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VSAT Technology andApplications
Prepared for the Israel Amateur Radio Club
By: 4X1DA Rich Harel
November 14, 2002
http://www.qrz.com/callsignmailto:[email protected]:[email protected]://www.qrz.com/callsignhttp://www.iarc.org/ -
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Agenda
Introduction to Gilat Satellite NetworksWhat is a VSAT ?Typical VSAT ApplicationsSatellite Communication FundamentalsVSAT Network ArchitecturesAccess SchemesNetwork ComponentsNetwork ManagementVSATs Applications in Amateur RadioDemonstration of EquipmentSummary
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Gilat Satellite Networks Ltd.
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Gilat Satellite Networks Ltd.
Founded in 1987Over 950 employees worldwideCore technology: End-to-end two-way satellite broadband platformSales, service and support offices worldwideTraded on NASDAQ (GILTF) since 1993Revenues in 2001: $389MHeadquartered in Petech Tikva, IsraelThree Regional Headquarters:
Spacenet (North America) Mclean, VA
Gilat Latin America Sunrise, FL
Gilat Asia, Pacific Rim and Africa Petach Tikva, Israel
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What is a VSAT ?
VSAT = Very Small Aperture TerminalSatellite-based Wide Area Network (WAN), withcentrally managed hubRemote site: less than 1.2m dish antennaMulti-service platform: Data, telephony andmultimedia communicationsOptimal for continent-wide networks ofhundreds or thousands of units
Small networks integrated in shared hubservice
Large networks, in the tens of thousands, forInternet access
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VSAT Advantages
Full or partial independence from terrestrial infrastructureCost savings over terrestrial linesNationwide reach, distance-independent Network management from a single pointQuick deployment, network flexibilityConsistent and rapid response timeIncreased network availabilityand reliabilityInherent broadcast / multicast platform
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Unicast, Multicast, Broadcast
Each Unicast Packet is Numbered and Acknowledged
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Unicast, Multicast , Broadcast
Multicasts Packets are Not AcknowledgedDifferent Data Steams can be sent simultaneously to many users
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Unicast, Multicast, Broadcast
Broadcast Packets are sent to all users in the Network SimultaneouslyBroadcasts are Not AcknowledgedVSAT Networks can use Reliable Br oadc ast Protocols and applicationsthat are based on NACK s, not ACK s
http://localhost/var/www/apps/conversion/tmp/scratch_9/Reliable.exehttp://localhost/var/www/apps/conversion/tmp/scratch_9/Reliable.exehttp://localhost/var/www/apps/conversion/tmp/scratch_9/Reliable.exehttp://localhost/var/www/apps/conversion/tmp/scratch_9/Reliable.exe -
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VSAT SpeedsCompared to Dialup Modem
The name of the game is THROUGHPUT !A 56K Modem will typically connect at speeds of only 43Kbps
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VSAT Markets
EnterpriseRetail; Oil & Gas; Banking; Government
POS; Back Office; Browsing; Telemetry
TelephonyPublic: Public Call Offices, small businesses,farmers, private lines
Corporate: Telephony/Data infrastructure
Internet (IP)High-speed, always-on, Internet-access forconsumers, small businesses and schools
Intranet and IP infrastructure for the enterpriseIP multicast-based services
BTV
Content delivery
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Characteristics of GEO Satellites
35,680 Km above the Earth~24 Hour PeriodAverage 14-17 Year LifespanSingle Satellite theoretically can provide up to 42% Earth CoverageLarge, expensive, difficult to launchLocated approximately every 2
above the equatorSeveral Satellites may operate at the same azimuth on differentfrequencies/polarization
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The Clarke Belt
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GEO/LEO ComparisonGeosychronous (GEO) Low Earth Orbit (LEO)
Example Eurosat Hot-Bird Series IridiumReferredto as:
Fleet Constellation
SuitableFor:
TV/Radio Broadcasts;VSAT/Data CommunicationsNetworks; Telephony Networks;Data Multicast
Handheld Global Telephony Networks;Remote Sensing; Reconnaissance;Weather
Altitude 35,680 km 200-1400 kmOrbit Geosynchronous (Inclination 0 0) Polar (Inclination 90 0)Period 24 Hours AOS-LOS Depends on Altitude
(Period Typically 90 Minutes)Cost 200-300m $US Relatively CheapStand-Alone
Yes (Bent -Pipe) No (Works in a Constellation)(*Single LEO Satellites must beconstantly tracked and suffer fromDoppler Effect )
Size 20-30 meter span As small as 13
mBands C; X-C; KU; Ka Primarily VHF/UHF; L-BandDelay Minimum 240ms MinimalBitrate DVB 2.5-52 Mbps Low Bit RatesEIRP 30-54 dBW Depends on SatelliteFrequencyRe-Use
No (Only on OrthogonalPolarization)
Yes (On Non-Adjacent Spot Beams)
Launch Single Payload (>4000 kg LiftCapability)
Multiple; Can be Piggybacked
Life Span 14-17 Years 4-8 Years
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Geosynchronous Orbit Fleet
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LEO Orbit ConstellationGlobalstar
Loral initiativeSubsidiary of Airtouch (Cellular)
Aimed at global cellular phone coverageQualcomm based CDMA
48 satellite constellation (8 planes x 6 ea. + 4spares)
52 now in orbit !8 orbital planes of 6 satellites each80% Earth coverage (+/- 68 degrees)
LEO orbit (1414 km)Ground Operations Control Centers (GOCCs)and Satellite Operations Control Centers(SOCCs) control gateway and control functions
Qualcomm GSP1600
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Obtaining Satellite Detailshttp://www.lyngsat.com
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Obtaining Satellite Detailshttp://www.lyngsat.com
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Satellite Details Amos 1http://www.spacecom.co.il/
Middle East Beam
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Satellite Details Amos 1http://www.spacecom.co.il/
European Beam
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VSAT Network ArchitecturesOne Way
One-Way Receive OnlyHigh Bit-Rate DVB Compliant Outbound
Inbound Return Channel via Dial-Up Modem
Can be used with existing infrastructure
Example: Harmonic s CyberStream TM
Satellite
Router
Internet
RFTIP Encapsulator
DVB Modulator
VSAT TVRO Antenna
DVB Receiver
LAN
Modem/ISDNReturn
BasebandEquipment
TCP/IP ACK s NACK s
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VSAT Network ArchitecturesTwo-Way Star Topology
All VSATs Communicate via a Single HubNetwork is Independent of Existing InfrastructureVSAT Antenna Size dependent upon Power and Gain of Hub Antenna
Also Upon Inbound Bitrate, ODU Power and Satellite Footprint
Contention Based Access Usually TDMA or FTDMATypical Ping Times Approximately 650-700ms
Hub
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
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VSAT Network ArchitecturesTwo-Way Star Topology Double Hop
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VSAT Network ArchitecturesTwo-Way Mesh Topology
VSATs communicate directly with each otherSome systems require initial signaling via the HubLarger Antennas, Higher Power required at the VSATSmaller Antenna, Lower Power required at the HubUsed extensively in Telephony NetworksDelay minimized on VSAT to VSAT Calls
VSAT
VSAT
VSATVSAT
VSAT
VSAT
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Network Components
Skystar 360E
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Typical Hub Configuration
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Network Management
Entire Network Controlled, Configured and Monitored from a SingleLocation called the NOC (Network Operations Center)
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Typical VSAT Indoor Unit(Skystar 360E)
(Front) (Rear)
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Typical VSAT Outdoor Unit/Antenna
LNB
Reflector
LNB-F (Optional)
(Front) (Rear)
Feed-Assembly
SSPA (HPC)
LNB-F (Optional)
LNB
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VSAT Communication Bands
VSAT Networks use Geostationary Satellites (GEO) All located directly above the equator, at an altitude of ~36,000 kmand spaced approximately every 2 degrees
Band Up-Link
(GHz)
Down-Link
(GHz)
Notes
L .9-1.6 .9-1.6 Shared with terrestrial
S 1.610-1.625 2.483-2.5 Shared with ISMBand
C 3.7-4.2 5.925-6.425 Shared with terrestrial
Ku 11.7-12.2 14-14.5 Attenuation due torain
Ka 17.7-21.7 27.5-30.5 High Equipment cost;attenuation due torain
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Space Segment
VSAT Networks lease space segment from the Fixed Satellite Service(FSS) ProviderPrice is mainly determined by Bandwidth and PowerGeosynchronous Satellites frequencies consist of an Uplink andDowlink, each covering a 500 MHz bandwidth
The many transponders operating within this range typically extendfrom 36-72 MHz each
Each Transponder has a finite power level that is shared amongst theusers
Excessive Power levels can cause distortion to all users on thetransponder
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Bit Rate/Symbol Rate
Symbol Rate =Bit Rate
# of bits transmitted with each symbol
If more bits can be sent with each symbol, then the same amount ofdata can be sent in a narrower spectrumFor example, for a bitstream of 80 kbps using BPSK (1 bit persymbol), the symbol rate is the same. For QPSK (2 bits per symbols),the symbol rate is the bit rate or, 40 kbps. For 8PSK (3 bits per
symbol) is would be 1/3 the bit rate, or 26.66 kbps
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0 1
0deg "0"180deg "1"
45deg 00
135deg 10
315deg 01
225deg 11
45o 11 State
135o 10 State
315o 00 State
225o 00 State
Q
I
1 State0 State
Q
I
Q
I
Modulation Types
BPSK Binary Phase Shift KeyingUse alternative sine wave phase toencode bitsSimple to implementInefficient use of BandwidthVery Robust
One bit per symbol (2 States)QPSK Quadrature (Quarternary) PhaseShift Keying
Efficient use of BandwidthRequires more complex receiver fordemodulation
Two bits per symbol (4 States)MSK Minimal Shift Keying
Easy to Generate More ComplexReceiverSpecial form of FSKSpectrally efficient, better noise
performance at receiver
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Forward Error Correction (FEC)
FEC provides the ability for transmitted data to be self -correctingwithout the need for re-transmission (As in ARQ)
Thus, we can transmit with LESS POWER - The price is Overhead and Bandwidth !
FEC means that for every bit sent, an additional bit of overhead issent; means for every 3 bits, one bit of overhead, and so on
BER
10E-1
10E-2
10E-3
10E-4
10E-5
10E-6
3 4 5 6 7 8 9 Eb/N0
Un coded
Coded
Coding
Gain
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Forward Error Correction (FEC)
Two classes of Forward Error Correction codes
Convolutional Codes and Block Codes
Convolutional Coding (Viterbi Decoding)Based on minimum hamming distance code words feed through ashift register
Reed Solomon Code (RS) is a form of Block Code that breaks the
data stream up into fixed size blocks and adds redundancy symbolsOn the other side of the link, the data is decoded using linear algebraicalgorithms . This type of code adds considerable overhead
Concatenated Viterbi refers to an error correction technique whichuses Viterbi in conjunction with Reed Solomon coding. Addsapproximately 2dB to the link budgetTurbo Codes with an even stronger coding gain will eventuallyreplace Convolutional and RS coding
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Bit Error Rate (BER) & Eb/N0
Bit error rate is Directly Proportional to the Eb/N0 ThresholdTypical BER in some VSAT Systems can be
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Link Budget (Margin)
The process of correctly sizing uplink and downlink pathsfor:
Satellite
Hub
Remotes
Takes into account:Satellite performance
Path Loss
Atmospheric effects
Frequency bands
Uplink antenna and amplifier performance
Download antenna size and receiver noise figure
Path Loss at 12 GHz over 36,000 km can exceed 205 dB !
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Access SchemesThe Need for Bandwidth Efficiency
Bandwidth (and power) = $Better bandwidth efficiencytranslates into Cost Savings
Outbound and Inbound BWproportional to:
Number of Users
Bit RatePower/Modulation & ErrorCorrection CodingType of trafficQoS (Quality of Service)
Outbound Transmission:
Constant, Single FrequencyInbound Transmission: Bursty,Frequency HoppingAll VSATs must share theallocated inbound BW
OB IB
F1 F2 F3 F4 F5 F6 F7 Fn
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Access SchemesTime Division Multiple Access (TDMA)
Transmissions occur on thesame frequency frommultiple sourcesWhen a collision occurs,each source waits a randomamount of time before re-transmittingTime slots are allow ed topas s unused
In a loaded network, morecollisions will occur,increasing the random wait
time
Frequency 1
17
11
19
12 17 11
17
18
T i m e
Collision Recognized
11 Retransmits after 3 slots delay time
Retransmits after 5 slots delay time 17
Collision Occurs
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Access SchemesTime Division Multiple Access (TDMA)
Transmissions occur on thesame frequency frommultiple sourcesWhen a collision occurs,each source waits a randomamount of time before re-transmittingTime slots are allow ed topas s unused
In a loaded network, morecollisions will occur,increasing the random wait
time
Frequency 1
17
11
19
12 17 11
17
18
T i m e
Collision Recognized
11 Retransmits after 3 slots delay time
Retransmits after 5 slots delay time 17
Collision Occurs
A S h
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Time
Slots
Time
Frequency
Allocated Bandwidth
120kHz
1.2MHz
053102 006021
Inbound Frequencies
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10
102 053 021006
102021 006
Retransmission 102 006
VSAT 006 VSAT 021 VSAT 053 VSAT 102
Collision102006
Access SchemesFrequency/Time Division MultipleAccess Random Access (RA)
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Access SchemesAutomatic Dedicated Access
A private frequency isallocated to a single VSATCollision free, high throughputchannel for batch applicationsand file transferWhen a DA is required by aVSAT, initiate request is sent in
RA mode, triggered According to IP-socket or IPaddress
According X.25 destinationaddressThroughput based
Then, a DA frequency isallocated
11
25
21
21
14
14
14
f
31
25
17
17
17
17
17
17
17
17
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DA DA RA
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34
34
34
t
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Access SchemesAutomatic Partial Dedicated Access
Partial allocation for betterutilization of DA channelOptimal for Constant Bit Rate(CBR) applications, such as voiceGuarantees fixed response timeDA can be flexibly divide intoPDAs
11
25
t
21
21
14
14
14
f
31
25
15
32
15
32
15
32
17
17
17
17
17
17
17
17
RA
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Access SchemesDual Bit Rate
Support of dual bit rateimproves space segmentsutilizationAny 2 bit rates can besupportedEach VSAT supports two bitrates with multiple access
modesLower bit rate for RA andhigher bit rate for DA
Each Receiver Cage at thehub can handle two bit rates
t
f
17
17
17
17
17
1717
17
15
32
32
15
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DA PDA
76.8 76.8 153.6
36
11
25
21
21
14
14
14
RA
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Acknowledgments over SatelliteSpoofing
The Problem: TCP/IP requires acknowledgment of each and everypacket
The Satellite delay [(36,000/300000)2]2 in addition to all the routersalong the way adds significant latency
Spoofing Concept:
Acknowledge TCP packets locally at the VSAT/Hub SendAcknowledge Summary periodically
No Spoof ing Wi th Spoof ing
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Acknowledgments over SatelliteInternet Page Acceleration (IPA)
On Terrestrial Based Networks, each HTML object is requested andacknowledgedIPA requests all the objects on a specific URLAll objects on an HTML Page are sent to the VSATs at once
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Amateur Radio ApplicationsInternet-to-Radio Link
Typical Node
VSAT Antenna
PC + Sound Card + VoIP Application
VSAT
Radio/PC Interface
VHF/UHF Conventional or Trunked Repeater
VHF or UHFOmni
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Amateur Radio ApplicationsInternet-to-Radio Link
New York Repeater/VSAT
Boston Repeater/VSAT
London Repeater/Direct
Hub
VoIPServers
Internet
VoIP Internet Direct
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Amateur Radio ApplicationsInternet-to-Radio Link - eQSO
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Amateur Radio ApplicationsInternet-to-Radio Link - Echolink
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Amateur Radio ApplicationsHF Remote Base/Diversity Reception
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FAQs (1)
What are the Largest VSAT Networks in the World ?Starband ~44,000 (US ISP); US Postal Service ~33,000
How many VSATs are operation World-Wide ?>400K installed by Gilat alone
Can a Star VSAT communicate with another VSAT without a Hub ?Star Topology No. Mesh Topology VSATs can operate Point-to-Point.
Can a VSAT work Mobile ?No, due to the associated delay is some systems and antenna pointing issues.Mobile systems are under development.
Can a VSAT be used anywhere ?No. It can not be used at the extreme North and South latitudes due to coverageof Geostationary satellites. You must have line-of-site coverage towards thesatellite your network is working on.
What are typical upsteam and downsteam speeds that can be achieved with aVSAT ?
Depends on the VSAT ISP. Btopenworld in the UK is offering 500/120 kbps(Upstream/Downstream) service. Theoretically, much higher speeds can beachieved.
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FAQs (2)
Can I view DVB-S video stream from the same antenna/LNB ?Yes. (So long as it is on the same satellite). Elliptical antennas allow adding twoadditional LNBs with switchable polarization.
How many PC s can I connect to a VSAT ? Theoretically, as many as you want. The limiting factor is that they will be sharingthe Inbound/Outbound Bandwidths. The other limiting factor is the total number
of TCP/IP sockets and whether or not the VSAT ISP set up the VSATs to assignan IP address to connected PC. Up to 4 is recommended.
What applications are NOT suitable for VSATs ?VSAT traffic has an inherent latency due to the distance. Real-Time InternetGamming other time-critical applications will not work as well as terrestrial lines.
What changes can we expect to see in the future concerning VSAT technology,markets ?
When Ka-Band Satellite service begins, we can expect to see much smallerdishes. 8PSK instead of the current QPSK on the Outbound, Internal Caching onVSAT, plus much more.
The Rural Telephony market is booming and when mobile VSAT equipmentbecomes available, the industry is expected to change entirely.
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Probing Further
Gilat Satellite Networks Spacenet (Gilat Subsidiary in US) FAQ s (Btopenworld Satellite Service) Lyngsat (Geostationary Satellite Database) Phase Modulation Tutorials
Digital Modulation Basics MPEG Tutorial DVB Standards Tutorial FEC Tutorial Spectrum Analysis Basics Spectrum Analysis AM-FM Measurements www.satil.com (Israeli TVRO Information in Hebrew)AFRTS TVRO Satellite Handbook Channel Master VSAT Antennas Telecommutations Glossary
http://www.gilat.com/Home.asphttp://12.32.10.154/tools/satellite_basics/http://www.btopenworld.com/satellite/faqs.htmlhttp://www.lyngsat.com/http://www.newwaveinstruments.com/resources/rf_microwave_resources/sections/digital_modulation_tutorial_theory_technique.htmhttp://cp.literature.agilent.com/litweb/pdf/5965-7160E.pdfhttp://www.educatorscorner.com/tools/lectures/slides/pdf/MPEGtutorial1.pdfhttp://www.dvb.org/dvb_technology/whitepapers.htmlhttp://grouper.ieee.org/groups/802/16/tutorial/80216t-00_01.pdfhttp://cp.literature.agilent.com/litweb/pdf/5952-0292.pdfhttp://www.ece.wpi.edu/research/analog/resources/hp-am-fm.pdfhttp://www.satil.com/http://www.afrts.osd.mil/tech_info/page.asp?pg=handbookhttp://www.channelmaster.com/http://www.its.bldrdoc.gov/fs-1037/http://www.its.bldrdoc.gov/fs-1037/http://www.channelmaster.com/http://www.afrts.osd.mil/tech_info/page.asp?pg=handbookhttp://www.satil.com/http://www.ece.wpi.edu/research/analog/resources/hp-am-fm.pdfhttp://www.ece.wpi.edu/research/analog/resources/hp-am-fm.pdfhttp://www.ece.wpi.edu/research/analog/resources/hp-am-fm.pdfhttp://cp.literature.agilent.com/litweb/pdf/5952-0292.pdfhttp://grouper.ieee.org/groups/802/16/tutorial/80216t-00_01.pdfhttp://www.dvb.org/dvb_technology/whitepapers.htmlhttp://www.educatorscorner.com/tools/lectures/slides/pdf/MPEGtutorial1.pdfhttp://cp.literature.agilent.com/litweb/pdf/5965-7160E.pdfhttp://www.newwaveinstruments.com/resources/rf_microwave_resources/sections/digital_modulation_tutorial_theory_technique.htmhttp://www.lyngsat.com/http://www.btopenworld.com/satellite/faqs.htmlhttp://12.32.10.154/tools/satellite_basics/http://www.gilat.com/Home.asp