Post on 03-Apr-2018
1
VSAT Technology and Applications
Prepared for the Israel Amateur Radio ClubBy: 4X1DA – Rich HarelNovember 14, 2002
2
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
3
Gilat Satellite Networks Ltd.
4
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, VAGilat Latin America – Sunrise, FLGilat Asia, Pacific Rim and Africa – Petach Tikva, Israel
5
What is a VSAT ?
VSAT = Very Small Aperture TerminalSatellite-based Wide Area Network (WAN), with centrally managed hubRemote site: less than 1.2m dish antennaMulti-service platform: Data, telephony and multimedia communicationsOptimal for continent-wide networks of hundreds or thousands of units
Small networks integrated in shared hub serviceLarge networks, in the tens of thousands, for Internet access
6
VSAT Advantages
Full or partial independence from terrestrial infrastructure Cost savings over terrestrial linesNationwide reach, distance-independentNetwork management from a single pointQuick deployment, network flexibilityConsistent and rapid response timeIncreased network availability and reliabilityInherent broadcast / multicast platform
7
Unicast, Multicast, Broadcast
Each Unicast Packet is Numbered and Acknowledged
8
Unicast, Multicast, Broadcast
Multicasts Packets are Not AcknowledgedDifferent Data Steams can be sent simultaneously to many users
9
Unicast, Multicast, Broadcast
Broadcast Packets are sent to all users in the Network SimultaneouslyBroadcasts are Not AcknowledgedVSAT Networks can use Reliable Broadcast Protocols and applications that are based on NACK’s, not ACK’s
10
VSAT SpeedsCompared to Dialup Modem
The name of the game is THROUGHPUT !A 56K Modem will typically connect at speeds of only 43Kbps
11
VSAT Markets
EnterpriseRetail; Oil & Gas; Banking; GovernmentPOS; Back Office; Browsing; Telemetry
TelephonyPublic: Public Call Offices, small businesses, farmers, private linesCorporate: Telephony/Data infrastructure
Internet (IP)High-speed, always-on, Internet-access for consumers, small businesses and schoolsIntranet and IP infrastructure for the enterpriseIP multicast-based services
BTVContent delivery
12
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 2o above the equator
Several Satellites may operate at the same azimuth on different frequencies/polarization
13
The Clarke Belt
xx
14
GEO/LEO Comparison Geosychronous (GEO) Low Earth Orbit (LEO) Example Eurosat Hot-Bird Series Iridium Referred to as:
“Fleet” “Constellation”
Suitable For:
TV/Radio Broadcasts; VSAT/Data Communications Networks; Telephony Networks; Data Multicast
Handheld Global Telephony Networks; Remote Sensing; Reconnaissance; Weather
Altitude 35,680 km 200-1400 km Orbit Geosynchronous (Inclination 00) Polar (Inclination 900) Period 24 Hours AOS-LOS Depends on Altitude
(Period Typically 90 Minutes) Cost 200-300m $US Relatively Cheap Stand-Alone
Yes (“Bent-Pipe”) No (Works in a Constellation) (*Single LEO Satellites must be constantly tracked and suffer from ‘Doppler Effect’)
Size 20-30 meter span As small as 13m Bands C; X-C; KU; Ka Primarily VHF/UHF; L-Band Delay Minimum 240ms Minimal Bitrate DVB 2.5-52 Mbps Low Bit Rates EIRP 30-54 dBW Depends on Satellite Frequency Re-Use
No (Only on Orthogonal Polarization)
Yes (On Non-Adjacent Spot Beams)
Launch Single Payload (>4000 kg Lift Capability)
Multiple; Can be “Piggybacked”
Life Span 14-17 Years 4-8 Years
15
Geosynchronous Orbit Fleet
16
LEO Orbit ConstellationGlobalstar
Loral initiativeSubsidiary of Airtouch (Cellular)
Aimed at global cellular phone coverage Qualcomm based CDMA
48 satellite constellation (8 planes x 6 ea. + 4 spares)
52 now in orbit ! 8 orbital planes of 6 satellites each 80% 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
17
Obtaining Satellite Detailshttp://www.lyngsat.com
18
Obtaining Satellite Detailshttp://www.lyngsat.com
19
Satellite Details – Amos 1http://www.spacecom.co.il/
Middle East Beam
20
Satellite Details – Amos 1http://www.spacecom.co.il/
European Beam
21
VSAT Network ArchitecturesOne Way
One-Way – Receive OnlyHigh Bit-Rate DVB Compliant OutboundInbound Return Channel via Dial-Up ModemCan be used with existing infrastructure
Example: Harmonic’s CyberStreamTM
Satellite
Router
Internet
RFTIP Encapsulator
DVB Modulator
VSAT TVRO Antenna
DVB Receiver
LAN
Modem/ISDN Return
Baseband Equipment
TCP/IP ACK’s NACK’s
22
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 FootprintContention Based Access – Usually TDMA or FTDMATypical Ping Times Approximately 650-700ms
Hub
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
23
VSAT Network ArchitecturesTwo-Way Star Topology – Double Hop
24
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
25
Network Components
IntranetIntranet
InternetInternet
Firewall/Content Filtering
Application Servers/Acceleration ServersFarm (Optional)
PCsPCs
SkyBlaster 360EVSAT
RFT
Satellite
DVB VideoReceiver
NMS
Two WayBaseband
DVB Outbound
Router
OptionalVideo/AudioBroadcastProgramming
Skystar 360E
26
Typical Hub Configuration
27
Network Management
Entire Network Controlled, Configured and Monitored from a Single Location called the NOC (Network Operations Center)
28
Typical VSAT Indoor Unit(Skystar 360E)
(Front) (Rear)
29
Typical VSAT Outdoor Unit/Antenna
LNB
Reflector
LNB-F (Optional)
(Front) (Rear)
Feed-Assembly
SSPA (HPC)
LNB-F (Optional)
LNB
30
VSAT Communication Bands
VSAT Networks use Geostationary Satellites (GEO) All located directly above the equator, at an altitude of ~36,000 km and spaced approximately every 2 degrees
BandUp-Link (GHz)
Down-Link (GHz)
Notes
L.9-1.6.9-1.6Shared with terrestrial
S1.610-1.6252.483-2.5Shared with ISM Band
C3.7-4.25.925-6.425Shared with terrestrial
Ku11.7-12.214-14.5Attenuation due to rain
Ka17.7-21.727.5-30.5High Equipment cost; attenuation due to rain
31
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 and Dowlink, each covering a 500 MHz bandwidthThe many transponders operating within this range typically extend from 36-72 MHz each
Each Transponder has a finite power level that is shared amongst the usersExcessive Power levels can cause distortion to all users on the transponder
32
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 of data can be sent in a narrower spectrumFor example, for a bitstream of 80 kbps using BPSK (1 bit per symbol), the symbol rate is the same. For QPSK (2 bits per symbols), the symbol rate is ½ the bit rate or, 40 kbps. For 8PSK (3 bits per symbol) is would be 1/3 the bit rate, or 26.66 kbps
33
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 to encode bitsSimple to implementInefficient use of BandwidthVery RobustOne bit per symbol (2 States)
QPSK – Quadrature (Quarternary) Phase Shift Keying
Efficient use of BandwidthRequires more complex receiver for demodulationTwo bits per symbol (4 States)
MSK – Minimal Shift KeyingEasy to Generate – More Complex ReceiverSpecial form of FSKSpectrally efficient, better noise performance at receiver
35
Forward Error Correction (FEC)
FEC provides the ability for transmitted data to be ‘self-correcting’ without the need for re-transmission (As in ARQ)
Thus, we can transmit with LESS POWER - The price is Overhead and Bandwidth !
FEC ½ means that for every bit sent, an additional bit of overhead is sent; ¾ 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
36
Forward Error Correction (FEC)
Two classes of Forward Error Correction codesConvolutional Codes and Block Codes
Convolutional Coding (Viterbi Decoding) Based on minimum hamming distance “code words” feed through a shift register
Reed Solomon Code (RS) is a form of Block Code that breaks the data stream up into fixed size blocks and adds redundancy symbols
On the other side of the link, the data is decoded using linear algebraic algorithms . This type of code adds considerable overhead
Concatenated Viterbi – refers to an error correction technique which uses Viterbi in conjunction with Reed Solomon coding. Adds approximately 2dB to the link budgetTurbo Codes with an even stronger coding gain will eventually replace Convolutional and RS coding
37
Bit Error Rate (BER) & Eb/N0
Bit error rate is Directly Proportional to the Eb/N0 ThresholdTypical BER in some VSAT Systems can be <1.00E -08 (Less than one error in every 100,000,000 bits) for an Eb/No of only 4.8dB“Robust” in the digital worlds describes a system that can be (near) error-free in a noisy signal path
Place Picture of C/N Here Place MSK Signal Here
CW DPSK Modulation
C
N
40
Link Budget (Margin)
The process of correctly sizing uplink and downlink paths for:
SatelliteHubRemotes
Takes into account:Satellite performancePath LossAtmospheric effectsFrequency bandsUplink antenna and amplifier performanceDownload antenna size and receiver noise figure
Path Loss at 12 GHz over 36,000 km can exceed –205 dB !
41
Access SchemesThe Need for Bandwidth Efficiency
Bandwidth (and power) = $Better bandwidth efficiency translates into Cost Savings
Outbound and Inbound BW proportional to:
Number of UsersBit RatePower/Modulation & Error Correction Coding Type of trafficQoS (Quality of Service)
Outbound Transmission: Constant, Single FrequencyInbound Transmission: Bursty, Frequency HoppingAll VSATs must share the allocated inbound BW
OB IB
F1 F2 F3 F4 F5 F6 F7 Fn
42
Access SchemesTime Division Multiple Access (TDMA)
Transmissions occur on the same frequency from multiple sourcesWhen a collision occurs, each source waits a random amount of time before re-transmittingTime slots are allowed to pass unusedIn a loaded network, more collisions will occur, increasing the random wait time
Frequency 1
17
1119121711 17
18Ti
me
Collision Recognized
11 Retransmits after 3 slots delay time
Retransmits after 5 slots delay time17
Collision Occurs
43
Access SchemesTime Division Multiple Access (TDMA)
Transmissions occur on the same frequency from multiple sourcesWhen a collision occurs, each source waits a random amount of time before re-transmittingTime slots are allowed to pass unusedIn a loaded network, more collisions will occur, increasing the random wait time
Frequency 1
17
1119121711 17
18Ti
me
Collision Recognized
11 Retransmits after 3 slots delay time
Retransmits after 5 slots delay time17
Collision Occurs
44
TimeSlots
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
Retransmission102 006
VSAT 006 VSAT 021 VSAT 053 VSAT 102
Collision102006
Access SchemesFrequency/Time Division Multiple Access – Random Access (RA)
45
Access SchemesAutomatic Dedicated Access
A “private” frequency is allocated to a single VSATCollision free, high throughput channel for batch applications and file transferWhen a DA is required by a VSAT, initiate request is sent in RA mode, triggered
According to IP-socket or IP addressAccording X.25 destination addressThroughput based
Then, a DA frequency is allocated
11
25
21
21
14
14
14
f
31
25
17
17
17
17
17
17
17
17
34 DA DARA
34
34
34
34
34
34
t
46
Access SchemesAutomatic Partial Dedicated Access
Partial allocation for better utilization of DA channelOptimal for Constant Bit Rate (CBR) applications, such as voiceGuarantees fixed response timeDA can be flexibly divide into PDAs 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
47
Access SchemesDual Bit Rate
Support of dual bit rate improves space segments utilizationAny 2 bit rates can be supportedEach VSAT supports two bit rates with multiple access modes
Lower bit rate for RA and higher bit rate for DA
Each Receiver Cage at the hub can handle two bit rates
t
f
17
17
17
17
17
17
17
17
15
32
32
15
32
15
DA PDA
76.876.8 153.6
36
11
25
21
21
14
14
14
RA
48
Acknowledgments over SatelliteSpoofing
The Problem: TCP/IP requires acknowledgment of each and every packet
The Satellite delay [(36,000/300000)2]2 in addition to all the routers along the way adds significant latency
Spoofing Concept:Acknowledge TCP packets locally at the VSAT/Hub – Send ‘Acknowledge Summary’ periodically
No Spoofing With Spoofing
49
Acknowledgments over SatelliteInternet Page Acceleration (IPA)
On Terrestrial Based Networks, each HTML object is requested and acknowledgedIPA requests all the objects on a specific URLAll objects on an HTML Page are sent to the VSATs at once
51
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
52
Amateur Radio ApplicationsInternet-to-Radio Link
New York Repeater/VSAT
Boston Repeater/VSAT
London Repeater/Direct
Hub
VoIPServers
Internet
VoIP Internet Direct
53
Amateur Radio ApplicationsInternet-to-Radio Link - eQSO
xx
54
Amateur Radio ApplicationsInternet-to-Radio Link - Echolink
55
Amateur Radio ApplicationsHF Remote Base/Diversity Reception
56
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 coverage of Geostationary satellites. You must have line-of-site coverage towards the satellite your network is working on.
What are typical upsteam and downsteam speeds that can be achieved with a VSAT ?
Depends on the VSAT ISP. Btopenworld in the UK is offering 500/120 kbps (Upstream/Downstream) service. Theoretically, much higher speeds can be achieved.
57
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 two additional 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 sharing the 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 assign an 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 Internet Gamming 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 smaller dishes. 8PSK instead of the current QPSK on the Outbound, Internal Caching on VSAT, plus much more.The Rural Telephony market is booming and when mobile VSAT equipment becomes available, the industry is expected to change entirely.
58
Probing Further…
Gilat Satellite NetworksSpacenet (Gilat Subsidiary in US)FAQ’s (Btopenworld Satellite Service)Lyngsat (Geostationary Satellite Database)Phase Modulation TutorialsDigital Modulation BasicsMPEG TutorialDVB Standards TutorialFEC TutorialSpectrum Analysis BasicsSpectrum Analysis AM-FM Measurementswww.satil.com (Israeli TVRO Information in Hebrew)AFRTS TVRO Satellite HandbookChannel Master VSAT AntennasTelecommutations Glossary