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VSAT–viable solution for remote sites connectivity
BY:
Syed Khurram Iqbal NaqviSystem Architect O3B Networks
For Pakistan and Central Asia
VSAT (Very Small Aperture Terminal)
A Very Small Aperture Terminal (VSAT), is a two-way satellite ground station with a dish antenna that is smaller than 3 meters.
VSATs access satellites to relay data from small remote earth stations (terminals) to other terminals (in mesh configurations) or master earth station "hubs" (in star configurations).
Motivation to use VSAT
Hard to reach areas Reliability Time to deploy (4-6 months vs. 1-2 weeks) Cost ( If distance is more than 500 km then the
VSAT solution is more cost-effective as compared to the optical fiber.)
Emergency Situations
VS
Satellite Services & Applications
Remote Sensing• Pipeline Monitoring• Infrastructure Planning• Forest Fire Prevention• Urban Planning• Flood and Storm watches• Air Pollution Management•
GPS/Navigation• Position Location• Timing• Search and Rescue• Mapping• Fleet Management• Security & Database Access• Emergency Services
Direct-To-Consumer • Broadband IP • Digital Audio Radio• Interactive Entertainment• Video & Data to handhelds
Voice/Video/Data Communications• Mobile Telephony• Rural Telephony• News Gathering/Distribution• Internet Trunking• Corporate VSAT Networks• Distance-Learning• Videoconferencing• Business Television• Broadcast and Cable Relay• VOIP & Multi-media over IP
Occasional Use Services• Newsgathering – First choice
for live coverage, providinghigh-bandwidth video links from remote locations to capture “breaking news”
• Program Delivery – Broadcasts from television networks and relayed via satellite
Users of Satellite Communications
Banking SectorData NetworksTelecommunications (Cellular) Power Production InfrastructureOil & Gas
Advantages Availability: anywhere—no limitations
Fast Deployment: Within hours!
Homogeneity: Same speed and SLA regardless of location
Multicast: broadcast schemes which allows broadcast at no additional cost
Few Points of Failure: just two on the earth!
Advantages (contd.)Reliability: reliable satellite transmission of data
between an unlimited number of geographically dispersed sites
Flexibility: expansion capabilities, unrestricted and unlimited reach.
Network Management: end-to-end monitoring and configuration control for all network subsystems.
A low mean-time to repair - lesser elements imply lower MTTR.
Disadvantages
Latency: round trip delay of 500ms or even more!
Cost of Bandwidth: high as compared to others!
Environmental concerns: “fading” due to rain/snow (frequency band dependent)
LOS dependency: outdoor antenna installation requires clear LOS.
Interference: common to all wireless media!
Comparison between Transmission Media
Optical Fiber
Microwave
Copper
VSAT
Satellite-Fiber ComparisonComparing Satellite and Fiber Characteristics
Capability Fiber Optic
Cable Systems
Geo Satellite in a Global System
Meo Satellite in a Global System
Leo Satellite in a Constellation
Transmission Speed
10 Gbps-3.2 Terabits/second*
Single Sat 1 Gbps-10 Gbps
Single Sat 0.5 Gbps- 5 Gbps
Single Sat .01 Gbps-2Gbps
Quality of Service
10-11 10 -12 10-6 10 -11 10-6 10 -11 10-210 91
Transmission latency
25 to 50 ms 250 ms 100-150 ms 25-75 ms
System Availability w/o
Backup
93 to 99.5% 99.98% (C-Ku band) 99% (Ka band)
99.9% (C-Ku band) 99% (Ka band)
99.5% (L-C-Ku band) 99% (Ka band))
Broadcasting Capabilities
Low to Nil High Low Low
Multi-casting Capabilities
Low High High Medium
Trunking Capabilities
Very High High Medium Low
Mobile Services Nil Medium-to-High High High
VSAT Vs. Leased Line VSAT
Footprint across the countryHigh initial investment High reliability – Uptime of 99.5%No recurring b/w costs
Leased LineOption not available in all areasLow initial investment Dependent on the capacity of the local
systemRecurring Bandwidth costs
“Typical” Fixed Satellite Network
Branch Offices
Corporate Data Center/HQ
Network HUB
Corporate Offices
Gas Stations
Apartment Buildings
Residential
Internet
Applications• Credit Card Validation• ATM/Pay at the Pump• Inventory Control• Store Monitoring• Electronic Pricing• Training Videos• In-Store Audio• Broadband Internet Access• Distance Learning
Some large scale corporate networks have as many as 10,000 nodes
Satellite Network ConfigurationsVSAT
Satellite Frequencies There are specific frequency ranges used by commercial satellites.
L-band (Mobile Satellite Services) 1.0 – 2.0 GHz
S-band (MSS, DARS ) 1.55 – 3.9 GHz
C-band (FSS, VSAT) 3.7 – 6.2 GHz
X-Band (Military/Satellite Imagery) 8.0 – 12.0 GHz
Ku-band (FSS, DBS, VSAT) 11.7–14.5 GHz
Ka-band (FSS “broadband” and inter-satellite links) 17.7 - 21.2GHz and 27.5 – 31 GHz
VSAT Technology Bands C-band (4-6 GHz), Ku-band (10-
20 GHz) and Ka-band (20-30 GHz) that require different licensing approaches.
Entities a) the Space Segment operator; b) the
satellite network operator, who operates one or more Gateway Stations or Network Control Stations (HUBs) or other ground stations; c) the Satellite Service Provider; d) the subscriber who uses individual VSAT equipment
Connectivity – Point to Point (Mesh), Point to Multipoint (star, hub at centre), Multipoint to multipoint (hybrid)
Orbital Options
A Geosynchronous satellite (GEO) completes one revolution around the world every 23 hrs and 56 minutes in order to maintain continuous positioning above the earth’s sub-satellite point on the equator.
A medium earth orbit satellite (MEO) requires a constellation of 10 to 18 satellites in order to maintain constant coverage of the earth.
A low earth orbit satellite (LEO) offers reduced signal loss since these satellites are 20 to 40 times closer to the earth in their orbits thus allowing for smaller user terminals/antennas.
Geostationary Orbit (GEO)
Characteristics of Geostationary (GEO) Orbit Systems• User terminals do not have to track the satellite• Only a few satellites can provide global coverage• Maximum life-time (15 years or more)• Above Van Allen Belt Radiation• Often the lowest cost system and simplest in terms of tracking and high
speed switching
Challenges of Geostationary (GEO) Orbit• Transmission latency or delay of 250 millisecond to complete up/down link • Satellite antennas must be of larger aperture size to concentrate power
and to create narrower beams for frequency reuse• Poor look angle elevations at higher latitudes
Geostationary Orbit Today
Low Earth Orbit (LEO)Characteristics of Low-Earth Orbit (LEO) Systems - Low latency or transmission delay - Higher look angle (especially in high-latitude regions) - Less path loss or beam spreading - Easier to achieve high levels of frequency re-use - Easier to operate to low-power/low-gain ground antennas
Challenges of Low-Earth Orbit (LEO) Systems - Larger number of satellites (50 to 70 satellites). Thus higher
launch costs to deploy, build, and operate. - Harder to deploy, track and operate. There is higher
TTC&M costs even with cross links. - Shorter in-orbit lifetime due to orbital degradation
Medium Earth Orbit (MEO)
Characteristics of Medium-Earth Orbit (MEO) Systems • Less latency and delay than GEO (but greater than LEO)• Improved look angle to ground receivers in higher latitudes• Fewer satellites to deploy and operate and cheaper TTC&M
systems than LEO (but more expensive than with GEO) • Longer in-orbit lifetime than LEO systems (but less than GEO)
Challenges of Medium-Earth Orbit (MEO) Systems • More satellites to deploy than GEO (10 to 18 vs. 3 to 4)• Ground antennas are generally more expensive and complex
because of the need to track satellites. Or, one must use lower-gain, complex antennas.
• Increased exposure to Van Allen Belt radiation
Transponders
• The transponder is the “brain” of the satellite - provides the connection between the satellite’s receive and transmit antennas.
• Satellites can have 12 to 96 transponders plus spares, depending on the size of the satellite.
• A transponder bandwidth can frequently be 36 MHz, 54 MHz, or 72 MHz or it can be even wider.
• A transponders function is to • Receive the signal, (Signal is one trillion times weaker then when transmitted)• Filter out noise, • Shift the frequency to a down link frequency (to avoid interference
w/uplink)• Amplify for retransmission to ground
Frequency Efficiency• The vital resource in satellite communications is spectrum. • As the demand for satellite services has grown, the solution has been;
• To space satellites closer together, • Allocate new spectrum in higher bands, • Make satellite transmissions more efficient so that more bits/Hz can be
transmitted, and • To find ways to re-use allocated spectrum such as through geographic
separation into separated cells or beams or through polarization separation
• Today the satellites systems transmit more efficiently than ever before but interference is now a bigger problem - there is a basic trade off; • The higher the frequency the more spectrum that is available • But, the higher the frequency the more problems with interference from
other users terrestrial, unlicensed, etc.
Fixed Satellite Technology Options
TDM/TDMATraditional data VSAT
systemsLow cost remotes,
expensive hubStar network topologyTransactional data
Credit card validation/POS Internet …
Low user data rate
Freq
uenc
yTime
Satellite Technology Options
TDMA/DAMAStar/Mesh/Hybrid
networksMultimedia,
multiserviceEfficient space
segment utilizationEasily expand
network and site capability
Satellite Technology Options
Freq
uenc
y
Time
SCPC
DAMA Freq
uenc
y
Time
One block = 64 Kbps
Sample when a DAMA system is cost-effectiveIf is a number of sites in a VSAT Network
Sample when a SCPC system is cost-effective
Type of VSAT technology
TDMA (time-division multiple access)
When numerous remote sites communicate with one central hub, this design is similar to packet-switched networks.
Because of competition with one another for access to the central hub, it restrict the maximum bandwidth in most cases to about 19.2 kbps.
all VSATs share satellite resource on a time-slot basis.
Usually used in STAR topology as a transmission technique.
Offered to domestic needs.
TDMA (time-division multiple access)
The VSAT Hub communicates with all dispersed VSATs (typically a 1.8-meter diameter parabolic-shaped dish) on an outgoing channel of up to 512kbps based on the TDM scheme. The incoming or return channel from the dispersed VSATs uses the TDMA channel technology that enables a large number of the respective VSATs to share this single return channel. The incoming routes typically operate at 128kbps, and can go up to a maximum bandwidth of 256kbps.
Copyright Maxis
SCPC (single-carrier per channel)
SCPC-based design provides a point-to-point technology, making VSAT equivalent to conventional leased lines.
Normally dedicated bandwidth of up to 2 Mbps
More than 2 Mbps can be acommodated with the use of different IDU/IDU.
SCPC (single-carrier per channel)
In the Hub-to-Remote configuration, one end of the VSAT link (normally the customer's HQ) is connected to the 11-meter VSAT Hub (Earth Station) via a terrestrial leased line. A VSAT antenna at the remote end or the distant end (normally the branch office) of the VSAT link is then interconnected to the VSAT hub via the satellite.
Copyright Maxis
SCPC (single-carrier per channel)
VSAT links with a Remote-to-Remote configuration bypass the VSAT Hub and has a stand-alone VSAT antenna at both ends of the link. Typical VSAT antenna size ranges from 1.8m to 2.4m.
Copyright Maxis
FDMA (Frequency Division Multiple Access)
oldest method for channel allocation the satellite channel bandwidth is broken into
frequency bands for different earth stations the earth stations must be carefully power-controlled
to prevent the RF power spilling into the bands for the other channels. Here, all VSATs share the satellite resource on the frequency domain only.
3 type: PAMA (Pre-Assigned Multiple Access); DAMA (Demand Assigned Multiple Access); and CDMA (Code Division Multiple Access).
PAMA (Pre-Assigned Multiple Access)
The VSATs are pre-allocated a designated frequency. Equivalent of the terrestrial (land based) leased line solutions.
PAMA solutions use the satellite resources constantly. Therefore, no call-up delay in the interactive data applications or high traffic volumes.
PAMA connects high data traffic sites within an organization.
DAMA (Demand Assigned Multiple Access)
The network uses a pool of satellite channels, which are available for use by any station in that network.
On demand, a pair of available channels is assigned, so that a call can be established. Once the call is completed, the channels are returned to the pool for an assignment to another call.
Since the satellite resource is used only in proportion to the active circuits and their holding times, this is ideally suited for voice traffic and data traffic in batch mode.
DAMA offers point-to-point voice, fax, data requirements and supports video-conferencing. Satellite connections are established and dropped only when traffic demands them.
CDMA (Code Division Multiple Access) Under this, a central network monitoring system allocates a
unique code to each of the VSATs. Enabling multiple VSATs to transmit simultaneously and share a common frequency band.
The data signal is combined with a high bit rate code signal which is independent of the data.
Reception at the end of the link is accomplished by mixing the incoming composite data/code signal with a locally generated and correctly synchronized replica of the code.
Since this network requires that the central network management system co-ordinates code management and clock synchronization of all remote VSATs, STAR topology is the best one.
Mainly used for interference rejection or for security reasons in military systems.
VSAT IMPLEMENTATION There are basically two ways to implement
a VSAT Architecture
STARVSATs are linked via a HUB
MESHVSATs are linked together without going
through a large hub
VSAT Topologies STAR - the hub station controls and monitors can
communicates with a large number of dispersed VSATs. Generally, the Data Terminal Equipment and 3 hub antenna is in the range of 6-11m in diameter. Since all VSATs communicate with the central hub station only, this network is more suitable for centralized data applications.
MESH - a group of VSATs communicate directly with any other VSAT in the network without going through a central hub. A hub station in a mesh network performs only the monitoring and control functions. These networks are more suitable for telephony applications.
HYBRID Network - In practice usually using hybrid networks,
where a part of the network operates on a star topology while some sites operate on a mesh topology, thereby accruing benefits of both topologies.
VSAT STAR ARCHITECTURE
• In this network architecture, all of the traffic is routed via the master control station, or Hub.
• If a VSAT wishes to communicate with another VSAT, they have to go via the hub, thus necessitating a “double hop” link via the satellite.
• Since all of the traffic radiates at one time or another from the Hub, this architecture is referred to as a STAR network.
VSAT STAR ARCHITECTURE (contd.)
Master Control Station (The Hub)
VSAT Community
All communications to and from each VSAT is via the Master Control Station or Hub
STAR ARCHITECTURE (satellite’s perspective)
Satellite HUB
VSAT
VSAT
VSAT
VSAT
VSAT
Topology of a STAR VSAT network viewed from the satellite’s perspectiveNote how the VSAT communications links are routed via the satellite to the Hub in all cases.
VSAT MESH ARCHITECTURE
• In this network architecture, each of the VSATs has the ability to communicate directly with any of the other VSATs.
• Since the traffic can go to or from any VSAT, this architecture is referred to as a MESH network.
• It will still be necessary to have network control and the duties of the hub can either be handled by one of the VSATs or the master control station functions can be shared amongst the VSATs.
VSAT MESH ARCHITECTURE
VSAT Community
MESH ARCHITECTURE (satellite’s perspective)
Satellite
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
VSAT
Topology of a MESH VSAT network from the satellite’s perspectiveNote how all of the VSATs communicate directly to each other via the satellite without passing through a larger master control station (Hub).
VSAT Topologies--comparison
Higher Propagation delayUsed by TDMA VSATsHigh central hub investmentSmaller VSAT antenna sizes (1.8 m typically)Lower VSAT costsIdeally suited for interactive data applicationsLarge organizations, like banks, with centralized
data processing requirements
Lower Propagation delay (250 ms)Used by PAMA/DAMA VSATsLower central hub investmentlarger VSAT antenna sizes (3.8 m typically)Higher VSAT costsSuited for high data trafficTelephony applications and point-to-point high-
speed links
Source: www.bhartibt.com
ADVANTAGES OF STAR Small uplink EIRP of VSAT (which can be a hand-
held telephone unit) compensated for by large G/T of the Hub earth station
Small downlink G/T of user terminal compensated for by large EIRP of Hub earth station
Can be very efficient when user occupancy is low on a per-unit-time basis
DISADVANTAGES OF STAR
VSAT terminals cannot communicate directly with each other; they have to go through the hub
VSAT-to-VSAT communications are necessarily double-hop
GEO STAR networks requiring double-hops may not meet user requirements from a delay perspective
ADVANTAGES OF MESH Users can communicate directly with each
other without being routed via a Hub earth station
VSAT-to-VSAT communications are single-hop.
GEO MESH networks can be made to meet user requirements from a delay perspective.
DISADVANTAGES OF MESH
Low EIRP and G/T of user terminals causes relatively low transponder occupancy
With many potential user-to-user connections required, the switching requirements in the transponder will almost certainly require On-Board Processing (OBP) to be employed
OBP is expensive in terms of payload mass and power requirements
Delay Considerations
Satellite Scenario:• Typical slant path range for GEO satellite: 36,000 km• One way transmission: ESSatelliteES: 2 x Range• One way delay: 2 x (range/velocity) = 260 ms
Fiber Optic Transcontinental Link: • 4000 km has about 13 ms delay
Additionally to either case: Processing delay.• Several tens to over a hundred ms.
Value of Satellite Systems
• Value of satellite systems grows with widely distributed networks and mobility of users
• Satellite systems perform most effectively when: • interconnecting wide distributed networks, • providing broadcasting services over very wide areas such as a country,
region, or entire hemisphere• providing connectivity for the “last mile” in cases where fiber networks
are simply not available for interactive services. • providing mobile wideband and narrow band communications • satellites are best and most reliable form of communications in the case of
natural disasters or terrorist attacks - fiber networks or even terrestrial wireless can be disrupted by tsunamis, earthquakes, etc..
World Satellite Industry Revenues
$0
$20
$40
$60
$80
$100
1996 1997 1998 1999 2000 2001 2002 2003
Rev
enue
(in
billi
ons)
$38.0
$49.1$55.0
$60.4
$73.7$78.6
$86.1$91.0
Global Supply vs. DemandGEO Communications Satellites and Launches
0
10
20
30
40
50
60
70
1995 1996 1997 1998 1999 2000 2001 2002 2003
Num
ber o
f Sat
ellit
es/L
aunc
hes
Launches Satellites OrderedSatellite Capacity Launch Capacity
-
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01
VSAT: A Consistent Performer
Opportunities in VSAT technology
Voice over IP (VoIP) via satellite Frame Relay via satellite ATM via satellite Video-on-demand via satellite Multimedia application
Internet/e-mail connectionTelemedicineDistance learning
Summary (of previous discussion)
Satellite technology is the fastest way to get a reliable connection from A to B in an emergency situation.Both a SCPC and a DAMA solution can be used
in an emergency situation as a VSAT connection. Both technologies can be used as a FlyAway (Quick deploy) system. Both systems can run the same services.
Implementation
Requirement
Customers
Locations
Time Lines
Solution Details
Frequency Band
Outdoor Equipment
Indoor Equipment
Interfacing
Ground Antennas The size of the antenna depends on the satellite
frequency band used, the data rate, and whether the service is bidirectional or receive only Higher data rates require larger antennas and/or higher
power Higher transmit capability (EIRP) of the satellite allows
the antenna size to be reduced The use of spot beams instead of global beams improves
VSAT link performance Receive-only antennas can be substantially smaller
Steps in Installation of a VSAT site
Technical Site Survey
Civil Work
Antenna Mounting
Pointing of Antenna
Configuration of ODU
Steps in Installation of a VSAT site
Configuration of Indoor Unit
Testing on RF level
Interfacing
BER testing
Integration (with the BTS/BSC)
Quality Assurance Tests
BER testing
Spectrum Analysis
Carrier to Noise Ratio measurement
Common Faults/Problems
Fading (due to rain etc.)
LOS obstructions
ODU/IDU malfunctions
De-pointing of Antenna
Interference
O & M Procedures
Carrier Monitoring
Spectrum Analysis
Fault Diagnosis/Localization
RF Power adjustment
etc. etc.
Thank You!