Connections Management Strategies in Satellite Cellular Networks

Malek Benslama, Wassila Kiamouche, Hadj Batatia

• Publisher: Wiley-ISTE
• Year: 2015
• Print ISBN:
  9781848217751
• Edition: 1
• eBook ISBN:
  9781119099833
• Topic: Technology & Engineering
• Subtopic: Mobile & Wireless Communications
• Index: Technology & Engineering

This book provides a novel method based on advantages of mobility model of Low Earth Orbit Mobile Satellite System LEO MSS which allows the evaluation of instant of subsequent handover of a MS even if its location is unknown. This method is then utilized to propose two prioritized handover schemes, Pseudo Last Useful Instant PLUI strategy and Dynamic Channel Reservation DCR-like scheme based respectively on LUI and DCR schemes, previously proposed in literature.  The authors also approach a different aspect of handover problem: calls with short durations dropped due to a handover failure. We propose a decision system based on fuzzy logic Rescuing System that allows the rescue of calls with short durations facing a premature at the expense of those lasting for long durations.

1

The Foundations of Satellite Networks

1.1. Introduction

Satellite networks are principally characterized by the use of a satellite. They were designed with the aim of achieving a global coverage of the earth and to provide different services, such as voice transmission, short messaging services, global positioning system (GPS) localization, etc. These networks also enable two distant points located anywhere on the earth to communicate. However, building a network always requires that a number of precautions be taken and, more specifically, that a precise set of specifications relating to performance be presented. Theoretically, these specifications are determined from market research that aims to forecast the different uses of the system. It would be very naïve to think, however, that this research could forecast the future needs of users with any degree of certainty.

The market can change very quickly and a property that was overlooked when the network was being designed can become the determining factor in getting one step ahead of the competition. In this event, it is imperative that the network follows the change.

For example, let us consider land mobile networks, which have undergone countless changes in infrastructure. At first operators were attached to the idea of covering the largest possible area in a populated zone. Then, however, the market grew exponentially and operators refocused their efforts on regions that already had a wide coverage for capacity reasons: in certain situations, a station was no longer able to meet the demand from the zone it was covering, a zone that is called a cell. An effort was then made to divide the overloaded cells into smaller cells that were associated with less powerful (and therefore less noisy) stations, thereby enabling radio channels to be used once again.

The idea of using more, smaller and less powerful cells can also be applied to satellite networks. To increase the capacity of a system, satellites can be brought closer to the earth, thus improving acuity for differentiating between ground terminals, as illustrated in Figure 1.1: to cover an equivalent air surface, a satellite that is far from earth must use a much more precise spotbeam than a satellite that is closer to earth.

Figure 1.1. The reuse of frequencies by satellites with varying altitudes

This chapter will first present the places where a telecommunications satellite can be positioned in the vicinity of the earth. We will then see how several satellites can work together to guarantee a global coverage. We will also tackle the question of the time it takes to pass through a network according to where it is located and, in concrete terms, we will discuss the resulting broad categories of satellite networks. The characteristics of cellular satellite networks will then be presented and the problem of handover in LEO satellite networks will be introduced.

1.2. Satellite orbits

An orbit is a path the satellite follows when there are no perturbations. There are many different types of satellite orbits. Contrary to common opinion, a device’s path without propulsion has nothing at all to do with its weight, though it is conditioned by precise rules (described next). Before this, it is useful to go over some basic properties of the ellipse.

1.2.1. Characteristics of the ellipse

Let us consider a plane with an orthonormal coordinate system (

). Given the two real positive constants a and b where a > b, the ellipse ξ centered on O of a semi major axis a and a semi minor axis b is the set of points P(x, y) that verify the following equation:

[1.1]

Figure 1.2. A few properties of the ellipse

A general parametric form of the ellipse exists. It can be formulated as follows:

[1.2]

Figure 1.2 shows different parameters. The two foci of the ellipse appear at points F(c, 0) and F′(-c, 0) with

. The eccentricity of the ellipse is thus defined by e = c / a. For every point P of ξ, the following relation is verified:

PF + PF′ = 2a

1.2.2. Kepler’s laws

The parameters used today to describe satellite orbits are inspired by the work of Kepler (1571–1630) [SUN 05, MON 05].

These laws describe the way in which planets move around the sun and are typical of the following parameters:

– the orbit of planets, that is the path they follow over time;

– the instantaneous speed of the path of each orbit by the associated planet;

– the orbital period of a planet, which is the total time it takes to complete its orbit;

Kepler’s laws can be summarized as follows:

– the orbit of each planet is an ellipse where the sun is one of the foci;

– the area swept out by a line between the sun and the planet is constant over a unit of time;

– the square of an orbital period of a planet is proportional to the cube of the major axis of its orbit.

These laws can, in fact, be applied to any system where a celestial body with a large mass (the sun), which is known as the primary element, determines the movement of bodies with small masses in comparison to the former (the planets), which is known as the secondary elements. More specifically, they describe the movement of satellites (secondary elements) around the earth (the primary element in this case).

It is useful to locate these orbits in relation to the movement of the earth around the sun. Seven parameters, often known as Keplerian parameters, can be used to characterize the movement of a satellite.

1.2.3. Orbital parameters for earth satellites

Let us take (Oxyz) as an orthonormal coordinate system, where O is the center of the earth, Oz its rotation axis and (Oxy) its equatorial plane, taking the direction of (Ox) as the intersection of the equatorial plane with the ecliptic plane (plane of the rotation of the earth around the sun).

Figure 1.3. The remarkable points of a satellite in orbit around the earth

There are several remarkable points for a satellite in orbit (Figure 1.3):

– Apogee A, a point where the satellite is furthest from the earth;

– Perigee P, a point where the satellite is closest to the earth;

– the nodes N and

the points where the satellite passes through the equatorial plane. In N, the satellite passes above the equatorial plane and in

, it passes below.

The movement of the satellite can be described with seven parameters.

Description of the orbit

The orbit is an ellipse given by:

– the semi major axis a, half the length of the major axis;

– eccentricity e: when e = 0, the orbit is described as circular and in the opposite case, it is described as elliptical.

Position of the orbit in relation to the earth

The parameters characterizing the position of the ellipse are:

– inclination i defined as the angle between the orbit plane and the equatorial plane, which is also the angle between the normal orbit and the rotation of the earth. By convention, inclination is between 0° and 90° when the satellite is turning in the same direction as the earth and between 90° and 180° when it is turning in the opposite direction;

– the perigee, which is the angle (ON, OP);

– the right ascension of the ascending node (Ω), which is simply the angle (Ox, ON).

Position of the satellite in the orbit

Now, when the orbit is defined, it is useful to specify where the satellite is located on it. To do so, it is necessary to specify an observation date and a place on the orbit:

– the observation date t is the moment the satellite is observed;

– the average anomaly M is the angle the satellite m...

Table of contents

• Cover
• Title page
• Copyright page
• PREFACE
• ABBREVIATIONS
• INTRODUCTION
• CHAPTER 1. THE FOUNDATIONS OF SATELLITE NETWORKS
• CHAPTER 2. AN INTRODUCTION TO TELETRAFFIC
• CHAPTER 3. CHANNEL ALLOCATION STRATEGIES AND THE MOBILITY MODEL
• CHAPTER 4. EVALUATION PARAMETERS METHOD
• CHAPTER 5. ANALYTICAL STUDY
• CHAPTER 6. THE RESCUING SYSTEM
• CHAPTER 7. RESULTS AND SIMULATION
• CHAPTER 8. PAB FOR IP TRAFFIC IN SATELLITE NETWORKS
• GENERAL CONCLUSION
• APPENDIX 1
• APPENDIX 2
• APPENDIX 3
• APPENDIX 4
• APPENDIX 5
• BIBLIOGRAPHY
• INDEX