Satellite Communications

1

• Satellite Communications

2
Course Outline

• Introduction
• 2 TTCF Subsystem
• 3 Overall Design Considerations
• 4 Unit Design

3

• Introduction

4
Introduction

• Satellite communication subsystems form part of a
  wireless telecommunication system, not unlike
  terrestrial (ground-based) wireless
  telecommunication systems
• Satellite communications function to receive,
  process and transmit radio frequency (RF) waves
  in the same way as terrestrial microwave relay
  towers
• One key difference lies in the fact that the
  satellite hardware cannot be serviced/repaired/rep
  laced after launch, so reliability is paramount

5
Introduction
6
Introduction

• All conventional communication satellite payloads
  perform the same basic functions
• receive signals from the earth (uplink beam)
• separate, amplify recombine the signals
• transmit the signals back to the earth (downlink
  beam)
• These basic functions resemble a bent-pipe in
  the sky more appropriately named a repeater
• Some advanced payload functions include digital
  signal processing and are called regenerative
  and non-regenerative on-board processors

7
Introduction

• Unlike ground based wireless systems that are
  limited to providing point-to-point,
  line-of-sight connectivity due to the curvature
  of the earth, satellite systems can provide
  instantaneous wide-area network (WAN)
  connectivity of an entire hemisphere
• This means that satellite communication systems
  are capable of providing different types of
  connectivity to the end user

8
Communication Definitions

• The International Telecommunications Union (ITU)
  recommended frequency assignments for satellite
  communications developed at WARC-85 are listed as
  follows
• Sub Band Designation Frequency Range
• L Band 1.5 - 1.6 GHz
• S Band 2.5 - 2.6 GHz
• C Band 3.4 - 4.2, 5.9 - 6.7 GHz
• Ku Band 10.7 - 14.5, 17.3 - 17.8 GHz
• Ka Band 18.3 - 22.2, 27.0 - 31.0 GHz

9
Communication Definitions

• Many C and Ku band payloads occupy a total
  bandwidth of 500 MHz. Each payload consists of a
  number of channels, also called transponders.
  Operating bandwidth of each channel is typically
• L - Band 1.7 3.4 MHz
• C - Band 36, 41 72 MHz
• Ku - Band 24, 27, 36, 54, 72, 77 150 MHz
• Ka - Band 250, 500 1000 MHz
• Each channel can be used to carry 1 signal or
  many signals each with a reduced bandwidth

10
Communication Definitions

• Because of operating frequency and bandwidth
  limitations, payloads typically employ frequency
  reuse schemes to maximize the system capacity
• Spatial frequency reuse is accomplished by using
  multiple uplink/downlink beams each dedicated to
  different coverage areas
• typically used for MSS and intercontinental
  traffic and is very effective for providing
  dedicated or switchable inter-beam connectivity

11
Communication Definitions

• Within each beam/coverage area, frequency reuse
  is accomplished by using orthogonally polarized
  beams
• linear polarization schemes use vertical and
  horizontal electric field (e-field) beams
• circular polarization schemes use left and right
  hand circularly rotating e-field beams
• the choice of polarization scheme affects the
  design cost of the ground terminals, ease of
  ground installation, adjacent satellite
  interference and cross-polarization interference

12
Communication Definitions
13
Communication Definitions

• Coverage refers to the uplink downlink beam
  patterns created on the earth by the satellite
  receive transmit antennas
• Coverage can be tailored to any predefined shape
  using conventional antenna reflector and feed
  technology
• Some examples of coverage beams include global,
  international, national and spot beams
• Multiple coverage area systems can provide
  dedicated or switchable inter-beam connectivity

14
Communication Definitions

• Key Specifications
• The downlink power is referred to as Effective
  Isotropic Radiated Power (EIRP) and is measured
  in units of power (i.e. decibel Watts or dBW)
• EIRP is a product of transmit antenna gain (GT)
  and transponder output power (PT)
• e.g. PT 100 W 20 dBW
• GT 1000 X 30 dBi
• EIRP 100 kW 50 dBW

15
Communication Definitions

• This implies that if an antenna that concentrates
  the beam within the service area was not used,
  the satellite would have to transmit 100 kW of
  power equally in all directions to provide an
  equivalent performance
• EIRP variation is typically due to antenna
  thermal distortion, satellite attitude
  instabilities, atmospheric disturbance (i.e.
  rain) and unit thermal and aging effects

16
Communication Definitions

• The signal power also diminishes as it propagates
  to the earth and this is called the path loss
• The path loss is proportional to the square of
  the distance from the satellite to the earth
  (which is 36,000 km) and amounts to 162 dB/m2
• Using our 50 dBW EIRP example
• 50 dBW - 162 dB/ m2 -112 dBW/m2
• 6 X 10-12 W/m2
• 6 pW/m2 at the ground station

17
Communication Definitions

• The uplink signal strength is referred to as the
  power flux density (PFD) measured in units of
  power per unit area (i.e. dBW/m2)
• The PFD required to saturate the power amplifier
  is called the Saturating Flux Density (SFD)
• SFD variation is due to the same phenomena as
  EIRP variation
• e.g. an uplink EIRP of 70 dBW 10 MW would also
  experience a path loss of 162 dB/m2
• the signal strength at the satellite would be
• -92 dBW/m2 600 pW/m2

18
Communication Definitions

• A figure of merit for the payload is the Gain to
  Noise Temperature Ratio - G/T
• G/T is the ratio between the receive antenna gain
  and the transponder noise temperature earth
  temperature
• G/T variation is due to antenna thermal
  distortion, satellite attitude instability,
  receiver thermal characteristics, etc
• Because of the very low signal strength received
  at the satellite, it is essential to maximize the
  G/T performance

19
Communication Definitions

• Certain functions in the payload are required to
  be controlled from the ground in order to
  optimize and maintain the service (called
  commanding)
• Likewise, certain indicators of performance are
  required to be monitored on a continual basis
  from the ground in order to optimize and maintain
  the service (called telemetry)

20
Communication Definitions

• Fundamental telemetry parameters include
• unit on/off status
• unit temperatures
• transponder channel gain setting status
• power amplifier health status parameters (i.e.
  helix or gate current, DC current anode
  voltage)
• antenna pointing position (if applicable)

21
Communication Subsystem Risks

• History
• Antenna misalignment can lead to offset earth
  coverage and degraded uplink downlink
  performance
• Poor polarization congruency can lead to
  cross-polarization interference from within the
  satellite
• Poor workmanship can lead to contamination that
  can migrate under the zero-g environment in-orbit

22
Communication Subsystem Risks

• Migrating contamination can lead to high power
  breakdown, restricted motion of moving parts,
  degraded performance
• Poor workmanship during spacecraft (S/C)
  construction can lead to electromagnetic
  interference (EMI) susceptibility, degraded
  thermal interfaces, electrostatic discharge (ESD)
  susceptibility
• Poor design and workmanship related to passive
  intermodulation (PIM), especially for L-band
  payloads, can lead to signal interference

23
Communication Subsystem Risks

• The need for increased EIRP performance has
  forced continual development of new power
  amplifiers (PAs), their associated electric power
  conditioners (EPCs) and all of the passive high
  power circuitry
• Significant changes through the evolution of
  these designs has lead to many in-orbit anomalies

24

• TTC Subsystem

25
TTC Key Requirements

• Receive, decrypt, authenticate, and process
  commands
• Collect, format, encrypt, and transmit satellite
  telemetry
• Support satellite control functions
• Attitude determination and control
• Battery charge management, solar array pointing
• Autonomous configuration management
• Support range determination from ground
  station(s)
• Provide antenna coverage for transfer drift
  orbit operations and during on-orbit attitude
  anomalies
• Credible single point failures of TTC H/W and S/W
  not permitted

26
TTC Equipment
- CMD TLM Database - ADC Software (Flight
S/W)
- Encoder/Decoder Units - Remote Terminal
Units - Payload - Bus - Computers - Harnesses
- CMD receivers - CMD Horn Antenna(s) - TLM Horn
Antenna(s) - CMD TLM Omni Antenna - MISC RF HW
and Cabling
27
TTC Key Items
HS 601

• TTC
• CMD Uplink 1-2 kbps
• TLM Downlink 2-4 kbps
• Commercial Encryption, Decryption
• Spacecraft Ranging
• Spacecraft Control

28
Command System Block Diagram
Commanded functions include unit configuration,
gain settings, redundancy settings, jet firings
etc.
29
TTC Units - 1

• Command Receiver
• These are narrowband RF units that reject all but
  the command frequencies. They are hardwired to
  the spacecraft bus and cannot be turned-off
• Decoder/Command Processors
• These units take the tones from the Receiver and
  decode them into digital address, command and
  data word. When the command string has been
  authenticated, it is directed to the appropriate
  unit for execution
• Remote Terminals
• These units control the payload Bus by
  processing the commands addressed to it. It also
  provides status to the telemetry processors

30
Command

• Each satellite has an unique command address
• Encryption is often used to protect the satellite
  from unauthorized access
• Most designs allow a series of commands to be
  uplinked for automatic execution

31
Command Format
SPACECRAFT COMMAND WORD

• Commands validated on-board prior to execution
• Synchronization pattern
• Spacecraft address
• Command length
• Command segment order content
• Parity

32
Telemetry System Block Diagram
Telemetered signals include unit status,
temperatures, voltages, currents, register
contents etc.
33
TTC Units - 2

• Telemetry Encoder
• These units collect signals and status
  information from the spacecraft, convert the data
  into a digital format and multiplex it into a
  continuous digital data stream
• Telemetry Tranmitter/Beacon
• These units take the digital data stream and
  superimpose it on an RF carrier and tranmitted to
  the ground

34
Telemetry Format
SPACECRAFT TELEMETRY FRAME
Provides spacecraft health and operational status
35
What is a frame rate

• The major frame rate is the time required to scan
  and update a complete set of telemetry data
• The major frame is made up of a number of minor
  frames, each of which is serially updated during
  the major frame repetition rate

36
Digital Coding
Telemetry systems typically receive a 5-volt
signal from the user that represents the range of
the signal being telemetered back to the ground.
The TTC Subsystem digitizes this analogue
signal such that full scale is represented by 8
bits (255 counts) and represented as 377 in octal
Counter
20
21
22
23
24
25
26
27
1
2
4
8
16
32
64
128
Decimal
Octal
2
1
4
2
1
0
1
1
1
0
0
1
1
Bit pattern
64
32
16
2
1
Decimal
1
6
3
Octal
1. Bit pattern 011 3 (dec)
2. Bit pattern 01 110 011 115 (dec) 163
(octal)
Examples
37
Encryption Example Exclusive OR Function
When 2 bits are the same, answer 1 2 bits are
different, answer 0
38
Failures, Degradation Margins

• Typical TTC designs offer low risk
  configurations
• No deployable antennas for transfer orbit
  operations
• No RF switches in the command path(s)
• Redundancy and cross-strapping of CMD/TLM/RNG
  signals
• Multiple modes of operation ie) High Low Power
  Transmitter outputs
• Positive RF link margins for CMD/TLM/RNG
• On-orbit problems are generally due to H/W
  failures or degradation
• Operational recovery is achieved by a combination
  of cross-strapping signal paths and redundant
  equipment selection
• In a loss of earth-lock, FSW typically
  reconfigures TLM transmission to high power wide
  angle coverage to facilitate S/C recovery attempts

39

• Communication Payloads

40
Types of Communication Payload

• There are a variety of communication satellites,
  but all types perform the same basic functions
• receive communication signals from the earth
  (uplinks)
• amplify the uplink signals downconvert the
  frequency
• separate the downconverted signals into channels
• amplify the channelized signals
• combine the amplified channels into a downlink
  signal
• transmit the downlink signal to the earth

41
Payload Types

• To accomplish these functions, conventional
  payloads typically comprise the following major
  units
• Receive Transmit Antennas
• Input Filters
• Receivers
• Input Multiplexers
• Redundancy Switch Networks
• Transponder Amplifiers
• Output Multiplexers

42
Fixed Service Satellites (FSS)

• FSS C Band Payloads
• Anik E1, 3024 _at_ 11.5 W Canada CONUS
• Anik F1, 3224 _at_ 40 W NA SA
• Galaxy 10, 3024 _at_ 40 W NA
• GE 4, 2X 1612 _at_ 20 W US

43
FSS Payloads
FSS C Band Functional Block Diagram
44
FSS Payloads

• FSS Ku Band Payloads
• Anik E1, 1816 _at_ 50 W Canada CONUS
• Anik F1, 5848 _at_ 115 W NA SA
• Galaxy 10, 3024 _at_ 108 W NA
• GE 4, 2X 1814 _at_ 110 W US

45
FSS Payloads
FSS Ku Band Functional Block Diagram
46
FSS Payloads

• Receive (Rx) Transmit (Tx) Antennas
• The function of the Rx antenna assembly is to
  collect the signals in the uplink beam and direct
  them into the payload
• Likewise, the Tx antenna functions to send the
  signals from the payload down to the earth in the
  downlink beam
• Each antenna assembly typically comprises a
  reflector and a feed horn as a minimum, although
  other types of antennas are also used

47
FSS Payloads

• In addition to a reflector and a feed horn
• a dual polarization antenna assembly requires a
  device to separate/combine the two orthogonally
  polarized beams called an orthomode transducer
  (OMT) for linearly polarized beams a polarizer
  for circularly polarized beams
• and a combined Rx/Tx antenna assembly requires a
  device to separate the two frequency bands called
  a diplexer

48
FSS Payloads

• Input Filters
• Input filters function to remove any unwanted
  signals from the uplink beam while permitting the
  wanted signals to pass into the receiver
• The receiver and the performance of the payload
  are sensitive to out-of-band signals so the input
  filters are typically comprised of
• a bandpass filter to reject near band signals
• a lowpass filter to reject far out-of-band signals

49
FSS Payloads

• Receivers
• The functions of the receiver are
• to amplify the uplink signal while suppressing
  the noise
• to downconvert the uplink signals to the downlink
  frequency band (e.g. C Band from 6 to 4 GHz, Ku
  Band from 14 to 12 GHz)
• Receivers typically provide approximately half of
  the total required transponder gain
• Receivers noise figure dominates the payload
  noise figure or G/T performance
• Receivers typically comprise
• a low-noise amplifier (LNA) a downconversion
  mixer with a local oscillator

50
FSS Payloads

• Input Multiplexers (IMUXes)
• The function of IMUX is to separate the
  individual signals from the 250 - 500 MHz
  downconverted uplink beam into narrow band
  channels (e.g. 27, 36 or 54 MHz)
• The key device in the IMUX is the high order
  bandpass filter
• Typical IMUX designs configure the filters in a
  non-contiguous (i.e. non frequency adjacent)
  arrangement using channel dropping circulators
• Basically, there are two types of IMUXes (i.e.
  waveguide or dielectric loaded)

51
2.1 FSS Payloads

• IMUXes are designed to provide a stable
  performance over the operating temperature range
  of the payload
• Typical IMUX designs comprise amplitude and phase
  equalization to enhance the passband performance

52
2.1 FSS Payloads
C Band Dielectric Resonator IMUXes
53
FSS Payloads

• Redundancy Switch Networks
• Electro-mechanical switches comprise an actuation
  mechanism to switch the RF transmission paths
  from port to port
• Typically, high power switches have waveguide RF
  paths low power switches have coaxial RF paths
• There are various switch configurations used for
  both types including
• waveguide C (2 position) R (3 or 4 position)
• coaxial C (2 position) T (3 position)

54
FSS Payloads

• Transponder Amplifiers typically consist of two
  amplifier stages and a common electric power
  conditioner (EPC)
• The first stage is the Driver Amplifier (DA)
• Typically, the DA is a high gain, low power,
  broadband, solid state amplifier
• The DA provides the commandable gain control for
  the transponder
• Some DA units also have an automatic level
  control circuit that maintains the output signal
  level constant as the input signal level varies
  over a large range

55
FSS Payloads

• The second stage is the Power Amplifier (PA)
• Typically, the PA is a high gain, high power,
  broadband amplifier
• The PA provides the RF power required for the
  downlink EIRP
• Some PA units also have a linearizer that
  functions to optimize the phase amplitude
• Depending on the output power level and frequency
  band, PAs fall into two different designs
• Travelling Wave Tube Amplifier (TWTA)
• Solid State Power Amplifier (SSPA)

56
FSS Payloads

• The power supply for both amplifier stages is
  provided by the EPC
• The EPC provides the required voltages for the PA
  (5 V for SSPAs up to 7 kV for TWTAs) from the
  bus
• For TWTAs, the EPC typically has circuitry that
  protects the amplifiers from the effects of
  microdischarge events that occur in-orbit
• If a large number of TWTAs are flown or if boost
  mode is required, it is common to have one EPC
  provide power to a pair of DAs and TWTAs this
  is called a dual EPC configuration
• For SSPA designs, it is common to house the DA
  and EPC with the PA all in one housing

57
2.1 FSS Payloads
Ku Band Radiation-Cooled TWT
58
2.1 FSS Payloads

• TWTAs
• Major components in the TWT are
• Electron gun which produces a high density
  electron beam
• Slow-wave circuit which supports a travelling
  wave of electromagnetic energy where the
  electron beam interact
• Collector which collects the spent electron beam
  emerging from the slow-wave circuit
• Packaging hardware which provides a means of
  attachment of beam focusing structure and cooling
  for power dissipated within TWT
• The electron gun design contains a cathode and an
  anode assembly

59
FSS Payloads

• The slow-wave circuit usually employs a step
  velocity taper helix
• The collector employs a multi-stage (i.e. 3 or 4
  stages) design with thermal conduction to a
  cooler outside surface
• The EPC supplies power to TWT, provides
  protection circuits and the command telemetry
  data
• The key TWTA performance specifications are
• RF Output Power 10-250 Watts
• Saturated Gain 50-60 dB Efficiency 55-65
• Weight 2.5 - 3.5 Kilograms

60
FSS Payloads

• SSPAs
• SSPA has been developed since late 1970s and
  started in commercial satellite services in early
  1980s.
• The SSPA capability depends on performance of the
  output stage transistors used and efficiency of
  the combining techniques
• The types of transistor typically used are
  gallium arsenide (GaAs) field effect transistors
  (FETs) or high electron mobility transistors
  (HEMTs)
• These devices can provide sufficient gain and
  power-added efficiency for high power modules

61
FSS Payloads

• The internally matched GaAs FETs have achieved a
  maximum output power of 40/20 watts in C/Ku Band
  respectively
• However, the transistor output power is limited
  by the device gate-width, gate-length and
  breakdown voltages
• Because of individual transistors output power
  limitation, the following combining techniques
  are frequently used
• Corporate splitter/combiner
• Serial splitter/combiner
• Radial power combiner
• The most commonly used is the pyramid structure
  of corporate splitter/combiner

62
FSS Payloads

• Typically, SSPAs have the EPC DA units
  integrated directly into the same housing as the
  high power amplifier stages
• Typical SSPA performance specifications are
• RF output power 5 - 40 Watts
• Saturated Gain 55-65 dB Efficiency 20-40
• More linear than TWTAs
• Weight 1.5 - 2.5 Kilograms

63
FSS Payloads

• OMUX
• The function of OMUX is to combine the
  channelized, amplified signals and direct the
  signals to transmit antenna input port
• OMUX typically comprise high power input
  isolators, lowpass or harmonic reject filters,
  high power, low order bandpass filters, a
  waveguide manifold and high power switches
• Some designs also employ a high power isolator
  and/or a high power receive band reject filter at
  the OMUX output

64

• Communication Subsystem Units

65
Communication Subsystem Units

• Payloads consist of three different types of
  units or devices that introduce different
  levels of insurance risk in the payload
• Passive RF units
• do not require the application of DC power to
  operate
• cause the RF signal passing through to lose power
• this loss of RF power produces heat and this is
  called RF heating
• do not typically exhibit wear-out or
  life-limiting features so redundant units are not
  typically provided

66
Communication Subsystem Units

• Active RF units
• require the application of DC power to operate
• cause the RF signal to either lose or gain power
• RF losses generate RF heating as does the
  consumption of DC power
• typically exhibit wear-out or life-limiting
  features so redundant units are typically
  provided to be utilized in case of a unit failure
  in-orbit
• On-board Processors
• can be analog active intermediate frequency (IF)
  or RF processors or digital processors

67
Passive Low Power Units

• These units typically have the most benign
  operating power levels and environmental
  conditions in the S/C
• Because of this, these units typically present
  the lowest risk of insurance issues in-orbit
• These units include
• input filter assemblies (IFAs), hybrid couplers,
  circulators isolators, input multiplexer (IMUX)
  assemblies, attenuators phase adjusters,
  switches input switch networks (ISNs),
  low-level beam-forming networks (BFNs),
  interconnecting waveguide and coaxial cable

68
Active Low Power Units

• These units typically have benign operating power
  levels and environmental conditions, but they
  typically comprise components (such as
  transistors, capacitors, monolithic microwave
  integrated circuits (MMICs) hybrids) that
  present the risk of failure in-orbit
• These units provide most of the required signal
  amplification in the satellite and perform all of
  the frequency down conversion and analog signal
  processing functions, so they typically present
  low to medium risk of insurance issues in-orbit

69
Active Low Power Units

• These units include
• low noise amplifiers (LNAs), down converters,
  driver amplifiers (DAs) with commandable gain
  controls, limiters (LIMs) and linearizers (LINs),
  ferrite and solid state switches and switch
  matrices, surface acoustic wave (SAW) IF RF
  signal processors

70
Passive High Power Units

• These units typically have the most stringent
  operating power levels and environmental
  conditions in the S/C because the higher the RF
  power, the higher the RF heating and the higher
  the operating temperature
• Also, RF heating can increase dramatically as the
  signal frequency drifts away from band-centre
  toward the band-edge (this is know as a
  band-edge carrier)
• Furthermore, units that pass multiple channels
  will exhibit a proportional increase in the RF
  heating (i.e. if one channel causes 10 W RF
  heating, then 8 channels would cause an average
  of 80 W RF heating)

71
Passive High Power Units

• In units that pass multiple channels, the signals
  can superimpose upon each other in a manner in
  which their total RF power briefly reaches peak
  levels that are much higher than the average
• in these cases, the increase is proportional to
  the square of the number of channels (i.e. from
  the earlier example of 8 channels, the increase
  is 82 64 times)
• This peak power level is not typically sustained
  long enough to increase the RF heating, but it
  can lead to a phenomenon known as multipaction
  that can cause a temporary interference to the
  signal or even permanent damage to the unit

72
Passive High Power Units

• Passive high power units are subjected to several
  potentially damaging operating conditions that
  must be precluded by
• proper design
• proper fabrication by special materials
  processes
• proper testing
• and proper in-orbit operation

73
Passive High Power Units

• And, since the industry trend toward higher
  downlink EIRP directly translates into higher RF
  power in these devices, the technology is
  continuously being driven to its limit
• Because of these stringent operating and
  environment conditions and the industry trend
  towards higher RF power, these units present low
  to medium risk of insurance issues in-orbit

74
Passive High Power Units

• These units include
• output receive reject filters, harmonic filters,
  power dividers/combiners, circulators with remote
  loads or isolators, output multiplexer (OMUX)
  assemblies, output switch networks (OSNs),
  high-level beam-forming networks (BFNs), coaxial
  connectors, receive/transmit diplexers, antenna
  feed horns, orthomode transducers (OMTs),
  polarizers and interconnecting waveguide

75
Active High Power Units

• These units have the most stringent operating
  power levels and environmental conditions in the
  S/C and require a large amount of DC power
• These units and their EPCs are susceptible to
  some well and some not-so-well understood
  performance degradation and or wear-out over the
  life of the satellite
• These units are susceptible to RF and DC power
  consumption heating effects and peak power effects

76
Active High Power Units

• Moreover, the performance reliability of these
  units significantly depends on the RF power
  operating points that are used
• With higher amplifier RF powers being used,
  operation above the well defined safe operating
  point for long or short periods of time, can
  introduce significant life-limiting damage to
  these units

77
Active High Power Units

• Because of these stringent operating requirements
  and their susceptibility to damage and wear-out,
  these units present medium to high risk of
  insurance issues in-orbit
• These units are the power amplifiers (PAs) and
  can be
• travelling wave tube amplifier assemblies
  (TWTAs), or
• solid state power amplifiers (SSPAs)

78
Digital Processors

• Two Types of Digital Processors
• Regenerative Where the original information is
  recover on-board the spacecraft by demultiplexing
  and demodulating the signal
• Non-regenerative The signal is not demodulated
  on-board, only demultiplexed for switching
  circuit by circuit
• Non-regenerative processors are ideal when uplink
  and downlink data rates are identical and same
  format is used

79
Digital Processors

• Main Functions
• Interconnect large number of inputs to a number
  of outputs according to ground commands or
  according to information located within the
  signal (regenerative)
• Performs data rates conversion
• Performs format conversion
• Power level measurement for uplink power control
  at Ka-band
• Synchronization of TDMA networks

80
Digital Processors
Regenerative On-Board Digital Processor
81
Digital Processors

• Main Components
• Analog-to-Digital (A/D) Converters
• Application Specific Integrated Circuit (ASIC)
• Random Access Memories - Registers, Ping-Pong
  Switches
• OBP Controller/Command Controller
• Internal or external power supply unit

82
Digital Processors

• Evolution
• First commercial non-regenerative processor
  deployed was Skyplex on-board Hotbird-4 and 5.
  No switching only multiplexing function.
• ACeS, being deployed, will be the first
  non-generative processor with only digital
  components with the exception of A/D converters,
  called hybrids
• Power consumption of ACeS ASICs is approximately
  0.5 micro watt per MHz per gate. Federal System
  is offering ASIC with 0.02 micro watt and
  Honeywell is offering 0.06, a reduction by 10 to
  20 times in 4 years

83
Digital Processors

• Design requirements
• ASICs are vulnerable to Single Event Upset. They
  must be radiation-Hardened
• ESD protection is required
• Clock distribution/timing could lead to serious
  problem
• Processor needs to meet performance specification
  in addition to functional requirements

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Digital Processors

• Digital Processor Units
• Performance specifications, such as
  implementation losses, can be measured during
  integration
• Functional requirements require a much more
  elaborate test set-up
• Terminals
• Command Link
• Gateways
• Extensive test equipment such as signal/ATM cells
  generators