Handover management algorithms in LEO satellite communication networks

Abstract

Since Low Earth Orbit (LEO) satellite constellations have important advantages over Geosynchronous Earth Orbit (GEO) satellite systems such as low propagation delay, low power requirements and more efficient spectrum allocation due to frequency reuse between satellites and spotbeams, they are considered to be used to complement the existing terrestrial fixed and wireless networks in the evolving global mobile network. However, one of the major problems with LEO satellites is their higher speed relative to the terrestrial mobile terminals, which move at lower speeds but at more random directions. This high mobility characteristic of LEO satellites causes mobile users to hand over between footprints of adjacent satellites very frequently. Therefore, handover management in LEO satellite networks becomes a very challenging task for supporting global mobile communication. Efficient and accurate methods are needed for LEO satellite handovers between the moving footprints. The main concern of researches done in this area is providing a reliable service to the user that prevents a communication from being dropped due to a handover. Currently, there are many studies dealing with the problems of handover management issues in LEO satellite communication networks. Related work in this area focuses on the development of new mobility management architectures as well as improving the handover decision mechanisms to quickly and accurately trigger handovers. The thesis discusses only the basic handover management schemes used in LEO satellite networks and points out their drawbacks. Handover decision schemes are not covered by this thesis. The thesis also includes a survey of recent handover management protocols proposed for LEO satellites. By taking into consideration the inconvenience and incompleteness of the current proposals in literature, this thesis proposes two new mobility management schemes for LEO satellite communication networks. The first one focuses on a new Seamless Handover Management Scheme for LEO Satellites (SeaHO-LEO), which utilizes the handover management protocols aiming at decreasing latency, data loss, and handover blocking probability. To show the performance of the proposed algorithm, an extensive set of simulations both for the proposed algorithm and well known handover management methods is run as a baseline model. The simulation results show that the proposed algorithm is very promising for seamless handover especially in highly crowded networks. In addition to this, another interesting handover management model called Satellite Mobility Pattern Based Handover Management in LEO Satellites (PatHO-LEO), which takes mobility pattern of both satellites and mobile terminals into consideration to minimize the handover messaging traffic, is presented in this thesis. Minimization of handover messaging traffic is achieved by the newly introduced Billboard Manager which is used for location updates of mobile users and satellites. The Billboard Manager makes the proposed handover model much more flexible and easier than the current solutions, since its centrical characteristic supports the manageability of the whole system. The analytical work done for this evaluation shows that the proposed PatHO-LEO architecture has a significantly lower mobility management cost.