VSAT-GPS1

Introduction

Global Navigation Satellite Systems (GNSS) characteristics

• 20 - 30 satellites constellation• 20 - 30 satellites constellation

• Medium Earth Orbit (MEO) approx. altitude 20,000 km

• Inclined orbital planes > 50°

• Provide autonomous geo-spatial positioning with global coverage

• Accuracy 10 m or better

September 2013 2

GNSS

• Global operational in 2013:

GPS (United States of America)

GLONASS (Russian Federation)

• Regional operational, expanding to be global in 2020:

BeiDou/Compass (China)BeiDou/Compass (China)

• Initial deployment phase, fully operational in 2020:

Galileo (European Union)

• France, India, and Japan are in the process of developing regional navigation systems.

WHAT IS GPS?

• GPS stands for global position satellite• worldwide radio-navigation system formed from a

constellation of 30 satellites up to now.• The GPS was developed as a US military navigation

system but now open to the public uses.

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• There are four satellites in each of 6 orbital planes.

• Each plane is inclined 55 degrees relative to the equator, which means that satellites cross the equator tilted at a 55 degree angle. angle.

• The system is designed to maintain full operational capability even if two of the 24 satellites fail.

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September 2013 7

CONTROL SEGMENT

• The U.S. Department of Defense maintains a master control station at Falcon Air Force Base in Colorado Springs

• There are four other monitor stations • There are four other monitor stations located in Hawaii, Ascension Island, Diego Garcia and Kwajalein

• The stations measure the satellite orbits precisely.

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September 2013 9

GPS Control Segment

SATELLITE SIGNALS

• GPS satellites continuously broadcast satellite position and timing data via radio signals on two frequencies (L1 and L2).

• Two kinds of code are broadcast on the L1 • Two kinds of code are broadcast on the L1 frequency (C/A code and P code)

• C/A (Coarse Acquisition) code is available to civilian GPS users and provides Standard Positioning Service (SPS).

• P code, used for the Precise Positioning Service (PPS) is available only to the military.

September 2013 11

GPS Basic Frequencies

• All signals and time information are coherently derived from the same clock with a frequency of f0 =10.23 MHz.

• Two carrier frequencies:

L1 = 1575.42 MHz (154 x f0) (wavelength 19.05 cm)L1 = 1575.42 MHz (154 x f0) (wavelength 19.05 cm)

Used in civil GPS receivers

L2 = 1227.60 MHz (120 x f0) (wavelength 24.45 cm)

mostly found in military GPS receivers.

• For (uplink), ground stations use S-band signals.

September 2013 13

GPS Basic Signals (3/4)

• NAV data message includes:

– Almanac

Approximate orbit information for all satellites in the constellation.

– Ephemeris– Ephemeris

Predictions of the transmitting satellite’s current position and velocity as determined by the Master Control Station and uploaded to the satellites.

– Satellite clock correction parameters

– Satellite health data

GPS Signals Modulation (2/2)

• Direct Sequence Spread Spectrum (DSSS) is used to limit the interference from other signals and to prevent jamming and spoofing.

• (C/A) code bandwidth = 2.046 MHz• (C/A) code bandwidth = 2.046 MHz

• (P) code bandwidth = 20.46 MHz

• Code Division Multiple Access (CDMA) is utilized for all the GPS signals.

(all of the satellites broadcast their signals upon the same carrier frequencies).

GPS Signals Spectrum

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• The satellites measure the distance between itself to the GPS receiver.

• The position of a GPS receiver is found by trilateration.

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TRILATERATION

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POSITION LOCATION IN GPS

• Four GPS satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock

• Three measurements can be used to • Three measurements can be used to locate a point

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R2 R3

R1

R4

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• Position dimensions are computed by the receiver in Earth-Centered, Earth-Fixed X, Y,Z (ECEF XYZ) coordinates.

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• The measured distance to satellite i is called a pseudorange, PRi

PRi = Ti × c

where where

PRi is the pseudorange

Ti is the time delay between the satellite and the receiver

c is the velocity of EM waves (3 × 108 ms-1)

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• The satellite and the receiver clocks must be synchronized

• If the two clocks are off by only a small fraction, the determined position data may be considerably distorted

• For example, suppose the receiver clock has an offset of 10ms relative to GPS time:offset of 10ms relative to GPS time:

PR = t x c

=

= 3000 km

( )( )183 1031010 −− ×× mss

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The equations which relate pseudorange to time delay are called ranging equations:

( ) ( ) ( ) ( )2

1

2

1

2

1

2

1 cPRUZUYUX zyx τ−=−+−+−

( ) ( ) ( ) ( )2

2

2

2

2

2

2


( ) ( ) ( ) ( )2222cPRUZUYUX τ−=−+−+−( ) ( ) ( ) ( )2

3

2

3

2

3

2


( ) ( ) ( ) ( )2

4

2

4

2

4

2


where τ is the receiver clock error

U is the location of the GPS receiver

c is the velocity of EM waves (3 × 108 ms-1)September 2013 25

GPS ERROR SOURCES

• The GPS system has been designed to be as nearly accurate as possible.

• There are several sources for these errors, the most significant of which are discussed the most significant of which are discussed below:

Atmospheric Conditions

Ephemeris Errors/Clock Drift/Measurement Noise

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HOW TO REDUCE GPS ERROR?

• Differential correction is a method used to reduce the effects of atmospheric error and other sources of GPS positioning error

• Differential GPS (DGPS) Techniques:-• Differential GPS (DGPS) Techniques:-

The idea behind all differential positioning is to correct bias errors at one location with measured bias errors at a known position. A reference receiver, or base station, computes corrections for each satellite signal.

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GPS ACCURACY

• The accuracy depends on:

– Type of equipments used

– Time of observation– Time of observation

– The position of the satellite being used to compute position

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Receiver using C/A code

Without differential correctionAccuracy between

5 – 15 meters

With differential correctionAccuracy between

1 – 5 meters

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• “Carrier-Smoothed code” can be used to increase the accuracy of C/A code

� involves measuring the distance from the receiver to the

satellites by

counting the number of waves thatcounting the number of waves that

carry the C/A code signal

• Accuracy increase to 10 cm to 1 meters

with differential correction.

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GPS APPLICATIONS

�AIRBONE

- Navigation by general aviation and commercial aircraft

�SEA

- Navigation by recreational boaters, commercial fisherman and professional mariners

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� LAND

a) Surveyors

b) Mapping

c) Recreational

d) Automobile

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� LAW ENFORCEMENT

- Support a variety of policing and criminal justice functions

- Enhance the efficiency of the aviation units

- Assist personal operating in ground - Assist personal operating in ground vehicles

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�MILITARY

- Navigation,reconnaissance and missile guidance systems

� AGRICULTURE

- Precision on farming techniques that can help increase profits and protect the environment.

- Precision involves when applying fertilizer and pesticides

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REFERENCE• Pratt, Bostian and Allnutt, Satellite

Communications, John Wiley and Sons, pp. 458-485. 2003.

• http://www.colorado.edu/geography/gcraft/notes/gps/gps_f.htmlnotes/gps/gps_f.html

• http://www.montana.edu/places/gps/understd.html

• http://www.cmtinc.com/gpsbook

September 2013 36

VSAT NETWORKS

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Overview

� Introduction

� Network Architecture, Protocols and Access techniques

38

� VSAT Earth stations (HUB and Remote) Engineering

� Link budget and performances

� Conclusion

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Introduction

• VSAT : Very Small Aperture Terminal

• A small earth station, usually from 1.2 to 2.4 meters, used for satellite data communications. One form of datacasting.

• In common practice, the VSAT label does not so much establish the size of the dish as it indicates two-way data communication.

39

the size of the dish as it indicates two-way data communication.

• Retail credit card authorizations are a widespread application of VSAT technology.

• Significant increase in the transmit power capabilities of satellites, and move to frequency bands above C Band made the access of the satellite more affordable.

September 2013

Introduction

• The basic structure of a VSAT network consists of a hub station which provides a broadcast facility to all the VSATs in the network…

• The hub station is operated by the service provider.

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• Each user organization has exclusive access to its own VSAT network.

• Transmitter power : 1 to 2 W

• Antenna diameters:– C-Band 1.8, 2.4, 3.5, and 3.5m

– Ku-Band 1.2, 2.4, 3.5

September 2013

VSAT Network Architecture

• VSATs are connected by radio frequency links via a satellite.

• The overall link from station to station, called hop, consists of an uplink and a downlink.

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• The are three network types of VSAT’s – One-way Implementation

– Split-two-way Implementation

– Two-way Implementation

September 2013


� One-way Implementation

� The mode of satellite used in broadcast satellite service (BSS)

� The hub transmits carriers to receive-only VSATs. � The hub transmits carriers to receive-only VSATs.

� This configuration supports broadcasting services from a central site where the hub is located to remote sites where the ROVSATs are installed.

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� Split-two-way Implementation

� This implementation is used when there is no normal return channel : BSS BSS

� The relatively high capacity of the downlink is not complemented by an uplink capability from the user terminal.

� Internet split IP

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� Two-way Implementation

� The VSATs can transmit and receive. Such networks support interactive trafficinteractive traffic

� Can be achieved either of two ways:

� Either direct links from VSAT to VSAT via satellite , should link performance meet the requested quality.

� Or by double hop from VSAT to hub and then a second hop using the hub as a relay to the destination VSAT.

44September 2013

Protocols• ISO/OSI seven-layer stack for interconnecting data terminals

• The satellite communications occupies primarily the physical layer where the bits are carried between terminals.

• A VSAT must have terminal controller at each end of the link (network & link layer)

• The network control center typically controls the system and is responsible for the remaining layers. responsible for the remaining layers.

• Error control method in TCP/IP : ACK NAK ARQ

• X.25, X.75 use ARQ

• Frame relay and ATM flag retransmission but continue the flow of information.

• The propagation delay and the induced errors are critical design elements in digital VSAT connections.

45September 2013

Protocols • User 1 and user 2 are

conducting a two-way communications session with each other.

• Each user interacts with their local device at the application layer of the ISO-OSI stack.layer of the ISO-OSI stack.

• The transaction is then routed via the various layers with suitable processing

• By then, the content is ready to be transmitted via the physical layer.

46September 2013

Access Techniques

• The most popular access method is FDMA which allows the use of comparatively low-power VSAT terminals.

• TDMA can also be used, but is not efficient for low-density up-link traffic from VSAT.– Inventory control– Credit verification

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– Credit verification– Reservation requests

• The traffic in VSAT network is mostly data transfer of a bursty nature occurring in random and possibly infrequent intervals.

• The allocation of time slots in the normal TDMA can lead to a low channel occupancy.

• Demand Access Multiple Access (DAMA)

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Access Techniques

• Channel capacity is assigned in response of the fluctuating demands of the VSATs in the network.

• DAMA can be used in both FDMA and TDMA

• Examples of access technologies: – SCPC (Single Channel Per Carrier)

– TDM/SCPC Return (Time Division Multiplex) – Asymmetrical SCPC

– TDM/TDMA Return (Time Division Multiple Access)

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Single Channel Per Carrier

• Each Carrier Pair Dedicated to

a Customer• No Sharing of Bandwidth

between Carriers

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Advantages•Simple•Easy to Troubleshoot •Minimal Equipment Required•Maximum Bandwidth Availability

Disadvantages

•Hard to manage centrally•High Maintenance•Bandwidth Inefficient•Extremely Inflexible

September 2013

TDM/SCPC

A

B

C

D1

1

•Outbound TX from HUB is shared among all remotes.•Each remote has individual carrier to return data (SCPC

• Shared outbound corresponds to the highest data rate direction

• Since shared, actual utilization tends to flatten out…

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A

D

A

B

C

D

1

A

B

C

1

Advantages

• Bandwidth efficient outbound• Flexible• Ability to burst• Dedicated return

Disadvantages• Inefficient return• More complex than SCPC• No reduction in eq. cost.

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TDM/TDMA Return

A

B

C

DC

D1

1

B

- Outbound and Inbound are shared.- Remotes are shared amongst assigne

return carriers.- Since shared, actual utilization tends

to flatten out for both Outbound andInbound.

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A

D

A

B

C

D

1

A

B1

B

C

D

A

Advantages• Bandwidth efficient• Flexible• Bursting, QoS, VPNs w/ TCP Acceleration, CIR/Burst Dedicatedreturn

• Centralized management

Disadvantages•Complexity

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Technologies Fit Different Usage ProfilesP

ric

e o

f S

erv

ice

SCPC Dedicated Link

• Single user sites

• Limited # phone lines

• Basic broadband access

• Infrequent use

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Shared DedicatedSemi-Dedicated

Pri

ce

of

Se

rvic

e

Bandwidth Utilization

TDMA

SCPC Asymmetric Cloud

• Infrequent use

• Call centers

• Streaming content

• Real-time video

• Continuous use

September 2013

VSAT Earth Station (HUB and Remote) Engineering

53September 2013

VSAT Network Earth Station

• VSAT station is made of two separate sets of equipment:

– The outdoor unit (ODU): Interface to the satellite

– The indoor unit (IDU) : Interface to the customer’s terminals or LANs

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Schematic of a VSAT User Setup

� The outdoor unit is located where it will have a clear line of sight to the satellite and is free from casual blockage.

� Interfacility link (IFL) carries the electronic signal between the ODU and indoor unit (IDU) aswell as power cables for the ODU well as power cables for the ODU and control signals from the IDU.

� IDU : Workstation ( baseband processor units and interface equipments)Modem, mux/demux.

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Typical Configuration of a VSAT Earth Station

� LNC receives the RF signal,amplifies, and mixes it down to IF for passing over the IFL to the IDU.

� In the IDU, demodulator extracts the information signal from thecarrier and passes it at basebandprocessor.processor.

� The data terminal equipment thenprovides the application layer forthe user to interact with the information input.

� On the transmit operation, the opposite is performed.

56September 2013

Typical Hub Master Control Station

� The line interface equipment handles the terrestrial ports tothe host computer.

� the control bus via the hubcontrol interface allows all of thetransmit, receive, and switchingfunctions to be carried out.

� The transmit processing andcontrol equipment (PCE)control equipment (PCE)prepares the TDM stream for theoutbound link to the VSATs.

� This stream passes through the IFinterface to the up-convertor thatmixes the IF to RF.

� On the receive side, the antennapasses individual inbound MF-TDMA signal to the LNA foramplification prior to DC, DEM, and so on to the user.

57September 2013

Link Budget and Performances• The minimum allowed carrier to noise (C/N)o for a typical

inbound VSAT is 6dB, with BPSK modulation and half rate FEC encoding, giving a BER of 10-6 (Threshold).

• Varies depending on the modulation and FEC methods used on the link.

• Rain fade on the uplink or rain fade on the downlink can reduce the clear sky (C/N)o

• The entire two way system drops below the performance minimum.

• Failure at Satellite-hub link should be much less likely, otherwise failure will affect the every VSAT in the network.

58September 2013

Link Budget : Preliminary Calculations

• All link budgets require knowledge of the – free space path loss between the earth station and the satellite and

– the noise power in the operation BW

• Noise powers: • Noise powers: – Noise power in transponder 1, Inbound SCPC FDMA Channels

– Noise power in the Hub Station Receiver, Inbound SCPC FDMA Channels

– Noise power in the Transponder 2, Outbound TDM Channels

– Noise power in the VSAT Receivers, Outbound TDM Channels.

59September 2013

Examples: Stabilized VSAT Systems

• Both C- & Ku-Band applications– C-Band Systems from 2.4

meter and larger– Ku-Band systems from 1.0

meter and larger

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Maritime VSAT Systems• 3-axis stabilization

• Pointing accuracy less than 0.2°

• Withstands harsh maritime conditions

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maritime conditions– Corrosion

– Shock & Vibration

– High wind load

– Vessel movements

September 2013

Mobile VSAT Systems• Self-contained & mobile

• Always ready for communication

• Full-motion video while moving

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moving

• Wireless connectivity to external voice, video and data sources

September 2013

Rapid-Deploy VSAT Systems• Self-contained

• Includes power & wireless links

• Automatic deployment of

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deployment of antenna

• Acquisition of satellite within 5 min.

September 2013

Conclusion

• The need to make access to the satellite more affordable and the rapid expansion of the satellite communications worldwide brought forward VSAT.

• A significant increase in the transmit power capabilities of satellite and the move to frequency bands above C band lead to the and the move to frequency bands above C band lead to the reduction of the size and cost of earth station antenna.

• VSAT technology now occupies the context of satellite communications in terms of network configuration, services, economics, operational and regulatory aspects.

64September 2013

References

• Pratt Timothy, Bostian C.W. and Allnutt J.E., (2003), Satellite Communications, John Wiley & Sons.

• G. Maral. VSAT Networks. 2nd Edition

65September 2013

Iridium

Satellite

September 2013 66

History

• Iridium communications service was launched on November 1, 1998. The first Iridium call was made by then-Vice President of the United States Al Gore. Motorola provided the technology and Motorola provided the technology and major financial backing.

September 2013 67

History • The 1990s The original Iridium LLC enters bankruptcy in August

1999.

Dec 2000“ Iridium Satellite LLC" acquires Iridium's assets out of bankruptcy. U.S. DoD awards contract.

Mar 2001 Iridium begins offering commercial service for mobile voice; shifts company's strategy to vertical markets.

June 2001 Introduces data and Internet services.June 2001 Introduces data and Internet services.

Feb 2002 Announces successful deployment of in-orbit spares.

June 2003 Introduces short-burst data (SBD) services.

Aug 2003 Announces short messaging services (SMS).

Mar 2004 Launches fax and enhanced messaging services.

June 2004 FCC grants access to 3.1 MHz of additional spectrum.

July 2004 Surpasses 100,000+ subscribers;September 2013 68

History • Sep 2005 Provides critical telecommunications to first

responders in Hurricane Katrina region. Regional traffic increases more than 3000%.

Feb 2006 Launches compact lower-cost satellite data transceiver for supply chain management, field force automation and remote asset tracking. Commences automation and remote asset tracking. Commences engineering studies for future satellite replenishment and replacement plan.

• Nov 2006 Announces 169,000+ subscribers.

Feb 2007 Announces 183,000+ subscribers.

July 2007 Announces 203,000+ subscribers.September 2013 69

Services

All Gateways Support Voice and Data

Services

– Dial-up

– Direct Internet – Direct Internet Access

– Short Message Service

– Short Burst Messaging

– PagingSeptember 2013 70

Global Commercial Usage

Telephony Traffic, November 2003September 2013 71

General Information• The satellites are in a near-polar orbit.

• Using 6 orbital planes with the inclination of 86.4 degrees.

• the altitude of 485 miles (780 km).

• The 66 active satellites plus 6 in-orbit backup satellites fly in formation in six orbital planes, fly in formation in six orbital planes,

• each with 11 satellites equally spaced apart from each other in that orbital plane.

• Orbital period 100 minutes, 28 seconds.

• traveling at a rate of 16,832 miles per hour, and traveling from horizon to horizon across the sky in about ten minutes.

• As a satellite moves out of reach, the call is seamlessly handed over to the next satellite coming into view.

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General Characteristics

• Satellite weight - 700 kg (1500 lb),

• Spot beams - 48 per satellite,

• link margin - 16 decibels (average),

• lifetime - 5-8 years.

Allocated frequencies:Allocated frequencies:

• Direction Frequency

Iridium Phone-Satellite 1616-1626.5MHz

Satellite-Iridium Phone/Pager 1616-1626.5MHz

Satellite-Satellite 23.18-23.38GHz

Satellite- Gateway 19.4-19.6GHz

Gateway-Satellite 29.1-29.3GHzSeptember 2013 73

How it Work

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Battery &

Radiator

Satellite weight…………..700 Kg

Instant. Peak Power…...>4000 W

Avg. Power Load…………620 W

Vehicle Length……………160 in

Vehicle “Wingspan”..........330 in

Iridium Satellite Vehicle (SV)• Three Principal Elements Of SV:

– Payload – Provides All Command, Control and Communications Functions

– Main Mission Antennas (MMAs) – Provide L-Band Telephony Functions

– Bus – Platform For SV Operations, Provides Power, Pointing, Propulsion

Solar Array Panels (2)

Ka-Band Cross-

Link Antenna (4)Ka-Band Feeder

Link Antenna (4)

L-Band

MMA (3)

Payload

Electronics

Vehicle “Wingspan”..........330 in

• Seven Power PC Processors

• Four Gimbaled K-Band Feederlinks

• Four K-Band Crosslinks (2 Fixed & 2

Gimbaled)

• Three L-Band Phased Arrays

• Two 42.5 sq. ft. GaAs Solar Arrays

• One 60A-hr SPV NiH2Battery

• Three-Axis Momentum-Biased Attitude

Control System

• Redundant Orbit Adjust

• Graphite Epoxy Structure

• Active & Passive Thermal Control

• Life time is 5-8 years.Launch Configuration

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Present Constellation Configuration6

6 O

per

ati

on

al

Sa

tell

ites

Plane 1 Plane 2 Plane 3 Plane 4 Plane 5 Plane 6

SV74 SV55 SV50Slot 1 MS-9 5/17/98 SV22 MS-8 3/30/98 SV19 MS-7 2/18/98 SV18 Slot 1

SV72 MS-3 8/21/97 SV28 MS-4 9/27/97 SV56 MS-2 7/9/97

Slot 2 MS-9 5/17/98 SV23 PR-2 9/14/97 SV34 MS-7 2/18/98 SV42 Slot 2

SV75 MS-3 8/21/97 SV29 MS-4 9/27/97 SV52 LM-1 12/8/97


SV70 LM-4 8/19/98 SV31 MS-4 9/27/97 SV53 MS-5 11/9/97


SV62 MS-3 8/21/97 SV30 MS-4 9/27/97 SV84 MS-5 11/9/97

Slot 5 PR-3 4/6/98 SV45 PR-2 9/14/97 SV05 MS-11 11/6/98 SV80 Slot 5

SV63 MS-6 12/20/97 SV32 MS-1 5/5/97 SV10 MS-10 9/8/98

Slot 6 PR-3 4/6/98 SV46 PR-2 9/14/97 SV06 PR-1 6/18/97 SV17 Slot 6

SV64 MS-6 12/20/97 SV33 MS-1 5/5/97 SV54 MS-2 7/9/97

Slot 7 PR-3 4/6/98 SV47 PR-2 9/14/97 SV07 MS-7 2/18/98 SV15 Slot 7

66

Op

era

tio

na

l S

ate

llit

es1

2 S

pa

re S

ate

llit

es

Slot 7 SV47 SV07 SV15 Slot 7

SV65 MS-6 12/20/97 SV57 MS-1 5/5/97 SV12 MS-2 7/9/97

Slot 8 PR-3 4/6/98 SV20 (89) MS-8 3/30/98 SV08 PR-1 6/18/97 SV81 Slot 8 Color Codes:

SV66 LM-5 12/19/98 SV58 MS-1 5/5/97 SV13 MS-10 9/8/98 Delta

Slot 9 PR-3 4/6/98 SV49 MS-8 3/30/98 SV04 PR-1 6/18/97 SV82 Slot 9 Proton

SV67 MS-6 12/20/97 SV59 MS-1 5/5/97 SV83 MS-10 9/8/98 Long March

Slot 10 PR-3 4/6/98 SV26 MS-8 3/30/98 SV37 MS-11 11/6/98 SV41 Slot 10 Eurockot

SV68 MS-3 8/21/97 SV60 MS-4 9/27/97 SV86 MS-5 11/9/97 NOTE: All launch dates

Slot 11 PR-3 4/6/98 SV03 (78) MS-8 3/30/98 SV61 MS-11 11/6/98 SV43 Slot 11 are GMT

LM-4 8/19/98 LM-2 3/25/98 MS-5 11/9/97

Spare1 SV14 (92) SV11 (88) SV90 SV51 SV77 Spare1LM-6 6/11/99 LM-5 12/19/98 IS-1 2/11/02 LM-2 3/25/98 MS-10 9/8/98

Spare2 SV21 (93) SV91 SV97 Spare2LM-6 6/11/99 IS-1 2/11/02 IS-2 6/20/02

Spare3 SV94 Spare3IS-1 2/11/02



Drifter SV98 DrifterIS-2 6/20/02

(May 2006)

September 2013 76

Multiple Launch Vehicles Used

DELTA IIDELTA II PROTONPROTON12 launches12 launches

5 SVs / LV5 SVs / LV

3 launches3 launches


LONG MARCH 2CLONG MARCH 2C EUROCKOTEUROCKOT6 launches6 launches


1 launch1 launch


September 2013 77

A Boeing Delta II rocket launched the latest additions to the Iridium satellite constellation Monday Feb. 11, 2002from Vandenberg Air Force Base, Calif. at 9:44 a.m. PST.

The Delta II launch vehicle deployed five vehicle deployed five satellites into low-Earth orbit to serve as spares for Iridium Satellite’s worldwide communications network.

September 2013 78

Iridium Satellite

Constellation

•Each Satellite Footprint is

Approximately 2800 Miles

in Diameter

•All Satellite Footprints •All Satellite Footprints

Overlap

•Each Satellite has 48 Spot

Beams

•Size of Each Spot Beam is

Approximately 250 Miles

in Diameter

•All Spot Beams on a

Satellite OverlapSeptember 2013 79

Handover in satellite systems• Several additional situations for handover in satellite systems

compared to cellular terrestrial mobile phone networks caused by the movement of the satellites

– Intra satellite handover

• handover from one spot beam to another

• mobile station still in the footprint of the satellite, but in another cell

– Inter satellite handover– Inter satellite handover

• handover from one satellite to another satellite

• mobile station leaves the footprint of one satellite

– Gateway handover

• Handover from one gateway to another

• mobile station still in the footprint of a satellite, but gateway leaves the footprint

– Inter system handover

• Handover from the satellite network to a terrestrial cellular network

• mobile station can reach a terrestrial network again

September 2013 80

Overview of LEO/MEO systems

Iridium Globalstar ICO Teledesic# satellites 66 + 6 48 + 4 10 + 2 288altitude(km)

780 1414 10390 ca. 700

coverage global ±70° latitude global global

min.elevation

8° 20° 20° 40°

frequencies 1.6 MS 1.6 MS ↑ 2 MS ↑ 19 ↓frequencies[GHz(circa)]

1.6 MS29.2 ↑19.5 ↓23.3 ISL

1.6 MS ↑2.5 MS ↓5.1 ↑6.9 ↓

2 MS ↑2.2 MS ↓5.2 ↑7 ↓

19 ↓28.8 ↑62 ISL

accessmethod

FDMA/TDMA CDMA FDMA/TDMA FDMA/TDMA

ISL yes no no yesbit rate 2.4 kbit/s 9.6 kbit/s 4.8 kbit/s 64 Mbit/s ↓

2/64 Mbit/s ↑# channels 4000 2700 4500 2500Lifetime[years]

5-8 7.5 12 10

costestimation

4.4 B$ 2.9 B$ 4.5 B$ 9 B$September 2013 81

VSAT-GPS1

Documents

gps basic signals

kinds of code

ca code bandwidth

gps basic frequencies

p code bandwidth

military gps receivers

l1 frequency ca code

civilian gps users