1 Prepared for Communication System Objectives Reliable and available connections where needed Good quality Minimum delay Sufficient capacity Affordable cost Efficient use of resources (recurring) Equipment value priced (one time)
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Communication System Objectives Reliable and available connections where needed Good quality Minimum delay Sufficient capacity Affordable cost
Efficient use of resources (recurring) Equipment value priced (one time)
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Digital Comm System Model
SourceEncoder
UpConverterModulatorChannel
EncoderPower
Amplifier
Low NoiseAmplifier
ChannelDecoder Demodulator Down
ConverterSource
Decoder
voicefax
videosensors
data
reconstructedinformation
TransmitAntenna
ReceiveAntenna
conditioned/encodeddata streamdigital version
of source content
analog signal
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Transmission Tradeoffs Analog or Digital Transmission
Analog signals represent information by varying some aspect of the signal in accordance with the original voice or video
Noisy channels degrade analog signals Amplifiers can be added, but they amplify noise as well
as signal The longer the signal path, the more noisy the result Digital transmission mitigates
Problems with additive noise during transmission Signal degradation during regeneration (e.g., repeaters)
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Signal with Added Noise
Signal
Signal plus Noise Amplified
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Digital Coding of Signals Represent information as a sequence of
samples:
At each sample time, choose the closest sample from the available set of values
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Sample Transmission Each sample is represented by a group of
bits (example: 8 bits) Sending the information consists of sending a
stream of bits Suppose a 1 is represented by a positive
voltage, and 0 by negative:
1
0 0
1 1 1
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Effects of Noise As long as the noise doesn’t obscure the bit
value, it will not affect ability to decode!
1
0 0
1 1 1
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Recovery of Analog Signal
Digital-to-Analog
Converter
SmoothingFilter
bits samples analogsignal
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Frequency Band Trade-off Frequency band
Lower frequencies bend, bounce, and follow the curvature of the earth, but do so in ways difficult to predict
Higher frequencies result in more dependable transmission characteristics, but travel only in straight lines
Covering a broad geographic region using the dependable higher frequencies requires a satellite to direct signals where they’re needed
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One Optimal Selection Microwave frequencies
Line-of-sight propagation Predictable characteristics Requires satellite for broad geographic coverage while
avoiding use of repeaters Digital transmission
Efficient source coding algorithms Performance independent of distance Speech, video compatibility with data
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Why Satellite? Can be more cost effective
Cost of use is independent of distance Service where you need it Price stability
Easy and fast service deployment No infrastructure required Remote sites can be assembled and on-air in under 30 minutes
Quality of service and capabilities can exceed terrestrial Availability & reliability Uniform service over coverage area Capability (rates, throughput, multicasting, etc.) Flexibility (types of service) Control & network monitoring
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Why Satellite? (cont.)
Commercial Applications Voice, fax and telco data Internet & intranet networking Data and Bandwidth-on-Demand Video conferencing
Consumer Applications TV & Radio broadcasting Internet services Future
Telephony Internet
Public
Networks
Private
Networks
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SATCOM Historical Summary
Viterbi Coding
Turbo Coding
RS Coding
SCPC Modem: 6-8 RU
SCPC Modem: 2 RU
SCPC Modem: 1 RU
1st (TDMA) VSATDeveloped & deployed(M/A-COM Linkabit)
DAMA: TDMA & SCPC
Big TDMA Systems
DVB / MPEG
BroadbandVSATs
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SATCOM Overview Satellite Orbits
Geosynchronous Low-earth orbit Medium earth orbit Specialized
Orbit has considerableeffect on system costand capability
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SATCOM Systems (by Service Type) Fixed Satellite Services (FSS)
Refers to fixed pointing requirement of the receiving /transmitting antenna used by the ground station as a GEO satellite system is used. Services include voice, fax, low and high-speed data. Terminal antennas range from very small (1.2 – 2.4M) VSAT to larger earth stations (3.7M to 18M).
Broadcast Satellite Services (BSS) A special category of FSS that requires the use of high-power GEO satellites for
the express purposes of broadcasting entertainment content (e.g., TV). FSS services are not permitted on a BSS satellite. The terminal antenna is small (0.5 to 1.0M) and is receive only.
Mobile Satellite Services (MSS) Provide voice and lower speed data services to a portable or mobile device on a
regional or global basis. Typically these systems operate in the lower frequency bands (S, L, and VHF). These terminals range from handheld phones (e.g., Iridium, Globalstar) to laptop sized terminals (e.g., Inmarsat)
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SATCOM Frequency Bands
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Satellite System Summary
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Satellite Payloads On-board electronics
Bent-pipe: Acts like a microwave repeater in the sky
(receive, frequency down convert, amplify, transmit) Onboard processing
Decodes data and makes intelligent decisions based on content (e.g., routing, multiplexing, beam reuse, etc.)
Antennas Fixed Adjustable: steerable, beam forming, phase array, etc.
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How FSS works
Satellite acts like a repeater in the sky Ground equipment translates signal
Am plifier/FrequencyConverter
Cu stom erPrem ises
Equipm ent
Custom erPrem ises
Equip m ent
Uplink Downlink
Outdoor Unit(ODU)
Indoor Unit (IDU)
ProtocolController Modem/Codec
I.F. Interface(70 or 140 MHz)
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Power & Bandwidth When either is used up, transponder is full
< 70 percent of transponder BW used (operational considerations) System designers try to match bandwidth and power allocation to maximize utilization
Calculate requirements (Link Budget) End-user pays for the maximum resource used
Bandwidth (or PEB) or Power Controllable design considerations
Antenna size Modulation & FEC Coding
Fixed design considerations Location Available satellites Satellite performance parameters
(somewhat adjustable if full transponder lease)
Space Segment Resources
dBWdBW
HzHz
Power Limited
BW Limited
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Space Segment Resources (cont.)
Transponder bandwidths 27, 36, 48, 54 or 72 MHz
Costs can vary widely Market location
Typical 36 MHz from US$1M - $2 M per year
Partial transponder use is higher Service type: premptable or non-premptable Coverage beam
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Satellite Resource Reuse Spatial Reuse
Antenna beam width is narrow enough to see only one satellite
Spot beams on satellite only illuminate a portion of the earth
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Satellite Resource Reuse (cont.)
Polarization Reuse Orthogonal signal polarization allows two links at same
frequency on same satellite Circular: right & left hand (no feed adjustment) Linear: vertical & horizontal (requires feed adjustment)
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Coverage Beams Global
Lowest power; large user antennas Greatest connectivity All sites receive all signals
Hemispherical Large geographical area
Spot/Regional Smallest coverage Highest power May not be able to receive own uplink signal
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Satellite Operator (example)
PamAmSat Polar View
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Satellite Example PanAmSat XI
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Trends in Transponder Usage (FSS)
33%
20%22%
20%5%
TV RelayDTH TVVoice TrunkingVSAT/WANInternet
2001 (Actuals)
Source: ViaSatellite Magazine
33%
28%
12%
15%
12%TV RelayDTH TVVoice TrunkingVSAT/WANInternet
2004 (Forecast)
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Trends in SATCOM Design More powerful transponders More sophisticated on-board processing
Focused primarily on mass-market services (consumer and business)
More sophisticated RF power management in VSAT terminals (e.g., mitigate need for “static” power margin)
Lower cost terminals by leveraging mass-market components (e.g., DBS (DVB/MPEG), Cable (DOCSIS))
More efficient transmission technology Higher order modulation (8-PSK, 16-QAM) More power forward error correcting codes (e.g., turbo) Bandwidth saving techniques (PCMA)
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The Network Cost Budget Three main factors in determining
total cost of ownership Satellite Space Segment Cost
(Recurring)
Equipment Cost(Capital)
Operating Costs(Maintenance, Staff, etc.)
Space segment costs typically dominate unless right technology is applied $6K/mo/MHz (a good rate) Can be much more expensive
Technology & design implementations can reduce bandwidth/power requirements substantially
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Link analysis is key trade-off tool Essential in making wise decisions
Capital cost vs. Recurring cost Implementation trade-off
Used to determine Antenna sizing across network Size of RF amplifiers Modem capability requirements Power head-room for future data rate increase
Optimize across entire network Helps to evaluate/compare various vendors’ solutions
SATCOM channel efficiencies Advanced features (e.g., power control, adaptive coding, etc.)
Must have concurrence with satellite operator for space segment pricing
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Signal Transmissions System components
Satellite Earth stations
Transmit Receive
Environment Space loss Weather
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Transmission Impairments Free space path loss
Absorptions, reflections, refractions, & scintillation Increases with lower antenna elevations Increases with frequency
Weather Frequency dependent Antenna elevation
Additive noise All electronic equipment creates noise Earth radiation/noise Sun (solar flares, sun outages, etc.) Induces transmission errors (random, statistical)
Interference (add’l slide)
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Degradations (cont.)
Free-space lossdominates
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That dB term Logarithmic ratio
10 Log (V1 / V2) Logs permit simple
addition
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Interference Sources Adjacent satellites Other earth stations
Impacts satellite receive front end Adjacent carriers Cross pole carrier “bleed thru” Solar radiation
Sun spots Sun Outages
2x / year around Spring & Fall Equinox
Local RF Radiation C-band terrestrial microwave
Pwr
BW
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Sun Outage Calculators Tools available on-line or in SatMaster Pro
http://www.panamsat.com/global_network/calc_sun_outage.asp
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Design Trade-offs Satellite trade-offs
Available footprints for geographical coverage Type of coverage (global, hemi, spot) Frequency (Ku or C) Performance parameters (fixed unless lease entire transponder)
Antenna Size Modulation Forward Error Correction (FEC) Coding Data rates & information compression Transmission channel access & transmission efficiency
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Antenna Size vs. Gain vs. Frequency A matter of physics Assumes 65% feed efficiency
Ant Size (M) Ku - Tx Ku - Rx C - Tx C - Rx0.75 39.1 37.6 31.8 27.91.0 41.6 40.1 34.3 30.41.2 43.2 41.7 35.9 32.01.8 46.7 45.2 39.4 35.52.4 49.2 47.7 41.9 38.03.7 53.0 51.4 45.7 41.74.5 54.7 53.1 47.4 43.45.6 56.6 55.0 49.3 45.36.0 57.2 55.6 49.9 45.97.6 59.2 57.7 51.9 48.08.1 59.8 58.2 52.5 48.59.5 61.2 59.6 53.8 49.9
Antenna Gain (dB)
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Modulation Method to convert digital input to analog signal Phase Shift Keying
BPSK – binary (2) QPSK – quadrature (4) 8-PSK
Quadrature Amplitude Modulation (QAM) 16 level
frequency
Magnitud
eModulation & BW
BPSKQPSK
16 QAM
8PSK
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Modulation improvements 8PSK & 16QAM available from several vendors
SCPC DVB 8PSK & 16QAM standardization coming
Higher level modulation waveforms are more susceptible to channel anomalies
Require higher power satellites and/or larger dishes High bandwidth applications driving demand
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Bandwidth vs. Power FEC Code Rate
Higher coding gain less power, but more bandwidth
FEC R=7/8
frequency
Magnitud
e FEC R=3/4
FEC R=1/2
Channel Spacing Power vs adjacent channel interference Nominal (1.4x) “Packed” (1.1x to 1.2x) requires additional signal power (0.2 to 0.5 dB) to compensate
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Turbo code performance Low throughput delay Occupies ~50% of BW
for equivalent RS coding performance
1E-1
1E-2
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8
1E-92 3 4 5 6 7 8 9 10 11 12
E /Nb oQPSK .32 TurboQPSK .79 Turbo
Rate ¾ Viterbi + RSRate ½ ViterbiUncoded
R1/2 +RS QPSK
1 MHz
0.79 Turbo QPSK
.56 MHz
Rate ½ Viterbi + RS
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The Impact of Modulation & Coding
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Link Analysis At CapRock Analysis guidelines being implemented
Consistency Calculation ease Cleaner interface to satellite operators Paper trail
Standardization of: Analysis tools
Intelsat: LST program Eutelsat: under consideration All other operators: SatMaster Pro
Assumptions and parameters to be used Link Budget Methods & Practices Link Budget Parameter Tables
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Key Guidelines Satellite parameters
Location specific (EIRP, SFD, G/T) parameters or an average approximation should be used for location specific parameters; worst case (contour edge) should be used only when directed
Power Equivalent BW (PEB) determination is dependent on satellite operator used
Earth station parameters Standard configurations FEC coding limits (min) RF power amplifier (PA) back-offs
Single carrier & multi-carrier configurations
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Key Guidelines (cont.) Other considerations
Bandwidth rounding Depends on satellite operator Round after summing all circuits, not on individual
Link performance: 1 x 10-6 (min) for data/IP data/VoIP and 1 x 10-4 (min) for compressed voice (non-VOIP)
Link availability: total amount of time that a service is available over a period of time (usually expressed over 12 months) The greater the availability the higher the operating costs Good starting point is 98% (175 outage hrs)
Availability = (1 – (HUB + RF + UNK)) / (TT-CI-SO) x 100 HUB = hub failuresRF = link outagesUNK = Unknown outagesTT = Total time in hours in reporting periodCI = Customer induced outagesSO = Schedule outages (maint, etc.)Typically excludes Force Majeure events
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Key Guidelines (cont.) Optimization guidelines
Circuit tariff (SCPC) approach: select coding to optimize the full duplex link for best balance between power (PEB) and BW; use asymmetric coding rates to further optimize (if available)
Bulk tariff/network/BOD approach: select coding to optimize for a TOTAL best balance between PEB and BW across network
One-time costs vs. recurring cost: trade-off remote antenna size for best power/bandwidth balance; customer tolerance to antenna size should be specified
Recurring optimization: : updates to teleport facilities or equipment configuration changes should be taken into account for existing customers; re-optimize for new services and participate in existing services review
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Link Budget Request Form
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Link Budget Generalizations All programs perform analysis using the same
rules but with varying degrees of incorporated details (e.g., adjacent satellite interference factor) If all assumptions are the same, then results between
programs should be within 5 to 15% Required BW and PEB scales linearly with data
rates (Intelsat – Subsea7 example) Data Rate
(Kbps)PEB
(MHz)BW
(MHz)512 0.4523 0.4779
1024 0.9046 0.95572048 1.8091 1.9115
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VSAT Terminal Characteristics Very Small Aperture Terminal (VSAT) Antenna (aperture) sizes < 3.5 M Low cost Terminals are located on user premises Data rates typically < 2 Mbps
VSAT-101 Part 2 has all the details
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Increasing FSS Resource Efficiency
(Supplement)
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Increasing FSS Resource Utilization Bandwidth can be a bottleneck
Higher power satellites are available Looking for > 1.5 bit/Hz capacity
(QPSK, Rate ¾ FEC)
New approaches in production 8 PSK & 16 QAM (multiple vendors) Turbo codes (multiple vendors) Frequency reuse
(PCMA--ViaSat patent)
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Frequency f1 & f2
W Hz
PCMA – Frequency Re-use Allows 2 different satellite signals on one carrier
2-way circuits only Can be used with asymmetric links (power or bandwidth)
Frequency
f1
f2
W HzW Hz
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PCMA -- “Paired Carrier Multiple Access” Overlapping uplink signal is subtracted
(cancelled) to get desired downlink
Terminal 1 Uplink Terminal2 Uplink
Downlink = Terminal1 +
Terminal2
- -Rx Terminal2 Rx Terminal1
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PCMA (Paired Carrier Multiple Access) Patented technology that permits two carriers to
operate on same frequency Bandwidth is reduced by up to 1/2 Power is slightly (0.3 dB) increased over standard
frequency pair approach Design network to take advantage of BW savings
Balance power & bandwidth with antenna size FEC (concatenated coding or turbo codes)
Operating BW reduction means Less space segment cost for given amount of services More services for given amount of space segment
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Cost Savings Example Scenario
10 site network with 384 Kbps carriers Star topology--hub and 10 remotes Full-duplex
QPSK Rate 1/2 Coding 11 MHz bandwidth needed Monthly cost = $66,000; $792K/year Equipment cost $300K (assumes SCPC)
With PCMA Savings = $33,000/mo Savings = $396K/year
Savings pays forthe hardware inless than a year!!
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System Availability(Supplement)
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Definition of Availability
Availability is the probability that an item will be able to perform its designed functions at the stated performance level, within the stated conditions and in the stated environment when called upon to do so.
ReliabilityReliability + Recovery
Availability =
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Quantification
Percent Availability
N-Nines Downtime Time Minutes/Year
99% 2-Nines 5,000 Min/Yr
99.9% 3-Nines 500 Min/Yr
99.99% 4-Nines 50 Min/Yr
99.999% 5-Nines 5 Min/Yr
99.9999% 6-Nines .5 Min/Yr
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PSTN : The Yardstick? Individual elements have an availability of
99.99% One Cut off call in 8000 calls (3 min for
average call). Five ineffective calls in every 10,000 calls.
Facility Facility EntranceEntrance Facility Facility
EntranceEntrance
ANAN0.01 %0.01 %
0.005 %0.005 % 0.005 %0.005 %
0.02 %0.02 %
0.005 %0.005 % 0.005 %0.005 %
LELE
NINI
LELE
NINI
LDLD
ANAN0.01 %0.01 %
PSTN End-2-End Availability 99.94%
NI : Network InterfaceLE : Local Exchange LD : Long Distance AN : Access Network
Source : http://www.packetcable.com/downloads/specs/pkt-tr-voipar-v01-001128.pdf
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Calculating Availability: Series
EE11 EE22 EE33
.999999 .999999
.999991xx = .9999890
Multiplicative method: E1 x E2 x E3= As
Additive method of UA (unavailability).00000
1.000009.00000
1++ = .000011
0Total Availability of a system (As) is always less than the least available element.
One Weak Link Significantly Weakens This One Weak Link Significantly Weakens This Chain!Chain!
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Calculating Availability: Parallel
Additive Rule: As = E1+ E2 – E1 E2
Multiplicative Rule: As = 1–[(1-E1)(1-E2)]Not for Parallel Systems Where Both Elements Are Not for Parallel Systems Where Both Elements Are RequiredRequiredAssumption is that Switchover Time is zeroAssumption is that Switchover Time is zero
As = .999999+.999999-(.999999*.999999)As = .999999999999
For 1 out of 2 redundancy..EE11
EE22