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Wireless Communication
Networks and Systems1st edition
Cory Beard, William Stallings
© 2016 Pearson
Higher Education, Inc.
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All material copyright 2016
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
Long Range Communications 16-2
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
Long Range Communications 16-3
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
PSTNISDN GSM
GWL
MUL
PSTN: Public Switched
Telephone Network
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.5
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
Long Range Communications 16-6
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)
Long Range Communications 16-7
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
Long Range Communications 16-8
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
Long Range Communications 16-9
FIGURE 16.1 COVERAGE AND ELEVATION ANGLES
Long Range Communications 16-10
𝑅
𝑅 + ℎ=
sin(∝)
sin 𝜃 +𝜋2
=
𝑠𝑖𝑛𝜋2− 𝛽 − 𝜃
sin 𝜃 +𝜋2
=cos(𝛽 + 𝜃)
cos(𝜃)
𝑑
𝑅 + ℎ=
sin(𝛽)
sin 𝜃 +𝜋2
=
=sin(𝛽)
cos(𝜃)
𝑑 =(𝑅 + ℎ) ∙ sin(𝛽)
cos(𝜃)
=𝑅 ∙ sin(𝛽)
sin(𝛼)
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.11
ELEVATION
Elevation:
angle e between center of satellite beam
and surface
eminimal elevation:
elevation needed at least
to communicate with the satellite
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.12
INCLINATION
inclination d
d
satellite orbit
perigee
plane of satellite orbit
equatorial plane
FIGURE 16.2 SATELLITE PARAMETERS AS A FUNCTION OF
ORBITAL HEIGHTLong Range Communications 16-13
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.14
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
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.15
ORBITS
earth
km
35768
10000
1000
LEO
(Globalstar,
Irdium)
HEO
inner and outer Van
Allen belts
MEO (Inmarsat)
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
Long Range Communications 16-16
FIGURE 16.3 GEOSTATIONARY EARTH ORBIT (GEO)
Long Range Communications 16-17
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
Long Range Communications 16-18
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
Long Range Communications 16-20
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
Long Range Communications 16-21
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
Long Range Communications 16-23
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.24
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
FIGURE 16.6 TYPICAL SATELLITE FOOTPRINT
Long Range Communications 16-26
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.27
ATMOSPHERIC ATTENUATIONExample: 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
FIGURE 16.7 SIGNAL ATTENUATION DUE TO
ATMOSPHERIC ABSORPTION (C BAND)Long Range Communications 16-28
FIGURE 16.8 SATELLITE COMMUNICATION
CONFIGURATIONSLong Range Communications 16-29
CAPACITY ALLOCATION
STRATEGIES
• Frequency division multiple access (FDMA)
• Time division multiple access (TDMA)
• Code division multiple access (CDMA)
Long Range Communications 16-31
FREQUENCY-DIVISION
MULTIPLEXING
• Alternative uses of channels in point-to-point
configuration
– 1200 voice-frequency (VF) voice channels
– One 50-Mbps data stream
– 16 channels of 1.544 Mbps each
– 400 channels of 64 kbps each
– 600 channels of 40 kbps each
– One analog video signal
– Six to nine digital video signals
Long Range Communications 16-32
FIGURE 16.10 TYPICAL SATELLITE TRANSPONDER FREQUENCY
PLAN FOR THE DOWNLINK CHANNELS
Long Range Communications 16-33
FREQUENCY-DIVISION MULTIPLE
ACCESS
• Factors which limit the number of subchannels
provided within a satellite channel via FDMA
– Thermal noise
– Intermodulation noise
– Crosstalk
Long Range Communications 16-34
FIGURE 16.11 FIXED-ASSIGNMENT FDMA FORMAT FOR
SATELLITE COMMUNICATIONLong Range Communications 16-35
FORMS OF FDMA
• Fixed-assignment multiple access (FAMA)
– The assignment of capacity is distributed in a fixed manner
among multiple stations
– Demand may fluctuate
– Results in the significant underuse of capacity
• Demand-assignment multiple access (DAMA)
– Capacity assignment is changed as needed to respond
optimally to demand changes among the multiple stations
Long Range Communications 16-36
REASONS FOR INCREASING USE OF
TDM TECHNIQUES
• Cost of digital components continues to drop
• Advantages of digital components
– Use of error correction
• Increased efficiency of TDM
– Lack of intermodulation noise
Long Range Communications 16-37
FIGURE 16.12 EXAMPLE OF TDMA FRAME FORMAT
Long Range Communications 16-38
FIGURE 16.13 TDMA OPERATION
Long Range Communications 16-39
FIGURE 16.14 RELATIVE EFFICIENCY FOR
VARIOUS SATELLITE CAPACITY ALLOCATION SCHEMESLong Range Communications 16-40
FIGURE 16.15 SS/TDMA OPERATION
Long Range Communications 16-41
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
Long Range Communications 16-42
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
Long Range Communications 16-43
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
Long Range Communications 16-45
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.47
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
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.48
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°
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.49
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)
• Note: Cisco’s antenna with Div= 12º has a gain of 21 dBi (vs 29.4 dBi in theory) due to losses in other directions (side lobes).
Cisco AIR-ANT3338
21dBi Parabolic DishAzimuth 3dB BW =12º
Elevation 3dB BW =12º
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 5.50
RECEIVED POWER BASED ON
ANTENNA APERTURE AREA (AE)
• Ae = Aphysical * h (h - Antenna efficiency 50%-80%)
• When Tx and Rx antennas are equal:
– 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 Km1.2º