3. Satellite Communication - VL-2

7/28/2019 3. Satellite Communication - VL-2

1/23

Basic Satellite Communication

(2)

Frequency Allocation, Spectrumand Key Terms

Dr. Joseph N. Pelton


2/23

Satellite Frequencies &

Spectrum Radio Frequencies are simply a part of the electromagnetic

spectrum. This extends from Extremely Low to Extremely

High Frequencies to Infra-red to Visible Light (Photons) to

Ultra-Violet to X-rays to Cosmic Radiation that represents

the highest frequencies of all and at the highest energy.

Spectrum is truly a vital resource for communications

satellites. Formula C (or 3x 108 m/sec) = Wavelength x

Frequency

The radio wave band that is used by satellites is divided

into the following categories that have been named over

time.


3/23


4/23

Satellite Frequencies &

Spectrum Very High Frequency

30 MHz to 300 MHz : 10 to 1 metersVHF

Ultra High Frequency 300 MHz to 3000 MHz : 100 to 10 metersUHF

Super High Frequency 3 GHz to 30 GHz : 10cm to 1 cm

SHF Extremely High Frequency

30 GHz to 300 GHz : 10mm to 1 mmEHF


5/23

Satellite Frequencies

Fixed Satellite Services (FSS)*StatusAvailable Usable

BandUp & DownLinksName of BandVirtually saturated

band

500MHz

500MHz

6GHz-Up

4GHz-Down

C-Band

Very heavily used

band

500MHz+250MHz

500MHz+250MHz

14 GHz-Up

11/12 GHz-Down

Ku-Band

Just beginning to

be used

3000 MHz

2500 MHz

27-30 GHz-Up

17-20 GHz-Down

Ka-Band

Largelyexperimental2000 MHz2000 MHz48-50 GHz-Up38-40 GHz-DownQ/V Band

* Note: Other allocations in X band 8/7 GHz for government services


6/23


Mobile Satellite Services (MSS)* Major MSS Assigned Bands*

1525~1559 MHz (L-Band)

1610~1626.5 MHz (L-Band) 1626.5~1660.5 MHz (L-Band)

1980~2025 MHz (L-Band)

2160~2200 MHz (S-Band)

2483~2500 MHz (S-Band)

30/20 GHz (Ka/Ku Band)**

*Available spectrum in L-Band is allocated in units of 5.25. MHz and thus

very intensive reuse is needed to support global demands

** Feeder Links in the Fixed Satellite Services (FSS) Bands.


7/23


Mobile Satellite Services (MSS)* Satellite Messaging (Store & Forward)*

137~138 MHz (down) 148~149.9 MHz (up)

149.9~150.05 MHz (up) 399.9~400.5 MHz (up)

400.15~401 MHz (down) and 432 MHz

*Typical application is for store and forward messaging to support

tracking of vehicles, trains, ships at sea, updates on pipeline flow orcommands to SCADA (Supervisory Control and Data Acquisition)

terminals at power plants etc. Many Security applications


8/23


Broadcast Satellite Services

17.3~18.1 FSS-Uplink Feeders

for BSS Downlinks

12.2~12.7 GHz (Reg. 2-Americas) 11.7~12.45 GHz (Reg. 1 & 3 Europe, Africa &

Asia)

(Plus other allocations at 700 MHz,

at 2.6 GHz, 22GHz and 42 GHz bands.

(2.6 GHz used for direct audio broadcasting)

Space Navigation Satellite Services

1.6 GHz (i.e. GPS)


9/23

Basic Terms and Concepts

The field of Satellite Communications is based on

large number of basic terms, concepts and

mathematics and physical theorems. Most of thesecan straightforward ideas.

These include spectrum, RF, bandwidth, Hz,

decibles, dBm, antenna gain, G/T, Quality of

Service, S/N, system availability, flux density,transponders, filters, amplifiers, analog and digital

modulation, multiplexing, intermediate Frequency

and Base band, carrier, etc.


10/23

Basic Terms and Concepts

The purpose of this lecture is to become familiar

with these terms, their meanings and how to use

them. We will return to these in greater depthlater. This is just a first introduction.


11/23

The Significance of

Frequencies and Line of Sight VHF signals involve long enough wavelengths that they

are not easily blocked by trees, foliage, power lines, etc.

But as one moves up to UHF and SHF the systems become

increasingly line of sight systems.

For FSS services it is possible to line an earth station up

with a satellite and no barriers intervene and thus use SHF

or EHF spectrum, but for mobile satellite services (MSS),

the frequencies must be low enough (and wavelengths longenough) to not be easily blocked. This means that high link

margins are needed for MSS services, especially for cars.


12/23

Electro-Magnetism

Electromagnetism is one of the four basic forces in the

universe. These are: (i) Gravity, (ii) Electromagnetism,

(iii) the strong nuclear force and (iv) the weak nuclear

force.

The elecro-magnetic spectrum covers a very wide range of

frequency for very low frequency cycles up to those that

we can hear to ultra-sonics to radiowaves to infrared,

optical signals, ultra-violet, X-rays on up to the very highenergy cosmic waves at the highest frequencies.


13/23

Radio Frequency (RF) Spectrum

The most often used radio wave bands that are

used by satellites is divided into the following

categories that have been named over time.

HF = 3 MHz to 30 MHz or 100 to 10 meters

VHF = 30 MHz to 300 MHz or 10 to 1 meters

UHF = 300 MHz to 3000 MHz or 100cm to 10 cm

SHF = 3 GHz to 30 GHz or 10cm to 1 cm

EHF = 30 GHz to 300 GHz or 10mm to 1 mm


14/23

Hertz

Hertz = Cycles per second. kHz or kiloHertz = 1000

Cycles per second. MHz or MegaHertz = 1,000,000 Cycles

per second GHz or GigaHertz = 1 billion cycles per

second.

Speed of light or C = 3 x 108 m/second

C=Frequency x Wavelength

Thus a frequency of 3 MHz or 3 million cycles/second is C

(or the speed of light which is 3 x 108 m/second divided by100 meters = 3 x 106 cycles/second. Thus 300 MHz

represents a wavelength of 1 meter and 3GHz represents a

wavelength of 10cm. What would be wavelength of 6GHz

in cm?


15/23

Decibels A decibel is a logarithmic scale measure that is used in

communications and particularly for satellite communications because

it allows for a dramatic range of power variations. Due to the high

orbit of Geo Satellites path loss represents effective power reduction

by many, many orders of magnitude. A decibel range on the basis of a logarithmic scale of 10. A 3 dB gain

means that a power level has doubled. 6 dB means a gain of 4, a 10 dB

gain means a gain of 10, 20 dB means a gain of 100 and 30 dB means

a gain of 1000 and 60 dB means a gain of 1 million times. It also

works the same way in terms of decreases. A -3 dB shift means poweris reduced by half. A -6 dB means power is reduced by 4, a -10 dB

reduction is shown by 10. Thus -30 dB is a reduction of 1000 times.

This is also a known as a dBm or a thousandth of a dB.

What would a gain of 1,000,000 be expressed in dB?What would a

million times reduction in gain be in terms of the decibel scale?


16/23

Antenna Gain

An omni antenna has a gain of 1 or 0 dB.

Any time you focus a signal to concentrate its radiation

pattern you are increasing its gain. This means that the flux

density of the radiated signal will increase at the earthssurface if you use a higher gain antenna on a satellite.

The history of satellite development has been largely

linked to using higher gain space antennas. The larger the

aperture of an antenna the more concentrated the beam andthe higher the gain. The formula for antenna gain is

G=(pi x d)2/lambda2 in this case is the efficiency of the

reflector, d=the diameter of the parabolic antenna reflector

and lambda the wavelength.


17/23

E.I.R.P.

This terms that refers to satellite irradiated power

stands for Effective Isotropic Radiated Power.

Isotropic refers to a signal sent in all directions

equally from a single point.

With a high gain antenna the power of the satellite

can be radiated within specific beam coverage

areas to create increased power flux density in thistraffic catchment area and thus improve the

communications throughput to earth stations on

the ground in a particular area.


18/23

G/T, C/N and Eb/No G on T or Gain to Thermal Noise is a measure of

the effective gain or performance of a ground

station. For larger antennas this might be 32.9 dB/K

for large 30m antenna to 22.9 dB/K for multi-meterantenna and for a VSAT about 8 to 12 dB/K.

Carrier Signal to Noise is a measure of the

transmitted power of a carrier in relation to thenoise or interference in the carrier band.

Eb/No is the ratio of the power per data bit to the

noise power density per Hz. This is the basis for

determining the quality of a digital channel.


19/23

System Availability and BER The calculation of system availability is simply the

ratio of the time a service or circuit is available for

service to when it is not. The Integrated Services

Digital Network (ISDN) standard for this is99.98% or outage of about an hour and a half out

of year.

Bit Error Rate is the determination of Quality ofService QoS in a digital system. Again the ISDN

Standard for BER in a simple sense is 10-6.


20/23

Power Flux Density Power Flux Density of a radio wave or signal that is used

to measure satellite communications links. The power from

the antenna radiates outwards to an ever expanding sphere

until a signal is received. Thus flux density is the powerflow per unit surface area. The greater the distance travel

the flux density decreases by the square of the distance

traveled. This is why LEO with the same antenna gain as a

GEO satellite can have up to 1600 time greater flux density

because it is 40 times closer to the Earth.

The power flux density is thus a vector quantity

determined by how little of a spheres surface it

illuminates. The tighter the antenna beam the higher the

received power flux density.


21/23

Transponders and Filters A typical transponder bandwidth is 36 MHz but it may be 54 MHz, 72

MHz or even wider.

A transponders function is to receive the signal, filter out noise, shift

the frequency to a downlink frequency and then amplify it for

retransmission to the ground. The main amplifier may be a TravelingWave Tube (TWT) or Klystron Tube (now usually used for higher

frequencies above 20 GHz and at very high power levels (i.e. 100 to

200 watts) or it may be a Solid State Power Amplifier (SSPA) that

would be used at lower L, C or Ku band frequencies. If the transponder

is a regenerative transponder then the signal will be converted to baseband frequencies and processed there rather than handled at RF bands.

The transponder is the device that provide the connection between the

satellites transmit and receive antennas.


22/23

Intermediate and Base band

Frequencies The baseband is the frequency that is in theoriginal source of the information such as a

spoken voice.

Baseband signaling involves transmission of

information at its original range of frequencies.

Intermediate frequencies are sometime needed too

shift the baseband information through to themuch higher RF signaling where satellite

transmissions occur in the SHF and EHF bands.


23/23

Assignment

Assignment 3:

Solve all the mathematical questions asked in the

presentation and send the answers with thecalculations steps performed to get the result.

Summarize the Frequency Spectrum Diagram (on

Slide 3) in terms of following table columns:

Frequency Band, Operating Frequency,

Commercial/Military, Satellite/Component using this

frequency, Description of Application/Service

Documents

3. Satellite Communication - VL-2