Stefano Cioni

On the adaptive DVB-S2 physical layer: design and performance

The successful DVB standard has now evolved into the DVB-S2 standard, which promises to bring very significant capacity gains. The main DVB-S2 feature is its adaptive air interface, where coding and modulation techniques are varied flexibly to maximize performance and coverage. This article addresses the design of the entire DVB-S2 communication chain, considering practical algorithms for coding, modulation, predistortion, carrier and SNR estimation, frame synchronization, and data recovery. The design complexity is exacerbated by the fact that DVB-S2 foresees 28 different coding/modulation pairs, demanding specific optimization and variable frame length. The performance achieved considering all possible impairments is compared to the ideal performance achievable in the Gaussian channel in terms of integral degradation, which ranges from 0.4 to 2,5 dB in going from QPSK to 32-APSK.

Channel estimation and physical layer adaptation techniques for satellite networks exploiting adaptive coding and modulation

The exploitation of adaptive coding and modulation techniques for broadband multi-beam satellite communication networks operating at Ka-band and above has been shown to theoretically provide large system capacity gains. In this paper, the problem of how to accurately estimate the time-variant channel and how to adapt the physical layer taking into account the effects of estimator errors and (large) satellite propagation delays is analyzed, and practical solutions for both the forward and the reverse link are proposed. A novel pragmatic solution to the reverse link physical layer channel estimation in the presence of time-variant bursty interference has been devised. Physical layer adaptation algorithms jointly with design rules for hysteresis thresholds have been analytically derived. The imperfect physical layer channel estimation impact on the overall system capacity has been finally derived by means of an original semi-analytical approach. Through comprehensive system simulations for a realistic system study case, it is showed that the devised adaptation algorithms are able to successfully track critical Ka-band fading time series with a limited impact on the system capacity while satisfying the link outage probability requirement. Copyright

LTE adaptation for mobile broadband satellite networks

One of the key factors for the successful deployment of mobile satellite systems in 4G networks is the maximization of the technology commonalities with the terrestrial systems. An effective way of achieving this objective consists in considering the terrestrial radio interface as the baseline for the satellite radio interface. Since the 3GPP Long Term Evolution (LTE) standard will be one of the main players in the 4G scenario, along with other emerging technologies, such as mobile WiMAX; this paper analyzes the possible applicability of the 3GPP LTE interface to satellite transmission, presenting several enabling techniques for this adaptation. In particular, we propose the introduction of an inter-TTI interleaving technique that exploits the existing H-ARQ facilities provided by the LTE physical layer, the use of PAPR reduction techniques to increase the resilience of the OFDM waveform to non linear distortion, and the design of the sequences for Random Access, taking into account the requirements deriving from the large round trip times. The outcomes of this analysis show that, with the required proposed enablers, it is possible to reuse the existing terrestrial air interface to transmit over the satellite link.

Adaptive coding and modulation for the forward link of broadband satellite networks

The exploitation of adaptive coding and modulation (ACM) techniques for the forward link (satellite-to-user) of broadband communication satellites operating at Ka-band and above has been shown to theoretically provide large system capacity gains. In this article, the problem of how to accurately estimate the time variant channel and to adapt the physical layer mitigating the effects of estimator errors and propagation delays is analyzed. A comprehensive system simulator is then developed to assess the performance of the proposed solution and the impact on outage probability and system capacity due to estimation errors.

A performance review of PSP for joint phase/frequency and data estimation in future broadband satellite networks

In unknown channels, nonadaptive maximum likelihood sequence detection (NA-MLSD) is far from optimum in the presence of channel-induced uncertainty. To counteract this uncertainty, conventional solutions augment MLSD with external channel estimators. However, for very low SNR values this estimation procedure becomes marginal and the conventional adaptive MLSD (CA-MLSD) approaches perform poorly. We consider joint data decoding and parameter estimation techniques, and in particular per survivor processing (PSP) techniques, as a potentially effective solutions to this problem, at the expense of increased complexity. The performance/complexity tradeoff is addressed for a convolutionally encoded Q-PSK return link of an SHF/EHF satellite system for multimedia services impaired by phase noise and frequency offsets. By contrasting NA-MLSD, CA-MLSD, and PSP, ranges are provided for channel conditions where the tradeoff favors a particular technique. Further, CA-MLSD and PSP are also contrasted in terms of scalar/ vector estimation performance.

Advanced fade countermeasures for DVB-S2 systems in railway scenarios

This paper deals with the analysis of advanced fade countermeasures for supporting DVB-S2 reception by mobile terminals mounted on high-speed trains. Recent market studies indicate this as a potential profitable market for satellite communications, provided that integration with wireless terrestrial networks can be implemented to bridge the satellite connectivity inside railway tunnels and large train stations. In turn, the satellite can typically offer the coverage of around 80% of the railway path with existing space infrastructure. This piece of work, representing the first step of a wider study, is focusing on the modifications which may be required in the DVB-S2 standard (to be employed in the forward link) in order to achieve reliable reception in a challenging environment such as the railway one. Modifications have been devised trying to minimize the impact on the existing air interface, standardized for fixed terminals.

DVB-S2X-enabled precoding for high throughput satellite systems

Multi-user multiple-input multiple-output MU-MIMO has allowed recent releases of terrestrial long-term evolution LTE standards to achieve significant improvements in terms of offered system capacity. The publication of the DVB-S2X standard and particularly of its novel superframe structure is a key enabler for applying similar interference management techniques -such as precoding- to multibeam high throughput satellite HTS systems. This paper presents results from the European Space Agency-funded R&D activities concerning the practical issues that arise when precoding is applied over an aggressive frequency re-use HTS network. In addressing these issues, the paper also proposes pragmatic solutions that have been developed in order to overcome these limitations. Through the application of a comprehensive system simulator, it is demonstrated that important capacity gains beyond 40% are to be expected from applying precoding even after introducing a number of significant practical impairments. Copyright

Network‐coded diversity protocol for collision recovery in slotted ALOHA networks

SUMMARY We propose a collision recovery scheme for symbol-synchronous slotted ALOHA based on physical layer network coding over extended Galois fields. Information is extracted from colliding bursts allowing to achieve higher maximum throughput with respect to previously proposed collision recovery schemes. An energy efficiency analysis is also performed, and it is shown that by adjusting the transmission probability, high energy efficiency can be achieved. A performance evaluation is carried out using the proposed algorithms, revealing remarkable performance in terms of normalized throughput. Copyright

An Analytical Characterization of Maximum Likelihood Signal-to-Noise Ratio Estimation

In this work, the maximum-likelihood estimation of the signal-to-noise ratio is analytically characterized. In particular, the useful and the noise power are modelled by a X2-distribution, whereas the resulting signal-to-noise ratio is described in items of a non-central F-distribution. In addition, to better evaluate the estimator efficiency, the Cramer-Rao bound is computed. Finally, in order to completely verify the analytical characterization, the transmit-receive chain has been simulated, and the numerical results are compared to the analytical formulas

Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels

Two key advances are envisaged for future missions: (a) spectrally efficienttransmission to meet the increasing demand and (b) sharing of satellite capacityamong different links to meet power/mass requirements. Joint amplification ofmultiple-carrier DVB-S2 signals using a single High-Power Amplifier (HPA) is aparticular application of satellite resource sharing. However, effects specific to sucha scenario that degrade power and spectral efficiencies include (a) an increasedAdjacent Channel Interference caused by non-linear characteristic of the HPA and(b) increased peak to average power ratio. The paper studies signal processingtechniques – digital pre-distortion (DPD) at the gateway and equalization (EQ) atthe User Terminal – to mitigate the non-linear effects and improve power as well asspectral efficiencies. While the algorithms for DPD and EQ are described inliterature, their use in multi-carrier scenario is novel and poses new challenges thatare investigated in the paper.