Tomaso de Cola

Performance analysis of CCSDS File Delivery Protocol and erasure coding techniques in deep space environments

The rising demand for multimedia services even in hazardous environments, such as space missions and military theatres, and the consequent need of proper internetworking technologies have revealed the performance limits experienced by TCP protocol over long-delay and lossy links and highlighted the importance of the communication features provided by the protocol architectures proposed by the Consultative Committee for Space Data Systems (CCSDS). This paper proposes a CCSDS File Delivery Protocol (CFDP) extension, based on the implementation of erasure coding schemes, within the CFDP itself, in order to assure high reliability to the data communication even in presence of very critical conditions, such as hard shadowing, deep-fading periods and intermittent links. Different encoding techniques are considered and various channel conditions, in terms of Bit Error Ratio and bandwidth values, are tested.

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

Combined Congestion Control and Link Selection Strategies for Delay Tolerant Interplanetary Networks

In view of the dense and complex space network topologies envisioned for the future, the management of congestion control is a prominent issue that deserves a particular attention. Given the challenging peculiarities of interplanetary environments, this paper focuses on the advantages offered by storage-based routing and on potentials of implementing Random Early Detection (RED) and Explicit Congestion Notification (ECN) mechanisms within the Delay Tolerant Network (DTN) architecture. In this light, solutions relying upon the aforementioned concepts have been designed and tested. Preliminary results show that combination of RED and ECN schemes with network-selection strategies for storage-based routing is really promising and outperforms other solutions in terms of reliability, network resource utilisation and power consumption.

Reliable data delivery over deep space networks: Benefits of long erasure codes over ARQ strategies

Achieving reliable communications in deep space environments poses formidable networking challenges because of the extreme physical medium peculiarities. In this view, two possible approaches can be considered to carry out reliable data transfers over deep space channels: automatic repeat request schemes and packet layer coding algorithms applied with long erasure codes. In this respect, this article surveys the mechanisms currently available from the Consultative Committee for Space Data Systems protocol stack, by reserving special attention, on one hand, to the ARQ schemes currently implemented at the application layer and, on the other hand, to the potential offered by erasure coding schemes. A comparative analysis gives some insights about the performance improvements the packet layer coding methodology can bring. In particular, the results show that the use of erasure coding is able to attain more satisfactory performance results than ARQ-based schemes in terms of reliability, data transfer delay, resource network utilization, and power consumption.

A simulation study of network-coding-enhanced PEP for TCP flows in GEO satellite networks

This paper focuses on geostationary satellite scenarios and investigates the performance of several Transmission Control Protocol (TCP) variants in a novel Performance Enhancing Proxy (PEP) architecture solution, whose added value is the use of network coding beneath the transport layer. Comparison of TCP New-Reno, Vegas, Scalable, CUBIC, Hybla, and HTCP and the cases where these transport protocols are used along with network coding is carried out by means of simulation campaigns. The obtained results show the potentials of the proposed network coding technique, resulting in the improvement of TCP connections performance in a wide range of channel conditions and the possible exploitation of future increase of the satellite link capacity.

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.

Joint Use of Custody Transfer and Erasure Codes in DTN Space Networks: Benefits and Shortcomings

The features that DTN protocol architecture offers are particularly appealing to handle intermittent links and disruption events, by means of the Custody Transfer option. On the other hand, the implementation of long erasure codes proved to be promising to contrast short fading events in long delay networks, where the high latency makes the use of ARQ schemes less profitable. This paper proposes a protocol design to incorporate long erasure codes into the Bundle Protocol specification. The conducted performance analysis shows the benefits coming from this integrated approach but also points out the possible shortcomings deriving from the saturation of the buffer implemented at the Bundle Protocol layer.

Throughput maximization of optical LEO-ground links

The long-term throughput of optical links between a circular-LEO satellite and a ground station is assessed for systems with fixed and variable data rates. For a fixed data rate, we evaluate the minimum elevation angle above which the link should be established in order to maximize the throughput. The ratio of this optimized constant-data-rate throughput to the throughput of an adaptive transmission with a data rate proportional to the received power is found to depend mainly on the satellite altitude.

Channel prediction and network coding for smart gateway diversity in terabit satellite networks

This paper explores the network design implications to be taken into account in Smart Gateway Diversity (SGD) satellite systems, where gateway outage events have to be counteracted by efficient handover procedures. In more detail, enabling high data-rate satellite systems in these conditions requires efficient coordination strategies between gateways, upstream routers and Network Control Centre (NCC) to precisely estimate the need of handover and to efficiently manage the satellite resources. To this regard, this paper adopts a simple channel estimation algorithm and applies network coding to cope with packet losses deriving from possible inaccuracies on the prediction of the handover time. The results obtained via simulation confirm the capabilities of network-coding-based approaches and pave the way for further studies in the area of network for SGD satellite systems.

Mars to Earth communications through orbiters: Delay‐Tolerant/Disruption‐Tolerant Networking performance analysis

SUMMARY Delay-Tolerant/Disruption-Tolerant Networking (DTN) architecture will be used in future deep space missions, to enable autonomous networking operations and disruption-tolerant data communications. Therefore, it is worth analyzing the performance of the DTN Bundle Protocol (BP) in a realistic deep space environment, reproducing the characteristics of Mars missions. After a comprehensive introduction on data communications between Mars and Earth, the paper presents the essential features of both the BP DTN architecture and the Licklider Transmission Protocol (LTP), adopted here as BP convergence layer on deep space links, thanks to its ability to cope with the very long delays typical of this environment. The focus of our experiments is on analysis of the bundle flow from a Mars lander to an Earth control center through an intermediate relay node, for which two configurations are considered, inspired to Odyssey and Mars Reconnaissance Orbiter missions, respectively. Results are obtained by means of a test bed consisting of some GNU/Linux personal computers running either Interplanetary Overlay Network (ION) or DTN2 BP implementations. The analysis of results aims to highlight the role played by BP and LTP in tackling the challenges of Mars to Earth communications. Copyright