Cristina Parraga Niebla

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.

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.

Designing an efficient communications protocol to deliver alert messages to the population during crisis through GNSS

Multi-channel Early Warning Systems are currently used to warn the population at risk and reduce the impact of crisis. Nevertheless, satellite networks, which offer robust and reliable communication solutions during major disaster events, are not yet being fully considered for direct communication to the citizens. The paper will address solutions for the transmission of alert messages to warn/inform the population in risk during crisis through GNSS. The solution proposed is based on a protocol for alert messages that is compatible with the Common Alert Protocol (CAP), but lightweight in comparison with CAP, so that it can be applied over a variety of communication links, i.e. over different communication standards, even in very narrow band channels, such as Satellite-Based Augmentation System (SBAS). The paper will analyse the opportunities and implications of using GNSS to disseminate alert messages to the population and propose the principles for a flexible protocol that allows the translation of CAP messages (XML-based) into a very flexible and lightweight protocol for transmission in very narrow band channels.

The very short frame of mobile DVB‐RCS: Code design and QoS Performance

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.

Video Traffic Management in HSDPA via GEO Satellite

This paper investigates video traffic management and packet-scheduling aspects for satellite Universal Mobile Telecommunication System (S-UMTS) transmissions based on high speed downlink packet access via geostationary satellite (S-HSDPA). In particular, this paper surveys resource allocation constraints to be considered for S-HSDPA and investigates the performance of different scheduling schemes in the presence of a GOOD/BAD channel and their influence on the objective video quality for typical UMTS video streaming scenarios. This work has been carried out within the framework of the European SatNEx II network of excellence

System design for pan-European MSS services in S-band

This paper gives an overview of a suitable communications system capable of efficiently use the available S-band allocation for pan-European Mobile Satellite Services (15 MHz in both uplink and downlink for each of the two licensed operators) to provide different classes of services such as interactive mobile broadcast services enhancing DVB-SH offer, messaging services for handheld and vehicular terminals, realtime emergency services such as voice and file transfer, mainly addressing institutional users on-the-move such as fire brigades, civil protections, etc… The design is based on a modular, flexible and scalable system architecture enabling different channelisations and frequency allocations within each beam, allowing independent deployment of different service classes within different beams, whilst ensuring backward compatibility with DVB-SH legacy terminals.

Link Layer Coding for DVB-S2 Interactive Satellite Services to Trains

The railroad satellite channel is characterized by frequent signal outages due to tunnels, bridges and electrical trellises. While for medium/long tunnels the main option to offer reliable and uninterrupted connectivity deals with the adoption of gap-filling techniques, signal outages due to small bridges/tunnels or electrical trellises can be faced with ad-hoc recovery techniques. In this paper, we face the problem from a link layer perspective, showing how a proper design of an erasure correcting code operating at link layer represents a valuable countermeasure against short outage events. The performance evaluation is developed in comparison with a more traditional technique based on physical layer coding in combination with a long channel interleaver. Advantages of the link layer coding scheme will be shown.

Antenna diversity and GSE-based packet level FEC for DVB-S2 Systems in Railway scenarios

In this paper, we address the study of a broadband satellite system based on DVB-S2 for interactive services in a mobile scenario. In particular, we focus on the railway scenario when the train is moving with high speed under LOS (Line of Sight) conditions considering also the atmospheric effects for Ku band. We aim at the design of fading countermeasure to compensate the impact of short and medium term fading that is present in the LOS case, which is owed to the speed, the near environment (modelled by a Rice model) and the power arches. Long term signal blockage due to e.g. railway tunnels has not been considered in this study. With the purpose of compensating for these effects, the use of packet-level FEC and antenna diversity has been already proposed. In this paper, a further development of packet-level FEC, in combination or not with antenna diversity, is proposed. We propose a coding that differentiates classes of service thus avoiding guaranteeing quasi-error free PER performance for applications that do not need it with the consequent gain in capacity. Furthermore, we consider the adaptation layer to be based on the novel GSE (Generic Stream Encapsulation) encapsulation method currently under standardization process. Our results show that our proposed fade mitigation techniques yield improvements of average packet error rate.

Alerting over satellite navigation systems: lessons learned and future challenges

Public warning in emergency situations has experienced great momentum in recent years due to the increasing need for suitable communication means to disseminate alerts due to the increasing number of natural and technological disasters, as well as the consequent damage created and number of people affected by them. This goes along with a number of activities that promote multi-channel approaches to make use of different communication channels to disseminate alerts. However, only a little work has been performed so far considering the use of satellite communications in the last mile within a multichannel architecture for alerting purposes. This article addresses the feasibility and impact of deploying alert message services over satellite navigation systems.

Gap Filler Architectures for Seamless DVB-S2/RCS Provision in the Railway Environment

In this paper, we study the provision of broadband interactive services to passengers of Korean high-speed train in the ISM 2.4 GHz band. We address in particular the design of tunnel gap-fillers (GFs) able to provide bi-directional connectivity to train-based terminals. The work has been developed in the broader context of interactive services provision for high-speed trains through satellite networks. First, a channel model for the in-tunnel propagation is derived. Taking into account the results of the propagation analysis, a comparison between commercial technologies (belonging to both the IEEE and the DVB standard families) is provided, showing the possible strengths and weaknesses of the proposed solutions with respect to architectural and performance point of views.