Abstract-Low Earth Orbit (LEO) satellites will work as an important component in future data communication networks. LEO satellites provide low end-to-end delays and efficient frequency spectrum utilization, making it suitable for personal communication. However, due to high satellite speed, the ongoing communication using LEO constellations experiences frequent handover. In this paper, we provide an up-to-date comprehensive literature survey on proposed handover schemes for LEO satellite systems. We also present a detailed classification of handover schemes based on a common framework. We first classify the schemes into link layer and network layer handover schemes. Link layer handover schemes are further classified into three categories: (a) spotbeam handover schemes, (b) satellite handover schemes, and (c) ISL handover schemes. Spotbeam handover schemes are categorized based on channel capacity, handover guarantee, and handover prioritization techniques. Network layer handover schemes are also classified depending on connection transfer strategies. Finally, we compare the handover schemes using different Quality of Service.

Highly elliptical orbits can be used to provide targeted satellite coverage of locations at high latitudes. We review the history of use of these orbits for communication. How elliptical orbits can be used for broadband communication is outlined. We propose an addition of known elliptical orbits to the new equatorial O3b satellite constellation, extending O3b to cover high latitudes and the Earth's poles. We simulate the O3b constellation and compare this to recent measurement of the first real Internet traffic across the newly deployed O3b network.

No abstract

Transfer of chemicals from contaminated surfaces such as foliage, floors, and furniture is a potentially significant source of both occupational exposure and children's residential exposure. Increased understanding of relevant factors influencing transfers from contaminated surfaces to skin and resulting dermal-loading will reduce uncertainty in exposure assessment. In a previously reported study, a fluorescence imaging system was developed, tested, and used to measure transfer of riboflavin residues from surfaces to hands. Parameters evaluated included surface type, surface loading, contact motion, pressure, duration, and skin condition. Results of the initial study indicated that contact duration and pressure were not significant for the range of values tested, but that there are potentially significant differences in transfer efficiencies of different compounds. In the study reported here, experimental methods were refined and additional transfer data were collected. A second fluorescent tracer, Uvitex OB, with very different physicochemical properties than riboflavin, was also evaluated to better characterize the range of transfers that may be expected for a variety of compounds. Fluorescent tracers were applied individually to surfaces and transfers to skin were measured after repeated hand contacts with the surface. Additional trials were conducted to compare transfer of tracers and co-applied pesticide residues. Results of this study indicate that dermal loadings of both tracers increase through the seventh brief contact. Dermal loading of Uvitex tends to increase at a higher rate than dermal loadings of riboflavin. Measurement of co-applied tracer and pesticide suggest results for these two tracers may provide reasonable bounding estimates of pesticide transfer.

Abstract-NEtwork MObility (NEMO) handles mobility of a set of mobile nodes in an aggregate way using one or more mobile routers. NEMO introduces several advantages, such as reduced signaling, increased manageability, reduced power consumption and conservation of bandwidth when compared to individual host mobility. NEMO Basic Support Protocol (BSP), the IETF standard for NEMO, suffers from a number of limitations, like inefficient route and increased handoff latency. Most of the recent research efforts on NEMO have concentrated on solving the problem of inefficient route resulting in several route optimization schemes to solve the problem. To choose a route optimization scheme, it is very important to have a quantitative comparison of the available route optimization schemes. The objective of this article is to survey, classify and compare the route optimization schemes proposed in the literature over the last five years. We classify the schemes based on the basic approach for route optimization, and compare the schemes based on protocol overhead, such as header overhead, amount of signalling, and memory requirements. We conclude that performance of the classes of schemes has to be evaluated under criteria such as available bandwidth, topology of the mobile network and mobility type.

To reduce the uncertainty associated with current estimates of children's exposure to pesticides by dermal contact and indirect ingestion, residue transfer data are required. Prior to conducting exhaustive studies, a screening study to identify the important parameters for characterizing these transfers was designed. A fluorescence imaging system was developed (Ivancic et al., in press) to facilitate collection of surface residue transfer data for repeated contacts. Next, parameters that affect residue transfer from surface-to-skin, skin-to-other objects, and skin-to-mouth were evaluated using the imaging system and the fluorescent tracer riboflavin as a surrogate for pesticide residues. Riboflavin was applied as a residue to surfaces of interest. Controlled transfer experiments were conducted by varying contact parameters with each trial. The mass of a tracer transferred was measured and the contact surface area estimated using video imaging techniques. Parameters evaluated included: surface type, surface loading, contact motion, pressure, duration, and skin condition. Transfers both onto, and off of, the hand were measured. To efficiently identify parameter changes resulting in significant effects, the Youden ruggedness test was used to select the combination of parameters varied in each contact trial. In this way, more than one parameter could be varied at a time and the number of trials required was minimized. Results of this study showed that surface loading and skin condition (significant at alpha ¼ 0.05) are among the important parameters for characterizing residue transfers of riboflavin. Duration of contact within the time range investigated does not have a significant effect on transfer of this tracer. Results of this study demonstrate the potential for collecting dermal transfer data using the Ivancic et al. fluorescence imaging system and provide preliminary data to reduce uncertainty associated with estimating dermal exposures resulting from contact with residue-contaminated surfaces. These data will also aid in determining what additional residue transfer data should be collected and what type of microactivity data are needed to estimate dermal and indirect ingestion exposure to residues on household surfaces.

No abstract

We describe the first use from space of the Bundle Protocol for Delay‐Tolerant Networking (DTN) and lessons learned from experiments made and experience gained with this protocol. The Disaster Monitoring Constellation (DMC), constructed by Surrey Satellite Technology Ltd (SSTL), is a multiple‐satellite Earth‐imaging low‐Earth‐orbit sensor network in which recorded image swaths are stored onboard each satellite and later downloaded from the satellite payloads to a ground station. Store‐and‐forward of images with capture and later download gives each satellite the characteristics of a node in a disruption‐tolerant network. Originally developed for the ‘Interplanetary Internet,’ DTNs are now under investigation in an Internet Research Task Force (IRTF) DTN research group (RG), which has developed a ‘bundle’ architecture and protocol. The DMC is technically advanced in its adoption of the Internet Protocol (IP) for its imaging payloads and for satellite command and control, based around reuse of commercial networking and link protocols. These satellites' use of IP has enabled earlier experiments with the Cisco router in Low Earth Orbit (CLEO) onboard the constellation's UK‐DMC satellite. Earth images are downloaded from the satellites using a custom IP‐based high‐speed transfer protocol developed by SSTL, Saratoga, which tolerates unusual link environments. Saratoga has been documented in the Internet Engineering Task Force (IETF) for wider adoption. We experiment with the use of DTNRG bundle concepts onboard the UK‐DMC satellite, by examining how Saratoga can be used as a DTN ‘convergence layer’ to carry the DTNRG Bundle Protocol, so that sensor images can be delivered to ground stations and beyond as bundles. Our practical experience with the first successful use of the DTNRG Bundle Protocol in a space environment gives us insights into the design of the Bundle Protocol and enables us to identify issues that must be addressed before wider deployment of the Bundle Protocol. Published in 2010 by John Wiley & Sons, Ltd.