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VSAT–viable solution for remote sites connectivity<br />BY:<br />Syed Khurram Iqbal Naqvi<br />System Architect O3B Networks<br />For Pakistan and Central Asia<br />
VSAT (Very Small Aperture Terminal)<br />A Very Small Aperture Terminal (VSAT), is a two-way satellite ground station with a dish antenna that is smaller than 3 meters. <br />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). <br />
Motivation to use VSAT<br />VS<br />Hard to reach areas<br />Reliability <br />Time to deploy (4-6 months vs. 1-2 weeks)<br />Cost ( If distance is more than 500 km then the VSAT solution is more cost-effective as compared to the optical fiber.)<br />Emergency Situations<br />
Video & Data to handhelds</li></li></ul><li>Occasional Use Services<br /><ul><li>Newsgathering – First choicefor live coverage, providinghigh-bandwidth video links from remote locations to capture “breaking news”
Program Delivery – Broadcasts from television networks and relayed via satellite</li></li></ul><li>Users of Satellite Communications<br />Banking Sector<br />Data Networks<br />Telecommunications (Cellular) <br />Power Production<br />Infrastructure<br />Oil & Gas<br />
Advantages<br />Availability: anywhere—no limitations<br />Fast Deployment: Within hours!<br />Homogeneity: Same speed and SLA regardless of location<br />Multicast: broadcast schemes which allows broadcast at no additional cost<br />Few Points of Failure: just two on the earth!<br />
Advantages (contd.)<br />Reliability:reliable satellite transmission of data between an unlimited number of geographically dispersed sites <br />Flexibility:expansion capabilities, unrestricted and unlimited reach.<br />Network Management:end-to-end monitoring and configuration control for all network subsystems.<br />A low mean-time to repair - lesser elements imply lower MTTR. <br />
Disadvantages<br />Latency: round trip delay of 500ms or even more!<br />Cost of Bandwidth:high as compared to others! <br />Environmental concerns:“fading” due to rain/snow (frequency band dependent)<br />LOS dependency:outdoor antenna installation requires clear LOS.<br />Interference:common to all wireless media!<br />
VSAT Vs. Leased Line<br />VSAT<br />Footprint across the country<br />High initial investment <br />High reliability – Uptime of 99.5%<br />No recurring b/w costs<br />Leased Line<br />Option not available in all areas<br />Low initial investment <br />Dependent on the capacity of the local system<br />Recurring Bandwidth costs<br />
Distance Learning</li></ul>Network HUB<br />Apartment <br />Buildings<br />Internet<br />Gas Stations<br />Corporate Data Center/HQ<br />Corporate Offices<br />Residential<br />Branch Offices<br />Some large scale corporate networks have as many as 10,000 nodes<br />
Satellite Frequencies<br />There are specific frequency ranges used by commercial satellites.<br />L-band (Mobile Satellite Services)<br /> 1.0 – 2.0 GHz<br />S-band (MSS, DARS )<br /> 1.55 – 3.9 GHz<br />C-band (FSS, VSAT)<br /> 3.7 – 6.2 GHz<br />X-Band (Military/Satellite Imagery)<br /> 8.0 – 12.0 GHz<br />Ku-band (FSS, DBS, VSAT)<br /> 11.7–14.5 GHz<br />Ka-band (FSS “broadband” and inter-satellite links)<br /> 17.7 - 21.2GHz and 27.5 – 31 GHz<br />
VSAT Technology<br />Bands C-band (4-6 GHz), Ku-band (10-20 GHz) and Ka-band (20-30 GHz) that require different licensing approaches. <br />Entities <br />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<br />Connectivity – Point to Point (Mesh), Point to Multipoint (star, hub at centre), Multipoint to multipoint (hybrid) <br />
Orbital Options<br />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. <br />A medium earth orbit satellite (MEO) requires a constellation of 10 to 18 satellites in order to maintain constant coverage of the earth. <br />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. <br />
Geostationary Orbit (GEO)<br />Characteristics of Geostationary (GEO) Orbit Systems<br /><ul><li>User terminals do not have to track the satellite
Only a few satellites can provide global coverage
Often the lowest cost system and simplest in terms of tracking and high speed switching</li></ul>Challenges of Geostationary (GEO) Orbit<br /><ul><li>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
Low Earth Orbit (LEO)<br />Characteristics of Low-Earth Orbit (LEO) Systems<br /> - Low latency or transmission delay <br /> - Higher look angle (especially in high-latitude regions) <br /> - Less path loss or beam spreading <br /> - Easier to achieve high levels of frequency re-use <br />- Easier to operate to low-power/low-gain ground antennas<br />Challenges of Low-Earth Orbit (LEO) Systems<br /> - Larger number of satellites (50 to 70 satellites). Thus higher launch costs to deploy, build, and operate. <br /> - Harder to deploy, track and operate. There is higher TTC&M costs even with cross links.<br /> - Shorter in-orbit lifetime due to orbital degradation <br />
Medium Earth Orbit (MEO)<br />Characteristics of Medium-Earth Orbit (MEO) Systems <br /><ul><li>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)</li></ul>Challenges of Medium-Earth Orbit (MEO) Systems<br /><ul><li>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</li></li></ul><li>Transponders<br /><ul><li>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.
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.</li></li></ul><li>Fixed Satellite Technology Options<br />TDM/TDMA<br />Traditional data VSAT systems<br />Low cost remotes, expensive hub<br />Star network topology<br />Transactional data<br />Credit card validation/POS<br />Internet …<br />Low user data rate<br />Frequency<br />Time<br />
Satellite Technology Options<br />TDMA/DAMA<br />Star/Mesh/Hybrid networks<br />Multimedia, multiservice<br />Efficient space segment utilization<br />Easily expand network and site capability<br />
Satellite Technology Options<br />SCPC<br />DAMA<br />Frequency<br />Time<br />Frequency<br />Time<br />Sample when a SCPC system is cost-effective<br />Sample when a DAMA system is cost-effective<br />If is a number of sites in a VSAT Network<br />One block = 64 Kbps<br />
TDMA (time-division multiple access)<br />When numerous remote sites communicate with one central hub, this design is similar to packet-switched networks.<br />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.<br />all VSATs share satellite resource on a time-slot basis.<br />Usually used in STAR topology as a transmission technique.<br />Offered to domestic needs. <br />
TDMA (time-division multiple access)<br />Copyright Maxis<br />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.<br />
SCPC (single-carrier per channel)<br />SCPC-based design provides a point-to-point technology, making VSAT equivalent to conventional leased lines.<br />Normally dedicated bandwidth of up to 2 Mbps<br />More than 2 Mbps can be acommodated with the use of different IDU/IDU. <br />
SCPC (single-carrier per channel)<br />Copyright Maxis<br />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.<br />
SCPC (single-carrier per channel)<br />Copyright Maxis<br />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.<br />
FDMA (Frequency Division Multiple Access)<br />oldest method for channel allocation<br />the satellite channel bandwidth is broken into frequency bands for different earth stations<br />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. <br />3 type:<br />PAMA (Pre-Assigned Multiple Access);<br />DAMA (Demand Assigned Multiple Access); and<br />CDMA (Code Division Multiple Access). <br />
PAMA (Pre-Assigned Multiple Access)<br />The VSATs are pre-allocated a designated frequency. Equivalent of the terrestrial (land based) leased line solutions.<br />PAMA solutions use the satellite resources constantly. Therefore, no call-up delay in the interactive data applications or high traffic volumes. <br />PAMA connects high data traffic sites within an organization. <br />
DAMA (Demand Assigned Multiple Access)<br />The network uses a pool of satellite channels, which are available for use by any station in that network. <br />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. <br />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. <br />DAMA offers point-to-point voice, fax, data requirements and supports video-conferencing. Satellite connections are established and dropped only when traffic demands them.<br />
CDMA (Code Division Multiple Access)<br />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. <br />The data signal is combined with a high bit rate code signal which is independent of the data. <br />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. <br />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. <br />Mainly used for interference rejection or for security reasons in military systems.<br />
VSAT IMPLEMENTATION<br />There are basically two ways to implement a VSAT Architecture<br />STAR<br />VSATs are linked via a HUB<br />MESH<br />VSATs are linked together without going through a large hub<br />
VSAT Topologies<br />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. <br />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.<br />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. <br />
VSAT STAR ARCHITECTURE <br /><ul><li> 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.</li></li></ul><li>VSAT STAR ARCHITECTURE (contd.)<br />
STAR ARCHITECTURE (satellite’s perspective)<br />VSAT<br />VSAT<br />Satellite<br /> HUB<br />VSAT<br />VSAT<br />VSAT<br />Topology of a STAR VSAT network viewed from the satellite’s perspective<br />Note how the VSAT communications links are routed via the satellite to the Hub in all cases.<br />
VSAT MESH ARCHITECTURE <br /><ul><li> 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.</li></li></ul><li>VSAT MESH ARCHITECTURE <br />VSAT<br /> Community<br />
MESH ARCHITECTURE (satellite’s perspective)<br />VSAT<br />VSAT<br />VSAT<br />VSAT<br />Satellite<br />VSAT<br />VSAT<br />VSAT<br />VSAT<br />VSAT<br />VSAT<br />Topology of a MESH VSAT network from the satellite’s perspective<br />Note how all of the VSATs communicate directly to each other via the satellite without passing through a larger master control station (Hub).<br />
VSAT Topologies--comparison<br />Lower Propagation delay (250 ms)<br />Used by PAMA/DAMA VSATs<br />Lower central hub investment<br />larger VSAT antenna sizes (3.8 m typically)<br />Higher VSAT costs<br />Suited for high data traffic<br />Telephony applications and point-to-point high-speed links<br />Higher Propagation delay<br />Used by TDMA VSATs<br />High central hub investment<br />Smaller VSAT antenna sizes (1.8 m typically)<br />Lower VSAT costs<br />Ideally suited for interactive data applications<br />Large organizations, like banks, with centralized data processing requirements <br />Source: www.bhartibt.com<br />
ADVANTAGES OF STAR<br />Small uplink EIRP of VSAT (which can be a hand-held telephone unit) compensated for by large G/T of the Hub earth station<br />Small downlink G/T of user terminal compensated for by large EIRP of Hub earth station<br />Can be very efficient when user occupancy is low on a per-unit-time basis<br />
DISADVANTAGES OF STAR<br />VSAT terminals cannot communicate directly with each other; they have to go through the hub<br />VSAT-to-VSAT communications are necessarily double-hop<br />GEO STAR networks requiring double-hops may not meet user requirements from a delay perspective<br />
ADVANTAGES OF MESH<br />Users can communicate directly with each other without being routed via a Hub earth station<br />VSAT-to-VSAT communications are single-hop.<br />GEO MESH networks can be made to meet user requirements from a delay perspective. <br />
DISADVANTAGES OF MESH<br />Low EIRP and G/T of user terminals causes relatively low transponder occupancy<br />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<br />OBP is expensive in terms of payload mass and power requirements<br />
Delay Considerations<br />Satellite Scenario:<br /><ul><li> 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</li></ul>Fiber Optic Transcontinental Link: <br /><ul><li> 4000 km has about 13 ms delay</li></ul>Additionally to either case: Processing delay.<br /><ul><li> Several tens to over a hundred ms.</li></li></ul><li>Value of Satellite Systems<br /><ul><li>Value of satellite systems grows with widely distributed networks and mobility of users
Satellite systems perform most effectively when:
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 bytsunamis, earthquakes, etc..</li></li></ul><li>World Satellite Industry Revenues<br />$91.0<br />$86.1<br />$78.6<br />$73.7<br />$60.4<br />$55.0<br />$49.1<br />$38.0<br />
Global Supply vs. Demand<br />GEO Communications Satellites and Launches<br />
Opportunities in VSAT technology<br />Voice over IP (VoIP) via satellite<br />Frame Relay via satellite<br />ATM via satellite<br />Video-on-demand via satellite<br />Multimedia application<br />Internet/e-mail connection<br />Telemedicine<br />Distance learning<br />
Summary(of previous discussion)<br />Satellite technology is the fastest way to get a reliable connection from A to B in an emergency situation.<br />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. <br />
Ground Antennas<br />The size of the antenna depends on the satellite frequency band used, the data rate, and whether the service is bidirectional or receive only<br />Higher data rates require larger antennas and/or higher power<br />Higher transmit capability (EIRP) of the satellite allows the antenna size to be reduced <br />The use of spot beams instead of global beams improves VSAT link performance<br />Receive-only antennas can be substantially smaller<br />
Steps in Installation of a VSAT site <br />Technical Site Survey<br />Civil Work <br />Antenna Mounting<br />Pointing of Antenna<br />Configuration of ODU<br />
Steps in Installation of a VSAT site<br />Configuration of Indoor Unit<br />Testing on RF level<br />Interfacing<br />BER testing<br />Integration (with the BTS/BSC)<br />
Quality Assurance Tests<br />BER testing<br />Spectrum Analysis<br />Carrier to Noise Ratio measurement<br />
Common Faults/Problems<br />Fading (due to rain etc.)<br />LOS obstructions<br />ODU/IDU malfunctions<br />De-pointing of Antenna<br />Interference<br />
O & M Procedures<br />Carrier Monitoring<br />Spectrum Analysis<br />Fault Diagnosis/Localization<br />RF Power adjustment<br />etc. etc.<br />
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