Riccardo De Gaudenzi

Advances in Random Access protocols for satellite networks

In this paper we review key properties of recently proposed high performance protocols for Random Access (RA) satellite channels for both Time Division and Code Division Multiple Access (TDMA/CDMA) techniques. The proposed protocols by far outperform traditional satellite random access techniques without the need for quick feedback from the gateway. This makes possible to avoid the utilization of demand assigned capacity for the transmission of small/medium size bursts of packets. A fair comparative performance of state-of-the-art TDMA and CDMA RA schemes is provided together with a summary of their key performance results. It is shown that the proposed enhanced RA protocols, although different between TDMA and CDMA, share commonalities as they exploit iterative interference cancellation at the demodulator side and demonstrate to provide even better performance in the presence of received carrier power unbalance. Typical application scenarios of these enhanced random access protocols are then illustrated, as well as possible ways to combine random access and demand assigned protocols.

Capacity analysis and system optimization for the forward link of multi-beam satellite broadband systems exploiting adaptive coding and modulation

This paper deals with the system capacity analysis and assessment of the potential advantages provided by the introduction of Adaptive Coding and Modulation (ACM) in the reverse link of multi-beam broadband satellite systems. ACM is intended to increase the system throughput for a given terminal EIRP power by optimizing the individual links physical layer to the current channel conditions. The physical layer adaptation will be driven by the inbound demodulator signal over noise plus interference ratio (SNIR) estimation. A general methodology for ACM physical layer optimization based on the system capacity maximization is also illustrated. A theoretical analysis of ACM systems capacity is performed for both time division multiple access (TDMA) and code division multiple access (CDMA) schemes. As the exact analytical capacity computation results to be very complex while Monte Carlo approach leads to very time consuming simulations, a simplified semi-analytic approach is devised. Numerical results showing the huge improvement in terms of capacity by the ACM adoption are obtained for both the semi-analytic and the Monte Carlo approaches in a realistic study case corresponding to a Ka-band multibeam satellite system. A good match between the two approaches is also demonstrated. Copyright

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

Adaptive coding and modulation for satellite broadband networks: From theory to practice

This paper presents the detailed design and the key system performance results of a comprehensive laboratory demonstrator for a broadband Ka-band multi-beam satellite system exploiting the new DVB-S2 standard with adaptive coding and modulation (ACM). This complete demonstrator allows in-depth verification and optimization of the ACM techniques applied to large satellite broadband networks, as well as complementing and confirming the more theoretical or simulation-based findings published so far. It is demonstrated that few ACM configurations (in terms of modulation and coding) are able to efficiently cope with a typical Ka-band multi-beam satellite system with negligible capacity loss. It is also demonstrated that the exploitation of ACM thresholds with hysteresis represents the most reliable way to adapt the physical layer configuration to the spatial and time variability of the channel conditions while avoiding too many physical layer configuration changes. Simple ACM adaptation techniques, readily implementable over large-scale networks, are shown to perform very well, fulfilling the target packet-error rate requirements even in the presence of deep fading conditions. The impact of carrier phase noise and satellite nonlinearity has also been measured. Copyright

Adaptive Coding and Modulation for Next Generation Broadband Multimedia Systems

This paper investigates the potential advantages provided by adaptive coding and modulation (ACM) for next generation broadband satellite communication systems operating at Ka-band and above. The problem tackled in the manuscript is how to find an optimal physical layer structure able to efficiently support packet type of traffic and to adapt to the varying propagation channel conditions and location dependent signal-tointerference plus noise ratio (SNIR). In particular, the physical layer and key system parameters optimization problem (i.e. coding rate, modulation order, spreading factor, frequency and polarization reuse factors) is tackled for the general case of the downlink of a multibeam satellite system. Eventually, the average system capacity and bit rate distribution for the proposed adaptive coded modulation scheme is derived in a realistic scenario with different frequency reuse factors. The resulting large capacity advantage with respect to solutions currently envisioned for satellite multimedia systems is proved.

S-MIM: A novel radio interface for efficient messaging services over satellite

This article presents a radio interface recently standardized by ETSI under the name of S-band Mobile Interactive Multimedia (S-MIM) and especially designed to provide ubiquitous messaging services over S-band GEO satellites using low-power terminals. Thanks to low terminal cost and high bandwidth efficiency, this standard allows the development of new satellite services, particularly for vehicular and machine-to machine applications. The S-MIM standard relies on a broadcasting radio interface such as DVB-SH or ETSI SDR in the forward link, and reuses 3GPP W-CDMA technology properly adapted to the scope in the return link. Thanks to the use of spread spectrum ALOHA, terminals can access the channel in a totally asynchronous manner. The use of a packet-optimized iterative successive interference cancellation (i- SIC) algorithm at the receiver allows exploiting the inherent power imbalance among terminals in order to boost the throughput with respect to conventional SSA systems. In addition, advanced packet transmission control techniques have been adopted to maximize the probability of successful packet reception in the challenging land mobile satellite channel. Finally, the S-MIM link layer provides efficient and reliable transport of IP datagrams over the forward and return link radio interfaces.

MIMO for Mobile Satellite Digital Broadcasting: From Theory to Practice

This paper presents the detailed design and the key system performance results of a comprehensive laboratory demonstrator (testbed) for a hybrid satellite/terrestrial S-band mobile digital broadcasting system. The physical layer is based on an enhanced version of the digital video broadcasting-satellite to handheld (DVB-SH) standard, exploiting dual-polarization multiple-input-multiple-output (MIMO) technology. This complete digital MIMO demonstrator, which is the first of its kind, allows for an in-depth verification and optimization of the MIMO techniques applied to satellite broadcasting networks. Moreover, this demonstrator allows for complementing and confirming the theoretical or simulation-based findings published thus far. It is shown that dual-polarization MIMO diversity is able to provide remarkable gains in terms of satellite/terrestrial transmit power reduction and/or capacity increase compared with more conventional non-MIMO solutions. It is also demonstrated that the adoption of a relatively simple spatial multiplexing MIMO technique represents the best way to grasp these gains. This paper provides an extensive set of laboratory measurement results for existing stochastic satellite and hybrid MIMO channels, as well as results based on an S-band satellite-measured dual-polarization time series recently collected during a campaign sponsored by the European Space Agency. Results obtained using MIMO techniques are also compared with a dual- and single-polarization single-input-single-output (SISO) DVB-SH benchmark system and with computer simulation results.

Smart Gateways Concepts for High-Capacity Multi-beam Networks

The support of high capacity broadband multi-beam satellite networks requires the implementation of a large number of gateways to cope with the high feeder link throughput generated by the large number of satellite user beams. Although today the state-of-the-art satellite broadband systems exploit Ka-band for the feeder link, to further increase the system capacity Q/V-band exploitation will be required. When exploiting Ka or Q/V-band (the latter in particular) gateway site diversity becomes a must to ensure the required high feeder link availability. Conventional site diversity is too onerous when the number of gateways is large as it is doubling the number of system gateways. The novel Smart Gateway Diversity Concepts (SGC) described in the paper are representing possible ways to exploit the inherent presence of multiple physically separated gateways in high capacity systems to achieve the required feeder link capacity minimizing the number of required gateways. The key idea is to exploit the inherent presence of several spatially separated gateways to cope with the required large feeder link bandwidth to achieve the required fading link availability. This requires gateway interconnection and ad-hoc payload architectures allowing seamless user traffic hand-off from the faded gateway(s) to the unfaded ones. In current systems each gateway serves a distinct cluster of beams thus this approach is not possible. The proposed smart gateway schemes allow to significantly reducing the cost of the ground segment (number of gateway antennas and associated RF front-end). Depending on the SGC scheme, a certain level of the transparent payload complexity increase is required. Some payload reconfigurability will be in any case required to support the need for gateway switchover to a redundant one in case of failure. Furthermore, all the proposed payload architectures are all analogue and exploits technologies readily available. The paper provides a detailed description of the different Smart Gateway Diversity Concepts and associated architecture for the ground and space segment.

On signal structures for GNSS-2

This paper summarizes the main results of an early investigation on desirable signal structures for the European Galileo civil satellite navigation system. Stemming from the requirements for increased accuracy, reduced time-to-first-fix and integrity information provision, the report describes the logical steps and the related numerical results leading to a novel Galileo signal definition. Although the final parameter definition is largely based on European system constraints, a number of design guidelines like the use of spectrally efficient square-root raised-cosine chip shaping and enhanced data broadcasting are expected to be of general applicability to any future satellite navigation system.

Random access schemes for satellite networks, from VSAT to M2M: a survey

Summary In this survey paper, we review the random access (RA) techniques with particular emphasis on the issues and the possible solutions applicable to satellite networks. RA dates back to the 1970s when the ALOHA protocol was developed to solve the problem of interconnecting university computers located in different Hawaiian islands. Since then, several evolutions of the ALOHA protocol have been developed. In particular, solutions were devised to mitigate the problem of packet collisions severely degrading the RA protocols performance. The approach followed for many years has been to avoid the occurrence of collisions rather than solving them. More recently, techniques tackling the RA packet collision problem have appeared triggered by the need of improving RA performance in satellite and terrestrial wireless networks. In particular, satellite networks large propagation delay does not allow the adoption of enhanced terrestrial RA techniques based on channel sensing. Adopting conventional demand assignment multiple access protocols is not suitable for supporting a large number of sensors or devices transmitting small-size low duty cycle packets as required for machine-to-machine communications. This provided the stimulus to exploit successive interference cancelation schemes to solve packet collision issues. The use of successive interference cancelation in RA is relatively new and has opened up a promising research area. We provide an extensive review of recent high-performance RA techniques achieving more than three orders of magnitude throughput increase compared with the original ALOHA at low packet loss rate. In this survey, we cover both slotted and unslotted techniques. Finally, we review the use of RA in satellite systems and related standards including recent proposals for machine-to-machine applications. Copyright