Low Earth Orbit (LEO) satellites will work as an important component in future data communication networks. LEO satellites provide low end-toend delays and efficient frequency spectrum utilization, making them suitable for personal communication. However, due to high satellite speed, ongoing communication using LEO constellations experiences frequent handover. In this article 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: spotbeam handover schemes, satellite handover schemes, and 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 (QoS) criteria.

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Handover schemes in satellite networks: state-of-the-art and future research directions

This letter proposes a graph-based satellite handover framework for the low earth orbit (LEO) satellite communication networks. In order to maintain the connection with the communicating counterpart, the user has to switch between consecutive satellites covering the very user. A directed graph with covering period of the satellite as its node, and the link representing the possible handover between two overlapping periods, is calculated in advance, and then, the satellite handover process can be viewed as finding a path in the directed graph. By setting the link weight according to different handover criterions, the graph-based framework can support a variety of satellite handover strategies, which shows the improved flexibility over the existing research. The application of the framework to find the shortest handover path conducted on two typical LEO satellite networks, viz., Iridium and Globalstar, also corroborates the effectiveness of the proposed handover framework.

A Graph-Based Satellite Handover Framework for LEO Satellite Communication Networks

Low earth orbit satellite constellations could play an important role in future mobile communication networks due to their characteristics, such as global coverage and low propagation delays. Howev...

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Satellite handover techniques for LEO networks

Deterministic models for coverage time evaluation of Low Earth Orbit (LEO) satellites constituting a mobile satellite network may tend to unreliable results due to arbitrary locations of mobile users within the satellite coverage area. This inevitable phenomenon necessitates a statistical model for coverage time assessment of LEO satellite networks. In this letter, we propose a novel approach for effective analysis of coverage times during LEO satellite visits. The analysis is particularly useful for probabilistic investigation of intersatellite handovers in LEO satellite networks and also in designing mobile satellite systems.

On the Analysis of Random Coverage Time in Mobile LEO Satellite Communications

With rapid advances in satellite technology, space information network (SIN) has been proposed to meet the increasing demands of ubiquitous mobile communication due to its advantages in providing extensive access services. However, due to satellites’ resource constraint and SIN’s highly dynamic topology, it poses a challenge on management and resource utilization in the development of SIN. There have been some works integrating the software defined network (SDN) into SIN, defined as software defined space information network (SD-SIN), so as to simplify the management and improve resource utilization in SIN. However, these works ignore the security issue in SD-SIN. Meanwhile, the existing security mechanisms in SDN are still unable to cope with the uniqueness of satellite network, and some other critical security issues still haven’t yet been well addressed. In this paper, based on $(t,n)$ secret sharing, an SIN-specific lightweight group key agreement protocol is proposed for SD-SIN to ensure both the security and applicability. Moreover, considering the highly dynamic network topology, we also design a group key-based secure handover authentication scheme to reduce the overhead of handover authentication. Security analysis shows that the handover authentication protocol can resist to various known attacks. In addition, further performance evaluation shows its efficiency in terms of computation and communication overheads. Finally, the simulation results of computing overhead to the network entities demonstrate that our protocol is feasible in practical implementation.

A Lightweight and Secure Group Key Based Handover Authentication Protocol for the Software-Defined Space Information Network

It is anticipated that the satellite component of the future universal mobile telecommunications system (UMTS) will be based (partly or totally) on non-geostationary (nonGEO) constellations of satellites to serve mixed populations of users, each category being treated through different contracts stipulating different quality of service (QoS). In particular, we envisage a high-quality premium service which guarantees the success of each handover procedure, called guaranteed handover (GH) service, and a low-cost lower quality service called regular service, where handover failures are accepted provided that the probability of a call being unsuccessful does not exceed a given value. This paper proposes a strategy which eliminates forced call terminations due to handover failures, thus allowing the GH service. This procedure applies to low Earth orbit (LEO) constellations using the satellite-fixed cell technique. An analytical model has been derived to calculate QoS parameters for a mixed population of GH and regular users. Providing both GH service to some users and regular service to other users requires an increased satellite capacity with respect to the case where all the users are served with the regular service; this capacity increase has been evaluated as a function of the percentage of GH users, the traffic load per cell, and the considered satellite mobility environment. The GH approach has been validated through the comparison with another scheme which envisages the queuing of handover requests for privileged users.

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J. Restrepo

Papers

Performance analysis for a guaranteed handover service in an LEO constellation with a "satellite-fixed cell" system