Satellite Connections Research Articles

Virtual Surgical Pathology in Underdeveloped Countries: The Zambia Project

Only 1 surgical pathology laboratory is available in Zambia, a country with a population of 12 million people. Since 2004 the Italian association of pathologists Patologi Oltre Frontiera has been working to create a virtual laboratory through the use of telemedicine. The project has involved staining histologic preparations on site, with the interpretation of imaged slides performed abroad through telepathology. Starting in April 2007, all surgical specimens obtained in Mtendere Mission Hospital, Chirundu, Zambia, were submitted for microscopic examination through whole-slide scans. Two independent Italian pathologists evaluated the cases by means of satellite connection and the final diagnoses were sent to Zambian clinicians via the internet. This article describes the spectrum of diagnoses made via telepathology for the Zambian population. Also, we analyze the concordant and discordant data between this telepathology method and traditional microscopy in a developing country. Moreover, we provide possible solutions for providing pathology services in other underdeveloped countries.

The Effect of Social Presence on Affective and Cognitive Learning in an International Engineering Course Taught via Distance Learning

BackgroundDistance learning course formats can alter modes of information exchange and interpersonal interaction relative to traditional course formats.Purpose (Hypothesis)To determine the effect of a distance course format on the knowledge acquisition (cognitive learning) and satisfaction (affective learning) of students, we investigated student learning responses and social presence during a graduate‐level engineering course taught via traditional (i.e., professor present in the classroom) and synchronous distance‐learning formats.Design/MethodDirect quantification of participation, academic performance assessment based on homework and exam scores, and survey‐based assessments of student perceptions of the course were collected. Based on these data, cognitive and affective learning responses to different technological and interaction‐based aspects of the course were determined for each course format.ResultsWe show that while affective learning decreased for students in the distance format course relative to the traditional format, cognitive learning was comparable. Our results suggest that loss of satellite connection and audio losses had a stronger negative effect on student perceptions than video disturbances, and that participation was the most important factor influencing affective learning.ConclusionsWhile our findings do not suggest that cognitive learning is strongly affected by social presence, implementing strategies to enhance social presence may improve the overall learning experience and make distance learning more enjoyable for students.

Global Teleradiology - An Internet-Based Application for Optimization of Health Care Delivery Across Domestic and International Borders

Teleradiology refers to the electronic transmission of radiological images, such as X-rays, Computed Tomograms (CT's), and Magnetic Resonance Images (MRI's) across geographical locations for the purposes of interpretation and consultation. The digital radiological images are typically transmitted using standard telephone lines, satellite connections, or wide area networks (WANs). Teleradiology is an empowering technology and a facilitator for enhanced medical care. Teleradiology enables a single radiologist to simultaneously provide services to several hospitals independent of their location and also allows the exploitation of global time differences to provide emergency night coverage by personnel in a different time zone working a day shift. Additionally, the quality of care delivered by a wide awake, alert physician working a day shift is far superior to that provided by a radiologist who is up all night. Subspecialty opinions delivered to locations where the expertise is otherwise unavailable are an added benefit. In this paper, we describe the current state-of-art in teleradiology, the benefits of the clinical practice of teleradiology, and the technical, regulatory and security issues related to teleradiology. We begin by providing a historical background describing the evolution of global teleradiology.

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.

PEPsal: A Performance Enhancing Proxy for TCP Satellite Connections [for Internetworking and Resource Management in Satellite Systems (Series)

PEPsal: A Performance Enhancing Proxy for TCP Satellite Connections [for Internetworking and Resource Management in Satellite Systems (Series)

PEPsal: A Performance Enhancing Proxy for TCP Satellite Connections [Internetworking and Resource Management in Satellite Systems Series

PEPsal: A Performance Enhancing Proxy for TCP Satellite Connections [Internetworking and Resource Management in Satellite Systems Series

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.

Internetworking and Resource Management in Satellite Systems [Guest Editor's Introduction

Discusses the three articles that are part of a series on internetworking and resource management in satellite systems. The first article appears in the July 2007 Aerospace and Electronic Systems Magazine issue "Network architecture and radio resource management for satellite digital multimedia broadcast system"); the second article appears in the August 2007 issue ("PEPsal: A performance enhancing proxy for TCP satellite connections"); and the third article in the series appears in the September 2007 issue ("Advanced channel coding for Hap-based broadcast services").

Media Reporting, Mobility and Trauma

Media Reporting, Mobility and Trauma

The RAFT network: 5 years of distance continuing medical education and tele-consultations over the Internet in French-speaking Africa

Continuing education of healthcare professionals is a key element for the quality and efficiency of a health system. In developing countries, this activity is usually limited to capitals, and delocalized professionals do not have access to such opportunities, or to didactic material adapted to their needs. This limits the interest of such professionals to remain active in the periphery, where they are most needed to implement effective strategies for prevention and first-line healthcare. Telemedicine tools enable the communication and sharing of medical information in electronic form, and thus facilitate access to remote expertise. A physician located far from a reference center can consult its colleagues remotely in order to resolve a difficult case, follow a continuous education course over the Internet, or access medical information from digital libraries or knowledge bases. These same tools can also be used to facilitate exchanges between centers of medical expertise: health institutions of a same country as well as across borders. Since 2000, the Geneva University Hospitals have been involved in coordinating the development of a network for eHealth in Africa (the RAFT, Réseau en Afrique Francophone pour la Télémédecine), first in Mali, and now extending to 10 French-speaking African countries. The core activity of the RAFT is the webcasting of interactive courses. These sessions put the emphasis on knowledge sharing across care professionals, usually in the form of presentations and dialogs between experts in different countries. The technology used for the webcasting works with a slow (25 kbits/s) internet connection. Other activities of the RAFT network include visioconferences, teleconsultations based on the iPath system, collaborative knowledge bases development, support for medical laboratories quality control, and the evaluation of the use of telemedicine in rural areas (via satellite connections) in the context of multisectorial development. Finally, a strong emphasis is put on the development of capacities for the creation, maintenance, and publication of quality medical didactic contents. Specific courses are organized for the national coordinators of the network to develop these competencies, with the help of the Health-On-the-Net Foundation. The richness of the plurality of knowledge and know-how must be steered towards emulation and sharing, respectful of each partner's identity and culture. Collaborations with UNESCO and WHO have been initiated to address these challenges.

Air Interfaces for Satellite Based Digital TV Broadcasting in the Railway Environment

This paper deals with the analysis of possible air interfaces to be employed in order to provide digital TV services to high speed trains via satellite. This turns out to be an extremely challenging issue, since in addition to traditional impairments characterizing the land mobile satellite channel, one has to face the presence of frequent tunnels, whose duration can easily reach several kilometers, and the presence of a variety of peculiar obstacles, such as electrical trellises and posts with and without brackets, which may result in frequent and deep fades. A large variety of possible solutions, based on standardized air interfaces with proper modifications, are analyzed by means of extensive software simulations, showing that effective solutions can be devised. Some consideration concerning the deployment of terrestrial gap-fillers to bridge the satellite connectivity inside long railway tunnels, large train station and within dense urban areas are also briefly addressed.

A DVB/Inmarsat hybrid architecture for asymmetrical broadband mobile satellite services

AbstractIn order to bridge the gap, both regulatory and technologically, between offering mobile satellite services at L‐band today and broadband mobile services at C‐band, Ku‐band or Ka‐band in the future, a short‐term solution is foreseen. Therefore, a DVB/Inmarsat hybrid service offering bi‐directional asymmetrical satellite connectivity, with a broadband receive channel at Ku‐band based on DVB‐S, and with a transmit channel at L‐band based on Inmarsat Mobile Packet Data Service, has successfully been developed, implemented and tested. The article focuses on the rationale for, and a technical solution, and how this can be evolved to support use of Inmarsat Broadband Global Area Access as transmit channel at L‐band. There are no regulatory issues associated with global operation of such a system, and the users can access the services using cost‐efficient off‐the‐shelf equipment, since the well established Inmarsat and DVB standards are utilized. The system has proved its feasibility to offer services like Internet access, email access, fast file transfers, and IP streaming of audio and video, in addition to the traditional Inmarsat services. Copyright © 2006 John Wiley & Sons, Ltd.

Bent Pipe Satellite Network System and Area Routing Method

卫星网络(SN)主要包括两种体系结构:星上处理(OBP)和弯管(BP).OBP由于性能高而得到广泛关注,而BP由于成本低仍然被一些系统所采用.BP系统没有星间链路(ISL),但需要地面信关站的支持.不同的BP系统有不同的信关站布局,系统不兼容将造成重复和浪费.区域路由(AR)方法是一种通用性较强的路由方法,既可以应用在OBP系统中,也可以应用在BP系统中.使用该方法可以让多种BP系统共享卫星和信关站资源.文中介绍了AR原理及其计算机模拟结果;引入了"连通分析",综合考虑了系统的连通性和覆盖率,深化BP系统的分析.

Hot spots on rails [Internet hotspots in high-speed trains

Mobile data connectivity is spreading to the railway industry. While passengers and crews of ships and aircraft have increasingly been able to access the Internet and check their emails, train travelers have been forced to use their laptops `offline'. The widespread use of tunnels and carriages built as thick metal structures is a constant barrier to seamless cellular communications that radio waves find it difficult to penetrate from the outside. In this paper, the author looks at how rail operators are turning high-speed trains into Internet hotspot. Onboard WLANs is the approach unanimously chosen by a range of technology companies addressing the incipient market. While some vendors have based their systems on satellite connectivity, other are using a combination of satellite and cellular. WiMAX technology is currently being tested as a possible backhaul platform.

Deep‐space communications with a 2‐hop downlink with high link‐availability

AbstractWe recall and discuss the theory of a 2‐hop downlink in deep‐space communications. The first hop (length d1) links the deep‐space spacecraft to either a geostationary satellite or to a low Earth orbiting satellite. The second hop (length d2, with d2 ≪ d1) links the satellite to the Earth receiver through a transparent or regenerative transponder, in slant paths affected by troposphere attenuation. If we adopt a BPSK or QPSK modulation scheme and the same carrier frequencies in the two hops with a transparent transponder, a particular value of the carrier frequency makes the noise‐to‐signal ratio minimum. A better choice is to assign a low carrier frequency (X‐band) to the second hop and a high one (W‐band) to the first hop. A 2‐hop downlink is superior to a 1‐hop downlink with a large power gain proportional to (d1/d2)2 ≫ 1 at high microwave frequencies and large troposphere attenuation (high link‐availability). Shannon's capacity theorem provides the same large gain independently of the choice of the carrier frequencies in the two hops, if we use a regenerative transponder. The carrier frequencies of a 2‐hop downlink need not be those reserved to deep‐space communication, because the spacecraft could communicate as if it were transmitting ‘from the Earth’ through a conventional satellite connection. We have applied the theory to a first‐order design in the frequency range 10–100 GHz, slant path elevation angles 30°, 45° and 90° at Gera Lario or Fucino (Italy), and downlinks form Mars and Saturn, although the general findings and methodology are of global applicability. Copyright © 2005 John Wiley & Sons, Ltd.

Evaluation of AASHTO SiteManager Performance on High-Latency Satellite Communication Links

Most transportation agencies and departments have deployed transmission control protocol–Internet protocol (TCP-IP) applications in their offices and are beginning to deploy TCP-IP applications in remote or satellite field offices. Deployment of TCP-IP applications where broadband access is not available can be quite challenging. Satellite-based communication offers an opportunity to provide high-bandwidth connections quickly. However, satellite communications incur significant travel time delay that may result in poor performance of applications designed for a low-latency environment. This paper presents an evaluation of the AASHTO SiteManager software suite with two different satellite broadband providers. SiteManager clients performed poorly in the high-latency environment, in some cases up to 50 times slower than with SiteManager running on a low-latency terrestrial network with equivalent bandwidth. In general, the performance of SiteManager was relatively insensitive to the bandwidth provided by the satellite provider. In most tasks, SiteManager performed better over a 50-kbps dial-up connection than over a 384-kbps satellite connection. In an alternative architecture in which SiteManager was operated remotely via a terminal emulation service over a satellite connection, the performance was observed to be robust. This architecture requires considerably more equipment, software, and technical support. Furthermore, the delay in seeing some key-strokes and cursor movements appear can be somewhat awkward for the user. However, given the extensive bursts of short messages between SiteManager clients and the server, the high-latency constraints of a satellite network make a terminal emulation procedure the only viable method of deploying SiteManager via a commercial satellite IP service.

Monitoring of radioactivity in NW Irish Sea water using a stationary underwater gamma-ray spectrometer with satellite data transmission

A “sentinel”-type device, equipped with a NaI (Tl)-based underwater gamma-spectrometer mounted on a stationary buoy, transmitting data through satellite connection, was deployed in the north-western Irish Sea.The data recorded and received in real-time indicated that no detectable significant changes occurred in the concentrations of 137Cs at the mooring site in the period September to November, 2000. Other anthropogenic gamma-emitters were not detected.

Protection of Commercial Satellite Communications Infrastructure

Although a nation's interest in protecting its commercial assets in space would seem obvious, the task of protecting commercial satellites is inherently complicated. Protection of commercial space infrastructure requires coordination among multiple actors in the public and private sectors. Although most public sector actors ultimately report to the same political leadership, the process of establishing coherent policies across agencies can take time. Coordination is even more complicated in the private sector, where multi-national firms compete against each other for profits by serving a wide range of customers. Given the complexities of this process, it is not surprising that efforts to protect commercial satellite communications (SATCOM) networks have been slow in coming. At the same time, recent progress in the U.S. may pave the way for a more coherent approach to commercial SATCOM protection. If successful, these efforts can provide increased assurance of uninterrupted satellite connectivity, thus benefiting the economic and national security interests of America, its allies and its trading partners.

A Proposal for Efficient TCP Flow Control over Satellite Networks

Coventional TCP has several performance problems when deployed over long delay, high link error rate satellite connections. Long delay causes the TCP to open up slowly resulting in low bandwidth utilization. High link error rate affects the performance by slowing down transmission rate unnecessarily every time a data loss occurs. In this paper, we propose an efficient end to end flow control scheme, we name TCP Seamless, for TCP over satellite. Our proposal offers a fast opening up of transmission rate to effectively utilize the bandwidth as early as possible. At the occurrence of data loss, our scheme can determine whether the loss was caused by link error or due to congestion. In case of link error, TCP Seamless can restore the transmission rate in a transparent manner. Also during congestion, without violating the netiquette, our scheme can get more data segments acknowledged at a faster rate. The core of our proposal lies in probing the network using low priority data segments. Also we propose two new algorithms, namely, Express Start and Seamless Recovery for satellite TCP to attain our goals. Both operational description and simulation results show that our scheme yields the best throughput for TCP over satellite. Moreover, in doing so, it needs less overhead than its nearest counterpart, TCP Peach.

Native American technology access: the Gates Foundation in Four Corners

The Bill & Melinda Gates Foundation’s Native American Access to Technology Program (NAATP) was designed to provide computer and Internet access to Native peoples in the Four Corners area of the USA. Through this multi‐year effort, complex packages of hardware, software, installation and training have been made available to 43 tribes in 161 settings. An intensive, collaborative process resulted in a package carefully designed to fit tribal interests, circumstances and political arrangements, including multimedia (graphics‐intensive) equipment, language preservation software, and satellite connections to the Internet as necessary. This interim assessment concludes that the program has substantially increased tribal access to computing and information and has often fostered creative use of the technologies. Deeply embedded economic and political realities and their legacies remain, however, with substantial immediate and long‐term consequences.