CHAPTER 16 LONG RANGE COMMUNICATIONS - … range communications • rich history ... isdn pstn gsm...

Wireless Communication

Networks and Systems 1st edition

Cory Beard, William Stallings

© 2016 Pearson

Higher Education, Inc.

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Cory Beard and William Stallings, All Rights Reserved

CHAPTER 16

LONG RANGE

COMMUNICATIONS

Long Range Communications 16-1

LONG RANGE COMMUNICATIONS

• Rich History

• Satellite

– Communications

– GPS

– Television


SATELLITE-RELATED TERMS

• Earth Stations – antenna systems on or near earth

• Uplink – transmission from an earth station to a

satellite

• Downlink – transmission from a satellite to an earth

station

• Transponder – electronics in the satellite that convert

uplink signals to downlink signals


Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.4

base station

or gateway

CLASSICAL SATELLITE SYSTEMS

Inter Satellite Link

(ISL) Mobile User

Link (MUL) Gateway Link

(GWL)

footprint

small cells

(spotbeams)

User data

PSTN ISDN GSM

GWL

MUL

PSTN: Public Switched

Telephone Network


BASICS

• Satellites in circular orbits

– attractive force Fg = m g (R/r)²

– centrifugal force Fc = m r ²

– m: mass of the satellite

– R: radius of the earth (R = 6370 km)

– r: distance to the center of the earth

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

– : angular velocity ( = 2 f, f: rotation frequency)

• Stable orbit

– Fg = Fc 32

2

)2( f

gRr

WAYS TO CATEGORIZE

COMMUNICATIONS SATELLITES

• Coverage area

– Global, regional, national

• Service type

– Fixed service satellite (FSS)

– Broadcast service satellite (BSS)

– Mobile service satellite (MSS)

• General usage

– Commercial, military, amateur, experimental


CLASSIFICATION OF SATELLITE

ORBITS

• Circular or elliptical orbit – Circular with center at earth’s center

– Elliptical with one foci at earth’s center

• Orbit around earth in different planes – Equatorial orbit above earth’s equator

– Polar orbit passes over both poles

– Other orbits referred to as inclined orbits

• Altitude of satellites – Geostationary orbit (GEO)

– Medium earth orbit (MEO)

– Low earth orbit (LEO)


GEOMETRY TERMS

• Elevation angle - the angle from the horizontal to the

point on the center of the main beam of the antenna

when the antenna is pointed directly at the satellite

• Minimum elevation angle

• Coverage angle - the measure of the portion of the

earth's surface visible to the satellite


MINIMUM ELEVATION ANGLE

• Reasons affecting minimum elevation angle of earth station’s antenna (>0o)

– Buildings, trees, and other terrestrial objects block the line of sight

– Atmospheric attenuation is greater at low elevation angles

– Electrical noise generated by the earth's heat near its surface adversely affects reception


FIGURE 16.1 COVERAGE AND ELEVATION ANGLES


http://goo.gl/7lGgYH


ELEVATION

Elevation:

angle e between center of satellite beam

and surface

e minimal elevation:

elevation needed at least

to communicate with the satellite


INCLINATION

inclination d

d

satellite orbit

perigee

plane of satellite orbit

equatorial plane

FIGURE 16.2 SATELLITE PARAMETERS AS A FUNCTION OF

ORBITAL HEIGHT Long Range Communications 16-13

http://goo.gl/0UrO9G


SATELLITE PERIOD AND ORBITS

10 20 30 40 x106 m

24

20

16

12

8

4

radius

satellite

period [h] velocity [ x1000 km/h]

synchronous distance

35,786 km


LINK BUDGET OF SATELLITES

• Parameters like attenuation or received power determined by four parameters:

sending power

gain of sending antenna

distance between sender and receiver

gain of receiving antenna

• Problems

varying strength of received signal due to multipath propagation

interruptions due to shadowing of signal (no LOS)

• Possible solutions

Link Margin to eliminate variations in signal strength

satellite diversity (usage of several visible satellites at the same time) helps to use less sending power

24

c

frL

L: Loss

f: carrier frequency

r: distance

c: speed of light


ATMOSPHERIC ATTENUATION Example: satellite systems at 4-6 GHz

elevation of the satellite

5° 10° 20° 30° 40° 50°

Attenuation of

the signal in %

10

20

30

40

50

rain absorption

fog absorption

atmospheric

absorption

e


ORBITS

earth

km

35768

10000

1000

LEO

(Globalstar,

Irdium)

HEO

inner and outer Van

Allen belts

MEO (ICO)

GEO (Inmarsat)

Van-Allen-Belts:

ionized particles

2000 - 6000 km and

15000 - 30000 km

above earth surface

GEO ORBIT

• Advantages of the the GEO orbit

– No problem with frequency changes

– Tracking of the satellite is simplified

– High coverage area

• Disadvantages of the GEO orbit

– Weak signal after traveling over 35,000 km

– Polar regions are poorly served

– Signal sending delay is substantial


FIGURE 16.3 GEOSTATIONARY EARTH ORBIT (GEO)


http://goo.gl/kUi6zq

LEO SATELLITE

CHARACTERISTICS

• Circular/slightly elliptical orbit under 2000 km

• Orbit period ranges from 1.5 to 2 hours

• Diameter of coverage is about 8000 km

• Round-trip signal propagation delay less than 20 ms

• Maximum satellite visible time up to 20 min

• System must cope with large Doppler shifts

• Atmospheric drag results in orbital deterioration


FIGURE 16.4 LEO AND MEO ORBITS


FIGURE 16.5 MINIMUM FREE SPACE LOSS AS A FUNCTION OF

ORBITAL HEIGHT Long Range Communications 16-22

LEO CATEGORIES

• Little LEOs

– Frequencies below 1 GHz

– 5MHz of bandwidth

– Data rates up to 10 kbps

– Aimed at paging, tracking, and low-rate messaging

• Big LEOs

– Frequencies above 1 GHz

– Support data rates up to a few megabits per sec

– Offer same services as little LEOs in addition to voice and positioning services


MEO SATELLITE

CHARACTERISTICS

• Circular orbit at an altitude in the range of 5000 to

12,000 km

• Orbit period of 6 hours

• Diameter of coverage is 10,000 to 15,000 km

• Round trip signal propagation delay less than 50 ms

• Maximum satellite visible time is a few hours


FREQUENCY BANDS AVAILABLE

FOR SATELLITE

COMMUNICATIONS


SATELLITE LINK PERFORMANCE

FACTORS

• Distance between earth station antenna and satellite

antenna

• For downlink, terrestrial distance between earth

station antenna and “aim point” of satellite

– Displayed as a satellite footprint

• Atmospheric attenuation

– Affected by oxygen, water, angle of elevation, and higher

frequencies


FIGURE 16.6 TYPICAL SATELLITE FOOTPRINT


http://goo.gl/nS0uJt

FIGURE 16.7 SIGNAL ATTENUATION DUE TO

ATMOSPHERIC ABSORPTION (C BAND) Long Range Communications 16-28

FIGURE 16.8 SATELLITE COMMUNICATION

CONFIGURATIONS Long Range Communications 16-29

http://goo.gl/vhfQFp

CAPACITY ALLOCATION

STRATEGIES

• Frequency division multiple access (FDMA)

• Time division multiple access (TDMA)

• Code division multiple access (CDMA)


FIGURE 16.9 TYPICAL VSAT CONFIGURATION


GLOBAL POSITIONING SYSTEM

• GPS was developed by U.S. Department of Defense

• 24 MEO satellites

– Six orbital planes at 20,350 km altitude

– Orbit every 12 hours

• GPS receiver must observe at least 4 satellites

– Three provide distance measurement

– Intersection of three spheres provides two points of intersection, one of which is unrealistic

– Fourth satellite is used to adjust timing offsets


GLOBAL POSITIONING SYSTEM

• Uses Direct Sequence Spread Spectrum

– Can keep from unauthorized use

• Until 2000, GPS signals were intentionally degraded

– Low received signal energy is required

– All satellites can use the same frequency band

• Complexities of operation

– Knowing satellite locations

– Atmospheric effects

– Differential GPS can provide more accuracy if a terrestrial reference point is also known


FIGURE 16.16 GLOBAL POSITIONING SYSTEM


DIRECT BROADCAST SATELLITE

• Provides television services

• C-band (4-8 MHz) requires 3 m dishes

• Ku band (12-18 GHz) requires 1 m dishes

• Providers send signals up to satellites

– Satellites rebroadcast on various frequencies

– Receivers decrypt by permission of service

provider

• High compression for best use of the channel


FIGURE 16.17 DIRECT BROADCAST SATELLITE



LINK BUDGET

• Pr = Pt - 92.4 - 20 Log F(GHz) - 20 Log D(Km) - At + Gt + Gr

• G- Gain of antenna t – transmission; r – reception

• At – atmospheric attenuation (dust, rain)

• D = 36000 Km -> 20 LogD = 91,1

• F= 2 GHz -> 20 LogF = 6

• A=10 dB

• Gt = Gr = 30 dBi

• Pt = 40 dBm (10 W) -> Pr = - 99,5 dBm


ANGLES - DIVERGENCE & SPOT SIZE

1 mrad

1 km

1 m

Small angle approximation:

Angle (in milliradians) * Range (km)= Spot Size (m)

Divergence Range Spot Diameter

1 mrad 36000 km 36 Km

17 mrad (1 deg) 36000 km 612 Km

1° ≈ 17 mrad → 1 mrad ≈ 0.0573°


ANTENNA GAIN VS DIVERGENCE

• Gain(dBi) = 10 Log (2 / Div) = 10 Log (360º/Divº)

• Isotropic Antenna -> Div = 2 / 360º (both Vert. and Hor.)

Gain(dBi) = 0

• Examples:

• Div =2º -> Gain(dBi) = 22,6 dBi (2x 22,6 if in both planes)

• Div =4º -> Gain(dBi) = 19,6 dBi

• Div =8º -> Gain(dBi) = 16,6 dBi

• Div=12º -> Gain(dBi) = 14,7 dBi (Vert and Hor: 14,7 x 2 = 29,4 dBi)

• Nota: a antena da Cisco com Div= 12º tem 21 dBi de ganho, (vs 29.4 dBi teórico) devido a perdas noutras direcções.

Cisco AIR-ANT3338

21dBi Parabolic Dish Azimuth 3dB BW =12º

Elevation 3dB BW =12º


RECEIVED POWER BASED ON

ANTENNA APERTURE AREA (AE)

• Ae = Aphysical * h (h - Antenna efficiency 50%-80%)

• Pr = Pt – 10 Log(4 * Footprint / (PI2 *Ae)) – At

• Pt = 40dBm (10W)

• Footprint = 471 716 Km2 (PI x 387.5km x 387.5km) (Iberian peninsula 582 860 km2)

• Aphy = 1m2 ; h = 50%

• At = 10 dB

• Pr = 40 – 115.6 -10 = - 85.6 dBm

36000 Km

775 Km 1.2º

CHAPTER 16 LONG RANGE COMMUNICATIONS - … range communications • rich history ... isdn pstn gsm...

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