Evangelos Papapetrou

Distributed on-demand routing for LEO satellite systems

Notwithstanding the limited commercial success of the first narrowband low earth orbit (LEO) satellite systems, the interest of the scientific community in this type of systems has been revived on the basis of the current trend toward the migration to all IP-based services. LEO systems can play a pivotal role in providing services to areas where there is no substantial terrestrial infrastructure. Above all, LEO satellite systems can be used as backbone networks to interconnect autonomous systems worldwide. Such an approach provides flexibility in managing the resulting integrated network infrastructure and supporting innovative applications. In this context, routing data from the source all the way to the destination constitutes a daunting challenge. In this paper, a location-assisted on-demand routing (LAOR) protocol is proposed and evaluated. The proposed protocol introduces for the first time in satellite systems the concept of on-demand routing. However, its implementation is tailored to the requirements imposed by the characteristics of the topology of LEO satellite systems. The performance of the LAOR protocol is assessed for different link-cost metrics and compared to the one of centralized routing protocols proposed in the literature so far. Simulation studies further document and confirm the positive characteristics of the proposed protocol.

QoS Handover Management in LEO/MEO Satellite Systems

Low Earth Orbit (LEO) satellite networks are foreseen to complement terrestrial networks in future global mobile networks. Although space segment topology of a LEO network is characterized by periodic variations, connections of mobile stations (MSs) to the satellite backbone network alter stochastically. As a result the quality of service delivered to users may degrade. Different procedures have been proposed either as part of a resource allocation mechanism or as part of an end-to-end routing protocol to manage transitions of MSs from one satellite to another (handover). All of these techniques are based on the prioritization of requested handovers to ease network operation and therefore enhance provision of service. This paper proposes a new handover procedure that exploits all geometric characteristics of a satellite-to-MS connection to provide an equable handover in systems incorporating onboard processing satellites. Its performance is evaluated by simulations for a variety of satellite constellations to prove its general applicability.

Performance evaluation of LEO satellite constellations with inter-satellite links under self-similar and Poisson traffic

A real-time simulation study for the evaluation of traffic flow in low earth orbit (LEO) satellite constellations, used for the interconnection of high-speed networks, is presented in this paper. The proposed model simulates the traffic process end to end at the packet level, supporting successfully the implementation of self-similar traffic sources, a modelling approach that has been considered more realistic than the well-known Poisson, for real-time communications. An in-depth study for the establishment of inter-satellite links (ISLs) and the design of the terrestrial and space segments is presented and the performance of the integrated system is evaluated in terms of delay and throughput parameters. Copyright

Satellite handover techniques for LEO 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. However, because of the non-stationarity of the satellites, a call may be subjected to handovers, which can be cell or satellite handovers. Quite many techniques have been proposed in the literature dealing with the cell handover issue. In this paper, a satellite handover procedure is proposed, that investigates and exploits the partial satellite diversity (namely, the existing common coverage area between contiguous satellites) in order to provide an efficient handover strategy, based always on a tradeoff of blocking and forced termination probabilities for a fair treatment of new and handover calls. Three different criteria were examined for the selection of a satellite. Each one of them could be applied either to new or handover calls, therefore we investigated nine different service schemes. A simulation tool was implemented in order to compare the different service schemes and simulation results are presented at the end of the paper.

Analytic study of Doppler-based handover management in LEO satellite systems

The problem of dynamic handover management in low Earth orbit (LEO) satellite systems is addressed. Particularly, an analytical study of a newly proposed method for handover management, called dynamic Doppler-based handover prioritization scheme (DDBHP), is presented. DDBHP utilizes Doppler shift monitoring of each communicating user terminal onboard the satellite and geometric characteristics to accurately predict the handover load. As a result, handover requests are more effectively managed, resulting in an improved performance in terms of blocking and forced termination probabilities. Moreover, by supporting guaranteed handovers, DDBHP can be used to provide QoS to users of future broadband satellite networks. An extensive mathematical model that justifies Doppler shift monitoring is presented along with a detailed queueing model used not only to evaluate DDBHP performance but also to provide a methodology for associating DDBHP operational parameters with desired performance. Comparison of analytical and simulation results validate the proposed model.

Multiservice on-demand routing in LEO satellite networks

In this paper, a distributed on-demand routing protocol for Low Earth Orbit (LEO) satellite systems, named multiservice on-demand routing (MOR), is proposed and evaluated. The proposed protocol adjusts the routing procedure to the QoS requirements of different traffic classes. The performance of the MOR protocol is compared to the unique proposal for traffic class dependent routing in the literature and the good characteristics of the proposed scheme are corroborated by ample simulation experiments, where significant gains in performance are witnessed.

Speeding-up Cache Lookups in Wireless Ad-Hoc Routing using Bloom Filters

On demand routing protocols that exploit local caches have received a lot of attention lately in wireless ad-hoc networking. In this paper, we specifically address cache management, an issue that has been a main source of criticism for the applicability of such protocols. In particular, we tackle the problem of accessing the cache content efficiently. To this end, we propose summarizing the cache content so that we achieve efficient lookups. This not only saves both the restrictive resources of the wireless devices such as computational power and energy but also improves the overall protocol performance. We use Bloom filters as summaries. Our experimental results using the ns simulator show that both resource savings and performance improvements are attained when such filters are integrated within the DSR protocol which is one the most widely used instance of an on demand protocol

Developing Mobile Commerce Applications

In this article, we deal with context-aware query processing in ad-hoc peer-to-peer networks. Each peer in such an environment has a database over which users execute queries. This database involves (a) relations which are locally stored and (b) virtual relations, all the tuples of which are collected from peers that are present in the network at the time when a query is posed. The objective of our work is to perform query processing in such an environment and, to this end, we start with a formal definition of the system model. Next, we formally define SQLP, an extension of SQL that covers the termination of queries, the failure of individual peers and the semantic characteristics of the peers of such a network. Moreover, we present a query execution algorithm as well as the formal definition of all the operators that take place in a query execution plan.

A Proposal of Optimal Routing Techniques for non-GEO Satellite Systems

The continuously increasing number of mobile subscribers has generated a strong interest in expanding terrestrial wireless networks and supporting real-time communications regardless of the user location. These targets require a cautious management of available resources since the development of global systems implies a quite high cost. Routing is an important network function and must be very carefully considered. This paper proposes the implementation of optimal routing techniques for connection oriented mode and variable network topology, as non-GEO satellite systems require. In particular a well known optimal routing technique, named Flow Deviation, is modified by adding new procedures that render its applicability to a handover environment feasible and effective. Its performance is investigated through extended real time simulations in terms of delay, throughput, link utilization and also in terms of parameters related to the topology variations and the interruptible operation of ISLs. The pros and cons of the proposed scheme are discussed with respect to the well known shortest path scheme and helpful conclusions for the design of satellite constellations are obtained.

Distributed Load-Aware Routing in LEO Satellite Networks

In this paper, we propose a lightweight distributed routing algorithm, called Distributed Load-Aware Routing (DLAR). The proposed protocol adopts a distributed approach to handle the complexity of the satellite system and at the same time provides a hop-by-hop mechanism for splitting traffic load in order to alleviate the problem of congestion that occurs near polar regions. The performance of DLAR is assessed through extensive simulations and compared to the performance of centralized routing schemes proposed so far in the literature. Simulation results document and confirm the positive characteristics of the proposed protocol.