Alberto Gotta

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

Simulating dynamic bandwidth allocation on satellite links

In the last years, DVB-RCS has emerged as a flexible technology offering broadband Internet access to a large community of users at a relatively low cost. At the same time, the spreading of networked multimedia applications has highlighted the need to investigate mechanisms that guarantee a certain level of Quality of Service (QoS) to the end users. In particular, the DVB-RCS standard specifies different capacity request categories to support QoS at the link layer.We describe Tdma-bod, an ns-2 improvement that implements generic bandwidth-on-demand allocation in TDMA satellite systems; the patch is available as free software. This simulator has been validated through experimental tests performed on the Skyplex satellite system. Specifically, we run CBR UDP flows to measure the characteristics of the satellite link in terms of throughput and delay and to verify that the simulative model output matches the experimental dynamic throughput and one-way delay behaviour. The simulations and experiments show that bandwidth-on-demand allocation mechanisms may cause large delays when sudden variations in the incoming traffic rate occur, a behaviour typical of multimedia flows.

Long-lived TCP connections via satellite: cross-layer bandwidth allocation, pricing, and adaptive control

The paper focuses on the assignment of a common bandwidth resource to TCP connections over a satellite channel. The connections are grouped according to their source-destination pairs, which correspond to the up- and down-link channels traversed, and each group may experience different fading conditions. By exploiting the tradeoff between bandwidth and channel redundancy (as determined by bit and coding rates) in the maximization of TCP goodput, an overall optimization problem is constructed, which can be solved by numerical techniques. Different relations between goodput maximization and fairness of the allocations are investigated, and a possible pricing scheme is proposed. The allocation strategies are tested and compared in a fading environment, first under static conditions, and then in a real dynamic scenario. The goodput-fairness optimization allows significant gains over bandwidth allocations only aimed at keeping the channel bit error rate below a given threshold in all fading conditions.

Performance Evaluation of SPDY over High Latency Satellite Channels

Originally developed by Google, SPDY is an open protocol for reducing download times of content rich pages, as well as for managing channels characterized by large Round Trip Times (RTTs) and high packet losses. With such features, it could be an efficient solution to cope with performance degradations of Web 2.0 services used over satellite networks. In this perspective, this paper evaluates the SPDY protocol over a wireless access also exploiting a satellite link. To this aim, we implemented an experimental set-up, composed of an SPDY proxy, a wireless link emulator, and an instrumented Web browser. Results confirm that SPDY can enhance the performances in terms of throughput, and reduce the traffic fragmentation. Moreover, owing to its connection multiplexing architecture, it can also mitigate the transport layer complexity, which is critical when in presence of middleboxes deployed to isolate satellite trunks.

Radio resource management across multiple protocol layers in satellite networks: a tutorial overview

Satellite transmissions have an important role in telephone communications, television broadcasting, computer communications, maritime navigation, and military command and control. Moreover, in many situations they may be the only possible communication set-up. Trends in telecommunications indicate that four major growth market/service areas are messaging and navigation services (wireless and satellite), mobility services (wireless and satellite), video delivery services (cable and satellite), and interactive multimedia services (fibre/cable, satellite). When using geostationary satellites (GEO), the long propagation delay may have great impact, given the end-to-end delay users requirements of relevant applications; moreover, atmospheric conditions may seriously affect data transmission. Since satellite bandwidth is a relatively scarce resource compared to the terrestrial one (e.g. in optical transport networks), and the environment is harsher, resource management of the radio segment plays an important role in the systems efficiency and economy. The radio resource management (RMM) entity is responsible for the utilization of the air interface resources, and covers power control, handover, admission control, congestion control, bandwidth allocation, and packet scheduling. RRM functions are crucial for the best possible utilization of the capacity. RRM functions can be implemented in different ways, thus having an impact on the overall system efficiency. This tutorial aims to provide an overview of satellite transmission aspects at various OSI layers, with emphasis on the MAC layer; some cross-layer solutions for bandwidth allocation are also indicated. Far from being an exhaustive survey (mainly due to the extensive nature of the subject), it offers the readers an extensive bibliography, which could be used for further research on specific aspects. Copyright

Performance Analysis of Systematic Upper Layer FEC Codes and Interleaving in Land Mobile Satellite Channels

This paper provides an analytical method for evaluating the performance of upper layer forward error correction (FEC), when used together with interleaving on land mobile satellite channels, in terms of residual (after decoding) packet loss rate (PLR). In addition, the analysis highlights the overheads introduced by this technique, which depend on the channel statistics, in terms of additional packet delivery delay, bandwidth consumption, and computation power required. We show why the interleaver is mandatory in some environments, due to the severe disruptive characteristics of the channel, according to measurement campaigns promoted by the European Space Agency. This analysis provides the expression of the residual PLR when systematic FEC coding blocks are interleaved at the packet level (i.e., when a cyclic redundancy check and a sequence number identify a correct data unit). This method can be employed for the performance evaluation of recent and future mobile communication systems that take advantage of upper layer FEC and interleaving techniques.

Experimental video broadcasting in DVB-RCS/S2 with land mobile satellite channel: A reliability issue

This paper aims at studying the behaviour of satellite DVB systems in a vehicular mobile environment by deriving a channel model at packet level that accounts for the mobile characteristic of the channel and the performance of the DVB architecture at physical layer. Moreover the paper provides some solutions based on error recovery techniques, i.e. packet level FEC and interleaving, in order to boost the Quality of Service of streaming applications by providing quantitative and qualitative metrics of the reliability of such transmissions over a land mobile satellite channel.

Networking with multi‐service GEO satellites: cross‐layer approaches for bandwidth allocation

Cross-layer Radio Resource Management (CL-RRM) has been recently investigated by quite a few research groups in wireless communications. In the specific satellite-networking environment, the paper presents an overview of different CL-RRM techniques devoted to dynamic bandwidth allocation, whose interactions span the physical, data link, network and transport layers, in various combinations. A multi-service setting is considered, in the presence of variations in both traffic and channel conditions. Regarding the latter, bit and coding rate adaptation are adopted as fade countermeasure, and their effect on the higher layers is modelled as a bandwidth reduction. Traffic models and methodologies for dynamic bandwidth allocation and performance optimization are discussed. Numerical examples are presented to highlight throughput/fairness trade-offs for long-lived TCP connections that share multiple channels with different fading depth. Copyright

Experimental Results with Forward Erasure Correction and Real Video Streaming in Hybrid Wireless Networks

In a heterogeneous MANET, based on wireless LANs linked together by satellite, the overall channel efficiency is impaired by multiple effects, because of multipath fading in the terrestrial segment and atmospheric fading on the satellite link. In this paper we address this issue by applying forward erasure correction codes (FZC) to MPEG-4 video sequences exchanged by the hosts of a hybrid network, made of a satellite link and a wireless LAN using 802.11b devices. A standard video streaming application runs on one end of the satellite link while, at the other end, a wireless ad hoc network receives the multicast video stream. This work aims at demonstrating the improvement in quality of service (QoS) of the video transmitted in the hybrid network. The main parameters measured are the packet loss, the delivery delay, and the overhead in bandwidth occupancy imposed by the use of FZC. The received video is then evaluated by using a MOS (mean opinion score) procedure

An Analysis of TCP Startup over an Experimental DVB-RCS Platform

Satellite systems are evolving towards higher available bandwidths and dynamic allocation based on instantaneous traffic rates offered at the stations, so called BoD (bandwidth on demand) channel sharing. This trend is paired with more and more powerful error correcting schemes, like those adopted in the recent DVB-S2 standard, which promise to make the channel virtually immune from packet errors. These factors, together with the significant round-trip delay of geostationary satellites, combine so that most TCP connections would send all of their data during the slow start phase. We investigate the performance of TCP during startup on recent BoD system by observing and explaining the behavior of different TCP flavors on different systems when transmitting data over the Eutelsats Skyplex data satellite system. We make recommendations for choosing and improving TCP implementations and for future BoD allocation schemes