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OSCAR – An Opportunistic Call Admission Protocol for LEO Satellite Networks
Stephan Olariu, Rajendra Shirhatti and Albert Y. Zomaya

Low Earth Orbit (LEO) satellite networks complement terrestrial networks in an effort to provide broadband services to users regardless of their location. Part of the vision behind these systems was to support a growing population of users equipped with hand-held devices and to provide anytime-anywhere connectivity at moderate cost, suggesting LEO satellites as promising platforms for Personal Communication Services (PCS). However, in order for this promise to become reality, LEO satellites must support multimedia traffic and must provide their users with adequate Quality of Service (QoS) guarantees. This is a daunting task since the limited bandwidth of the satellite channel, rotation around the Earth and mobility of end-users makes QoS provisioning difficult. In particular, if LEO satellites are to become a truly universally accepted platform for global mobility they must be able to provide their users with seamless intra-satellite handoff. The main contribution of this work is to propose OSCAR — an Opportunistic Call Admission Protocol, that provides a lightweight and robust solution to both call admission and handoff management in LEO satellite networks. Being simple and robust OSCAR was designed with efficiency and scalability in mind. Along this line of thought, one of the features that sets OSCAR apart from existing protocols is that it avoids the overhead of reserving resources for users in a series of future spotbeams. Instead, OSCAR relies on a novel opportunistic bandwidth allocation mechanism that is very simple and efficient. OSCAR relies, in part, on an idea borrowed from the recently-proposed Q-Win protocol in that it uses a number of virtual windows to make an opportunistic decision for admission of new users. Extensive simulation results have shown that, without maintaining any queues or expensive reservations, OSCAR achieves results comparable to those of Q-Win: it offers very low call dropping probability, providing for reliable handoff of on-going calls, good call blocking probability for new call requests, and high bandwidth utilization.

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