Maria Angeles Vázquez-Castro

Shadowing correlation assessment and modeling for satellite diversity in urban environments

Non-geostationary orbit satellite networks have dynamic, yet deterministic topologies. This paper deals with the consequences of relying on the use of multiple visible satellites to improve availability with time/locations through satellite diversity techniques. The assumption of independent blockage events in two different satellite-to-mobile links is generally not accurate and information on shadowing correlation should be taken into account in the assessment of availability.In this paper a shadowing correlation study for urban environments is presented and a model for the real environments, as well as for a generic urban environment is inferred. The model proposed here is simple and can be run on a computer. It also relates urban and constellation geometries thus allowing the identification of those cases for which satellite diversity gain should be expected. As a result of this analysis and modelling, we present empirical analytical expressions describing positive correlation coefficient as a function of satellite angular separation (azimuth and elevation). We also show that an angle exists above which correlation can be negative and satellite diversity can sensibly improve link availability. Copyright

Joint Power and Carrier Allocation for the Multibeam Satellite Downlink with Individual SINR Constraints

A novel multibeam satellite system design is proposed in this paper based on jointly optimizing power and carrier allocation in order to best match the asymmetric traffic requests. This design introduces higher and asymmetric interference levels throughout the coverage. However, both power and bandwidth will be used more efficiently. Even though the problem of power and bandwidth allocation has been addressed in terrestrial wireless communications, it is new in satellite systems and since architecture and channel are different, available results and algorithms are not applicable to satellite payload systems. In this paper we formulate the resource allocation problem as max-min SINR balancing based on the recently introduced axiomatic-based interference model, but in addition, we also optimize the carrier allocation when performing the SINR balancing problem. An analytical solution for the optimal carrier allocation is proposed and we iteratively find the optimal power allocation for each beam. The Shannon (upper bound) and current state-of-the art PHY layer technology: DVB-S2 are proposed to be implemented in order to obtain the gap between them. Simulation results show significant improvements in terms of power gain, spectral efficiency and traffic matching ratio comparing with conventional system, which is designed based on uniform bandwidth and power allocation.

NUM-Based Fair Rate-Delay Balancing for Layered Video Multicasting over Adaptive Satellite Networks

Trading delay and rate in upcoming satellite networks are of paramount interest. In this paper, we present a solution to optimally distribute resources across MAC, IP and APP layers to deal with the problem of efficiently and reliably delivering low latency and high rate inelastic services over such networks. In order to do so, we formulate the problem of rate/delay balancing according to a Network Utility Maximization (NUM) paradigm assuming Scalable Video Coding (SVC) feeding a cross-layer DiffServ architecture, and an adaptive physical layer. We solve not only the bit loading balancing across the IP queues but also the video layers distribution to be sent among the adaptive physical layers, all constrained by delay requirements. The solution, which provides a fair rate-delay trade-off, happens to be on a water filling load across the queuing architecture, and it is suitable for multicasting scenarios. Finally, we propose a full protocol design, implementation, and performance evaluation based on truly available standardized tools, hence, it is ready-to-use. Our solution significantly outperforms non cross-layer approaches in terms of delay and video quality, and it dynamically adapts to channel and traffic variations.

Multibeam satellite frequency/time duality study and capacity optimization

In this paper, we investigate two new candidate transmission schemes, non-orthogonal frequency reuse (NOFR) and beam- hopping (BH). They operate in different domains (frequency and time/space, respectively), and we want to know which domain shows overall best performance. We propose a novel formulation of the signal-to-interference plus noise ratio (SINR) which allows us to prove the frequency/time duality of these schemes. Further, we propose two novel capacity optimization approaches assuming per-beam SINR constraints in order to use the satellite resources (e.g., power and bandwidth) more efficiently. Moreover, we develop a general methodology to include technological constraints due to realistic implementations, and obtain the main factors that prevent the two technologies dual of each other in practice, and formulate the technological gap between them. The Shannon capacity (upper bound) and current state-of-the-art coding and modulations are analyzed in order to quantify the gap and to evaluate the performance of the two candidate schemes. Simulation results show significant improvements in terms of power gain, spectral efficiency and traffic matching ratio when comparing with conventional systems, which are designed based on uniform bandwidth and power allocation. The results also show that BH system turns out to show a less complex design and performs better than NOFR system specially for non-real time services.

System capacity optimization in time and frequency for multibeam multi-media satellite systems

Current Ka-band, multi-media satellite systems employ spot beam technology to accommodate a wide range of multi-media type services. These satellites typically employ uniform allocation of RF power and bandwidth to spot beams. Since the traffic distribution tends to be highly asymmetrical and with a high degree of uncertainty, the satellite does not have sufficient flexibility to satisfy the traffic request on a beam per beam basis in an efficient manner. This paper investigates two new candidate multibeam system transmission schemes, namely, the Flexible and Beam-Hoping (BH) scheme, focusing on the forward link. We formulate the system-level optimization and propose an iterative algorithm that always converges given the constraints posed by the payload. The algorithm feeds a detailed system-level simulator which takes into account Ka-band channel and physical layer statistics. Our results show that both candidates outperform the conventional system in terms of both adaptation throughput matching to traffic demands and a more efficient use of available resources. The results were obtained during a project funded by the European Space Agency, with title “Beam Hopping techniques for multibeam satellite systems”.

SAT03-3: Joint Time Slot Optimization and Fair Bandwidth Allocation for DVB-RCS Systems

This paper introduces a novel operational framework for the problem of time slot assignment in a digital video broadcast-return channel via satellite (DVB-RCS) system. The approach is compliant with the latest technical specifications emitted by the European telecommunications standards institute (ETSI) about quality of service (QoS) in satellite earth stations and systems (SES). It is a cross-layer MAC-PHY optimization approach sustained by the powerful framework of convex optimization. The paper proposes a hierarchical dynamic bandwidth allocation approach, which is motivated by the computational complexity of the single-step solution. More specifically, we obtain and analyze the optimal time duration of the time slots and jointly, we make a fair allocation of slots to areas, which is the highest level in the bandwidth allocation hierarchy. Results show up to a 10% increase in transported capacity.

Offered capacity optimization mechanisms for multi-beam satellite systems

In this paper we investigate capacity optimization mechanisms for multi-beam satellite systems built on a realistic payload model. The first proposed mechanism deals with long term traffic variations, for which capacity optimization algorithms are proposed based on per-beam traffic requests. Due to the high asymmetry of the traffic, our algorithms provide time and spatial flexibility illuminating a specific set of beams within a window of several time-slots. Our algorithms maximize the amount of capacity actually offered while providing reduced power consumption. The second proposed mechanism deals with short-term traffic variations, for which we propose Network Coding (NC) based techniques at the link layer. The aim is to increase the offered capacity taking advantage of overlapping beam coverage, usually considered as a source of interference. This technique is meant to be applied not only in classical multi-beam systems, but also on top of the per-beam capacity optimization as a method to deal with fast traffic unbalances not evaluated in the first mechanism. Analysis and simulations results show that system capacity can be increased up to 13% in the first case and up to 90% in the second case.

Spatial Diversity with Network Coding for ON/OFF Satellite Channels

In this letter, we investigate the advantages of network coding (NC) combined with spatial diversity (SD) in scenarios with multiple sources, a single satellite and a single receiver. Each link source-satellite is modeled as an ON/OFF channel. We show that our system matches a wide number of realistic scenarios, from Wireless Sensor Networks (WSN) to Delay Tolerant Networks (DTN). We propose employing random linear network coding (RLNC) together with SD to reduce the system outage probability with respect to traditional SD scheme. The theoretical expressions we derive and the simulations performed show that the proposed scheme significantly reduces the system outage probability for a wide range of channel conditions. Moreover, we also propose a method for obtaining the optimal code rate constrained to a maximum system outage probability, which can serve as system design methodology.

The Future of Satellite TV: The Wide Range of Applications of the DVB-S2 Standard and Perspectives

The first two generations of TV broadcasting are almost history, at least from the standardization perspective. Analog and digital satellite distributions both have addressed mass markets. The next-generation TV systems are close to primetime deployments: HDTV, 3DTV, interactive services, hybrid services, and additional innovations will dominate the next-generation TV. With the efficiency and maturity of DVB-S2, satellite distribution is a cost-efficient and well-established broadcast technology with significant potential for extensions. In this paper, the future perspectives of digital TV and HDTV broadcasting will be first explored, considering ongoing and future standardization activities that will be carried out. Particular attention to innovative solutions based on adaptive modulation and coding, source and channel coding, and error resilience techniques for satellite TV transmission is paid. In addition to broadcast TV, also the perspectives of hybrid and IPTV will be considered in a satellite scenario with their pros and cons, trying to understand if satellite IPTV will be in competition with “conventional” broadcast satellite TV services (like it already happens in terrestrial scenarios).

Network Coding Advantage over MDS Codes for Multimedia Transmission via Erasure Satellite Channels

In this paper, we focus on the performance analysis of packet-level Forward Error Correction (FEC) codes based on Systematic Random Linear Network Coding (SRNC) for multimedia transmission via erasure satellite channels. A performance comparison is presented against maximum distance separable (MDS) codes currently used in state-of-the-art satellite transmission air interfaces, specifically Reed Solomon (RS) codes. Firstly, a theoretical analysis is presented for which we first develop a matricial erasure channel model. The theoretical analysis shows that both the RS and SRNC have, as expected, similar error correction performance over different packet erasure lengths for commonly used size fields. Secondly, we present an on-the-fly progressive algorithm for SRNC, which takes advantage of the inherent randomness of SRNC encoding. Thirdly, a performance comparison is presented for two different satellite scenarios: 1) DVB-S2/RCS railway scenario and 2) Broadband Global Area Network (BGAN) mobile scenario. We use real channel parameters for the first scenario and channel traces of video streaming sessions for the second scenario. Our simulation results confirm that both the RS codes and SNRC have the same packet recovery capabilities. However, for low coding rates, SRNC is shown to achieve up to 71% delay gain as compared to RS codes.