VSAT Technology and
Applications
Prepared for the Israel Amateur Radio Club
By: 4X1DA – Rich Harel
November 14, 2002
1
Agenda
Introduction to Gilat Satellite Networks
What is a VSAT ?
Typical VSAT Applications
Satellite Communication Fundamentals
VSAT Network Architectures
Access Schemes
Network Components
Network Management
VSATs Applications in Amateur Radio
Demonstration of Equipment
Summary
2
Gilat Satellite Networks Ltd.
3
Gilat Satellite Networks Ltd.
Founded in 1987
Over 950 employees worldwide
Core technology: End-to-end two-way satellite broadband platform
Sales, service and support offices worldwide
Traded on NASDAQ (GILTF) since 1993
Revenues in 2001: $389M
Headquartered in Petech Tikva, Israel
Three Regional Headquarters:
Spacenet (North America) Mclean, VA
Gilat Latin America – Sunrise, FL
Gilat Asia, Pacific Rim and Africa – Petach Tikva, Israel
4
What is a VSAT ?
VSAT = Very Small Aperture Terminal
Satellite-based Wide Area Network (WAN), with
centrally managed hub
Remote site: less than 1.2m dish antenna
Multi-service platform: Data, telephony and
multimedia communications
Optimal for continent-wide networks of
hundreds or thousands of units
Small networks integrated in shared hub
service
Large networks, in the tens of thousands, for
Internet access
5
VSAT Advantages
Full or partial independence from terrestrial infrastructure
Cost savings over terrestrial lines
Nationwide reach, distance-independent
Network management from a single point
Quick deployment, network flexibility
Consistent and rapid response time
Increased network availability
and reliability
Inherent broadcast / multicast platform
6
Unicast, Multicast, Broadcast
Each Unicast Packet is Numbered and Acknowledged
7
Unicast, Multicast, Broadcast
Multicasts Packets are Not Acknowledged
Different Data Steams can be sent simultaneously to many users
8
Unicast, Multicast, Broadcast
Broadcast Packets are sent to all users in the Network Simultaneously
Broadcasts are Not Acknowledged
VSAT Networks can use Reliable Broadcast Protocols and applications that
are based on NACK’s, not ACK’s
9
VSAT Speeds
Compared to Dialup Modem
The name of the game is THROUGHPUT !
A 56K Modem will typically connect at speeds of only 43Kbps
10
VSAT Markets
Enterprise
Retail; Oil & Gas; Banking; Government
POS; Back Office; Browsing; Telemetry
Telephony
Public: Public Call Offices, small businesses,
farmers, private lines
Corporate: Telephony/Data infrastructure
Internet (IP)
High-speed, always-on, Internet-access for
consumers, small businesses and schools
Intranet and IP infrastructure for the enterprise
IP multicast-based services
BTV
Content delivery
11
Characteristics of GEO Satellites
35,680 Km above the Earth
~24 Hour Period
Average 14-17 Year Lifespan
Single Satellite theoretically can provide up to 42% Earth Coverage
Large, expensive, difficult to launch
o
Located approximately every 2 above the equator
Several Satellites may operate at the same azimuth on different
frequencies/polarization
12
The Clarke Belt
xx
13
GEO/LEO Comparison
Example
Referred
to as:
Suitable
For:
Altitude
Orbit
Period
Geosychronous (GEO)
Eurosat Hot-Bird Series
“Fleet”
Low Earth Orbit (LEO)
Iridium
“Constellation”
TV/Radio Broadcasts;
VSAT/Data Communications
Networks; Telephony Networks;
Data Multicast
35,680 km
Geosynchronous (Inclination 00)
24 Hours
Handheld Global Telephony Networks;
Remote Sensing; Reconnaissance;
Weather
Cost
StandAlone
200-300m $US
Yes (“Bent-Pipe”)
Size
Bands
Delay
Bitrate
EIRP
Frequency
Re-Use
Launch
20-30 meter span
C; X-C; KU; Ka
Minimum 240ms
DVB 2.5-52 Mbps
30-54 dBW
No (Only on Orthogonal
Polarization)
Single Payload (>4000 kg Lift
Capability)
14-17 Years
Life Span
200-1400 km
Polar (Inclination 900)
AOS-LOS Depends on Altitude
(Period Typically 90 Minutes)
Relatively Cheap
No (Works in a Constellation)
(*Single LEO Satellites must be
constantly tracked and suffer from
‘Doppler Effect’)
As small as 13m
Primarily VHF/UHF; L-Band
Minimal
Low Bit Rates
Depends on Satellite
Yes (On Non-Adjacent Spot Beams)
Multiple; Can be “Piggybacked”
4-8 Years
14
Geosynchronous Orbit Fleet
15
LEO Orbit Constellation
Globalstar
Loral initiative
Subsidiary 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
16
Obtaining Satellite Details
http://www.lyngsat.com
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Obtaining Satellite Details
http://www.lyngsat.com
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Satellite Details – Amos 1
http://www.spacecom.co.il/
Middle East Beam
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Satellite Details – Amos 1
http://www.spacecom.co.il/
European Beam
20
VSAT Network Architectures
One Way
One-Way – Receive Only
High Bit-Rate DVB Compliant Outbound
Inbound Return Channel via Dial-Up Modem
Can be used with existing infrastructure
Example: Harmonic’s CyberStreamTM
Baseband
Equipment
Satellite
DVB Modulator
LAN
DVB Receiver
RFT
IP Encapsulator
VSAT TVRO
Antenna
TCP/IP ACK’s NACK’s
Router
Internet
Modem/ISDN
Return
21
VSAT Network Architectures
Two-Way Star Topology
All VSATs Communicate via a Single Hub
Network is Independent of Existing Infrastructure
VSAT 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 FTDMA
Typical Ping Times Approximately 650-700ms
VSAT
VSAT
VSAT
Hub
VSAT
VSAT
VSAT
VSAT
VSAT
22
VSAT Network Architectures
Two-Way Star Topology – Double Hop
23
VSAT Network Architectures
Two-Way Mesh Topology
VSATs communicate directly with each other
Some systems require initial signaling via the Hub
Larger Antennas, Higher Power required at the VSAT
Smaller Antenna, Lower Power required at the Hub
Used extensively in Telephony Networks
Delay minimized on VSAT to VSAT Calls
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
24
Network Components
Skystar 360E
25
Typical Hub Configuration
26
Network Management
Entire Network Controlled, Configured and Monitored from a Single
Location called the NOC (Network Operations Center)
27
Typical VSAT Indoor Unit
(Skystar 360E)
(Front)
(Rear)
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Typical VSAT Outdoor Unit/Antenna
Reflector
Feed-Assembly
LNB-F (Optional)
LNB-F (Optional)
LNB
LNB
SSPA (HPC)
(Front)
(Rear)
29
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
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 ISM
Band
C
3.7-4.2
5.925-6.425
Shared with terrestrial
Ku
11.7-12.2
14-14.5
Attenuation due to
rain
Ka
17.7-21.7
27.5-30.5
High Equipment cost;
attenuation due to
rain
30
Space Segment
VSAT Networks lease space segment from the Fixed Satellite Service
(FSS) Provider
Price is mainly determined by Bandwidth and Power
Geosynchronous Satellites frequencies consist of an Uplink and
Dowlink, each covering a 500 MHz bandwidth
The 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
users
Excessive Power levels can cause distortion to all users on the
transponder
31
Bit Rate/Symbol Rate
Bit Rate
Symbol 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 spectrum
For 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
32
Modulation Types
Q
0 State"1"
180deg
o
315 00 State
315deg
“01”
1 State
0deg
"0"
I
Q
0
o
45deg
45 11 “00”
State
I
135o 10“10”
State
135deg
225o 00 “11”
State
225deg
Q
I
1
BPSK – Binary Phase Shift Keying
Use alternative sine wave phase to
encode bits
Simple to implement
Inefficient use of Bandwidth
Very Robust
One bit per symbol (2 States)
QPSK – Quadrature (Quarternary) Phase
Shift Keying
Efficient use of Bandwidth
Requires more complex receiver for
demodulation
Two bits per symbol (4 States)
MSK – Minimal Shift Keying
Easy to Generate – More Complex
Receiver
Special form of FSK
Spectrally efficient, better noise
performance at receiver
33
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
Un coded
10E-2
Coded
10E-3
10E-4
10E-5
Coding
10E-6
Gain
3
4
5
6
7
8
9
Eb/N0
35
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 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 budget
Turbo Codes with an even stronger coding gain will eventually
replace Convolutional and RS coding
36
Bit Error Rate (BER) & Eb/N0
Bit error rate is Directly Proportional to the Eb/N0 Threshold
Typical 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
C

Place Picture of C/N Here
Place MSK Signal Here
N
CW
DPSK Modulation
37
Link Budget (Margin)
The process of correctly sizing uplink and downlink paths
for:
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 !
40
Access Schemes
The Need for Bandwidth Efficiency
Bandwidth (and power) = $
Better bandwidth efficiency
translates into Cost Savings
Outbound and Inbound BW
proportional to:
Number of Users
Bit Rate
Power/Modulation & Error
Correction Coding
Type of traffic
QoS (Quality of Service)
Outbound Transmission:
Constant, Single Frequency
Inbound Transmission: Bursty,
Frequency Hopping
All VSATs must share the
allocated inbound BW
OB
IB
F1
F2
F3
F4
F5
F6
F7
Fn
41
Access Schemes
Time Division Multiple Access (TDMA)
Frequency 1
17
11
19
Time
Transmissions occur on the
same frequency from
multiple sources
When a collision occurs,
each source waits a random
amount of time before retransmitting
Time slots are allowed to
pass unused
In a loaded network, more
collisions will occur,
increasing the random wait
time
12
11
17
17
Collision Occurs
18
Collision Recognized
11
Retransmits after 3 slots delay time
17
Retransmits after 5 slots delay time
42
Access Schemes
Time Division Multiple Access (TDMA)
Frequency 1
17
11
19
Time
Transmissions occur on the
same frequency from
multiple sources
When a collision occurs,
each source waits a random
amount of time before retransmitting
Time slots are allowed to
pass unused
In a loaded network, more
collisions will occur,
increasing the random wait
time
12
11
17
17
Collision Occurs
18
Collision Recognized
11
Retransmits after 3 slots delay time
17
Retransmits after 5 slots delay time
43
Access Schemes
Frequency/Time Division Multiple
Access – Random Access (RA)
Allocated Bandwidth
Inbound Frequencies
1.2MHz
F1
120kHz
F2
F3
102
Time
Slots
F4
F5
F6
F7
053 021
006
F8
F9
006
053
102
021 102
021
006
102
006
102
F10
Frequency
Collision
Retransmission
006
Time
VSAT 006
VSAT 021
VSAT 053
VSAT 102
44
Access Schemes
Automatic Dedicated Access
A “private” frequency is
allocated to a single VSAT
Collision free, high throughput
channel for batch applications
and file transfer
When a DA is required by a
VSAT, initiate request is sent in
RA mode, triggered
According to IP-socket or IP
address
According X.25 destination
address
Throughput based
t
Then, a DA frequency is
allocated
RA
34
11
31
14
17
21
17
34
17
34
17
34
17
34
17
34
17
34
21
14
25
25
f
DA DA
17
14
45
Access Schemes
Automatic Partial Dedicated Access
Partial allocation for better
utilization of DA channel
Optimal for Constant Bit Rate
(CBR) applications, such as voice
Guarantees fixed response time
DA can be flexibly divide into
PDAs
f
RA
11
31
17
15
14
17
32
21
17
21
14
25
17
15
17
32
17
25
t
14
17
15
17
32
46
Access Schemes
Dual Bit Rate
Support of dual bit rate
improves space segments
utilization
Any 2 bit rates can be
supported
Each 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
RA
DA
17
f
PDA
15
14
17
32
21
17
11
21
25
14
14
76.8
17
15
17
32
17
36
17
15
17
32
153.6
76.8
t
47
Acknowledgments over Satellite
Spoofing
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
48
Acknowledgments over Satellite
Internet Page Acceleration (IPA)
On Terrestrial Based Networks, each HTML object is requested and
acknowledged
IPA requests all the objects on a specific URL
All objects on an HTML Page are sent to the VSATs at once
49
Amateur Radio Applications
Internet-to-Radio Link
Typical Node
VSAT Antenna
PC + Sound Card + VoIP Application
VHF or UHF
Omni
VSAT
Radio/PC Interface
VHF/UHF Conventional or Trunked Repeater
51
Amateur Radio Applications
Internet-to-Radio Link
New York Repeater/VSAT
Hub
VoIP
Servers
Boston Repeater/VSAT
VoIP Internet Direct
Internet
London Repeater/Direct
52
Amateur Radio Applications
Internet-to-Radio Link - eQSO
xx
53
Amateur Radio Applications
Internet-to-Radio Link - Echolink
54
Amateur Radio Applications
HF Remote Base/Diversity Reception
55
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.
56
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.
57
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
58