Basic Satellite Communication Basic Satellite Communication (2)(2)

Frequency Allocation, Spectrum Frequency Allocation, Spectrum and Key Termsand Key Terms

Dr. Joseph N. Pelton

http://web.uettaxila.edu.pk/CMS/SP2015/teSNms/http://web.uettaxila.edu.pk/CMS/SP2015/teSNms/

Satellite Frequencies & Satellite Frequencies & SpectrumSpectrum

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.

Satellite Frequencies & Satellite Frequencies & SpectrumSpectrum

Satellite Frequencies Satellite Frequencies Fixed Satellite Services (FSS)*Fixed Satellite Services (FSS)*

Name of Band Up & Down Links

Available Usable Band

Status

C-Band 6GHz-Up4GHz-Down

500MHz500MHz

Virtually saturated band

Ku-Band 14 GHz-Up11/12 GHz-Down

500MHz+250MHz500MHz+250MHz

Very heavily used band

Ka-Band 27-30 GHz-Up17-20 GHz-Down

3000 MHz2500 MHz

Just beginning to be used

Q/V Band 48-50 GHz-Up38-40 GHz-Down

2000 MHz2000 MHz

Largelyexperimental

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

Satellite Frequencies Satellite Frequencies Mobile Satellite Services (MSS)*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.

Satellite Frequencies Satellite Frequencies Mobile Satellite Services (MSS)*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 or commands to SCADA (Supervisory Control and Data Acquisition) terminals at power plants etc. Many Security applications

Satellite FrequenciesSatellite FrequenciesBroadcast 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)

Basic Terms and ConceptsBasic Terms and Concepts

The field of Satellite Communications is based on large number of basic terms, concepts and mathematics and physical theorems. Most of these can 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.

Basic Terms and ConceptsBasic 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 depth later. This is just a first introduction.

The Significance of The Significance of Frequencies and Line of SightFrequencies 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 long enough) to not be easily blocked. This means that high link margins are needed for MSS services, especially for cars.

Electro-MagnetismElectro-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-sonic to radio waves to infrared, optical signals, ultra-violet, X-rays on up to the very high energy cosmic waves at the highest frequencies.

Radio Frequency (RF) SpectrumRadio 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

HertzHertz

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/secondC=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 by 100 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?

DecibelsDecibels 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 power is 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?

Antenna GainAntenna 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 earth’s surface 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 and the higher the gain. The formula for antenna gain is G=µ(pi x d)2/lambda2 in this case µ is the efficiency of the reflector, d=the diameter of the parabolic antenna reflector and lambda the wavelength.

E.I.R.P.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 this traffic catchment area and thus improve the communications throughput to earth stations on the ground in a particular area.

G/T, C/N and EG/T, C/N and Ebb/N/Noo

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-meter antenna 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 the noise 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.

System Availability and BERSystem 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 is 99.98% or outage of about an hour and a half out of year.

Bit Error Rate is the determination of Quality of Service QoS in a digital system. Again the ISDN Standard for BER in a simple sense is 10-

6.

Power Flux DensityPower 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 power flow 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 sphere’s surface it illuminates. The tighter the antenna beam the higher the received power flux density.

Transponders and FiltersTransponders 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 Traveling Wave 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 base band frequencies and processed there rather than handled at RF bands.

The transponder is the device that provide the connection between the satellite’s transmit and receive antennas.

Intermediate and Base band Intermediate and Base band FrequenciesFrequencies

The baseband is the frequency that is in the original 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 the much higher RF signaling where satellite transmissions occur in the SHF and EHF bands.

AssignmentAssignment

Assignment 3: Solve all the mathematical questions asked in

the presentation and send the answers with the calculations 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, Frequencies at Risk