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This section offers a view on trends currently characterizing the ICT world, with special focus on wireless technologies in line with the NEWCOM++ research objectives. To approach this complex task, the activities carried out withinWPI.6 are considered as a reference. At first, an attempt to classify personal needs is provided in order to present the rationale towards which ICT trends and technologies are growing and evolving. Then, an overview of ICT trends is presented through an original metaphor of the current ICT picture and biological DNA. Continuing our analysis, cutting-edgestandards and technologies in the ICT wireless context are recalled, providing for each a mapping onto ICT trends, showing which trends are embodied by the technology and which personal needs can be satisfied in this manner. Finally, we conclude this section discussing the impact of ICT pervasiveness on society, human relations, and even individual psychology: a new phenomenon is created, which we identify as the information divide, which includes both the digital divide affecting all those who have no or limited access to the Internet, as well as the psychological divide, related with the information overload which impacts upon all those who do have access [1].

The paper introduces a statistical channel model which is a combination of Rice and lognormal statistics, and is suitable in principle to all types of environment (rural, suburban, urban) simply by tuning the model parameters. The model validity is confirmed by comparisons with measurement data collected in the literature. Empirical formulas are derived for the model parameters to fit measured data over a wide range of elevation angles. In particular, the model is applied to nongeostationary satellite channels, such as low-Earth orbit and medium-Earth orbit channels, in which for a given user located in a generic site the elevation angle changes continuously. Finally, examples of average bit error probability evaluations in the channel are provided. >

This paper presents a comprehensive evaluation of multi-user interference mitigation techniques for a broadband multi-beam satellite system. More in detail, present multi-beam satellite systems are strongly limited by the effect of inter-beam interference, which has to be necessarily reduced with the adoption of advanced signal processing techniques. The limitation in the bandwidth of the feeder link further exacerbates this problem, forcing gateways to operate only on a fraction of the total beams number, thus limiting the effectiveness of multi-user interference mitigation techniques unless some form of gateway collaboration is not adopted. This paper discusses the possible performance gain achievable by gateway cooperation, as opposed to centralized operations, and results are presented for the return link, based on both analytical considerations and numerical simulations on a realistic scenario.

In a wireless sensor network, distributed beamforming is a cooperative technique that enables a group of nodes to emulate a virtual array and to steer a beam in a particular direction in space. This allows for shared message delivery to a distant receiver in a condition where typically communication range is limited due to power consumption constraints. Potential gains in terms of received power are compelling, but one of the main challenges is to achieve coherence of the transmitted signals at the destination in such a distributed scenario. This work presents innovative phase synchronization algorithms for a wireless sensor network that not only prove to be very efficient in terms of energy consumption, but also present good channel tracking capabilities in a time varying scenario.

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 presents an improvement to the Frequency Shift Keying - Fast Frequency Hopping demodulator, which provides increased resilience to interference with a very slight complexity increase. The additional robustness against jamming is achieved by jointly observing the FSK demodulator branches. This allows the proposed demodulator to distinguish the jammer from the signal more accurately. This demodulator is particularly robust for the case of high J/S (Jammer to Signal Ratio), while for the case of low J/S its performance is in line with state-of-the-art receivers.

The radio resource shortage is one of the most important characteristic to take into account when deploying modern wireless telecommunication systems. A novel communication paradigm named Cognitive Radio, has been introduced in the last years for better exploiting the limited available spectrum and the inefficiency in the spectrum usage. Its main aim is to allow the co-existence of different wireless systems on the same spectral resource by limiting the mutual interference. One of the main challenge is to extend the cognitive paradigm also to satellite networks by considering hybrid satellite and terrestrial scenarios. Aim of this paper is to evaluate the coexistence of terrestrial and satellite networks by considering a cognitive approach when radio resource sharing is employed. The paper deals with the presentation of a statistical interference model that aims at evaluating the mutual interference among the two systems.

In the satellite communications component of the future Internet, peer-to-peer mesh connectivity of satellite terminals is an impellent necessity. In particular, delay sensitive applications such as real-time multimedia, collaborative conferencing and cellular backhauling are appealing use-cases for adopting mesh network topologies. Moreover, the use of a single satellite hop for directly connecting remote terminals (as opposed to a double-hop connection required in star topologies) reduces the satellite traffic load and leads to savings in operational costs of the satellite network. In this paper, we propose a multi-beam satellite mesh network based on a semi-transparent or fully regenerative satellite with different on board switching capabilities. In particular, four network solutions have been assessed in terms of flexibility, complexity and capacity, trading-off between network performance and implementation cost.

A new upper bound is presented to the probability of error in detecting one out of M equiprobable signals in additive white Gaussian noise. This bound employs the same number of erfc function evaluations as the well-known Union Bound, but it is tighter. For high cardinality constellations, the Union Bound is useless for low signal-to-noise ratios being above 1, while the proposed new bound maintains its significance. This bound can also be extended to the Bit Error Probability computation associated to the same decision problem, and again it is tighter than the Union Bound.

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.

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.

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 propose a novel method that considerably reduces the Peak-to-Average Power Ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) systems, yielding a quasi constant signal envelope in the time domain (PAPR close to 1 dB). 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.

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 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 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.

The mobile satellite broadcasting arena is witnessing a constant increase in demand for improved transmission quality and higher number of services in order to remain on par with the corresponding terrestrial counterparts. A promising way forward in this regard is the migration from the conventional single polarization per beam to an advanced dual polarization per beam architecture for effective spectrum exploitation; this also enables the application of advanced multiple antenna (MIMO) techniques. The present paper moves from DVB-SH the current state-of-the-art for mobile satellite services towards a more advanced system architecture doubling the overall system capacity with a minimum power increase. It turns out that a multiplexing gain equal to two comes at a cost of about 6 dB for the conventional single polarization system, whereas for the advanced system the corresponding cost is about 3.5 dB.

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.

We consider windowed decoding of LDPC Convolutional Codes on the Binary Erasure Channel (BEC) to study the trade-off between the decoding latency and the code performance. We make some key observations about regular LDPC Convolutional code ensembles under windowed decoding and give modified constructions of these codes that allow us to efficiently trade-off performance for gains in latency.

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.

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.

A satellite system for land mobile applications to be integrated with terrestrial cellular systems is described. The concept of cellular architecture is applicable to the proposed satellite system allocated at Extremely High Frequencies. Coverage flexibility and remarkable spectrum efficiency are consequent advantages. Criteria for service availability determination are presented, along with a system design overview. The challenging technological requirements for the on-board payload and for the user terminal are pointed out and some possible solutions are described.

An EHF satellite system for land-mobile applications to be integrated with a terrestrial cellular system is described. An approach to evaluate the carrier-to-cochannel interference occurring in multispot satellite coverage adopting frequency reuse is introduced, and results from the analysis are shown. Criteria for spectrum efficiency evaluation are also outlined along with traffic and link budget estimates. Possible options for payload implementation and mobile terminal design are presented. >

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.

The ISICOM concept has been defined in the framework of the ISI Technology Platform as a mean to provide the necessary communication infrastructure in support to the achievement of the European Space Policy goals. In this paper, we introduce the ISICOM Architecture: starting from the ISICOM devised missions, we describe the founding architecture concepts that shall be taken into consideration in the design of the ISICOM architecture in order to meet the challenging requirements set forth by the ISICOM missions.

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 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. (6 pages)

Some recently proposed robust methods for time-domain timing and frequency synchronization in OFDM systems incorporate the use of cross-correlation based threshold detection in their timing adjustment and joint time-frequency algorithms. In this paper, we analyze the threshold criterion used and derive its theoretical performance. This translates into a better characterization of these OFDM synchronization algorithms, leading to a closer match between design expectations and practical performance. Computer simulations show a strong agreement between theoretical predictions and numerical results.

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 presents a novel reduced complexity SNR estimator, whose performances are comparable with the maximum-likelihood estimator while saving one half of the floating point multiplications and one third of the floating point sums. A detailed statistical description of the estimate, as well as simulation results, are provided. (4 pages)

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.

This paper provides an overview of the configurations and performance of the 3GPP UTRA FDD WCDMA radio interface to operate over a satellite link. A technical study has been carried in ETSI by the Satellite Earth Satellite Technical Committee (TC SES) via the Mobile Satellite System Working Group [1]. The configurations and performance of the WCDMA over a satellite link are described in the recently published technical specification set

The great effort that is devoted to the definition of the '4G' highlights the need for the MSS ecosystem to explore the opportunity to include satellite into the paradigm of '4G' networks of networks. Satellites may appear as a way to 'fill the holes' of the terrestrial coverage thus offering global mobility to end user. We consider here two missions to be delivered over Europe : an interactive broadcast mission and a two-way broadband mission, both targeting handset, vehicular and nomadic terminals. Firstly a general discussion and a candidate hybrid satellite and terrestrial network architecture is proposed for low- frequency bands under CGC (Complementary Ground Component) license. Secondly the dimensioning of the space segment for both missions is presented. The paper stresses the demand for satellites with large antennas and high amplified power. It also briefly touches on the required adaptation of the 4G air interfaces to the satellite constraints. In addition it shows that the system capacity is mainly driven by the spectrum resource.

Assisted-GNSS (A-GNSS) is an interesting technology that can consistently improve positioning performance and reduce terminal complexity. One of the possible data that the A-GNSS can provide is the satellite orbit (satellite ephemeris) necessary to determine the user position starting from pseudorange measurements. In this paper, we propose two novel data structures for the transmission of ephemeris through the assistance network. It is shown that, adopting different interpolation techniques, it is possible to consistently reduce the amount of data to be transmitted and extend the ephemeris validity to 24 hours.

The paper investigates coding and encapsulation techniques for the possible extension of the digital video broadcasting-return channel satellite (DVB-RCS) to ensure a global coverage for mobile terminals. specifically, link layer- forward error correction (LL-FEC) appears to be a reliable solution, allowing to improve the C/N performance and to counteract the Doppler effect typical of mobile channels, avoiding scalability and latency issues of Automatic Repeat reQuest (ARQ) approaches. In the paper we evaluate LL-FEC performance when applied to the railway environment. It is shown how this scenario deeply affects the LL-FEC code performance both in the multi protocol encapsulation (MPE), and the generic stream encapsulation (GSE) cases. In order to counteract this performance reduction two different approaches are considered. In the first case, we increase the number of rows of the LL-FEC Reed Solomon (RS) matrix. In the second case we exploit the sliding encoding mechanism. We also introduce a modified version of GSE that shows reduced overhead and improved performance. Results show that DVB-RCS can greatly benefit from LL-FEC RS coding in reducing residual errors that cannot be counteracted at the physical layer for efficiency reasons.

As the worldwide telecommunications network is evolving fast, and histori-cally separate sectors are converging into a single competition arena, there is an apparent need to coordinate efforts in the field of satellite communications, in order to maximize its chances for business consolidation and growth. This is precisely the purpose of the Integral Satcom Initiative (ISI), a Technology Platform which is being set up in Europe in view of the upcoming 7th Framework Programme (FP7) of the European Union (EU), and of the im-plementation of the European Space Policy, in collaboration with the Euro-pean Space Agency (ESA). This perspective article highlights the ISI found-ing principles and its present status.

In this paper, we investigate the applicability of the 3GPP Long Term Evolution standard to mobile satellite systems. In order to counteract the satellite specific propagation conditions, we propose a novel inter-TTI (transmission time interval) interleaving technique allowing to break the channel correlation in slowly time varying channels. The Inter-TTI transmission is achieved through the reuse of the existing HARQ facilities provided by the LTE physical layer. Simulation results show that the proposed technique can be successfully used to improve the performance of the LTE physical layer when applied to the transmission over satellite links. Performance improvement depends on the considered parameters, while complexity can be traded off with the data rate to achieve the best quality of service for the considered system.

The problem of post-FFT carrier frequency recov- ery is investigated in the paper proposing a novel approach for both pilot structure and receiver design. In particular, a novel pilot distribution is introduced in order to minimize overlaps between two pattern shifted replicas. This allows to replaces conventional pilots with nulls in the frequency domain, introducing the so called Silent Pilots. As a result, the optimal receiver turns out to be very robust against severe Rayleigh fading multipath and characterized by low complexity. Performance has been analytically and numerically evaluated, comparing the proposed approach with state of the art alternatives, in both AWGN and multipath fading channels, showing considerable performance improving. I. INTRODUCTION Orthogonal Frequency Division Multiplexing (OFDM) and its counterpart for multiple access (ODFMA) are increasingly used in wireless communications. This trend is testified by the adoption of OFDM as a standard for Fourth-Generation Communications Systems such as WiMAX and 3GPP Long Term Evolution (LTE). OFDM has been also chosen for the most recent standards for digital broadcasting: DVB-H (Dig- ital Video Broadcasting-Handheld), DVB-SSP (Digital Video Broadcasting-Satellite Services to Portables) DVB-T2 (Digital Video Broadcasting-Terrestrial, version 2), T-DMB (Terrestrial Digital Multimedia Broadcasting), MediaFLO. The success of OFDM is due to its intrinsic robustness against severe frequency selective channels, which is typical for wireless broadband transmissions, and to the flexibility it offers to resource management. On the other hand, as well known, OFDM systems are very sensitive to Carrier Frequency Offset (CFO) so that accurate frequency synchronization be- comes crucial to mitigate this potential vulnerability, moreover initial CFO can be several times larger than the subcarrier frequency spacing, fu. The integer part and the fractional part of CFO normalized to fu introduce different effects. The former is responsible of a spectral shift in the receiver symbols in the frequency domain (after FFT), while the latter breaks the sub-carrier orthogonality introducing Inter Carrier Interference (ICI).

This paper tackles the problem of frame synchro- nization in the presence of timing and frequency uncertainty. Considering a discretization of the timing uncertainty domain in time slots, and of the frequency uncertainty domain in frequency bins, this novel technique, called staggered time and frequency search, exploits a joint controlled single dwell Threshold Crossing criterion in both domains. In fact, differently from the conven- tional techniques, this method does not require any parallelism, but digitally controlling the sampler and the oscillator is in charge to scan different hypotheses in time and frequency until the acquisition is completed. According to the analytical and simulated results shown in this paper, this novel technique can obtain performance that is close to the one that can be achieved with the classical techniques, with complexity and power consumption reduction. Synchronization is a key issue in TDM/TDMA systems, since it is the necessary prerequisite for correct data demodu- lation and decoding. Conventionally, frame synchronization is based on a data-aided approach that has to detect the start of a known preamble, identified as Unique Word (UW), which marks the start of the entire frame. This operation is typically divided in two phases in cascade: acquisition and tracking. Acquisition is in charge of getting a first rough estimate, while tracking is asked to possibly detect erroneous synchronization events. This paper addresses the problem of frame acquisition, which is typically the most critical phase because it has to be performed in the presence of unknown carrier parameters and large uncertainty regions, up to the entire frame duration at the terminal cold start. In order to reduce complexity, the uncertainty region is usually discretized in one or more hypotheses per symbol, so transforming the epoch estimation problem in to a detection problem, where the correct hypoth- esis H1 has to be selected among many wrong hypotheses H0. In this scenario, the two main impairments that have to be considered for a robust design are frequency errors, due to oscillator mismatches and Doppler effects, and non-ideal sampling, which introduces useful energy degradation and inter-symbol interference when discretizing the uncertainty region. These two impairments are responsible for a strong degradation of the detection performance making acquisition a critical issue in the system design. Considering a discretization of the timing uncertainty do- main in time slots, and of the frequency uncertainty domain in frequency bins, acquisition can be seen as a two-dimensional problem that translates into the exploration of a bidimensional matrix which can be scanned serially or in parallel. The

A gradient method is used to obtain the signal constellation that yields to the minimum error probability over a channel affected by non-linear amplification and additive noise. The results show the dominance of Phase Shift Keying when the amplifier is driven near saturation, and the better performance given by Amplitude-Phase Shift Keying if the amplifier is operated in its linear region.

In this paper, we present a novel joint symbol timing and carrier frequency synchronization algorithm for orthogonal frequency division multiplexing (OFDM) system with very low hardware complexity. Although we developed the proposed algorithm with reference to the DVB-SH standard, it is easily adaptable to other OFDM based systems. A well-known problem in OFDM modulation is its vulnerability to synchronization errors. In particular, accurate recovery of carrier frequency and symbol timing is crucial for the proper demodulation of the received packets. The proposed algorithm has low hardware complexity, and at the same time achieves very good performance in both AWGN and multipath channels. Finally, the paper includes also a detailed comparison of the proposed technique with several time and frequency synchronization algorithms already presented in the scientific literature and compliant with the DVB-SH physical layer.

This contribution explores the use of interference mitigation techniques applied to broadband satellite systems with co-channel interference. In particular, our focus is on nonlinear precoding techniques, borrowing ideas from the theory of broadcast MIMO channels. A number of schemes are compared, including several implementations of Tomlinson-Harashima precoding and their linear precoding counterparts. Simulations on realistic scenarios show potential improvements of non-linear precoding with respect to linear interference mitigation and classical countermeasures based on frequency division among beams. Also, we identify several practical issues related to the implementation of Tomlinson-Harashima Precoding in satellite communication systems.

In this paper, we propose a Single-Input Multiple- Output (SIMO) diversity technique to improve the link reliability of a satellite communications system. In particular, the DVB-S2 communication system is investigated in a land mobile satellite environment. Realistic physical layer simulations are carried out to better evaluate the possible gain of using multiple receiving antennas at the receiver side. A hybrid selection technique of the available antennas is presented to reduce the complexity and the cost of the user terminal.

This paper proposes a method for interference mitigation (IM) in the Galileo system based on a joint time-frequency domain (TFD) technique. In particular, the proposed approach is based on the use of an adaptive finite impulse response (FIR) 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 IF. In this way, it is possible to largely reduce the distortion induced over the desired signal due to filtering, with respect to simpler notching techniques irrespective of the actual interfering power. In this paper we introduce a new analytical model which accurately characterizes the output signal-to-interference-plus-noise-ratio (SINR) for narrowband sinusoidal interference considering Galileo BOC modulated signals. This is achieved for both three and five coefficients excision filters, for which optimum filter coefficients can be derived to maximize output SINR.