T. de Cola

A survey of architectures and scenarios in satellite‐based wireless sensor networks: system design aspects

This paper is not a survey related to generic wireless sensor networks (WSNs), which have been largely treated in a number of survey papers addressing more focused issues; rather, it specifically addresses architectural aspects related to WSNs in some way connected with a satellite link, a topic that presents challenging interworking aspects. The main objective is to provide an overview of the potential role of a satellite segment in future WSNs. In this perspective, requirements of the most meaningful WSN applications have been drawn and matched to characteristics of various satellite/space systems in order to identify suitable integrated configurations. Copyright

Congestion Aware Routing Strategies for DTN-Based Interplanetary Networks

The networking and communication challenges posed by interplanetary environments make the design and the deployment of complex telecommunication infrastructures particularly difficult, especially with regard to routing and congestion control issues. To this end, the paper proposes a congestion-aware routing paradigm that applies multi attribute decision making (MADM) concepts for next-hop selection, by formulating an optimisation problem and proposing some possible resolution criteria. Effectiveness of the proposed solutions is assessed through a preliminary performance analysis that shows promising results.

Performance analysis of data transfer protocols over space communications

The work presented here concerns the study and the investigation of data transmission mechanisms, employed above the network layer of the protocol stack, used to transmit a data file through an end-to-end path composed of low Earth orbit (LEO) and geostationary (GEO) portions. A link built in the unexplored band W connects the Earth station to a LEO satellite (called DAVID). The communication among DAVID and other sites is performed by means of an inter-satellite link in Ka band, which connects the LEO satellite to a GEO one (called ARTEMIS) and the latter to the Earth stations. The main peculiarities of the investigated scenario consist of the visibility of a LEO satellite, limited to a few minutes, and of the only partial availability over time of a return link on the GEO path. LEO visibility may seriously affect the data communication because it implies suspend/resume mechanisms to match nonvisibility periods. The partial unavailability of the return link makes (transmission control protocol) TCP-based solutions barely applicable and implies the design of effective protocol architectures, in order to guarantee a reliable data communication. Several investigations about alternative novel architectures have been produced in order to individuate solutions that meet all the network requirements in terms of service reliability, exploitation of the network resources, and overall service time. The analysis is two-fold: on one hand the attention has been addressed to the LEO path, highlighting the features offered by a transport layer splitting approach and by an application-based solution exploiting the CCSDS (Consultative Committee for Space Data Systems) protocol stack, whose performance is compared with the results provided by the TCP/IP protocol stack, commonly used in the Internet (where IP stands for Internet Protocol). Concerning CEO path, assuming the return link only partially available, two alternatives of the CCSDS protocol stack have been investigated: the first one implies the use of a negative acknowledgement scheme, the second one does not require any availability of a return link. The two paths together compose the end-to-end communication, which is also globally analyzed on the basis of the performance offered by the solutions presented for the two portions. All the results have been obtained by using a simulator developed for the aim.

Analysis of TCP live experiments on a real GEO satellite testbed

The paper describes a measurement campaign carried out by the University of Bologna (UoB), the National Inter-University Consortium for Telecommunications (CNIT) and the University of California Los Angeles (UCLA). The aim of the experiments was the performance assessment of a wide range of TCP enhancements on network environments that include a real GEO satellite link. To this end, UoB and CNIT integrated their network tools and set up a testbed composed of a cluster of UoB Linux PCs connected to the CNIT GEO Skyplex satellite platform. Tests were conducted considering both end-to-end TCP enhancements and a TCP-splitting Performance Enhancing Proxy (PEP) developed by UoB. The analysis was not limited to isolated satellite links, but embraced more complex heterogeneous networks, where satellite connections have to compete with wired cross traffic for the network resources. The analysis of the large set of experimental data presented in the paper confirms the challenges posed by GEO satellite channels, which, in this case, were worsened also by the presence of Bandwidth on Demand technique, which impacts TCP performance. Among the end-to-end TCP variants, best results are generally shown by TCP Hybla, especially when heterogeneous environments are considered. On the other hand, the splitting PEP solution offers the best performance with respect to all TCP enhancements, due to its ability to isolate satellite channel impairments. The possible drawback of this approach is in that it violates the end-to-end semantics and is incompatible with IPsec protocol implementation.

An integrated testbed for wireless advanced transport protocols and architectures

The challenges posed by data communications over both satellite and terrestrial wireless systems make the adoption of adequate countermeasures advisable. In particular, the poor performance experienced by TCP transport protocol in such environments has fed the scientific community to propose novel solutions, from both the protocols and architecture points of view. In order to perform a thorough assessment of such proposals, University of Bologna (UoB) and National Inter-University Consortium for Telecommunications (CNIT) have conceived and set-up an integrated testbed. Its characteristics and capabilities are presented and discussed in this work, focusing in particular on the advantages offered by the ubiquitous remote control of the testbed, provided by a powerful web interface specifically designed for this purpose

Study and performance analysis of transport layer mechanisms over LEO satellite environment

The paper concerns the study of transmission mechanisms employed in telecommunication environments, where LEO (low earth orbit) orbits are present Several investigations about novel network architectures have been produced in order to individuate the solution that meets all the network requirements and characteristics in terms of delay, reliability and speed. Two types of solutions are proposed: the first one, where the terminals are modified and no additional tool is inserted in the network; the second one, based on a protocol-splitting philosophy. This latter supposes to add special tools called gateways to improve the performance. The effectiveness of the proposed solution is then evaluated by using a software simulator that has been adapted for the communication in the different protocol architectures studied.

Communications and networking over satellites: SatNEx experimental activities and testbeds

One of the aims of the SatNEx (Satellite Network of Excellence, http://www.satnex.de) European project is to provide the scientific community that operates on satellite communications with measurement campaign results and evaluation tools, in order to support research activities that investigate problems in satellite communications at different levels of the OSI stack. In fact, the research activities developed in SatNEx address the most relevant aspects of satellite communications, such as channel modulation and coding schemes, access strategies, advanced networking, end-to-end quality of service, transport performance, delay tolerant networks, and new applications. Even if SatNEx is mainly devoted to satellite communications, integration of satellite and terrestrial wireless segments has also been taken into account. This paper presents the results obtained in the specific research activity devoted to trials and testbeds developed during the SatNEx project. The high number of authors of this paper is an indication of the strong collaborative work sustained, the numerous measurement campaigns, and the complexity in developing integrated testbeds. Copyright

Power and Bandwidth Effective Data Communications in Disaster Relief Operations through a Satellite-Based Disruption Tolerant Network Paradigm

Providing effective telecommunication infrastructures for disaster relief and emergency operations can be achieved by taking advantage of anywhere-anytime communication capabilities offered by satellite and wireless technology. In this perspective, designing a network architecture able to ensure reliable and timely delivery of data, and able to resist against link disruption is of utmost importance. To this end, this work proposes a mobility-aided routing strategy, derived from other proposals, that aims at delivering data to destinations by taking into account power consumption issues. The efficacy of the proposed solutions is assessed by simulation, considering different scenario configurations.

TCP Live Experiments on a Real GEO Satellite Testbed

The paper describes a measurement campaign recently carried out by University of Bologna (UoB), National Inter-University Consortium for Telecommunications-(CNIT) and University of California Los Angeles (UCLA), on the CNIT GEO Skyplex platform. The aim of the experiments is the performance assessment of a wide range of TCP enhancements on network environments that include a real GEO satellite link. Measurements were carried out by means of the integrated UoB-CNIT testbed, fully controlled by remote through a Web interface. Analysis of live experiments data confirm the challenges posed by GEO sat channels, and show a negative influence of the Skyplex BoD technique on TCP start-up performance. Among the TCP enhancements compared in the paper, best results are provided by TCP Hybla and TCP Westwood, with an advantage of the former in heterogeneous environments characterized by a high level of RTT unfairness.

High Performance Communication and Navigation Systems for Interplanetary Networks

The increasing development of technologies enabling efficient space exploration and data communications has recently fostered a number of scientific missions, aimed at supporting the research in the field of geology and astronomy. To this end, the design of an effective telecommunication infrastructure is the challenge offered to research scientists and space engineers. In particular, the definition of a network architecture suitable to support both communication and navigation services is of paramount importance for future space missions. In this view, this paper reviews protocols and architectures presently used in space missions and proposes improved transmission strategies, relying upon a packet-layer coding approach, which is expected to improve the overall performance.