Rita Rinaldo

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 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.

DVB-S2 ACM modes for IP and MPEG unicast applications

The DVB-S2 standard (ETSI: EN 302 307. Digital Video Broadcasting (DVB): second generation framing structure, channel coding and modulation systems for Broadcasting, Interactive Services, News Gathering and other broadband satellite applications (DVB-S2)) has been conceived for several satellite broadband applications: Television Broadcast Services, Interactive Services including Internet Access by consumers, Professional Applications such as Digital Satellite News Gathering (DSNG) and TV distribution, data trunking. This paper focuses on the profiles supporting interactive type of services, for which Adaptive Coding and Modulation (ACM) has been included in the new generation of the standard. Following the DVB-S2 specifications, a number of modem configurations and tools are made available for implementing ACM in interactive systems. However, the different approaches have important impacts on the design of the system architecture and of the scheduling/resource management algorithms. The aim of the present contribution is providing a first discussion on the critical issues at system and MAC level, which need to be addressed when implementing a DVB-S2 ACM system. A general introduction to ACM is also provided, as well as an illustration of the key elements included in the DVB-S2 standard for supporting physical layer adaptivity. Copyright

R&D DIRECTIONS FOR NEXT GENERATION BROADBAND MULTIMEDIA SYSTEMS: AN ESA PERSPECTIVE

The scope of the present paper is to outline ESA’s R&D directions for the development of new technologies required for future broadband satellite communication systems. The document outlines likely trends and technological issues that will need to be tackled in the medium and long term (e.g. 5 to 10 years) to improve by more than one order of magnitude satellite communication networks efficiency, thus increasing their economical appeal. It is shown that by timely developing in a co-ordinated fashion a number of techniques and technologies encompassing both ground and space segment it is possible to attain the ambitious target set forth above.

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 the DVB-S2 Standard Interactive Applications: Capacity Assessment and Key System Issues

Point-to-point multibeam satellite systems based on the DVB-S standard are currently designed for link closure in the worst-case propagation and location conditions. The DVB-S standard, conceived for broadcasting applications, considers a fixed coding rate and modulation format that are selected according to the assumed coverage and availability requirements. This approach implies the occurrence of high margins in the majority of the cases, when interference and propagation conditions allow for higher signal-to-noise-plus-interference ratio. The adaptive coding and modulation (ACM) introduction in the new DVB-S2 standard for the interactive service profile opens up a number of appealing opportunities for the design and development of satellite broadband networks. In this article we show how the ACM introduction in the satellite downlink enables greatly enhanced system performance but also has a profound impact on the way the system and some of the key system components are designed.

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.

Beam Hopping in Multi-Beam Broadband Satellite Systems: System Performance and Payload Architecture Analysis

When considering the inherent uncertainty of the broadband communication market evolution as well as the spatial non-uniform distribution of capacity requests through the satellite coverage, flexibility to adapt to different traffic configurations is a key requirement for future satellite systems to maintain their competitiveness. Beam hopping solutions appear as good candidates to match system offered capacity with traffic demand. Although the introduction of flexible bandwidth and power allocation to beams brings some benefits in terms of demand satisfaction for hot spots with respect to traditional systems with regular frequency reuse and equal power to beam allocation, utilization of beam hopping techniques offers an additional mean to cope with irregular and time variant traffic distributions. In this paper the forward link of a multibeam transparent satellite system for providing broadband Internet access to users sparse over the coverage area is analyzed. The utilization of Adaptive Coding and Modulation (ACM) techniques is considered, according to the recently approved DVB-S2 standard. The advantage in terms of system performance brought by the utilization of beam hopping techniques is assessed. In this type of system, only a few beams of the overall coverage are selected at each time-slot for transmission. This set of illuminated beams changes on a slot-by-slot basis over the duration of a repetition window. This creates a time and spatial transmission plan that repeats periodically with a given duty cycle. In the present contribution the problem of optimizing the beam hopping transmission plan in order to best match the traffic demand is tackled. Genetic algorithms appear as the most suited optimization tool because of their global optimization nature, their capability of working with a large number of optimization parameters and their suitability to accept a discontinuous figure of merit function. Extensive simulations have been carried out to adapt genetic algorithms functions and parameters to the problem under investigation. The target has been optimizing the beam allocation in the transmission plan to maximize system capacity. System performance is assessed considering the traffic demand distribution over Europe foreseen for broadband satellite services in 2015, as derived by recent market analysis studies. A throughput increase of about 30% compared to a system with regular power and bandwidth allocation capabilities is achieved. The impact of a beam hopping type of system at payload level is then investigated. In particular, efficient ways to implement beam hopping combining payload flexibility with affordable complexity are investigated. Both Direct Radiating Array (DRA) and Array Fed Reflector (AFR) solutions are considered.

Study of a Satellite Multimedia Broadcasting Mobile System Mission for the European @BUS Platform

In this paper we present the design of a Satellite Multimedia Broadcasting Mobile System (S-MBMS) operating at S-band as a possible mission embarked on-board of the European @BUS proto-flight platform in the frame of the ESA’s @SAT program. The mission definition includes the system targets in terms of service, user terminals and coverage. System design trade-off will be then discussed as well as the selected frequency plan for the feeder and user links (satellite and terrestrial repeaters), key payload performance parameters in terms of gain, C/I as well its mass and power estimate. Link budget analysis is then provided to show the achievable link margins over the coverage region.