Satellite Comm Fundamentals

Satellite RF Fundamentals 1

TCOM 750Satellite Communications Fundamentals

Sept 15, 2004

2Satellite RF Fundamentals

Announcements

Tonight we will view a video on amateur radio satelliteoperations and discuss some concepts presented in theclass notes.Next week: Perspectives on Winning Proposals

Guest Lecturer: Steve TrieberRecommended URLs:

Surrey Space Centre: http://www.ee.surrey.ac.uk/SSC/Surrey Satellite Technology LTD: http://www.sstl.co.ukSpaceQuest LTD: http://www.spacequest.com/Space Systems Development Lab: http://ssdl.stanford.edu/US Naval Academy Satellite Lab:http://web.usna.navy.mil/~bruninga/satstation.html


Team Rosters

TEAM 1 TEAM 2 TEAM3

1 Naim Kassar David Davis Yingjie Hall2 Heng Fan Azzie Legesse Ravi Bhalotia3 Arpan Shah Ayele Antenagegnehu Roger Ensminger4 Mark Norton Timothy Maier Shelley Mountjoy5 Kenneth Lim Shahid Nasim Yang Liu6 Dana Jaff Padmanabhan Raman Anouar Benahmed


Objectives

Refresh your knowledge of basic RF communicationsconcepts related to the operation of spacecraft.Analyze how amateur radio satellite operations andmethods can apply to our project.


Satellite RF Communications Architecture

EARTH

Datato

ProcessorReceiver

Receiver

Datato

Processor

Transmitter

Instrument

Data

Sensor

Spacecraft

GeostationaryRelay Satellite(s)

Space Link

OR

Space Link

Antenna


Modulator

Transmitter

Subsystems of Satellite RF Communications

Satellite transmitter-to-receiver link with typical loss and noise sources

PointingLoss

SpaceLoss

PolarizationLoss

AtmosphericLoss,

Rain Loss

PointingLoss

Galactic, Star,Terrestrial Noise

Demodulator

Receiver Noise

Antenna

Receiver

Power Amplifier

Antenna

InformationSource

Transmitter

InformationSink

ImplementationLoss

ReceiverSPACECHANNEL


Definitions & Some Basics

dB = 10 log10 (x); x is usually a power ratiodBW ≡ 10 log10 (watts)

For 100 watts; dBW = 10 log10 (100) = 20 dBWdBm ≡ 10 log10 (milliwatts)

For 100 watts; dBm = 10 log10 (100000) = 50 dBm

Carrier FrequencyUnits are HzMHz = Hz x 106

GHz = Hz x 10 9

Frequency Bands (of interest)S-Band = 2-3 GHzX-Band = 7-8 GHzKu-Band = 13-15 GHzKa-Band = 23-28 GHz


Logarithmic Scale

dBW dBm20 dBW 50 dBm100 Watts

13 dBW 43 dBm20 Watts

10 dBW 40 dBm10 Watts

0 dBW (Ref) 30 dBm1 Watts

-10 dBW 20 dBm0.1 Watts

-30 dBW 0 dBm (Ref)0.001 Watts(1 milliwatt)

-40 dBW -10 dBm0.0001 Watts

Always a 30 dBdifference betweendBm and dBW

A power below the reference level hasnegative value, for either dBm or dBW


+∆ f

- ∆ f

DopplerShift

DopplerRate

Nominal (at-rest)frequency

A

B

C

LOSAOS

EARTHORBIT

What is Doppler & Doppler Rate?

ss

s f VC

V ∆fShift Doppler ⎟⎟⎠

⎞⎜⎜⎝

⎛−

±==

Vs = Radial velocity component between S/C and Site in the direction of the observer

C = Speed of Light = 2.997925 x 108 meters/sec.

Fs = Frequency of Transmission

( ) s2s

s s f

VCVa

∆t∆fchange of rate Doppler

−==

where as = rate of change of Vs = acceleration

Doppler shifts become greater as the frequenciesbecome higher.

A B C


Phase lock loops

Enable receiving & tracking of Doppler shifted signalsUsed in virtually all spacecraft & ground station designs toaccommodate dynamic frequency changes

Doppler & Doppler Rate

Input Signal ±

Doppler

Phase &FrequencyComparer

Low PassFilter

Error Signal

VoltageControlledOscillator

FilteredErrorSignal


Analog and Digital Data



Most instrument data starts out as analog data

Most analog data is converted to digital data (binary 2n)

3 bit system

Binary0 0 00 0 10 1 00 1 11 0 01 0 11 1 01 1 1

Analog01234567

1 0 1 1 1 1 1 1 0 1 0 0

5 7 6 4

Serial data stream transmitted

Volts

time

Volts

time

7654



Why use digital data+ Better performance vs. noise+ Lends itself to computer processing & coding- Consumes more bandwidth

Sampling Rate ≥ Nyquist rate (≥ 2 fmax)

fmax – max frequency component of the original signal

Volts

t

AnalogSignal

t

DigitalSampling

t

DigitalBit

Stream


Spectra Basics


Spectra (Baseband Signals)

t

V(t) = Asin2πft

Period = T

Time Domain

Fourier

Transform

Fourier

Transform

( ) ( )∫∞

∞=

-dtftj2-e tvfv π

Frequency Domain

( ) ( )∫∞

∞=

-dtftj2-e tyfy π

t

T

y(t)

Amplitude

Hz

T1 f =

A

1/T 2/T 3/T 4/T 5/T 6/T 7/T1/T2/T3/T4/T5/T6/T7/T

( )x

xsin

Amplitude


½ M(0)

Spectra (Modulated Signal)

Given: an arbitrary modulating signal M(t)an arbitrary “carrier signal” cos 2πfctthen the modulated signal V(t) ≡ M(t) cos 2πfct

Find: The Fourier transform of V(t)

using the identity

Then:

Then: The Fourier transform of V(t) = V(f)A

( ) ( ) M(t) of transform Fourier the is dt e tMfM-

tf j2- m∫∞

∞= π

( ) tf2jtfj2c

cc e)t(M21 M(t)e

21 t f2 cos tM π−π +=π

( ) ( ) ( ) dte tM 21 dte tM

21 fV

-

)tf f(j2-

-

)tf f(j2- cmcm ∫∫∞

∞

−π∞

∞

+π += M(0)

ffm-fm 0

-fc

f0

½ M(0)

fc

tfj2tfj2c

cc e21 e

21 t f2 cos πππ −+=


Coding/Spreading/Data Compression


The Effects of Channel Noise

In digital communications, raw data is put into the form ofbits, 1’s and 0’s.A carrier signal is modulated using this raw data forconvenient transmission over the channel.The carrier signal is subject to noise corruption in thechannel, sometimes making it impossible to reconstructthe raw bits at the receiver.

If a transmitted bit is received as its opposite (e.g., a 1 receivedas a 0 or vice versa), then a “bit error” has occurred.

This results in a progressive loss of information at thereceiver as the number of mistranslated bits grows.


BER and Eb/No

The rate at which bits are corrupted beyond the capacityto reconstruct them is called the BER (Bit Error Rate).

A BER of less than 1 in 100,000 bits is generally desired for anaverage satellite communications channel (also referred to as aBER of 10-5).For some types of data, an even smaller BER is desired (10-7).

The BER is directly dependent on the Eb/No, which is theBit Energy-to-Noise Density ratio.

Since the noise density present on the channel is difficult tocontrol, this basically means that BER can be reduced throughusing a higher powered signal, or by controlling other parametersto increase the energy transmitted per bit.

As the following chart shows, the BER will decrease (i.e.,fewer errors) if the Eb/No increases.


Higher Eb/No Reduces the BER

10-3

10-4

10-5

10-6

BE

R

lower higherEb/No

Some ways ofIncreasing Eb/No

These methods canbe expensive

• Increase signal power• Use a bigger antenna• Use a super cooled receiver

BER Versus Eb/No


Another Strategy to Reduce BER

10-3

10-4

10-5

10-6

BE

R

lower higherEb/No

BER Versus Eb/No

This change in performancecan be achieved by usingError Correction Coding

Less expensive method ofmitigating channel noise

Another strategy is to shift thewhole curve over to the left

Now the same BER can beachieved using a lower Eb/No


Error Detecting versus Error Detecting/Correcting Codes

An error detecting code can only detect the presence of errors,not correct them.

This implies error detection and a subsequent request forretransmission.

There are times when retransmission of the message is notpractical.

If a spacecraft is transmitting a playback dump of a storage device whilemaking a short pass over a ground station, it may not have time to stopthe transmission and retransmit in a short enough time.

An error detecting/correcting code, on the other hand, has theability to detect a defined number of errors and correct themfor a prescribed environment that caused the errors, which iscommonly called Forward Error Correction (FEC).

Usually, for a given code, more errors can be detected than can actuallybe corrected.


Error Correction Codes

Error control coding aims to correct errors caused by noiseand interference in a digital communications scheme.In error control coding, the information bits are represented asanother sequence of bits, also called coded symbols; this newsequence is sent over the channel.This new sequence will use redundant information, often calledparity bits, to provide error protection (e.g., send a 0 as 00000and a 1 as 11111).Now individual bit errors will not necessarily result in theincorrect decoding of the original information bits.

For instance, if 1 or 2 of the five 0’s sent over the channel in the aboveexample are interpreted as 1’s at the receiver, the original 0 can still bedecoded correctly if one makes a final decision based on the majority ofthe received coded symbols.


Types of Error Correction Codes

A rate 1/2 convolutional code, an example of one family of codes, is oftenused on NASA space communication links.

2 coded symbols for every 1 data symbol (i.e., 100% overhead)Provides improved performance in a Gaussian noise environment

The Reed-Solomon code, a special type of “block” code, also has theadvantage of smaller bandwidth expansion and also has the capability toindicate the presence of uncorrectable errors.

Provides improved performance in a bursty noise environmentOverhead approximately 12%

Where a greater coding gain is needed than can be provided by theconvolutional code or the Reed-Solomon code alone, the two codes areoften concatenated to provide a higher error-correction performance.

One code serves as the “outer” code, one as the “inner” code


Typical Encoded Link

Data Bits1 Mbps Rate ½

ConvolutionalEncoder

Modulator &Transmitter

Data symbols

2.24 Msps

LNA

Receiver

ConvolutionalDecoder

Data Bits1 Mbps

(with some errors)

Data symbols2.24 Msps

Antenna Antenna

R/SEncoder

R/SDecoder

fc2.24 MHz

2.24 MHz

02.24 MHz

fc

02.24 MHz

1.12 MHz

Data symbols1.12 Msps

2 MHz01 MHz

Data symbols

1.12 Msps

BasebandSignal

RFSignal

Note: Coding increases the bandwidthof the baseband RF signal


Example Error Correcting Performance

For a BER of 10-5, TheoreticalRequired Eb/N0 is as follows:

Uncoded PSK: 9.6 dBReed-Solomon (R-S) Coding: 6.0 dBConvolutional Coding (7,1/2)PSK: 4.4 dBConvolutional + R-S(no R-S interleave): ~3.0 dBConvolutional + R-S(ideal R-S interleave): ~2.4 dB

(7,1/2), where rate 1/2 indicates thatfor every 1 bit into the encoder 2symbols are output of the encoderand 7 is the number of shiftregisters used to generate theoutput symbol of the encoder.Interleaving takes adjacent bits andseparates them to help protect frominterference.

Pe

(dB)Eb/No

10 -10

10 -9

10 -8

10 -7

10 -6

10 -5

10 -4

10 -3

10 -2

10 -1

1

1 2 3 4 5 6 8 9 10 11 120

THEORETICAL CURVES

IDEAL PSK, NO CODING

CONV. CODING (7, 1/2)

R-S CODING (255, 223)

CONV. + R-S (IDEAL INTERLEAVE)

CONV. + R-S (NO INTERLEAVE)


Data Compression

Data transmission and storage cost money.Despite this, digital data are generally stored in efficient ways such asASCII text or binary code.These encoding methods require data files about twice as large asactually needed to represent the information.

Data compression is the general term for the variousalgorithms and programs developed to address this problem.

A compression program converts data from an easy-to-use format forone optimized for compactness. Basically it discards redundant datawith a prescribed algorithm.An uncompression program returns the information to its original form.

As an example of compression, a fax device compresses thedata before it sends it to reduce the time needed to transmitthe document.

This can reduce the cost of transmission 10 or more times.Compression will be required for the Design Project Problem.


Spread Spectrum Definition

Spread Spectrum (SS) was developed originally as an anti-jammingtechnique.

A jamming signal is a narrowband, high power signal which falls in thebandwidth of the desired signal, thus disrupting communicationsJamming can be intentional, or it can result from natural phenomenasuch as multipath.

SS works by spreading the desired signal over a much largerbandwidth, Wss, much in excess of the minimum bandwidth Wnecessary to send the information.

A spreading signal, or coding signal, which is independent of the data, isused to accomplish spreading.At the receiver, the original data is recovered through a process calleddespreading, in which a synchronized replica of the spreading signal iscorrelated with the received spread signal.

Spreading used in the NASA Tracking and Data Relay Satellite (TDRS)Reduce flux density of signals to meet Spectrum Managementrequirements.Provide isolation for signals on same frequency.


Basic Spread Spectrum Technique: Direct Sequence

Multiplication by the spreading signal once spreads the signal bandwidth.Multiplication by the spreading signal twice recovers the original signal.The desired signal gets multiplied twice, but the jamming signal getsmultiplied only once.g(t) must be deterministic, since it must be generated at both thetransmitter and receiver, yet it must appear random to authorizedlisteners.

Generally g(t) is generated as a pre-defined pseudo-random sequence of 1s and–1s through the use of prescribed shift registers.

x x Filter Recovereddata

Signal x(t)Symbol (Data)

rate R

spreading codesignal g(t)

chip rate Rch

spreading codesignal g(t)

chip rate Rch

Rch ≈ ≥ 10 symbol (data) rate


Spreading: Effect of Spread Spectrum

Before Spreading

After Spreading

G(f)

w

Jammer with total power JJO = J/W

Gss(f)

wss

J'o = Jo (W/Wss)


Spreading: Overview of Various SpreadingTechniques

Direct Sequencing (DS) is the SS technique described above.Allows separation between desired signals all at the same frequency &polarizationAids in meeting required flux density regulationsEnables range determination of spacecraftRule of thumb – spreading chip rate x 10 of symbol (data) rate

In Frequency Hopping (FH), the frequency spectrum of the desiredsignal is shifted pseudorandomly over M different frequencies.

Each hop lasts a very short time, making the presence of a jamming signal in anyone hopped frequency band much less effective.FS is still a form of SS, as it requires greatly expanded bandwidth to operate.

Time Hopping (TH) uses a coded sequence to turn the transmitter onand off in a pseudorandom fashion to counter a pulsed jammingsignal.

Requires, not more bandwidth, but a greater time duration for transmission.Not effective against continuous wave jammers, so it is usually combined withother techniques.

Hybrids of the three techniques above are often used.DS/FH, FH/TH, or DS/FH/TH are examples.


Modulation Schemes


Definition of Modulation

Modulate means to change somethingIn telecommunications, it means to change the amplitude,frequency or phase of the carrier signal.

Digital symbols (usually bits) are transformed intowaveforms by a process called digital modulation.

These digital waveforms are then used to modulate the carrier.The following slide shows some commonly used PulseCode Modulation (PCM) waveforms.Definition: Baseband signals are those signals that areused to modulate a high frequency carrier signal.


Pulse Code Modulation (PCM) Waveforms

1 1 1 1110 0 0 0 0

0

1

0

1

0

1

0

1

0

0

1

0

1

1

1 0 0 0 0 0 11111

NRZ-L

NRZ-M

NRZ-S

R-Z

Biø-L

Biø-S

Biø-M

NRZ-Level (or NRZ-Change)"One" is represented by one level"Zero" is represented by the other level

NRZ-Mark"One" is represented by a change in level"Zero" is represented by no change in level

NRZ-Space"One" is represented by no change in level"Zero" is represented by a change in level

RZ"One" is represented by a half-bit wide pulse"Zero" is represented by no pulse condition

Bi-Phase-Level (or SplitPhase, Manchester 11+ 180o )"One" is represented by a 10"Zero" is represented by a 01

Bi-Phase-SpaceA transition occurs at the beginning of every bit period"One" is represented by no second transition"Zero" is represented by a second transition one-half bit period later

Bi-Phase-MarkA transition occurs at the beginning of every bit period"One" is represented by a second transition one-half bit period later"Zero" is represented by no second transition

MIS-01 NG5061


Motivation for Modulation

It would be very difficult to send a baseband signal directly over achannel because antennas are used to transmit electromagneticfields through space.The size of an antenna depends on the wavelength of the signal to betransmitted.

Often the antenna size is taken to be λ/4.A baseband signal has a relatively low frequency and therefore a verylarge wavelength that is calculated as c/f, where c is the speed of lightand f is the frequency.

An antenna might need to be unacceptably long to directly transmit a basebandsignal.If the baseband information is first modulated on a high frequency carrier, then therequired antenna diameter will be much more reasonable.

In addition, by modulating carriers at different frequencies, more thanone baseband signal may be sent over the same channel, thusincreasing data throughput. This is call frequency multiplexing(similar to current radio and TV broadcasting).


The Carrier Wave/How to Modulate

The general form of a carrier wave is:

s(t) = A(t) cos [wct + ø(t)]

wc = carrier freqA(t) = amplitudeø(t) = phase

The carrier can be modulated by using the baseband signal tovary one or more of the above parameters over a duration of T,the symbol period.Coherent modulation may be used when the receiver canexploit knowledge of the actual carrier phase.Noncoherent modulation is used when knowledge of theabsolute phase is unavailable.

Less complicated, but comes with a performance degradation.

ModulatorS(t)

fc reference fc

( )x

xsin


QPSK versus BPSK

BPSK modulation results in 1 symbol/Hz, where QPSKmodulation results in 2 symbols/Hz).

As a result, the spectrum of QPSK is narrower than that of BPSK.The mainlobe of QPSK is half the width of the BPSK spectrummainlobe.

The probabilities of bit error for BPSK and QPSK areequal, but QPSK can support twice the data rate thatBPSK can.Higher orders of PSK can be designed (8-PSK, 16-PSK,etc.), but there is a tradeoff (higher required power orhigher BER).


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 2 4 6 8 10 12Theoretical Required Eb/N0 for BER of 10 , dB

Req

uire

d R

F B

andw

idth

/ D

ata

Rat

e

BPSK, Uncoded

QPSK, Uncoded

QPSK, Rate 1/2 Coded

BPSK, Rate 1/2 Coded

-5

Comparison of Spectra for BPSK and QPSK for aGiven Data Rate

BPSK

QPSK

Twostates

forBPSK

1 0

BPSK 1 = 180 DEGREES 0 = 0 DEGREES Inphase and

Quadrature biphasesignals

QPSK: Delay Databy 90 degrees on 1channel

IQ

1a

0b

0a1b

Four statesfor QPSK

CodingGain

BandwidthDifference

CodingGain

BandwidthDifference


Noise Basics


Sources of System Noise

The presence of noise degrades the performance of a satellite linkThe noise present in a satellite communications system (often called the“system noise”) comes from many different sources

Some of it is injected via the antenna from external sourcesSome of the noise is generated internally by various receivercomponents

The noise which comes in through the antenna can be seen as randomnoise emissions from different sources, and it is also called the sky noise

Terrestrial sources such as lightning, radio emissions, and theatmosphereSolar radiationGalactic background (moon, stars, etc.)

The receiver-generated noise can be caused by various receivercomponents

Results from thermal noise caused by the motion of electrons in allconductorsThe principal components that generate noise are the active devicessuch as LNA and random noise stemming from passive elements, suchas the line from the antenna to the receiver


Noise Temperature of a Device

Noise temperature is a useful concept in communicationsreceivers, since it provides a way of determining howmuch thermal noise is generated by active and passivedevices in the receiving system

The physical noise temperature of a device, Tn, results in a noisepower of Pn = KTnBK = Boltzmann’s constant = 1.38 x 10-23 J/K; K in dBW = -228.6 dBW/KTn = Noise temperature of source in KelvinsB = Bandwidth of power measurement device in hertz

Because satellite communications systems work withweak signals, it is mandatory to reduce the noise in thereceiver as far as possible

Generally the receiver bandwidth is made just large enough topass the signal, in order to minimize noise power


The System Noise Temperature

To determine the performance of a receiving system, we must findthe total thermal noise against which the signal must bedemodulated.

The combination of all the noisy devices plus the antenna noise.This can be done by representing the receiver components asnoiseless devices with their individual gains and, at their inputs,noise sources with the same noise power as the original noisycomponents.

The next slide shows how this is done for an earth station receiver.It is then easy mathematically to combine all of the noise sourcesinto one noise source, located at the input of a noiseless receiver.

The noise temperature of this source, Ts, is called the system noisetemperature.

The total noise power can then be calculated easily, for linkbudget purposes, as Pn = KTsBG.

G is the total gain of the receiver.B is the bandwidth of interest.


Noise figure can also be used to specify the noise generatedwithin a deviceNF = (S/N)in/(S/N)out

The noise figure of a device is related to its noise temperatureby:Td = T0(NF - 1), where T0, the reference temperature, is usually 290° K (room

temperature)

NFdB = 3 dB; NF= 103/10= 2 Td = 290 (2-1) = 290° K

The receiver gain and the system noise temperature can becombined as a ratio, Gr/Ts, often just written as G/T

For example, if the receive antenna is 50 dBi and the system noisetemperature is 500° K , then Gr/Ts = 50-10log (500) ≅ 23.0 dB/° K

The G/T is often used as a figure of merit for an earth stationAs G/T goes up, so does the quality of the earth station

Noise Figure and the G/T Figure of Merit

RF AMP


The Calculation of System Noise Temperature(Cont’d)

Example:

LNA DEMODULATOR IF AMP RECEIVERTsky = 50°

3 dB

Loss = L

L1

∈=NFLNA = 3 dB = 2GLNA = 30 dB

Ts @ Reference Point

NFDC = 10 dB = 10GDC = 30 dB

NFIF = 10 dB = 10GIF = 30 dB

NFR = 10 dB = 10GR = 30 dB

System Noise Temperature ≡ Ts °K

( ) ( ) ( ) ( ) ...GG

T1NFG

T1NFT1NFT1TTDCLNA

oIF

LNA

oPCoLNAoskys +

−+

−+−+∈−+≈∈

( ) ( ) ...1000x10002901 10

10002901 10290)1 2(290)5.0 1()50(5.0 +

−+

−+−+−+≈

...0026.6.229014525 +++++≈

≈462 °K

5.01

10/ 310=∈= dB

To is reference temperature of each device = 290°K (assumed)


Components


Components of Interest

AntennasReceive & transmit RF (radio frequency) energySize/type selected directly related to frequency/required gain

360°0 dBi

Omni Antenna (idealized) Directional (Hi-Gain) AntennaGain Pattern

Side Lobes

Boresight

Peak Gain = X dBi

-3 dB Beamwidth

Gain is relative toisotropic with units ofdBi

Isotropic antenna

0

10

20

30

40

5060

708090100

110120

130

140

150

160

170

180

190

200

210

220

230240

250260 270 280

290300

310

320

330

340

350

Theta Cut

plot1mtheta

plot2mtheta

Three_dB 0

10

20

30

40

5060

708090100

110120

130

140

150

160

170

180

190

200

210

220

230240

250260 270 280

290300

310

320

330

340

350

Theta Cut

plot1mtheta

plot2mtheta

Three_dB

Omni Antenna (typical)


Components of Interest (Cont’d)

Antennas (cont’d)Polarization: the orientation of the electrical field vector;specifically, the figure traced as a function of time by theextremity of the vector at a fixed location in space, as observedalong the direction of propagationTo minimize polarization loss, the transmit and receive antennasshould have the same polarization.

Linear PolarizationVertical

Linear PolarizationHorizontal

Circular Polarization Left hand

Circular PolarizationRight hand



Filters & Diplexers

Diplexer

Receive fr

Transmit ft

fr (2106.4 MHz)

ft (2287.5 MHz)

A

f

BandPassFilter

A

ff1 f2

f1 – f2

Diplexer provides isolation between transmit & receive signals



Transmitters (modulators) & Receivers (demodulators)

Transponders & Transceivers

TransmitterOriginalSignal

f

ReceiverOriginalSignal

Diplexer

Transmitter

ReceiverTransponderMode Transceiver

Mode

Power Amplifier

TransmitterPower

AmplifierG = 13 dB

1 watt (0 dBW) 20 watt (13 dBW)

Switch

1/T 2/T 3/T 4/T 5/T 6/T 7/T1/T2/T3/T4/T5/T6/T7/T

A

fc1/T 2/T 3/T 4/T 5/T 6/T 7/T1/T2/T3/T4/T5/T6/T7/T

( )x

xsin

A

fc

( )x

xsin


Link Equation

For an isotropic antenna in free space conditions, the power suppliedto the antenna, PT, is uniformly distributed on the surface of a sphereof which the antenna is the centerThe power flux-density is the power radiated by the antenna in agiven direction at a sufficiently large distance, d, per unit of surfacearea is:

The power flux-density radiated in a given direction by antennahaving a gain, GT, in that direction is:

The equivalent isotropically radiated power (EIRP) = PT GT

The power received by an antenna with area AR is:

The gain of any antenna, for example GR, is:

distance d ;d4

P density flux Power2

T

i=

π=

d4AGP Apfd P

2

R T T

R R π==

fc λ;

λA4G

2

r

R=

π=

2

TT

d4GP(pfd) density flux Powerπ

=


Link Equation (Cont’d)

In general, dBdBRdBdBR (L))(G(EIRP))(P −+=

dBdBRdBdBR losses) all (Σ)(G(EIRP))(P −+=

GT

PT d

HypotheticalSphere

ReceivingAntenna

Area = AR

)derivation for backup (seeMHzf log 20 kmd log 20 32.44dB(L) Loss Path Space Free ++==

( ) ( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛ π==

π=

π=

π=

λd 4 2

L whereL

GEIRP λ

d 4G EIRP

λd 4

GGP d 4AGP P R

2R

2R T T

2R T T

R


The power received to noise density is related to the data rate by the energy per bitas follows:

The actual Eb/N0 can be compared to the required Eb/N0 to see how much “margin”the system contains.

If the margin is not high enough, or is less than 0 dB, then, using the link budget, a systemengineer can easily determine how the communication system needs to be improved toachieve the desired performance.

Link Equation

KT N density, spectral noise theLet o ≡

LossesKTG

EIRP NP Hz 1 in

noisepower the Then

r

o

r =≡ ( ) ( ) ( ) dBdBdB

rdB

dBo

r Losses - K - TG EIRP

NP

⎟⎠⎞

⎜⎝⎛+=⎟⎟

⎠

⎞⎜⎜⎝

⎛

R NE

NP

ro

b

ro

r⎟⎟⎠

⎞⎜⎜⎝

⎛=⎟⎟

⎠

⎞⎜⎜⎝

⎛

dBdBo

r

ro

b R - NP

NE

dB

⎟⎟⎠

⎞⎜⎜⎝

⎛=⎟⎟

⎠

⎞⎜⎜⎝

⎛

RateBit R = received Energy/bit NE

ro

b =⎟⎟⎠

⎞⎜⎜⎝

⎛

dB dReq'o

b

ro

b

NE

NE Margin

dB

⎟⎟⎠

⎞⎜⎜⎝

⎛−⎟⎟

⎠

⎞⎜⎜⎝

⎛=

dB dReq'o

b

NE

⎟⎟⎠

⎞⎜⎜⎝

⎛

where:

is related to BER (seetheoretical curves for givenmodulation and coding scheme)

where K = Boltzmann’s constant = 1.38 x 10-23 J/K; K in dBW = -228.6 dBW/K

T = system noise temperature in Kelvins


Link Budget Analysis

A link budget is an engineering tool for satellitecommunication systems, used to demonstrate and analyze linkperformance

Generally the desired end result is Bit Error Rate (BER), or the Eb/N0required to achieve a desired BER

Link performance is analyzed in terms of:Transmit powerAntenna parameters (e.g. gain)Received system noise levels (usually specified as noise temperature)Other factors (e.g. propagation losses, interference, intermodulation)

As for any budget, numbers are added and subtracted togetherin a table format, with the “bottom line” at the bottom

Factors that contribute to a higher Eb/N0 are added as positive numbers,like “credits”Factors that contribute to a lower Eb/N0 are added as negative numbers,like “debits”


Additional Losses on a Real Satellite Link

On an ideal link, the only power loss term would be thepath loss caused by the dispersion of the transmit powerover the transmitter-to-receiver range.For a real satellite communications link, many otherlosses need to be considered as well.

Polarization loss, caused by the a mismatch between thetransmitting and receiving antennas.Rain attenuation and atmospheric loss.The receiver implementation loss.Pointing loss, caused by imperfect pointing of the antennasMiscellaneous other losses.

In the link budget, these losses are sometimes listed asline items subtracted from the received power, but someof them may be combined in different ways.


Sample Link Budget (direct to ground)

Encoder& Transmitter

I = 75 MBPS

Q = 75 MBPS

LNA Receiver

Decoder

Loss = 1.13 dB

Gain = 4.84 dBi

SPACE

G/T = 33.3 dB/K

11mGroundAntenna

11.6 dBW 10.49 dBW EIRP = 15.31 dBW Hz dB 95.95oN

C=

data

I Q

dB 19.12roN

bE=⎟⎟

⎠

⎞⎜⎜⎝

⎛

dB 25.4D'REQoN

bE=⎟⎟

⎠

⎞⎜⎜⎝

⎛

Implementation Loss = 2.0 dB

MARGIN = 5.94 dB

Decoded Data

Σ Losses = 0.67 dB Polarization loss178.95 dB space loss @ 2575 KM and 5° elevation0.45 dB atmospheric loss1.2 dB rain loss

8212.5 MHz

QPSK

Alaska SAR Facility11 meter antenna


Example Link Budget (direct to ground)*** DOWNLINK MARGIN CALCULATION***

GSFC C.L.A.S.S. ANALYSIS #1 DATE & TIME: 4/ 1/99 10:13:39 PERFORMED BY: Y.WONG LINKID: EOS-AM/SGS FREQUENCY: 8212.5 MHz RANGE: 2575.0 km MODULATION: QPSK I CHANNEL Q CHANNEL --------- --------- DATA RATE: 75000.000 kbps DATA RATE: 75000.000 kbps CODING: RATE 1/2 CODED CODING: RATE 1/2 CODED BER: 1.00E-05 BER: 1.00E-05 99.95 AVAILABILITY GR EL=5 DEGREES PARAMETER VALUE REMARKS --------------------------------------------------------------------------------------------------------------------- 01. USER SPACECRAFT TRANSMITTER POWER - dBW 11.60 NOTE A; EOL 02. USER SPACECRAFT PASSIVE LOSS - dB 1.13 NOTE A 03. USER SPACECRAFT ANTENNA GAIN - dBi 4.84 NOTE A include multipath loss 04. USER SPACECRAFT POINTING LOSS - dB .00 NOTE A 05. USER SPACECRAFT EIRP - dBWi 15.31 1 - 2 + 3 - 4 06. POLARIZATION LOSS - dB .67 NOTE A 07. FREE SPACE LOSS - dB 178.95 NOTE B 08. ATMOSPHERIC LOSS - dB .45 NOTE B; EL: 5.0 DEG 09. RAIN ATTENUATION - dB 1.20 Include Scintillation loss 1.1 dB 10. MULTIPATH LOSS - dB .00 NOTE A 11. GROUND STATION G/T - dB/DEGREES-K 33.30 G/T with rain at 5 degrees 12. BOLTZMANN'S CONSTANT - dBW/(Hz*K) -228.60 CONSTANT 13. RECEIVED CARRIER TO NOISE DENSITY - dB/Hz 95.95 5 - 6 - 7 - 8 - 9 - 10 + 11 - 12 I CHANNEL Q CHANNEL --------- --------- 14. I-Q CHANNEL POWER SPLIT LOSS - dB 3.01 3.01 NOTE B; 1.00 TO 1.00 15. MODULATION LOSS - dB .20 .20 NOTE A 16. DATA RATE - dB-bps 78.75 78.75 NOTE A 17. DIFFERENTIAL ENCODING/DECODING LOSS - dB .20 .20 NOTE A 18. USER CONSTRAINT LOSS - dB 1.60 1.60 2 dB Includes diff encoding and modulation losses 19. RECEIVED Eb/No - dB 12.19 12.19 13 - 14 - 15 - 16 - 17 - 18 20. IMPLEMENTATION LOSS - dB 2.00 2.00 21. REQUIRED Eb/No - dB 4.25 4.25 I: NOTE B; Q: NOTE B 22. REQUIRED PERFORMANCE MARGIN - dB 3.00 3.00 NOTE A 23. MARGIN - dB 2.94 2.94 19 - 20 - 21 - 22 NOTE A: PARAMETER VALUE FROM USER PROJECT - SUBJECT TO CHANGE NOTE B: FROM CLASS ANALYSIS IF COMPUTED


TDRSS Return Link Power Received

For ease of calculation, TDRSS defines the relationshipbetween data rate and the signal power level receivedisotropically at TDRS (Prec) for a Bit Error Rate of 10-5

Ideal required Prec = RbdB + KFor rate 1/2 coded signals, assume: K = -221.8 (MA); -231.6 (SSA); -245.2(KuSA); -247.6 (KaSA)

Due to defining the Prec isotropically at TDRS, the predicted receivedpower is calculated the same as identified earlier (see Link Equationslide); however, GR is set to 1 (= 0 dB) for the isotropic antenna. (i.e.,Prec = Pr = GRGTPT(λ/4πR)2 Watts)

In dB, this can be expressed as PR = GR + GT + PT + 20Log(λ/4πR) dBW

Margin = Predicted Prec – Ideal Prec – Other LossesOther Losses are treated as debits and encompass items such aspolarization loss (mismatch of the transmit polarization with receivingpolarization), pointing loss (inability of transmit antenna to point toreceiving antenna), incompatibility loss, and interference degradation.


Example Simple TDRS Link Budget using PrecEquation

*** RETURN LINK CALCULATION -- NETWORK SYSTEMS ENGINEER ANALYSIS ***GSFC C.L.A.S.S. ANALYSIS #0 DATE & TIME: 03/03/03 10: 1:31 PERFORMED BY: R. BROCKDORFFUSERID: EOS-AM LINKID: KSA8L RELAY SYS.: TDRS-East TO STGT

SERVICE: FREQUENCY: DATA GROUP/MODE: POLAR: RANGE CASE: ALTITUDE: ELEVATION: RANGE: KuSA 15003.4 MHz DG-2 MODE-2A LCP MAXIMUM 710.6 Km 1.5 Deg 44592.7 Km---------------------------------------------------------------------------------------------------- I CHANNEL Q CHANNEL

DATA RATE = 75000.00 KBPS DATA RATE = 75000.00 KBPS MOD TYPE = QPSK MOD TYPE = QPSK SYMBL FMT = NRZ-M SYMBL FMT = NRZ-M RATE 1/2 CODED RATE 1/2 CODED

---------------------------------------------------------------------------------------------------- SPACE-SPACE LINK NOTES------------------------------------------------------ -------------------------------- 1 USER TRANSMIT POWER, dBW 12.00 User Provided Data 2 PASSIVE LOSS, dB 1.80 User Provided Data 3 USER ANTENNA GAIN, dBi 44.30 User Provided Data 4 POINTING LOSS, dB 2.20 User Provided Data 5 USER EIRP, dBW 52.30 (1)-(2)+(3)-(4) 6 SPACE LOSS, dB 208.95 CLASS Analysis 7 ATMOSPHERIC LOSS, dB 0.00 Not Considered 8 MULTIPATH LOSS, dB 0.00 Not Considered 9 POLARIZATION LOSS, dB 0.10 User Provided Data10 SSL RAIN ATTENUATION, dB 0.00 User Provided Data11 Prec AT INPUT TO TDRS, dBW -156.75 (5)-(6)-(7)-(8)-(9)-(10)12 Required Prec AT INPUT TO TDRS, dBW -163.44 -245.2 + 10*log (Data Rate)13 DYNAMICS LOSS, dB 0.00 Not Considered14 USER CONSTRAINT LOSS, dB 0.00 CLASS Analysis15 RFI LOSS, dB 0.00 CLASS Analysis16 MARGIN, dB 6.69 (11)-(12)-(13)-(14)-(15)

• Slight difference in simplified link budget vs detailed link budget due to exactcustomer configuration and space-to-ground link effects


Sample Link budget (thru TDRS)

Encoder& Transmitter

I = 75 MBPS

Q = 75 MBPS Gain = 44.30 dBi

Space

12 dBW 10.2 dBW EIRP = 52.30 dBW

15003.4 MHz

QPSK

Receiver

Decoder

data

Decoded Data

LNA

Space Ground Link

QPSK

I = 150 Msps Q = 150 Msps

Prec is defined here for a unity gainantenna and BER = 10-5

Predicted Prec = -156.75 dBWIdeal Required Prec = -163.44 dBWMargin = 6.69 dB

Loss = 1.8 dBLoss = 2.2 dB

Σ Losses = 0.10 dB Polarization loss208.95 dB space loss @ 44592.7 KM and 1.5° elevation

Transparent tothe link budgetwhen using theideal Precequation

Note: Significantly more EIRP needed ascompared to a direct downlink(52.3 vs. 15.31 dBW)


Geometric Coverage (Ground)Florida ground station with spacecraft altitudes 400, 800, and 1200 km

400 km

800 km

1200 km

Merritt Island

Elevation angle is the angle between local horizontal at ground station and spacecraft


Geometric Coverage (Ground)

Merritt IslandGround station elevation angles of 0, 10, and 20 degrees

El = 0O

El = 10O

El = 20O



Building

Antennalimits

Anotherantenna

Effects of terrain and antenna limitationsElevation angel = 0°

Merritt Island

Spacecraft altitude = 1200 km



SvalbardLocation

Coverage circle for Svalbard at a spacecraft altitude of 400 km

0° elevation angel


Geometric Coverage (Ground)Spacecraft Orbit of 400 KM, 65 deg inc circular

Hawaii (HAW3), Alaska (AGIS), Wallops Island (WPSA), Svalbard (SGIS), McMurdo (MCMS)

Svalbard

AGIS

WPSA

MCMS

HAW3


Geometric Coverage (Ground)Spacecraft Orbit of 400 KM, 98 deg inc circular

Hawaii (HAW3), Alaska (AGIS), Wallops Island (WPSA), Svalbard (SGIS), McMurdo (MCMS)

AGIS

WPSA

HAW3


Geometric Coverage (TDRS)

Spacecraft height = 500 km

Synsat location

Coverage

No coverage

Synchronous Satellite Coverage at 319 deg long


TDRS Basics


NASA’s Tracking and Data Relay Satellite (TDRS)

The TDRSs are in geosynchronous orbit at allocated longitudesA geostationary satellite is in a circular orbit parallel to and 35786.43 km above theequator with an angular velocity that matches that of the earth.

It hovers above a fixed point on the equator and therefore appears to be motionless.A geosynchronous satellite has the same orbit period as a geostationary satellite,but its orbit may be elliptical and inclined.

A geosynchronous satellite in an inclined circular orbit moves in a figure-8 pattern as viewed fromearth.To maintain a geosynchronous orbit, a satellite must periodically make east-west corrections or itwill drift in longitude.

The TDRSs, along with supporting ground systems, make up NASA’sSpace Network.The Space Network was established to act as a bent-pipe relay (i.e.,repeater) and dramatically increase coverage to low earth orbitingsatellites as compared to a worldwide network of ground stations.

The SN dramatically increased tracking and data acquisition (T&DA) coverage from15% to 85% per orbit of low earth orbiting spacecraft as well as decreasedoperational costs (see coverage slides for depiction).

Requires ~ 30 dB additional EIRP vs direct to groundToday, 100% line-of-sight coverage can be provided to LEO customers.

Use of 2 TDRS constellation has a Zone of Exclusion (ZOE)Use of 3 TDRS constellation does not have ZOE


TDRSS Constellation

F-5174°WTDW

F-7171°W

(in storage)

F-1049°W

F-6047°WTDS

F-4041°WTDE

F-3275°WTDZ

WHITE SANDSCOMPLEX

GUAM REMOTE GROUND TERMINAL

TDRS-8170.7°W

TDRS-I149.5°W

McMurdo Ground StationMcMurdo TDRS Relay System

(McMurdo, Antarctica)

TDRS-J150°W


TDRSS FIELDS OF VIEW

WHITESANDSCOMPLEX

0/360180W

GUAM

-180W

174° TDW 94°

121°321°

41° TDE

127° 47° TDS 327°

254°TDW

275° TDZ

355° 195°

TDRS VIEWS BASED ON 600KM USER ALTITUDE ATTHE EQUATOR

91°171° F-7

251° F-7


TDRSS Ground Segment

TWO FUNCTIONALLY IDENTICAL,GEOGRAPHICALLY SEPARATED GROUNDTERMINALS AT THE WHITE SANDS TESTFACILITY

THE WHITE SANDS COMPLEX (WSC) HASFIVE SPACE TO GROUND LINKTERMINALS (SGLTs)

A SIXTH SGLT HAS BEEN INSTALLED ATTHE REMOTE GROUND TERMINAL ONGUAM AS AN EXTENDED WSC SGLT

DATA SERVICES MANAGEMENT CENTER

OPERATIONAL HUB LOCATED AT WSCFOR COORDINATING ALL SPACENETWORK ACTIVITIES BETWEENCUSTOMERS AND SN


Space Segment: Tracking and Data RelaySatellite (F1 - F7)

• Forward (FWD): link from TDRSS Ground Station through TDRS to Customer Spacecraft• Return (RTN): link from Customer Spacecraft through TDRS to TDRSS Ground Station

Single Access AntennaDual frequency communications

and tracking functions: S-band TDRSS (SSA) K-band TDRSS (KSA) K-band auto-tracking

4.9 meter shaped reflector assemblySA equipment compartment

mounted behind reflectorTwo axis gimballing

Space-to-Ground-Link AntennaTDRS downlink2.0 meter parabolic reflectorDual orthogonal linear polarization TDRS:

single horn feedorthomode transducer

Two axis gimballed

Omni Antenna (S-band) and Solar Sail

Multiple Access Antenna30 helices:

12 diplexers for transmit30 receive body mounted

Single commanded beam, transmit20 adapted beams for receiveGround implemented receive function

Solar arrayPower output isapproximately 1800watts


Multiple Access (MA) vs Single Access (SA)

Multiple Access (MA):Fixed S-band frequency (2106.4 MHz fwd and 2287.5 MHz rtn)Fixed polarization (left hand circular)Low data rate (<= 300 kbps)Forward service operations are time-shared amongst customersReturn service supports multiple customers simultaneously(lower service cost to customer vs SA)

Phased array antenna and beamforming equipment allow for spatial discrimination betweencustomers; PN spreading provides additional discrimination

Return Demand Access Service allows customers to have a dedicated return linkcontinuously (lower service cost to customer)

Single Access (SA):Multiple frequency bands (S-band, Ku-band, Ka-band)

S-band: selectable frequency (2025.8 – 2117.9 MHz fwd; 2200-2300 MHz rtn)Ku-band: fixed frequency (13775 MHz fwd; 15003.4 MHz rtn)Ka-band: selectable frequency (22550-23550 MHz fwd; 25250-27500 MHz rtn)S-band and K-band simultaneously

Selectable polarization (left or right hand circular)High data rate (up to 300 Mbps)Forward service operations are time-shared amongst customersReturn service operations are time-shared amongst customers (higher service costto customer vs MA)


Data Rates Associated with Space Network Services

3. For customer data configurations, see 450-SNUG, Space Network Users’ Guide4. Current WSC configuration supports 7 Mbps5. Guam Remote Ground Terminal (GRGT) is not currently configured to support TDRS F8-F106. F8 may experience lower G/T performance less than 12 hrs per day

Service WSC & TDRS F1-F7 Capabilities(3) WSC & TDRS F8-F10 Capabilities

Forward Up to 7MBps; EIRP = 43.6 dBW (normal); 48.5dBW (high)

Up to 7 MBps; EIRP = 43.6 dBW (normal); 48.5dBW (high)

Return Up to 6 Mbps; G/T (min) = 9.0 dB/K Up to 6 Mbps; G/T (min) = 9.0 dB/K

Forward Up to 25 Mbps(4); Autotrack EIRP = 46.5 dBW(normal); 48.5 dBW (high)

Up to 25 Mbps(4); Autotrack EIRP = 46.5 dBW(normal); 48.5 dBW (high)

Return Up to 300 Mbps; Autotrack G/T = 24.4 dB/K Up to 300 Mbps; Autotrack G/T = 24.4 dB/K

Forward N/A Up to 25 Mbps(5); Autotrack EIRP = 63 dBW

Return N/A Up to 300 Mbps/800 Mbps(1);Autotrack G/T = 26.5 dB/K

Number of Single Access LinksSSA: 2/TDRS; 10/WSC; 2/GRGTKuSA: 2/TDRS; 10 KuSA/WSC; 2/GRGT

SSA: 2/TDRS; 10/WSC; 2/GRGT(5)

KuSA: 2/TDRS (2); 10/WSC; 2/GRGT(5)

KaSA: 2/TDRS (2); 8/WSC(5)

Multiple Access

Forward 1/TDRS @ up to 300 kbps; 4/WSC; 1/GRGTEIRP = 34 dBW

1/TDRS @ up to 300 kbps; 4/WSC(5)

EIRP = 42 dBW (LEOFOV)

Return 5/TDRS @ up to 300 kbps; 20/WSC; 2/GRGT;Formed Beam G/T= 3.1 dB/K (Does not includeDAS)

5/TDRS @ up to 3 Mbps; 20/WSC(5)

G/T = 4.5 dB/K (LEOFOV) (6)

User Tracking Range, 1&2 way Doppler Range, 1&2 way Doppler(No Ka-band Tracking)

1. Spacecraft only2. The SN can simultaneously support S-band or Ku/Ka-band (F8-

F10 only) forward and/or return services through 1 SA antenna tothe same ephemeris. F8-F10 cannot simultaneously supportKu/Ka-band services through 1 SA antenna.

S-Band

SingleAccess

Ku-Band

Ka-Band

Notes:


Spectrum Management


Purpose of Spectrum Management

Ensure that the system in which time and money hasbeen invested to develop provides the required quality ofservice (i.e., Bit Error Rate) when it is deployed orinstalled.

Apply order to the use of the orbit/spectrum resource.

Provide technical bases for coordination.

Ensure that systems operate as intended.

Promote the efficient use of the radio frequency spectrum.

Accommodate new services, applications and technology.


Frequency Allocations

The radio frequency spectrum is a national andinternational resource whose use is governed by Federalstatutes and international treaty.

Internationally: The International Telecommunication Union(ITU), which is a specialized agency of the United Nations, acts asthe global spectrum coordinator and develops bindinginternational treaty governing the use of the radio spectrum bysome 40 different services around the world.

The Radio Regulations contain a number of provisions governing the waythe radio frequency spectrum is to be used.

Nationally (within the US): responsibility is broken into 2 areas:National Telecommunications and Information Agency (NTIA) manages theGovernment spectrumFederal Communications Commission (FCC) manages the non-government spectrum

The international and national Table of Allocations shows whatsegments of the radio frequency spectrum are to be used bywhich services.


Spectrum Allocations Available to NASA LEOMissions for Telecommunications

Band Ground Network Space NetworkLink/Frequency Allocated Services Link/Frequency Allocated ServicesUplink:2025-2110 MHz

Primary: Space Operation, EarthExploration-Satellite,Space Research

Forward Link:2025-2110 MHz

Primary: Space Operation,Earth Exploration-Satellite,Space Research

S-band

Downlink:2200-2290 MHz


Return Link:2200-2290 MHz


Uplink:7190-7235 MHz

Primary: Space Research (non-deepspace)

Forward Link: N/A No AllocationX-band

Downlink:8025-8400 MHz;8450-8500 MHz

Primary:Earth Exploration-Satellite(8025-8400 MHz)Space Research (8450-8500 MHz)

Return Link: N/A No Allocation

Uplink: N/A No Allocation Forward Link:13.75-14.0 GHz

Primary with Fixed-SatelliteService: Space Research (note)Secondary with all other services:Space Research

Ku-band

Downlink: N/A No Allocation Return Link:14.8-15.35 GHz

Secondary: Space Research

Uplink: N/A No Allocation Forward Link:22.55-23.55 GHz

Primary: Inter-SatelliteKa-band

Downlink:25.5-27 GHz

Primary: Earth Exploration-Satellite Return Link:25.25-27.5 GHz

Primary: Inter-Satellite

Note: In the band 13.75 –14.0 GHz geostationary space stations in the space research service, for which information for advancepublication has been received by the IFRB prior to 31 January 1992, shall operate on an equal basis with stations in the fixed satelliteservice; new geostationary space stations in the space research service advanced published after that date will operate on a secondarybasis.


Background Material


References

“Digital Communications,” Bernard Sklar“Antennas,” J.D. Ravs“Space Network Users’ Guide,” Rev. 8, June 2002,http://gdms.gsfc.nasa.gov/

Sign on as GuestSelect CCMSSelect Document LibrarySelect Code 450

“Error Bounds for Convolutional Codes and Asymmetrically OptimumDecoding Algorithum,” A.J. Viterbi, IEEE Trans information Theory,Vol. IT13, April 1967, pp 260-169“Principles of Digital Communications and Coding,” A.J. Viterbi andJ.K. Omura“Ground Network Users’ Guide,” February 2001,http://www.wff.nasa.gov/~code452/“Digital Communications,” Kamilo FeherConsultative Committee for Space Data Systems (CCSDS)http://www.CCSDS.ORG


Compression: Lossy versus Lossless Compression

A lossless compression technique means that therestored data file is identical to the original.

This is necessary for many types of data, like executable code,word processing files, etc.GIF images are examples of lossless compressed files.

On the other hand, data files that represent images,among others, do not have to be kept in perfect condition.

A lossy compression technique allows a small level of noisydegradation to the original data.Lossy techniques are much more effective at compression thanlossless methods: for a digital image, JPEG can achieve a 12-to-1compression ratio, as opposed to a 2-to-1 ratio for GIF.


Link Equation: Pr/N0 for Cascaded Links

Often a satellite communications link will consist of more thanone point-to-point path.

For example, a satellite at low earth orbit often will send its data up to asatellite at high earth orbit, which will then relay the data down to aground station.

For a two-path system, the total Pr/N0 can be found as:

As an example, if a link has uplink Pr/N0 of 60 dB-Hz and adownlink Pr/N0 of 60 dB-Hz, then the overall Pr/N0 is 57 dB-Hz.Sometimes either the uplink or the downlink will be much morehigh powered than the other.

In this case, the total Pr/N0 will be almost identical to that of the weakerlink, and the link budget for the stronger link need not even be done atall.

Down0rUp0r

Total0r

)/N(P1

)/N(P1

1)/N(P+

=


Link Equation: Geometric Coverage (TDRS)TDRSS Satellite System: Areas of non coverage


Space Segment: Tracking and Data Relay Satellites

TDRSSGroundStation

TDRSSGroundStation

NASA andCustomerGround

Operations

NASA andCustomerGround

Operations

Space-Space Link

Fwd: 2.025-2.120 GHz (S-band)

2.1064 GHz (MA)13.775 GHz (Ku-band)22.55-23.55 GHz (Ka-band)

Fwd: 2.025-2.120 GHz (S-band)


Space-Space Link

Fwd: 2.025-2.120 GHz (S-band)


Fwd: 2.025-2.120 GHz (S-band)


Space-Ground Link

Fwd: 14.6-15.225GHz

Rtn: 13.4-14.05 GHz

Space-Ground Link

Fwd: 14.6-15.225GHz

Rtn: 13.4-14.05 GHz

1 of 2 Single Access (SA) AntennasS & Ku-Band for F1-F7S, Ku, & Ka-Band for F8-F10

Field of View (Primary): ±22° E-W, ±28.0° N-SExtended FOV (HIJ only): ±76.8° E-W*, ±30.5° N-S**

S-Band Phased – Array forMultiple-Access (MA) Service

1 Fwd, 5 Rtn Links for F1-F7*** 1 Fwd, 5 Rtn Links for F8-F10

Field of View (Primary): ±13° conical

RTNLink

FWDLink

CustomerSpacecraft

* - 76.8° outboard** - 24°E-W (inboard)*** - Demand Access Service allows large expansion on the number of non-coherent return link services available through F1 – F7

Primary site atWhite Sands, NM- STGT- WSGTUAdditional site atGuam to supportTDRS at 85E- GRGT

Primary site atWhite Sands, NM- STGT- WSGTUAdditional site atGuam to supportTDRS at 85E- GRGT

Satellite RF Fundamentals

Spectrum: Available Allocations for theGround Network and/or the Space Network

Only bands that support boththe Ground Network (GN) andthe Space Network (SN) on aprimary basis.Basic capabilities of theGround Network at S-band are:

Command rates to 32 kbps(note)Telemetry and mission datarates to 10 Mbps (note)Support available fromselected sites worldwide

Basic capabilities of the SpaceNetwork at S-band are:

Command rates to 300 kbpsPN spreadTelemetry and mission datarates to 6 MbpsVirtually global support.

Efforts to control the inter-service interference are under-way within the ITU-R.

S-bandS-band

Note: Maximum support data rate is dependent on the particularground station capabilities

MHz

2 010 – 2 170

Allocation to Services

Region 1 Region 2 Region 3

2 010 – 2 025

FIXED

MOBILE

2 010 – 2 025

FIXED

MOBILE

MOBILE-SATELLITE(Earth-to-space)

2 010 – 2 025

FIXED

MOBILE

S5.388S5.388 S5.389C S5.389DS5.389E S5.390 S5.388

2 025 – 2 110 SPACE OPERATION (Earth-to-space) (space-to-space)

EARTH EXPLORATION-SATELLITE(Earth-to-space) (space-to-space)

FIXED

MOBILE S5.391

SPACE RESEARCH (Earth-to-space) (space-to-space)

S5.392

2 110 – 2 120 FIXED

MOBILE

SPACE RESEARCH (deep space) (Earth-to-space)

S5.388

2 120 – 2 160

FIXED

MOBILE

S5.388

2 120 – 2 160

FIXED

MOBILE

Mobile-Satellite(space-to-Earth)

S5.388

2 120 – 2 160

FIXED

MOBILE

S5.388

2 160 – 2 170

FIXED

MOBILE

S5.388 S5.392A

2 160 – 2 170

FIXED

MOBILE

MOBILE-SATELLITE(space-to-Earth)

S5.388 S5.389C S5.389DS5.389E S5.390

2 160 – 2 170

FIXED

MOBILE

S5.388

MHz

2 170 – 2 450



2 170 – 2 200 FIXED

MOBILE

MOBILE-SATELLITE (space-to-Earth)

S5.388 S5.389A S5.389F S5.392A

2 200 – 2 290 SPACE OPERATION (space-to-Earth) (space-to-space)

EARTH EXPLORATION-SATELLITE(space-to-Earth) (space-to-space)

FIXED

MOBILE S5.391

SPACE RESEARCH (space-to-Earth) (space-to-space)

S5.392

2 290 – 2 300 FIXED

MOBILE except aeronautical mobile

SPACE RESEARCH (deep space) (space-to-Earth)

2 300 – 2 450

FIXED

MOBILE

Amateur

Radiolocation

S5.150 S5.282 S5.395

2 300 – 2 450

FIXED

MOBILE

RADIOLOCATION

Amateur

S5.150 S5.282 S5.393 S5.394 S5.396


Bands only support GroundNetwork operations on a primarybasisThe 7190-7235 MHz band may beused to command subject to theearth station being coordinatedwith terrestrial systems operatingin the bands that might experienceinterference.The 8025-8400 MHz and 8450-8500MHz bands may be used fortransmissions in the space-Earthdirection.Basic capabilities of the GroundNetwork at X-band are:

Telemetry and mission data ratesto 150 Mbps (note)

X-bandX-bandS5.460 Additional allocation: the band 7 145 - 7 235 MHz is alsoallocated to the space research (Earth-to-space) service on a primarybasis, subject to agreement obtained under No. S9.21. The use of theband 7 145 -7 190 MHz is restricted to deep space; no emissions todeep space shall be effected in the band 7 190 - 7 235 MHz.

MHz8 175-8 750



8 175-8 215 EARTH EXPLORATION-SATELLITE (space-to-Earth)

FIXED

FIXED-SATELLITE (Earth-to-space)

METEOROLOGICAL-SATELLITE (Earth-to-space)

MOBILE

S5.462A S5.463

8 215-8 400 EARTH EXPLORATION-SATELLITE (space-to-Earth)

FIXED

FIXED-SATELLITE (Earth-to-space)

MOBILE

S5.462A S5.463

8 400 – 8 500 FIXED

MOBILE except aeronautical mobile

SPACE RESEARCH (space-to-Earth) S5.465 S5.466

S5.467

8 500-8 550 RADIOLOCATION

S5.468 S5.469

8 550-8 650 EARTH EXPLORATION-SATELLITE (active)

RADIOLOCATION

SPACE RESEARCH (active)

S5.468 S5.469 S5.469A

8 650-8 750 RADIOLOCATION

S5.468 S5.469

Note: Maximum support data rate is dependent on the particular ground stationcapabilities

Spectrum: Available Allocations for the GroundNetwork and/or the Space Network


Bands only support SpaceNetwork Operations (13.775 GHzforward/15.0034 GHz return) ona secondary basisFor TDRSS advancedpublications received prior toJanuary 31 1992, the 13.775 GHzforward link operates on aprimary basis with respect tothe Fixed-Satellite Service (E-S).Basic capabilities of the SpaceNetwork at Ku-band are:

Forward link will support up to25 Mbps.Return link will support up to300 Mbps.Virtually global support.

Ku-bandKu-bandGHz

12.5-14.25



13.75-14 FIXED-SATELLITE (Earth-to-space) S5.484A

RADIOLOCATION

Standard Frequency and Time Signal-Satellite(Earth-to-space)

Space Research

S5.499 S5.500 S5.501 S5.502 S5.503 S5.503A

14-14.25 FIXED-SATELLITE (Earth-to-space) S5.484A S5.506

RADIONAVIGATION S5.504

Mobile-Satellite (Earth-to-space)except aeronautical mobile-satellite

Space Research

S5.505

GHz

14.8 – 17.3



14.8 – 15.35 FIXED

MOBILE

Space Research

S5.339

15.35 – 15.4 EARTH EXPLORATION-SATELLITE (passive)

RADIO ASTRONOMY

SPACE RESEARCH (passive)

S5.340 S5.511



The pair of Ka-band allocations(22.55-23.55 GHz and 25.25-27.5GHz) support only the SpaceNetwork on a primary basis.The 25.5-27 GHz band isavailable globally on a primarybasis for S-E transmissions fromEarth-exploration satellites.Basic capabilities of the SpaceNetwork at Ka-band are:

Forward links in the 22.55-23.55GHz band will support datarates up to 25 Mbps.Return links in the 25.25-27.5GHz band will support datarates up to 300/800 Mbps (note)

Ka-bandKa-band

Note: Capable of supporting 800 Mbps with upgrades to the TDRSS ground stations

GHz

22.55 – 23.55



22.55 – 23.55 FIXED

INTER-SATELLITE

MOBILE

S5.149

GHz

25.25 – 28.5



25.25 – 25.5 FIXED

INTER-SATELLITE S5.536

MOBILE

Standard Frequency and Time Signal-Satellite(Earth-to-space)

25.5-27 EARTH EXPLORATION-SATELLITE (space-to Earth)S5.536A S5.536BFIXEDINTER-SATELLITE S5.536MOBILEStandard Frequency and Time Signal-Satellite(Earth-to-space)

27.5-28.5 FIXEDFIXED-SATELLITE (Earth-to-space) S5.484A S5.539MOBILE

S5.538 S5.540



Spectrum: Definition of Spectrum Allocations

Space Research Service: A radiocommunication service in which spacecraft orother objects in space are used for scientific or technological research purposes.Space Operation Service: A radiocommunication service concerned exclusivelywith the operation of spacecraft, in particular space tracking, space telemetry andspace telecommand.Earth Exploration-Satellite Service: A radiocommunication service between earthstations and one or more space stations, which may include links between spacestations, in which:

information relating to the characteristics of the Earth and its natural phenomena, including datarelating to the state of the environment, is obtained from active sensors or passive sensors on Earthsatellites;similar information is collected from airborne or Earth-based platforms;such information may be distributed to earth stations within the system concerned;platform interrogation may be included.This service may also include feeder links necessary for its operation.

Meteorological-Satellite Service: An earth exploration-satellite service formeteorological purposes.Inter-Satellite Service: A radiocommunication service providing links betweenartificial satellites.

Documents

Satellite Comm Fundamentals