Wireless Technologies Review: Satellite RF Fundamentals

1
Wireless Technologies ReviewSatellite RF
Fundamentals
2
Announcements

• Class web site http//teal.gmu.edu/coursepages.htm
  and click on TCOM 690 sect 3or go directly
  tohttp//teal.gmu.edu/ececourses/tcom690/fall2003
  /sect3/TCOM690-3-fall03.htm
• Email ebonilla_at_gmu.edu
• Open your GMU email account
• Make sure I have your correct email address
• Question of the Day What is the most important
  quality or asset that you bring to your clients
  and/or employer as a telecommunications
  professional?

3
Objectives

• Review fundamental concepts of wireless
  communications.
• Provide basics of RF communications related to
  the operation of spacecraft.
• Information provided will allow you to understand
  and perform an RF link calculation.
• Enable you to do basic link calculations for the
  course project.

4
Satellite RF Communications Architecture
5
Subsystems of Satellite RF Communications
AtmosphericLoss,Rain Loss
PointingLoss
SpaceLoss
PolarizationLoss
PointingLoss
Transmitter
Receiver
SPACECHANNEL
Galactic, Star,Terrestrial Noise
Antenna
Antenna
Power Amplifier
Receiver Noise
Receiver
Transmitter
ImplementationLoss
Modulator
Demodulator
Information Source
Information Sink
Satellite transmitter-to-receiver link with
typical loss and noise sources
6
Definitions Some Basics

• dB 10 log10 (x) x is usually a power ratio
• dBW ? 10 log10 (watts)
• For 100 watts dBW 10 log10 (100) 20 dBW
• dBm ? 10 log10 (milliwatts)
• For 100 watts dBm 10 log10 (100000) 50 dBm
• Carrier Frequency
• Units are Hz
• MHz Hz x 106
• GHz Hz x 10 9
• Frequency Bands (of interest)
• S-Band 2-3 GHz
• X-Band 7-8 GHz
• Ku-Band 13-15 GHz
• Ka-Band 23-28 GHz

7
Logarithmic Scale
dBW
dBm
20 dBW
50 dBm
100 Watts
Always a 30 dB difference between dBm and dBW
13 dBW
43 dBm
20 Watts
10 dBW
40 dBm
10 Watts
0 dBW (Ref)
30 dBm
1 Watts
-10 dBW
20 dBm
0.1 Watts
-30 dBW
0 dBm (Ref)
0.001 Watts(1 milliwatt)
-40 dBW
-10 dBm
0.0001 Watts
A power below the reference level has negative
value, for either dBm or dBW
8
What is Doppler Doppler Rate?
B
A
C
AOS
LOS
ORBIT
EARTH
Doppler Rate
Doppler Shift
? f
C
A
B
Nominal (at-rest) frequency
- ? f
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
Doppler shifts become greater as the frequencies
become higher.
where as rate of change of Vs acceleration
9
Doppler Doppler Rate

• Phase lock loops
• Enable receiving tracking of Doppler shifted
  signals
• Used in virtually all spacecraft ground station
  designs to accommodate dynamic frequency changes

Error Signal
Phase Frequency Comparer
Input Signal Doppler
Low PassFilter
FilteredErrorSignal
VoltageControlledOscillator
10
Analog and Digital Data
11
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

Volts
7
6
5
4
time
Binary 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1
0 1 1 1 0 1 1 1
Analog 0 1 2 3 4 5 6 7
12
Analog and Digital Data

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

Volts
Analog Signal
t
Sampling Rate ? Nyquist rate (? 2 fmax) fmax
max frequency component of the original signal
Digital Sampling
t
Digital Bit Stream
t
13
Spectra Basics
14
Spectra (Baseband Signals)
Frequency Domain
Time Domain
A
Amplitude
V(t) Asin2?ft
t
Hz
Period T
15
Spectra (Modulated Signal)

• Given an arbitrary modulating signal M(t)an
  arbitrary carrier signal cos 2?fctthen the
  modulated signal V(t) ? M(t) cos 2?fct
• Find The Fourier transform of V(t)
• using the identity
• Then
• Then The Fourier transform of V(t) V(f)

A
M(0)
f
fm
-fm
0
½ M(0)
½ M(0)
f
-fc
0
fc
16
Coding/Spreading/Data Compression
17
The Effects of Channel Noise

• In digital communications, raw data is put into
  the form of bits, 1s and 0s.
• A carrier signal is modulated using this raw data
  for convenient transmission over the channel.
• The carrier signal is subject to noise corruption
  in the channel, sometimes making it impossible to
  reconstruct the raw bits at the receiver.
• If a transmitted bit is received as its opposite
  (e.g., a 1 received as a 0 or vice versa), then a
  bit error has occurred.
• This results in a progressive loss of information
  at the receiver as the number of mistranslated
  bits grows.

18
BER and Eb/No

• The rate at which bits are corrupted beyond the
  capacity to reconstruct them is called the BER
  (Bit Error Rate).
• A BER of less than 1 in 100,000 bits is generally
  desired for an average satellite communications
  channel (also referred to as a BER 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 the Bit Energy-to-Noise Density ratio.
• Since the noise density present on the channel is
  difficult to control, this basically means that
  BER can be reduced through using a higher powered
  signal, or by controlling other parameters to
  increase the energy transmitted per bit.
• As the following chart shows, the BER will
  decrease (i.e., fewer errors) if the Eb/No
  increases.

19
Higher Eb/No Reduces the BER
BER Versus Eb/No
10-3
Some ways of Increasing Eb/No
10-4

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

BER
10-5
These methods can be expensive
10-6
Eb/No
lower
higher
20
Another Strategy to Reduce BER
BER Versus Eb/No
10-3
Another strategy is to shift the whole curve over
to the left
10-4
This change in performance can be achieved by
using Error Correction Coding
Now the same BER can be achieved using a lower
Eb/No
BER
10-5
Less expensive method of mitigating channel noise
10-6
Eb/No
lower
higher
21
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 for retransmission.
• There are times when retransmission of the
  message is not practical.
• If a spacecraft is transmitting a playback dump
  of a storage device while making a short pass
  over a ground station, it may not have time to
  stop the transmission and retransmit in a short
  enough time.
• An error detecting/correcting code, on the other
  hand, has the ability to detect a defined number
  of errors and correct them for a prescribed
  environment that caused the errors, which is
  commonly called Forward Error Correction (FEC).
• Usually, for a given code, more errors can be
  detected than can actually be corrected.

22
Error Correction Codes

• Error control coding aims to correct errors
  caused by noise and interference in a digital
  communications scheme.
• In error control coding, the information bits are
  represented as another sequence of bits, also
  called coded symbols this new sequence is sent
  over the channel.
• This new sequence will use redundant information,
  often called parity bits, to provide error
  protection (e.g., send a 0 as 00000 and a 1 as
  11111).
• Now individual bit errors will not necessarily
  result in the incorrect decoding of the original
  information bits.
• For instance, if 1 or 2 of the five 0s sent
  over the channel in the above example are
  interpreted as 1s at the receiver, the original
  0 can still be decoded correctly if one makes a
  final decision based on the majority of the
  received coded symbols.

23
Types of Error Correction Codes

• A rate 1/2 convolutional code, an example of one
  family of codes, is often used 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 the advantage of smaller bandwidth
  expansion and also has the capability to indicate
  the presence of uncorrectable errors.
• Provides improved performance in a bursty noise
  environment
• Overhead approximately 12
• Where a greater coding gain is needed than can be
  provided by the convolutional code or the
  Reed-Solomon code alone, the two codes are often
  concatenated to provide a higher error-correction
  performance.
• One code serves as the outer code, one as the
  inner code

24
Typical Encoded Link
BasebandSignal
RFSignal
Data symbols 1.12 Msps
Data symbols 2.24 Msps
Data Bits 1 Mbps
Rate ½ Convolutional Encoder
Modulator Transmitter
R/SEncoder
LNA
fc
Antenna
Antenna
Receiver
Data symbols 2.24 Msps
Convolutional Decoder
2 MHz
Data symbols 1.12 Msps
R/SDecoder
Note Coding increases the bandwidth of the
baseband RF signal
Data Bits 1 Mbps(with some errors)
25
Example Error Correcting Performance

• For a BER of 10-5, Theoretical Required Eb/N0 is
  as follows
• Uncoded PSK 9.6 dB
• Reed-Solomon (R-S) Coding 6.0 dB
• Convolutional Coding (7,1/2) PSK 4.4 dB
• Convolutional R-S (no R-S interleave) 3.0
  dB
• Convolutional R-S (ideal R-S interleave)
  2.4 dB
• (7,1/2), where rate 1/2 indicates that for every
  1 bit into the encoder 2 symbols are output of
  the encoder and 7 is the number of shift
  registers used to generate the output symbol of
  the encoder.
• Interleaving takes adjacent bits and separates
  them to help protect from interference.

26
Data Compression

• Data transmission and storage cost money.
• Despite this, digital data are generally stored
  in efficient ways such as ASCII text or binary
  code.
• These encoding methods require data files about
  twice as large as actually needed to represent
  the information.
• Data compression is the general term for the
  various algorithms and programs developed to
  address this problem.
• A compression program converts data from an
  easy-to-use format for one optimized for
  compactness. Basically it discards redundant
  data with a prescribed algorithm.
• An uncompression program returns the information
  to its original form.
• As an example of compression, a fax device
  compresses the data before it sends it to reduce
  the time needed to transmit the document.
• This can reduce the cost of transmission 10 or
  more times.
• Compression will be required for the Design
  Project Problem.

27
Spread Spectrum Definition

• Spread Spectrum (SS) was developed originally as
  an anti-jamming technique.
• A jamming signal is a narrowband, high power
  signal which falls in the bandwidth of the
  desired signal, thus disrupting communications
• Jamming can be intentional, or it can result from
  natural phenomena such as multipath.
• SS works by spreading the desired signal over a
  much larger bandwidth, Wss, much in excess of the
  minimum bandwidth W necessary to send the
  information.
• A spreading signal, or coding signal, which is
  independent of the data, is used to accomplish
  spreading.
• At the receiver, the original data is recovered
  through a process called despreading, in which a
  synchronized replica of the spreading signal is
  correlated with the received spread signal.
• Spreading used in the NASA Tracking and Data
  Relay Satellite (TDRS)
• Reduce flux density of signals to meet Spectrum
  Management requirements.
• Provide isolation for signals on same frequency.

28
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 gets multiplied only once.
• g(t) must be deterministic, since it must be
  generated at both the transmitter and receiver,
  yet it must appear random to authorized
  listeners.
• Generally g(t) is generated as a pre-defined
  pseudo-random sequence of 1s and 1s through the
  use of prescribed shift registers.

29
Spreading Effect of Spread Spectrum
G(f)
Jammer with total power J JO J/W
Before Spreading
w
Gss(f)
J'o Jo (W/Wss)
After Spreading
wss
30
Spreading Overview of Various Spreading
Techniques

• Direct Sequencing (DS) is the SS technique
  described above.
• Allows separation between desired signals all at
  the same frequency polarization
• Aids in meeting required flux density regulations
• Enables range determination of spacecraft
• Rule of thumb spreading chip rate x 10 of
  symbol (data) rate
• In Frequency Hopping (FH), the frequency spectrum
  of the desired signal is shifted pseudorandomly
  over M different frequencies.
• Each hop lasts a very short time, making the
  presence of a jamming signal in any one 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 on and off in a pseudorandom
  fashion to counter a pulsed jamming signal.
• Requires, not more bandwidth, but a greater time
  duration for transmission.
• Not effective against continuous wave jammers, so
  it is usually combined with other techniques.
• Hybrids of the three techniques above are often
  used.
• DS/FH, FH/TH, or DS/FH/TH are examples.

31
Modulation Schemes
32
Definition of Modulation

• Modulate means to change something
• In telecommunications, it means to change the
  amplitude, frequency or phase of the carrier
  signal.
• Digital symbols (usually bits) are transformed
  into waveforms by a process called digital
  modulation.
• These digital waveforms are then used to modulate
  the carrier.
• The following slide shows some commonly used
  Pulse Code Modulation (PCM) waveforms.
• Definition Baseband signals are those signals
  that are used to modulate a high frequency
  carrier signal.

33
Pulse Code Modulation (PCM) Waveforms
34
Motivation for Modulation

• It would be very difficult to send a baseband
  signal directly over a channel because antennas
  are used to transmit electromagnetic fields
  through space.
• The size of an antenna depends on the wavelength
  of the signal to be transmitted.
• Often the antenna size is taken to be ?/4.
• A baseband signal has a relatively low frequency
  and therefore a very large wavelength that is
  calculated as c/f, where c is the speed of light
  and f is the frequency.
• An antenna might need to be unacceptably long to
  directly transmit a baseband signal.
• If the baseband information is first modulated on
  a high frequency carrier, then the required
  antenna diameter will be much more reasonable.
• In addition, by modulating carriers at different
  frequencies, more than one baseband signal may be
  sent over the same channel, thus increasing data
  throughput. This is call frequency multiplexing
  (similar to current radio and TV broadcasting).

35
The Carrier Wave/How to Modulate

• The general form of a carrier wave iss(t)
  A(t) cos wct ø(t)
• wc carrier freqA(t) amplitudeø(t) phase
• The carrier can be modulated by using the
  baseband signal to vary one or more of the above
  parameters over a duration of T, the symbol
  period.
• Coherent modulation may be used when the receiver
  can exploit knowledge of the actual carrier
  phase.
• Noncoherent modulation is used when knowledge of
  the absolute phase is unavailable.
• Less complicated, but comes with a performance
  degradation.

S(t)
Modulator
fc
fc reference
36
QPSK versus BPSK

• BPSK modulation results in 1 symbol/Hz, where
  QPSK modulation 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 spectrum mainlobe.
• The probabilities of bit error for BPSK and QPSK
  are equal, but QPSK can support twice the data
  rate that BPSK can.
• Higher orders of PSK can be designed (8-PSK,
  16-PSK, etc.), but there is a tradeoff (higher
  required power or higher BER).

37
Comparison of Spectra for BPSK and QPSK for a
Given Data Rate
BPSK
QPSK
Bandwidth Difference
Coding Gain
Coding Gain
Bandwidth Difference
1a
BPSK 1 180 DEGREES 0 0 DEGREES
I
Q
Inphase and Quadrature biphase signals
1b
0a
Two states for BPSK
QPSK Delay Data by 90 degrees on 1 channel
Four states for QPSK
1
0
0b
38
Noise Basics
39
Sources of System Noise

• The presence of noise degrades the performance of
  a satellite link
• The 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 sources
• Some of the noise is generated internally by
  various receiver components
• The noise which comes in through the antenna can
  be seen as random noise emissions from different
  sources, and it is also called the sky noise
• Terrestrial sources such as lightning, radio
  emissions, and the atmosphere
• Solar radiation
• Galactic background (moon, stars, etc.)
• The receiver-generated noise can be caused by
  various receiver components
• Results from thermal noise caused by the motion
  of electrons in all conductors
• The principal components that generate noise are
  the active devices such as LNA and random noise
  stemming from passive elements, such as the line
  from the antenna to the receiver

40
Noise Temperature of a Device

• Noise temperature is a useful concept in
  communications receivers, since it provides a way
  of determining how much thermal noise is
  generated by active and passive devices in the
  receiving system
• The physical noise temperature of a device, Tn,
  results in a noise power of Pn KTnB
• K Boltzmanns constant 1.38 x 10-23 J/K K in
  dBW -228.6 dBW/K
• Tn Noise temperature of source in Kelvins
• B Bandwidth of power measurement device in
  hertz
• Because satellite communications systems work
  with weak signals, it is mandatory to reduce the
  noise in the receiver as far as possible
• Generally the receiver bandwidth is made just
  large enough to pass the signal, in order to
  minimize noise power

41
The System Noise Temperature

• To determine the performance of a receiving
  system, we must find the total thermal noise
  against which the signal must be demodulated.
• The combination of all the noisy devices plus the
  antenna noise.
• This can be done by representing the receiver
  components as noiseless devices with their
  individual gains and, at their inputs, noise
  sources with the same noise power as the original
  noisy components.
• The next slide shows how this is done for an
  earth station receiver.
• It is then easy mathematically to combine all of
  the noise sources into one noise source, located
  at the input of a noiseless receiver.
• The noise temperature of this source, Ts, is
  called the system noise temperature.
• The total noise power can then be calculated
  easily, for link budget purposes, as Pn KTsBG.
• G is the total gain of the receiver.
• B is the bandwidth of interest.

42
Noise Figure and the G/T Figure of Merit

• Noise figure can also be used to specify the
  noise generated within a device
• NF (S/N)in/(S/N)out
• The noise figure of a device is related to its
  noise temperature by
• 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 be combined as a ratio, Gr/Ts,
  often just written as G/T
• For example, if the receive antenna is 50 dBi and
  the system noise temperature 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 station
• As G/T goes up, so does the quality of the earth
  station

43
The Calculation of System Noise Temperature
(Contd)

• Example

3 dB
DEMODULATOR
IF AMP
RECEIVER
Tsky 50
Loss L
NFR 10 dB 10 GR 30 dB
NFDC 10 dB 10 GDC 30 dB
NFLNA 3 dB 2 GLNA 30 dB
NFIF 10 dB 10 GIF 30 dB
Ts _at_ Reference Point
System Noise Temperature ? Ts K
To is reference temperature of each device
290K (assumed)
?462 K
44
Components
45
Components of Interest

• Antennas
• Receive transmit RF (radio frequency) energy
• Size/type selected directly related to
  frequency/required gain

Gain Pattern
Directional (Hi-Gain) Antenna
Omni Antenna (idealized)
Isotropic antenna
Omni Antenna (typical)
Gain is relative to isotropic with units of dBi
46
Components of Interest (Contd)

• Antennas (contd)
• Polarization the orientation of the electrical
  field vector specifically, the figure traced as
  a function of time by the extremity of the vector
  at a fixed location in space, as observed along
  the direction of propagation
• To minimize polarization loss, the transmit and
  receive antennas should have the same
  polarization.

Linear Polarization Vertical
Linear PolarizationHorizontal
Circular Polarization Left hand
Circular PolarizationRight hand
47
Components of Interest (Contd)

• Filters Diplexers

Band Pass Filter
A
A
f1 f2
f
f
f1
f2
Receive fr
fr (2106.4 MHz)
ft (2287.5 MHz)
Transmit ft

• Diplexer provides isolation between transmit
  receive signals

48
Components of Interest (Contd)

• Transmitters (modulators) Receivers
  (demodulators)

Transmitter
Receiver
Original Signal
Original Signal
A
A
f
fc
fc

• Transponders Transceivers

Switch
Transponder Mode
Transceiver Mode

• Power Amplifier

Power AmplifierG 13 dB
Transmitter
1 watt (0 dBW)
20 watt (13 dBW)
49
Link Equation and Examples(Stop Here)
50
Link Equation

• For an isotropic antenna in free space
  conditions, the power supplied to the antenna,
  PT, is uniformly distributed on the surface of a
  sphere of which the antenna is the center
• The power flux-density is the power radiated by
  the antenna in a given direction at a
  sufficiently large distance, d, per unit of
  surface area is
• The power flux-density radiated in a given
  direction by antenna having 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

51
Link Equation (Contd)

• In general,

PT
d
GT
Receiving Antenna Area AR
HypotheticalSphere
52
Link Equation
where K Boltzmanns constant 1.38 x 10-23
J/K K in dBW -228.6 dBW/K T system noise
temperature in Kelvins

• The power received to noise density is related to
  the data rate by the energy per bit as 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 system
  engineer can easily determine how the
  communication system needs to be improved to
  achieve the desired performance.

where
is related to BER (see theoretical curves for
given modulation and coding scheme)
53
Link Budget Analysis

• A link budget is an engineering tool for
  satellite communication systems, used to
  demonstrate and analyze link performance
• Generally the desired end result is Bit Error
  Rate (BER), or the Eb/N0 required to achieve a
  desired BER
• Link performance is analyzed in terms of
• Transmit power
• Antenna 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 together in 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

54
Additional Losses on a Real Satellite Link

• On an ideal link, the only power loss term would
  be the path loss caused by the dispersion of the
  transmit power over the transmitter-to-receiver
  range.
• For a real satellite communications link, many
  other losses need to be considered as well.
• Polarization loss, caused by the a mismatch
  between the transmitting and receiving antennas.
• Rain attenuation and atmospheric loss.
• The receiver implementation loss.
• Pointing loss, caused by imperfect pointing of
  the antennas
• Miscellaneous other losses.
• In the link budget, these losses are sometimes
  listed as line items subtracted from the received
  power, but some of them may be combined in
  different ways.

55
Sample Link Budget (direct to ground)
S Losses 0.67 dB Polarization loss 178.95 dB
space loss _at_ 2575 KM and 5? elevation 0.45 dB
atmospheric loss 1.2 dB rain loss
11m Ground Antenna
SPACE
I 75 MBPS
Loss 1.13 dB
Encoder Transmitter
LNA
Receiver
Gain 4.84 dBi
G/T 33.3 dB/K
Q 75 MBPS
data
11.6 dBW
10.49 dBW
EIRP 15.31 dBW
I
Q
Decoder
Implementation Loss 2.0 dB
Decoded Data
Alaska SAR Facility 11 meter antenna
MARGIN 5.94 dB
56
Example Link Budget (direct to ground)
DOWNLINK MARGIN CALCULATION

GSFC C.L.A.S.S. ANALYSIS 1 DATE TIME
4/ 1/99 101339 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 EL5
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/(HzK)
-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
57
TDRSS Return Link Power Received

• For ease of calculation, TDRSS defines the
  relationship between data rate and the signal
  power level received isotropically at TDRS (Prec)
  for a Bit Error Rate of 10-5
• Ideal required Prec RbdB K
• For 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 received power is calculated the
  same as identified earlier (see Link Equation
  slide) however, GR is set to 1 ( 0 dB) for the
  isotropic antenna. (i.e., Prec Pr
  GRGTPT(?/4?R)2 Watts)
• In dB, this can be expressed as PR GR GT PT
  20Log(?/4?R) dBW
• Margin Predicted Prec Ideal Prec Other
  Losses
• Other Losses are treated as debits and encompass
  items such as polarization loss (mismatch of the
  transmit polarization with receiving
  polarization), pointing loss (inability of
  transmit antenna to point to receiving antenna),
  incompatibility loss, and interference
  degradation.

58
Example Simple TDRS Link Budget using Prec
Equation
RETURN LINK CALCULATION --
NETWORK SYSTEMS ENGINEER ANALYSIS GSFC
C.L.A.S.S. ANALYSIS 0 DATE TIME
03/03/03 10 131 PERFORMED BY R. BROCKDORFF
USERID 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
Data 10 SSL RAIN ATTENUATION, dB
0.00 User
Provided Data 11 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 10log (Data Rate) 13 DYNAMICS
LOSS, dB 0.00
Not Considered 14 USER
CONSTRAINT LOSS, dB 0.00
CLASS Analysis 15 RFI
LOSS, dB 0.00
CLASS Analysis 16
MARGIN, dB
6.69 (11)-(12)-(13)-(14)-(15)
 

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

59
Sample Link budget (thru TDRS)
QPSK
S Losses 0.10 dB Polarization loss 208.95 dB
space loss _at_ 44592.7 KM and 1.5? elevation
15003.4 MHz
Loss 2.2 dB
I 75 MBPS
Loss 1.8 dB
Encoder Transmitter
Space
Gain 44.30 dBi
Q 75 MBPS
Space Ground Link
EIRP 52.30 dBW
Transparent to the link budget when using the
ideal Prec equation
12 dBW
10.2 dBW
QPSK
LNA
Prec is defined here for a unity gain antenna and
BER 10-5 Predicted Prec -156.75 dBW Ideal
Required Prec -163.44 dBW Margin 6.69 dB
Receiver
data
I 150 Msps
Q 150 Msps
Decoder
Note Significantly more EIRP needed as compared
to a direct downlink (52.3 vs. 15.31 dBW)
Decoded Data
60
Geometric Coverage (Ground)
Florida ground station with spacecraft altitudes
400, 800, and 1200 km
Merritt Island
Elevation angle is the angle between local
horizontal at ground station and spacecraft
61
Geometric Coverage (Ground)
Ground station elevation angles of 0, 10, and 20
degrees
Merritt Island
62
Geometric Coverage (Ground)
Spacecraft altitude 1200 km
Merritt Island
Another antenna
Building
Antenna limits
Effects of terrain and antenna limitations Elevati
on angel 0
63
Geometric Coverage (Ground)
Coverage circle for Svalbard at a spacecraft
altitude of 400 km
Svalbard Location
0 elevation angel
64
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
HAW3
MCMS
65
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
66
Geometric Coverage (TDRS)
Synchronous Satellite Coverage at 319 deg long
Synsat location
Coverage
No coverage
Spacecraft height 500 km
67
TDRS Basics
68
NASAs Tracking and Data Relay Satellite (TDRS)

• The TDRSs are in geosynchronous orbit at
  allocated longitudes
• A geostationary satellite is in a circular orbit
  parallel to and 35786.43 km above the equator
  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 from earth.
• To maintain a geosynchronous orbit, a satellite
  must periodically make east-west corrections or
  it will drift in longitude.
• The TDRSs, along with supporting ground systems,
  make up NASAs Space Network.
• The Space Network was established to act as a
  bent-pipe relay (i.e., repeater) and dramatically
  increase coverage to low earth orbiting
  satellites as compared to a worldwide network of
  ground stations.
• The SN dramatically increased tracking and data
  acquisition (TDA) coverage from 15 to 85 per
  orbit of low earth orbiting spacecraft as well as
  decreased operational costs (see coverage slides
  for depiction).
• Requires 30 dB additional EIRP vs direct to
  ground
• Today, 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

69
TDRSS Constellation
WHITE SANDS COMPLEX
GUAM REMOTE GROUND TERMINAL
F-5 174W TDW
F-7 171W (in storage)
TDRS-8 170.7W
F-1 049W
F-6 047W TDS
F-4 041W TDE
TDRS-I 149.5W
F-3 275W TDZ
TDRS-J 150W
McMurdo Ground StationMcMurdo TDRS Relay
System(McMurdo, Antarctica)
70
TDRSS FIELDS OF VIEW
WHITE
SANDS
COMPLEX
GUAM
254
94
TDW
174 TDW
321
41 TDE
121
355
195
127
47 TDS
275 TDZ
327
91
251
F-7
171 F-7
0/360
180W
-180W
TDRS VIEWS BASED ON 600KM USER ALTITUDE AT THE
EQUATOR
71
TDRSS Ground Segment

• TWO FUNCTIONALLY IDENTICAL, GEOGRAPHICALLY
  SEPARATED GROUND TERMINALS AT THE WHITE SANDS
  TEST FACILITY
• THE WHITE SANDS COMPLEX (WSC) HAS FIVE SPACE TO
  GROUND LINK TERMINALS (SGLTs)
• A SIXTH SGLT HAS BEEN INSTALLED AT THE REMOTE
  GROUND TERMINAL ON GUAM AS AN EXTENDED WSC SGLT
• DATA SERVICES MANAGEMENT CENTER
• OPERATIONAL HUB LOCATED AT WSC FOR COORDINATING
  ALL SPACE NETWORK ACTIVITIES BETWEEN CUSTOMERS
  AND SN

72
Space Segment Tracking and Data Relay Satellite
(F1 - F7)
Solar array Power output is approximately 1800
watts
Single Access Antenna Dual frequency
communications and tracking functions S-band
TDRSS (SSA) K-band TDRSS (KSA) K-band
auto-tracking 4.9 meter shaped reflector
assembly SA equipment compartment mounted behind
reflector Two axis gimballing
Omni Antenna (S-band) and Solar Sail
Space-to-Ground-Link Antenna TDRS downlink 2.0
meter parabolic reflector Dual orthogonal linear
polarization TDRS single horn feed orthomode
transducer Two axis gimballed
Multiple Access Antenna 30 helices 12 diplexers
for transmit 30 receive body mounted Single
commanded beam, transmit 20 adapted beams for
receive Ground implemented receive function

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

73
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 (lt 300 kbps)
• Forward service operations are time-shared
  amongst customers
• Return service supports multiple customers
  simultaneously (lower service cost to customer
  vs SA)
• Phased array antenna and beamforming equipment
  allow for spatial discrimination between
  customers PN spreading provides additional
  discrimination
• Return Demand Access Service allows customers to
  have a dedicated return link continuously (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 customers
• Return service operations are time-shared amongst
  customers (higher service cost to customer vs MA)

74
Data Rates Associated with Space Network Services
75
Spectrum Management
76
Purpose of Spectrum Management

• Ensure that the system in which time and money
  has been invested to develop provides the
  required quality of service (i.e., Bit Error
  Rate) when it is deployed or installed.
• 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.

77
Frequency Allocations

• The radio frequency spectrum is a national and
  international resource whose use is governed by
  Federal statutes and international treaty. 
• Internationally The International
  Telecommunication Union (ITU), which is a
  specialized agency of the United Nations, acts as
  the global spectrum coordinator and develops
  binding international treaty governing the use of
  the radio spectrum by some 40 different services
  around the world.
• The Radio Regulations contain a number of
  provisions governing the way the radio frequency
  spectrum is to be used. 
• Nationally (within the US) responsibility is
  broken into 2 areas
• National Telecommunications and Information
  Agency (NTIA) manages the Government spectrum
• Federal Communications Commission (FCC) manages
  the non-government spectrum
• The international and national Table of
  Allocations shows what segments of the radio
  frequency spectrum are to be used by which
  services.

78
Spectrum Allocations Available to NASA LEO
Missions for Telecommunications
79
Background Material
80
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 Guest
• Select CCMS
• Select Document Library
• Select Code 450
• Error Bounds for Convolutional Codes and
  Asymmetrically Optimum Decoding Algorithum, A.J.
  Viterbi, IEEE Trans information Theory, Vol.
  IT13, April 1967, pp 260-169
• Principles of Digital Communications and
  Coding, A.J. Viterbi and J.K. Omura
• Ground Network Users Guide, February 2001,
  http//www.wff.nasa.gov/code452/
• Digital Communications, Kamilo Feher
• Consultative Committee for Space Data Systems
  (CCSDS)http//www.CCSDS.ORG

81
Compression Lossy versus Lossless Compression

• A lossless compression technique means that the
  restored 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 noisy degradation to the original data.
• Lossy techniques are much more effective at
  compression than lossless methods for a digital
  image, JPEG can achieve a 12-to-1 compression
  ratio, as opposed to a 2-to-1 ratio for GIF.

82
Link Equation Pr/N0 for Cascaded Links

• Often a satellite communications link will
  consist of more than one point-to-point path.
• For example, a satellite at low earth orbit often
  will send its data up to a satellite at high
  earth orbit, which will then relay the data down
  to a ground 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 a downlink 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 more high powered than the other.
• In this case, the total Pr/N0 will be almost
  identical to that of the weaker link, and the
  link budget for the stronger link need not even
  be done at all.

83
Link Equation Geometric Coverage (TDRS)
TDRSS Satellite System Areas of non coverage
84
Space Segment Tracking and Data Relay Satellites
85
Spectrum Available Allocations for the Ground
Network and/or the Space Network
S-band

• Only bands that support both the Ground Network
  (GN) and the Space Network (SN) on a primary
  basis.
• Basic capabilities of the Ground Network at
  S-band are
• Command rates to 32 kbps (note)
• Telemetry and mission data rates to 10 Mbps
  (note)
• Support available from selected sites worldwide
• Basic capabilities of the Space Network at S-band
  are
• Command rates to 300 kbps PN spread
• Telemetry and mission data rates to 6 Mbps
• Virtually global support.
• Efforts to control the inter-service interference
  are under-way within the ITU-R.

Note Maximum support data rate is dependent on
the particular ground station capabilities
86
Spectrum Available Allocations for the Ground
Network and/or the Space Network
X-band

• Bands only support Ground Network operations on a
  primary basis
• The 7190-7235 MHz band may be used to command
  subject to the earth station being coordinated
  with terrestrial systems operating in the bands
  that might experience interference.
• The 8025-8400 MHz and 8450-8500 MHz bands may be
  used for transmissions in the space-Earth
  direction.
• Basic capabilities of the Ground Network at
  X-band are
• Telemetry and mission data rates to 150 Mbps
  (note)

S5.460 Additional allocation the band
7 145 - 7 235 MHz is also allocated to the space
research (Earth-to-space) service on a primary
basis, subject to agreement obtained under No.
S9.21. The use of the band 7 145 -7 190 MHz is
restricted to deep space no emissions to deep
space shall be effected in the band 7 190 - 7 235
MHz.
Note Maximum support data rate is dependent on
the particular ground station capabilities
87
Spectrum Available Allocations for the Ground
Network and/or the Space Network
Ku-band

• Bands only support Space Network Operations
  (13.775 GHz forward/15.0034 GHz return) on a
  secondary basis
• For TDRSS advanced publications received prior to
  January 31 1992, the 13.775 GHz forward link
  operates on a primary basis with respect to the
  Fixed-Satellite Service (E-S).
• Basic capabilities of the Space Network at
  Ku-band are
• Forward link will support up to 25 Mbps.
• Return link will support up to 300 Mbps.
• Virtually global support.

88
Spectrum Available Allocations for the Ground
Network and/or the Space Network
Ka-band

• The pair of Ka-band allocations (22.55-23.55 GHz
  and 25.25-27.5 GHz) support only the Space
  Network on a primary basis.
• The 25.5-27 GHz band is available globally on a
  primary basis for S-E transmissions from
  Earth-exploration satellites.
• Basic capabilities of the Space Network at
  Ka-band are
• Forward links in the 22.55-23.55 GHz band will
  support data rates up to 25 Mbps.
• Return links in the 25.25-27.5 GHz band will
  support data rates up to 300/800 Mbps (note)

Note Capable of supporting 800 Mbps with
upgrades to the TDRSS ground stations
89
Spectrum Definition of Spectrum Allocations

• Space Research Service A radiocommunication
  service in which spacecraft or other objects in
  space are used for scientific or technological
  research purposes.
• Space Operation Service A radiocommunication
  service concerned exclusively with the operation
  of spacecraft, in particular space tracking,
  space telemetry and space telecommand.
• Earth Exploration-Satellite Service A
  radiocommunication service between earth stations
  and one or more space stations, which may include
  links between space stations, in which
• information relating to the characteristics of
  the Earth and its natural phenomena, including
  data relating to the state of the environment, is
  obtained from active sensors or passive sensors
  on Earth satellites
• 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 for meteorological
  purposes.
• Inter-Satellite Service A radiocommunication
  service providing links between artificial
  satellites.