Subject: Mobile Communication and Computing

Topic: Introduction to Mobile Computing

Difficulty: High

Global Mobile Communication

1. Each Satellite covers a certain area on earth this area is called as its footprints
2. Within the footprint, communication with Satellite is possible via Mobile user link (MUL).
3. For the base station controlling the satellite and act as a gateway to other network or footprints via Gateway link (GWL).
4. Satellite can either communicate via the gateway or they can use Inter Satellite link (ISL).
5. ISL reduce the latency for data packet and voice data. Because ISL save extra link that are arrive on the earth from Satellite.
6. GMC provide a smooth, seamless handover between a cellular network and Satellite system.

Satellite Basics

Satellites in circular orbits

1. attractive force on earth gravity Fg = m g (R/r)²
2. centrifugal force Fc = m r ω²

a. m: mass of the satellite

b. R: radius of the earth (R = 6370 km)

c. r: distance from the satellite to the center of the earth.

d. g: acceleration of gravity (g = 9.81 m/s²)

e. ω: angular velocity (ω = 2 π f, f: rotation frequency)

Stable orbit

1. Fg = Fc
2. The distance of a satellite to the earth’s surface depends on its rotation frequency f.
3. The satellite period equals 24 hours for a distance of 35,786 km.

From the preceding equation ,we notice that the mass of the satellite has no impact on its satiability as m appear on both side of the equation and get cancelled.

Fg = m g (R/r)²

Fc = m r ω²

Fg=fc m g (R/r)²= m r ω²

The distance r=(g.R2/w2)1/3

This equation shows that frequency of rotation of a satellite determine its distance4 from the earth’s surface.

1. The inclination angle: angle between the equatorial plane and plane by satellite orbit. a. Inclination angle 0 degrees - satellite above the equator. b. If satellite does not have circular orbit, the closest point to the earth is called the PERIGEE.
2. The elevation angle: angle between centre of satellite beam and plane tangential to earth surface so called FOORPRINT.