based on random phase updates, where noise had been disregarded, here it is explicitly included in the models and shown to have a considerable effect that cannot be ignored. With and without noise, analytical expressions that characterize the performance of the new algorithm are provided, with emphasis on various limiting regimes of interest.

This paper presents a new phase-alignment algorithm for distributed beamforming [1].1 This scheme is more energy-efficient than existing solutions, since it requires each node to transmit only once, but it converges at least as fast as all other previously proposed algorithms. In contrast with all other studies of distributed beamforming, where noise had been neglected, here it is explicitly included in the signal model and shown to have a considerable impact on synchronization that cannot be ignored. With and without noise, analytical expressions that characterize the performance of the new algorithm are provided, with emphasis on various limiting regimes of interest.

Peak Signal-to-Noise Ratio (PSNR) is the simplest and most widely used objective video quality evaluation method. However, traditional PSNR calculations do not take packet loss into account thus giving an inaccurate representation of the video quality. Indeed, transmission packet losses may be the cause of visible destructive distortions, which can result in a progressive quality degradation due to error propagation effects. This effect is even more visible in the mobile satellite video broadcasting scenario herein addressed. This paper proposes a novel video quality evaluation methodology, based on Y-PSNR (Luminance PSNR). This technique, called Windowed PSNR (WPSNR), allows to handle the packet loss problem and to evaluate the PSNR of the received sequence.

In the ”Internet of Things” (IoT) vision the physical world blends with virtual one, while machine-to- machine interaction improve our daily life. Clearly, how these virtual objects are exposed to us is critical, so that their user interface must be designed to support the easiness of usage that is driven by the users’ needs, which is different from what machines requires. These two requirements must be solved, and an integrated solution should emerge, if we want to bring the IoT to the 50 billions network that is predicted to became in the next years. We believe that these requirements cannot be met by the same communication protocol, and so we propose a new kind of broker, named QEST that can bridge the two worlds, represented by their state-of-the-art protocols: MQTT and REST. In this paper, we demonstrate that our approach allows rapid development of user-facing IoT systems, while grating machines all the performance they need.

This paper presents the study of the throughput distribution for several interference cancellation and gateway cooperation strategies for the return link of a multi-gateway multi-beam broadband satellite system. Different coverage schemes and frequency reuse patterns are considered, taking into account practical system parameters and antenna design. Aim of this work is to provide a tool to ease the seek of design trade-offs, as between spectral efficiency and system complexity. This is addressed showing the distribution of SINR (signal-to-interference plus noise ratio) and the throughput distribution considering different interference cancellation techniques, leveraging on different degrees of cooperation between gateways.

Signal processing in satellite applications is usually performed either on-ground or on-board, i.e. at the gateway station or in the payload. Within the framework of the European Space Agency (ESA) SatNEx III study, a hybrid approach has been considered by splitting the processing between the satellite and the gateway, aiming to strike a better balance between performance and payload complexity. The design of a highcapacity multi-beam system has been carried out, to assess the potential applicability of a hybrid space-ground processing architecture (DIGISAT) for satellite broadband systems; this is achieved via hybrid space-ground beamforming, MIMO and MIMO-MUD, Precoding, as well as Digital Feeder link techniques.

This paper analyzes the possibility to perform joint frame synchronization and code acquisition for the DVB-RCS mobile system. Since the standard foresees the adoption of Direct Sequence Spread Spectrum techniques, novel detectors able to cope with the scenario at hand are proposed. Comparison in terms of Mean Acquisition Time and complexity are carried out, and the best solution in terms of performance / complexity tradeoff is identified.

Distributed beamforming is a form of cooperation among nodes in a wireless network to efficiently deliver a common message to a distant receiver. The critical requirement to achieve electromagnetic coherence is to synchronize the initial phases of all local oscillators, introducing minimal overhead and complexity. In the paper we introduce random, deterministic and hybrid algorithms, all based on feedback from the common receiver as the driving force, but with different phase update strategies. Our numerical results show that these algorithms achieve faster convergence time than previously proposed approaches.

"We consider terminated LDPC convolutional codes (LDPC-CC) constructed from protographs and explore the performance of these codes on correlated erasure channels including a single-burst channel (SBC) and Gilbert-Elliott channel (GEC). We consider code performance with a latency-constrained message passing decoder and the belief propagation decoder. We give theoretical bounds on the code efficiency over the SBC and describe a construction that achieves this bound. We show that the designed codes with belief propagation (BP) decoding perform as well as the regular LDPC-CCs presented in the literature on the binary erasure channel (BEC) and the GEC, while achieving significant gains on the SBC. In the case of windowed decoding, our codes perform much better than the best known regular LDPC-CCs over the BEC and the GEC, with very low decoding latencies."

This paper tackles the problem of fast acquisition for dual band GNSS receiver. In particular, a novel technique is proposed based on the exploitation of the hierarchical structure of the Galileo E1 and E5 Open Service signals. The new procedure is based on the information exchange between the acquisition blocks of the two bands, and on the reduction of the uncertainty region in one band when the signal in the other one is already acquired. Numerical evaluation shows that the proposed method allows to achieve good performance in terms of Mean Acquisition Time with respect to classical stand alone acquisition while guaranteeing at the same time a significant complexity reduction.

We analyze a wireless communication system in which channel coding is applied to both physical and upper layer. In this scenario, we study the splitting of redundancy between the coding schemes applied to the two layers. Considering a frequency-flat, slowly varying fading channel, we derive the opti- mum splitting value for a given signalling format. The theoretical analysis is validated by means of numerical simulation.

In this paper we propose the usage of Single Carrier Frequency Division Multiple Access (SC-FDMA) in the Broadband Satellite Return Channel.Notably, SC-FDMA is able to improve the physical layer spectral efficiency with respect to single carrier systems, which has been used so far in the Return Channel Satellite (RCS) standards. However, it requires a strict synchronization and it is also sensitive to phase noise of local radio frequency oscillators. For this reason, we propose an effective pilot tone arrangement within the SC-FDMA frame, and a novel Joint Multi-User (JMU) estimation method for the SC-FDMA. As shown by numerical results, the proposed scheme manages to satisfy strict synchronization requirements and to guarantee a proper demodulation of the received signal.

SUMMARY In this paper, the design of a new very short frame introduced in the upcoming version of DVB-RCS standard targeting interactive mobile services will be described. The frame design with a special focus on channel coding and performance are addressed in detail, as well as an evaluation of the QoS performance for realistic traffic scenarios, propagation channel conditions, and carrier sizes. Copyright r 2009 John Wiley & Sons, Ltd.

We propose a windowed decoding scheme for protograph-based LDPC convolutional codes (LDPC-CC) that allows us to efficiently trade-off decoding performance for gains in latency. We study the performance of regular LDPC-CC with the windowed decoding scheme. In particular, we show that the class of LDPC-CC proposed in the literature with good belief propagation performance is ill-suited for windowed decoding. Further, we establish properties of code ensembles with good windowed decoding performance over erasure channels with and without memory.

This paper introduces the concept of peer-to-peer cooperation as an aiding technique in GNSS positioning and addresses the impact of the presence of professional receivers in the network. The impact of their higher accuracy is evaluated for the cases of both GNSS-data only and hybrid data exchange. Kalman Filters are considered as the data fusion engine.

This paper tackles the issue of increasing GNSS receivers reliability by presenting a novel ultra-tight integration scheme identified as Gaussian AUtocorrelation Scaled Sum (GAUSS). This hybridization approach is based on the concept that a completely artificial autocorrelation peak, generated starting from the information provided by the inertial sensors can be fused non-coherently into the received signal autocorrelation function to enhance the receiver robustness in harsh conditions as in the presence of interferers and multipath.

Aim of the present paper is to show the activity performed and related results and conclusions obtained in the preliminary design of a spread spectrum link for the protection of the satellite telecommand (TC) and payload control and configuration (PCC) links. This becomes fundamental for the telecommunication satellites and their supported networks in view of the growth of the technologies and, consequently, of the pervasive utilisation that they have today in the commercial (civilian) market. Satellite Telecommunication (SATCOM) access is ready to abandon the only utilisation as conventional broadcasting relay for the digital television or simple data feeder link to approach a similar Internet utilisation as possible network node and, even more for the wideband mobile applications and services (on aircraft, trains, ships etc.). Proper operation of such networks, mainly for these utilising emerging technologies and/or utilised in new application contexts, depends on a full availability of satellite TT&C and payload control and configuration (PCC) links at any time. Thus, these links have to be protected against unintentional as well as intentional interference. Today, this protection can be achieved by spread spectrum technology and a robust design of the receiver front end of the satellite. In addition, spread spectrum techniques complement authentication and encryption processes and remove some of their vulnerabilities. To implement the objectives above mentioned, the activity here described has been carried out initially identifying the geo-stationary service areas, i.e. Fixed, Broadcasting and Mobile Satellite Services (FSS. BSS and MSS) ones, two significant scenarios have been identified: (i) SATCOM for Unmanned Aerial Vehicle (UAV) systems, representative of the MSS and (ii) IP Routing on-board Satellite (IPRoS) that is the scenario representative of the Fixed Satellite Services (FSS). For what concern the Broadcasting Satellite Services (BSS), some suitable considerations have reduced the interest of the proposed technology for this satellite service category. The paper after the two mission definition, define a first scenario for the anti-jamming implementation. The scenario definition is used as input to define a suitable jamming model necessary for the following simulation activity. After this initial activity, defining mainly the mission environment, the paper describe the results coming from the analysis and definition phase mainly for what concern (i) the available bandwidths and the ability to interoperate without interfering with the satellite network being controlled for the frequency bands being used by commercial satellites, (ii) the expected levels of intentional and unintentional interference, (iii) the spread spectrum signal structure, (iv) the signal acquisition and tracking aspects and the technical aspect for the RF front end and the integration with the telecommunications payload and platform, considering the required signal processing complexity including data rates adapted to the instantaneous interference environment. All these items have been supported by developing a suitable simulation model verifying the performance of the link design and the signal processing in presence of significant interference. The activity has been concluded with an effectiveness evaluation summarising in an integrated scenario where several technical and market aspects have been considered and analysed in view of a future commercial development of the proposed system.

This paper provides an overview of a technical study on the satellite radio interfaces based on 3GPP WCDMA system. Firstly, the outcome of the technical study is introduced, which has been carried out by the Mobile Satellite System Working Group of the ETSI Satellite Earth Satellite Technical Committee (ETSI TC SES MSS). The study dealt with the configurations and performance of the 3GPP WCDMA (UTRAN) radio interface over a satellite link. Secondly, as an evolution of satellite-specific radio interface, the study results are addressed on the possible adaptations of WCDMA to the satellite link in order to maximize the radio link performance. The resultant outcome of the study was reflected in a detail on the G and C families of the satellite radio interface of the ITU-R Recommendation M.1457, respectively.

The proposed technique, named Rotation Invariant Subcarrier Mapping (RISM), is a novel scheme for subcarriers data mapping, where the symbols belonging to the modulation alphabet are not anchored, but maintain degrees of freedom. In other words, a bit tuple is not mapped on a single point, rather it is mapped onto a geometrical locus,which is totally or partially rotation invariant. The final positions of the transmitted complex symbols are chosen by an iterative optimization process to minimize the PAPR of the resulting OFDM symbol.Numerical results confirm that RISM makes OFDM usable even in severe non-linear channels.

Providing low-latency high-quality data services to mobile terminals has become a mandatory requirement for all mobile broadband standards. Therefore, effective countermeasures against mobile channel impairments, like small- and large-scale fading, are of the utmost importance whenever traditional physical layer channel codes do not provide sufficient resilience or request too much hardware resources. Among the possible countermeasures, the paper investigates the application of packet layer coding, which basically consists in applying forward error control techniques at upper layer (UL-FEC). In the paper the UL-FEC decoder performance analytical model already developed by authors is generalized and extended to include nonperiodic shadowing and small-scale fading. Analytical results are then validated through numerical simulation considering a real application scenario.

In this paper, we consider the adoption of the LTE radio interface for mobile satellite systems (MSS). Indeed, a key factor for the success of mobile satellite systems is the maximization of technology commonalities with terrestrial standards, which enjoy much larger economies of scale. As a consequence, the terrestrial radio interface becomes the baseline for the satellite radio interface, with minimal changes due to diverse propagation conditions. To cope with long satellite channel fading events, without affecting the physical layer interleavers, we introduce robust upper layer coding techniques. The obtained results, that include the analysis of the redundancy split between physical and upper layer coding, demonstrate the effectiveness of this technique in improving the robustness to prolonged channel fades, reaching performance very close to other satellite standards specifically designed for mobile broadcasting, such as DVB-SH. (7 pages)

This paper investigates the concept of Single Frequency Satellite Networks (SFSNs), whereby multiple satellite beams that have no form of mutual phase coherence are unified through baseband signal processing to achieve uniform coverage across wide areas. We present a realistic application scenario and its link budget analysis, which allows to highlight the advantages with respect to a classic single beam approach. Our technique is based on the use of orthogonal frequency division multiplexing and on the creation of synthetic multipath at the gateway, realizing a form of delay diversity. The synthetic power delay profile is beam specific, and it is the key instrument that allows to avoid destructive interference amongst the signals transmitted from the multiple beams. The main benefit is that homogeneous coverage is guaranteed with a generic multi-beam antenna, that can be easily reconfigured according to traffic and service needs.

This paper describes the novel concept of single frequency broadcast networks over multi-beam satellites. The technique is based on the use of orthogonal frequency division multiplexing and on the creation of synthetic multipath at the gateway. The synthetic power delay profile is beam specific, and it is the key instrument that allows to avoid destructive interference amongst the signals transmitted from the various beams. The main advantages of this approach consist in the possibility to: use high gain narrow beams that improve the link budget and the coverage contour; allow the efficient delivery of local content; enable to reuse the same satellite antenna pattern for broadband and broadcasting applications and triple-play services. (6 pages)

A novel approach is introduced for the design of a unique word (UW) for frame synchronization in time division multiplexing/time division multiple access (TDM/TDMA) systems. In particular, the UW symbols are distributed in each frame in a specific pattern in order to optimize the UW autocorrelation properties. The distribution patterns are scalable, since they preserve their autocorrelation properties under truncation. The resulting frame structure enables the use of several types of UWs, including the silent-UW (SUW) and the unit-UW (UUW), that are novel approaches for which the optimal Bayes detector is derived. An analytical performance characterization is presented along with comparisons with state-of-the-art alternatives. We show that SUW can significantly outperform the classic UW in the presence of frequency offsets or whenever data interference is the main impairment to cope with, i.e. at moderate to high signal to noise ratios. Interestingly, this performance improvement comes with the further advantage of a considerable complexity reduction. Hence UUW is shown to provide both performance improvement and complexity reduction.

This paper investigates the possibility of inserting in future satellite-terrestrial OFDM standards a preamble in order to improve frame detection and frequency estimation performance. The preamble, based on a complementary set of sequences, is exploited by a novel joint frame detection/frequency estimation scheme. Numerical results show that this strategy can outperform the classical guard interval based schemes, especially in very challenging scenarios, such as hybrid satellite-terrestrial mobile channels

In this paper, we address the problem of OFDM data-aided channel estimation based on the selection of the most significant samples (MSS) of the Channel Impulse Response (CIR), i.e. those samples which contain most of the useful energy. We provide a novel and complete analytical characterization for MSS selection based on threshold crossing, which yields a closed form for the estimate mean-square error (MSE), that we use to derive analytically the optimum threshold in the minimum MSE sense. The optimum threshold value is matched to the specific channel power profile, but this information is hardly available to the receiver. For these reason, we also propose a sub-optimal method for threshold setting that does not require any knowledge of channel statistics. We show that the performance of this sub-optimal method is very close to the optimum case, as well as to Wiener channel estimation in the case of sparse multipath channels. Our proposed method outperforms previous approaches based on heuristically set thresholds.

In this paper, the instantaneous capacity of Orthogonal Frequency-Division Multiplexing (OFDM) in frequencyselective Rayleigh fading is evaluated, based on constrained capacity arguments, to account for the signal constellations used on the sub-carriers, and on a form of the Central Limit Theorem suitable for correlated random variables. If the number of subcarriers is large, the overall capacity is shown to be Gaussiandistributed, and its mean and variance are derived, as well as their dependence on the selected constellation, the signalto- noise ratio and the channel parameters. The results show the separation between constrained and unconstrained capacity, and indicate the usefulness of adaptive modulation in exploiting all the signal-to-noise ratio range. Furthermore, the statistical characterization of the instantaneous capacity is instrumental in defining the outage capacity for OFDM systems.

The paper discusses the possible role that mobile satellite communications systems can play in 4G. The contribution is positioned into the context of the evolution of cellular/wireless 4G networks. Possible market segments and system architectures are described, including direct access to individuals and user groups on the move, mobile broadcasting applications, and backhauling. The challenges that satellite communications will face in the 4G arena are considered, in terms of market, business, technical, standardization, and regulatory aspects.

This paper proposes a method for interference mitigation (IM) in the Galileo system based on a joint timefrequency domain (TFD) technique. In particular, the proposed approach is based on the use of an open loop adaptive filter, which introduces a notch in correspondence of the instantaneous frequency (IF) of the jammer. The filter coefficients are adapted to both jammer power and instantaneous frequency (IF). In this way, it is possible to greatly reduce the distortion induced over the desired signal by the filter, with respect to more simple notching techniques irrespective of the actual interfering power. Considering Galileo signals, we apply three and five coefficients excision filters, introducing a new analytical model of the output signal-to-interference-plus-noise-ratio (SINR) and the Galileo navigation message uncoded Bit Error Rate (BER), showing the effects of the presence of BOC modulation.

SUMMARY This paper evaluates the applicability of the DVB-S2 standard in railway environments, where the most peculiar impairment is the periodic deep fading caused by power-supply arches distributed along the rail tracks. This effect induces a link loss every time the train antenna undergoes a power arch and cannot be counteracted with transmission power. Therefore, we propose and investigate the use of antenna diversity on the train. Simulation and semi-analytical results show that second-order diversity suffices to remove the packet error floor observed in the case of a single receiving antenna, thus enabling the application of DVBS2 to this harsh environment. Copyright # 2007 John Wiley & Sons, Ltd. Accepted 23 June 2007

Digital Satellite Communications focuses on the study and design of efficient and flexible physical layers for broadband mobile and fixed satellite links. The chapters address long-term developments for advanced physical layer techniques in broadband communications, fixed and mobile terminals, and 4G evolutions with a potential convergence between different technologies. A general description of satellite systems and services is provided which organizes the material into a generalized and readable framework. The approach is both analytical and descriptive. The book provides a unified view of essential topics, including: - fundamental theories - channel coding and modulation - synchronization and parameter estimation - distortions and countermeasures - diversity techniques - multiplexing and multiple access schemes - software radio Digital Satellite Communications is ideal for researchers and students in the fields of communication and signal processing.

Point-to-point communications occur between a single transmitter and a single receiver. In this chapter, we focus on multiuser communications, that occur between a network of fixed and/or mobile users and a common network center probably having access to a wireline network infrastructure. Multiuser communications in a satellite scenario usually refer to a star topology consisting of one or more gateways and a large number of small user terminals. Gateways communicate with the user terminals through the forward link and terminals may communicate with the Gateways through the return link, both links having a multiuser uplink channel and a multiuser downlink channel. Broadly speaking multiuser communications may refer either to a one-way communication as radio or TV broadcasting or to a two-way multiuser communication where each user is interested in a message specific to herself. In general, multiuser communications usually refer to the latter case. In order to support multiple users, a multiuser channel needs to be allocated to the different users. Given that an infinite number of possible allocations exist, multiuser channel capacity cannot be expressed by a single number but by a set of rates. The set of rates that can be supported simultaneously by the channel with an arbitrarily small error probability is called capacity region and its information theoretic limits are the subject of study of networking information theory. A multiuser system achieves a specific point in the capacity region depending on how the multiuser channel is shared by the users, which depends on the multiple access technique or MAC protocol used. MAC protocols are designed to coordinate multiuser transmissions as well as eventual retransmissions or resolution of collisions. In this chapter, we introduce a number of basic multiple access techniques and MAC protocols that are specific to the satellite scenario. This scenario poses some major constraints on a MAC protocol performance such as long propagation delay, remote control of on-board processing capabilities or power limitation that preclude the use of some protocols developed for a terrestrial scenario. A classification according to the most efficiently supported types of traffic is presented. The hybrid solution based on demand assignment is also discussed. We also present a brief introduction to some basic results of multiuser capacity discussing the effect of having channel side or state information. Finally, techniques able to mitigate or cancel the interference arising from spectrum sharing are also introduced and their applications to current satellite networks are presented.