Radio Comm & SatelliteComm

8/11/2019 Radio Comm & SatelliteComm

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Radio Communications Principles and

Applications


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Common Uses of Radio

1. I.D. Badge Tags

2. SW Radio

3. Broadcast Radio

4. TV5. Model RC

6. Intercom

7. Microwave oven

8. HF Asset tracking

9. UHF Truck/Trailer ID

10. Car door keys

11. Garage door opener

12. Bluetooth

13. G P S

14. Toll road tags15. Vehicle speed check

16. Cordless phone

17. Satellite TV

18. Mike & Amps

19. Emergency services

20. WiFi


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Radio Frequency Classification

ULF 300Hz3kHz

VLF 330 kHz

LF 30300kHz

MF 3003,000kHz (3 MHz)

HF 330MHz

VHF 30300MHz

UHF 3003,000 MHz (3GHz)

SHF 330 GHz

EHF 30300 GHZ


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Radio Frequency Spectrum


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Electromagnetic Spectrum

Managed by a number of bodies: Radio Communications Agency (UK)

ITUInternational Telecommunication Union

ETSI European Telecommunications StandardsInstitute

Stops user conflict

Preserves user integrity


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Periodic Signals


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Sine Wave

Peak Amplitude (A) maximum strength of signal

volts

Frequency (f)

Rate of change of signal

Hertz (Hz) or cycles per second

Period = time for one repetition (T)

T = 1/f Phase ()

Relative position in time


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Practice Exercise

Draw the Sine waves with followingdata:

i) A = 2 , F = 2 and = 0

ii) A = 2.5 , F = 3 and = 180 degrees


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Wavelength()

Distance occupied by one cycle Distance between two points of corresponding

phase in two consecutive cycles

Assuming signal velocity v

= vT

f = v

c = 3*108ms-1(speed of light in free space)


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Practice Questions. . .

1. Radio wave has 30m wavelength &

10MHz frequency

What is its Velocity?

2. Radio wave has 12.3m Wavelength

and 3 x10^8 m/sec

What is its frequency?


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Solution

A1. V = Freq x Wavelength

So V = 10x10^6 x 30m

= 3x 10^8metres / sec

A2. Freq = Velocity / Wavelength

= (3 x 10^8 cps) / 12.3m

= 24.39 MHz


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What We have achieved.

Electromagnetic Spectrum

Classification of Frequency bands

Characteristics of bands between 3KHzto 90 GHz

Relationship between frequency,wavelength and velocity of propagation


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Antennae


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Antenna

is an electrical conductor or system of conductors.

is a device whose function is to radiate

electromagnetic energy or to intercept

electromagnetic radiation

Transmission- radiates electromagnetic energy

into space

Reception - collects electromagnetic energy fromspace


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Microwaves

An electromagnetic waves with frequencies that ranges

from approximately 500 MHz to 300 GHz or more. And

its wavelengths fall between 1cm and 60 cm.

Wavelength

The distance between

repeating units of apropagating wave of a

given frequency.

Designated by lambda

().


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Categories of Microwave Systems:

A. Short haul used to carry information for relatively

short distances, e.i. between cities within the same state.


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Categories of Microwave Systems:

A. Long haul used to carry information for relatively

long distances, such as interstate.


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Advantages of Microwave Radio:

1. Radio systems do not require a right-of-way

acquisition between stations.

2. Each station requires the purchase or lease of only asmall area of land.

3. Because of their high operating frequencies,

microwave radio systems can carry large quantities of

information.

4. Short wavelengths, require relatively small antennas.

5. Radio signals are more easily propagated around

physical obstacles, such as high mountains


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Disadvantages of Microwave Radio:

1. It is more difficult to analyze and design circuits at

microwave frequencies.

2. Measuring techniques are more difficult to perfectand implement at microwave frequencies.

3. It is difficult to implement conventional circuit

components at microwave frequencies.

4. Transient time is more critical at microwave

frequencies.

5. Microwave frequencies propagate in a straight line,

which limits their use to line-of-sight applications.


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Satellite Communications


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Ways to Categorize


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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


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Classification of Satellite Orbits

Circular or elliptical orbit

Circular with center at earths center

Elliptical with one foci at earths center

Orbit around earth in different planes

Equatorial orbit above earths 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)


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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


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Minimum Elevation Angle

Reasons affecting minimum elevation angle

of earth stations 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 heatnear its surface adversely affects reception


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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


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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 20ms

Maximum satellite visible time up to 20 min

System must cope with large Doppler shifts Atmospheric drag results in orbital deterioration


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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 voiceand positioning services


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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


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Frequency Bands Available for

Satellite Communications

Satellite Link Performance


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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 (Figure 9.6)

Atmospheric attenuation

Affected by oxygen, water, angle of elevation, and

higher frequencies


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Satellite Footprint


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Satellite Network Configurations


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Capacity Allocation Strategies

Frequency division multiple access

(FDMA)

Time division multiple access (TDMA)

Code division multiple access (CDMA)


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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

Frequency-Division Multiple


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Frequency-Division Multiple

Access

Factors which limit the number of

subchannels provided within a satellite

channel via FDMA

Thermal noise

Intermodulation noise

Crosstalk


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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 multiplestations


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DAMA-FDMA

Single channel per carrier (SCPC)bandwidthdivided into individual VF channels

Attractive for remote areas with few user stations neareach site

Suffers from inefficiency of fixed assignment

DAMAset of subchannels in a channel is treatedas a pool of available links

For full-duplex between two earth stations, a pair of

subchannels is dynamically assigned on demand Demand assignment performed in a distributed fashion

by earth station using CSC

Reasons for Increasing Use of


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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


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FAMA-TDMA Operation

Transmission in the form of repetitive sequence offrames

Each frame is divided into a number of time slots

Each slot is dedicated to a particular transmitter

Earth stations take turns using uplink channel

Sends data in assigned time slot

Satellite repeats incoming transmissions

Broadcast to all stations Stations must know which slot to use for

transmission and which to use for reception


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FAMA-TDMA Uplink


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