VSAT (Very Small Aperture Satellite)

by JI, Fang

Introduction

As satellite technology becomes more widely used for telecommunication, extensive use of VSAT systems is growing throughout the world. With its quick development in the past 15 years, now more than one million VSAT systems have been installed and are in operation in over 120 countries.

What is VSAT?

VSAT stands for Very Small Aperture Terminal and refers to a small-sized earth station that receives and transmits one/two way wireless communications by connecting dispersed remote sites to a central hub or earth station via satellite using small antenna dishes whose diameter are between 0.6 to 3.8 meters , which gives it the name “very small.”

	VSAT consists of two modules--an outdoor unit (ODU) and an indoor unit (IDU). The Outdoor Unit can be placed in the backyard or mounted on a roof, working as the interface to the space segment.
Figure 1: VSAT Components

It is composed of a parabolic Antenna, Radio Frequency Transceiver (RFT) which “directs the transmitted power towards the antenna dish and collects the received power from it” [4], Low Noise Block (LNB) which blocks the noise by amplifying the received signal, and Power Amplifier which transmits the signal.

The indoor unit is usually a small desktop-box-size satellite modem located near the user’s existing computers. It contains “receiver and transmitter boards” supporting the interfaces to communicate with other in-house equipment such as LANs, servers, PCs and TVs. [5]

The outdoor unit and indoor unit are connected through an Interlink Facility (IFL), for example a coaxial cable. “The typical limit of an IFL cable is about 300 feet.” [6]

How does VSAT network work?

VSAT networks have different shapes and sizes ranging from 30 terminals to thousands and operate in way of point-to-point or point-to-multipoint data communication. Usually, there are two different VSAT system configuration—Star and Mesh, depending on different application requirements.

Figure 2: VSAT Star System

The Star system always has a high performance hub which hosting an antenna up to 11m in diameter. As many as several thousand VSAT remote sites (terminals) can be interconnected through this central hub. VSAT terminals can be very small and very easy to set up at anywhere that has a line of sight with the satellite. By linking the remote terminals to the central hub, a VSAT network can be easily established. Data, voice and video content can be broadcasted from the hub to all remote sites and vise versa. For practical reasons, most of the terminals are only conducting one-way data transmission though they are capable of doing two-way data transmission. In the USA, only about half of all installed VSATs operate in one-way data transmission. [7]

There are two reasons for use of a single high performance hub. First, it optimizes use of satellite capacity by broadcasting signals from one point to multi points. Secondly, one powerful hub offers a cost effective solution, allowing the operation of low cost remote VSAT terminals. “Typically, a VSAT terminal is 0.1 to 0.2% of the price of the hub.” [8] The Mesh system doesn’t have a hub. It offers point-to-point transmission letting remote sites communicate directly with each other through the satellite. The most common use of Mesh is for rural telephony.

Figure 3: VSAT Mesh System

VSAT Frequency:

The VSAT carries data through several frequencies. (See Figure 4) [9] The antennas of VSATs operating in the C-Band transmit at approximately 4-7 GHz. In general they are larger in size than those used for Ku/Ka-Band.
	Figure 4: VSAT Frequencies

The advantage for transmission in C-Band is that it is relatively unsusceptible to weather conditions while Ku-Band can easily suffer attenuation (loss of signals) due to rain fading or fog. The high frequency 25-30 GHz of Ka-Band supports smaller dish sizes which can be less than 1m but the speed can be up-to 2mb/s or even higher. [10] Ka-Band is ideal for high-speed data transmission.

The Background

As early as 1911, there was an idea of transmitting radio signals through space. It was in 1945 British author-scientist Arthur C. Clarke identified the “geostationary orbit”, the exact location in space where orbiting satellite could best be located. [11] On October 4, 1957, the Soviet Union launched the first manmade satellite, Sputnik. About three years later, US launched the first communication satellite--Echo I which could “reflect” messages back to earth. [12]

The VSAT was first developed in United States around 1980 and was mainly used for unidirectional transmissions via C-Band. The first business using Ku-Band VSATs appeared in 1983 with “low speed bi-directional operation, using simple contention protocols.” [13] From then on, more and more business clients began using VSATs to distribute and collect information between the remote sites and their headquarters.

Today, the global VSAT industry is dominated by three giants. Hughes Network Systems owns 55% share in the global markets while the Gilat Satellite Networks LTD and Scientific Altanta take the remaining part of 40% and 5%. The competition brings technology improvements and attracts more uses. In September 2004, Gilat announced an “upgrade” of Australia’s SingTel-Optus connection to its SkyEdge system. SkyEdge is one of the most advanced technologies owned by Gilat offering a “unified platform supporting a variety of applications and topologies including mesh, star and multi-star.” [14]

What specific problems it is designed to solve?

The biggest advantage of the VSAT network is that it well suited to the needs of large corporations with scattered facilities throughout the world. So organizations such as banks, government departments, schools, hospitals and home offices, VSAT offers end-to-end services and can easily be established as businesses grow with fast deployment. This doesn’t mean small size enterprises don’t need this kind of service. Small-to medium-sized enterprises are “the biggest potential market” for VSAT operators. [15] The cost of VSATs remains the same regardless of distance. As some VSAT user commented “Low initial cost, high levels of service and short time to market have resulted in VSAT being selected by the entire spectrum of commercial organizations.” [16]

VSAT Applications [17]

Another appeal of VSAT is that it is available everywhere. It can operate without terrestrial concerns which make it the ideal solution for communication in remote and rural areas. Concerning the cost of building the infrastructure, it always costs too much for communication operators to lay cable or telephone lines into rural areas. Fifty per cent of the world’s population still has never dialed a phone call, never watched TV or do not know what the Internet is. According to Barry Spielman, director of corporate marketing for satellite operator Gilat, “VSAT networks represent the most cost-effective solution for communities in areas where PSTN (Public Switched Telephone Network) is unavailable, overloaded or too expensive.” [18] In this way VSAT meets important economic needs for developing countries. Countries like Vietnam and Peru have established rural satellite telephony networks for public use. That may give an answer to that why the United Nations has underlined VSATs as “a pivotal technology for developing countries.” [19]

Beyond data broadcasting and telephony, the VSAT can become an Internet provider without replacing any existing equipment. For example, Gilat in Peru is trying to “provide a comprehensive VSAT network solution” by upgrading the existing rural telephony infrastructure. [20] At the same time, Gilat opened the first “always-on broadband Internet service via two-way satellite” in Brazil and users can browse WebPages at a speed “10 times higher than normal speed available in their country.” [21]

How it interconnects with other media?

In the global telecommunication industry, VSAT plays as an essential complement to terrestrial lines. It is widely believed that VSAT can’t compete on the speed in place where cable is widely available. But VSAT has placed its niche not in speed but as a solution which is efficient and effective. Three major advantages make VSAT stand out in the global competition.

Reach Further: wherever you are whether 20,000 miles away from the gulf coast drilling oil platform or living on a mountain 5,000 miles high, VSAT can easily get you connected with the rest of the world which cable can’t. Imagine how much it would cost to deliver a cable line to a rural area with only 100 residents. VSAT can provide services to those places that are impossible for cable to reach.

More Reliable: VSAT is always used as the backup system for terrestrial systems because it has quality transmission competitive or even more reliable than the terrestrial delivery. Interruptions in service are rare and usually take shorter time to repair than when terrestrial communications is in use. On the terrorist attack September 11, 2001, the largest VSAT user-the United States Postal office in New York went back online immediately by “pointing its existing VSAT network towards New York.” [22]

Less Expensive: Maybe the most important advantage is the cost of VSAT network which is much cheaper in installation and operation. As Tim Patterson, manger with the Unites States Postal Service, argued: “VSAT is optimal as stand-alone infrastructure at remote sites and in small-town offices that do not need the full bandwidth provided by terrestrial systems.” [23]

In short, with the advantages of real-time, low cost, easy installation, VSAT became an important player in telecommunications and extends its business widely to “blank areas” where Cable and Telephony is absent.

Technological, Economic, Regulatory Facts

Technological Constraints:

One of the main constraints facing VSAT is a relatively low transmission speed. As in the Star system, the VSAT terminals connect through a central hub. The VSAT terminals transmit to the Hub via an inbound channel using TDMA (Time Division Multiple Access) at a speed range from 64 Kbps to 128Kbps.
	Figure 5: TDMA inbound/ TDM outbound

Meanwhile the Hub communicates with the VSAT via an outbound channel using TDM (Time Division Multiplex) at a higher speed range from 64 Kbps to 512 Kbps. [24]

In this information age when everyone is demanding a higher speed, obviously, VSAT can’t compete with fiber which has the ability to transmit at speeds higher than 2 Mbps per second.

Economic Facts:

Industry analysts confirm that cost of VSATs has steadily dropped since they entered the market. According to Figure 6, it is clear that earth station pricing has declined dramatically from 1990 at $16,000 to $2000 in year 2000.
	Figure 6: 1990-2000 VSAT Terminal Pricing Trends – US$000 (Source: COMSYS)

However, the VSAT network is still costly to initiate and maintain especially in developing countries where people may not have the extra ability to afford VSAT. This problem will be solved in a long run depending on the economic development of developing countries and the rest of the world.

Regulation Facts:

To face the great need for satellite services, the United States published a series of publications to deal with the granting of licenses and the operation of VSATs. The following are cited from Report of the Work Group on the Use of VSATS in the Americas: [25]

1. "FCC Report and Order," published 17 December 1991, "CC Docket No. 90-219", dealing with routine license granting for large networks of small-antenna ground stations operating in the 12-14 GHz frequency bands.

2. "CC Docket No. 90-219, FCC Notice of Proposed Rule Making," published 27 April 1990, dealing with routine license granting for large networks of small-antenna ground stations operating in the 12-14 GHz frequency bands.

3. "FCC Declaratory Order," published 13 April 1987, dealing with routine license granting for ground stations in 6 GHz and 14 GHz bands using antennas smaller than 9 and 5 meters in diameter respectively, for narrow-band and full transponder transmissions.

4. "FCC Declaratory Order," published 9 April 1986, dealing with routine license granting for large networks of small-antenna ground stations operating in the 12-14 GHz frequency bands.

5. "FCC Declaratory Order," published 25 September 1985, dealing with routine license granting for ground stations in the 6 GHz band that use antennas less than 9 meters in diameter for narrow-band transmissions.

While the US VSAT market enjoys a rather open market, the Asian market is somewhat held back by government restriction. For example, the VSAT network in Iran has existed for a long time but was seriously hampered by local government. In mid-May 2001, the Tehran police closed 450 internet cafes, which was supposed to be “inspired by censorship.” [26]

The Global VSAT Forum included that there are four major obstacles in VSAT development: “(1) High licensing fees, (2) Cumbersome red tape, (3) Cost-prohibitive customs duties, and (4) Slow response to license applications.” [27]

The Future Trends:

From One-way to Two-way:

As a mature technology, VSAT is becoming less costly. “A company with 4,000 locations might pay about $60 per month, per VSAT site.” [28] Traditional VSAT services which focus on gas stations and retail chains now are extending into two-way business such as IP (Internet Protocol). The global two-way enterprise IP VSAT managed services are increasing dramatically. (See Figure 7)

According to Christopher Baugh, principle analyst for Northern Sky Research, giant VSAT vendors like Gilat now “place almost total focus on two-way VSAT shipments.” [29]

More Users in Developing Countries:

The great use in developing countries is distant learning. In March 2004, Gilat brought VSAT Connections to Russia’s First Distance Education Project. [30] In India, Gilat has supplied more than 1,500 VSAT network terminals in its rural areas. [31] And for China, the railway stations install the VSAT system for data transmission and voice communication and video conferencing. [32]

In conclusion, since the benefits of VSAT are becoming more apparent, we have reasons to believe that VSAT service with its high functionality and low expenses will support a wider range of global communications in the future.

References

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12. Report of the Work Group on the Use of VSATs in the Americas (August 1995). Inter-American Telecommunication Commission. Retrieved November 8, 2004 from http://www.citel.oas.org/Vsat_report_1.asp

13. VSAT Technology Advance (Sep 15, 2004). Voice&Data. Retrieved November 4, 2004 from http://www.voiceanddata.com.au/vd/pop_ups/pop_print.asp?id=6333.

14. Simon Bull. (April 2003). VSATs : Small Apertures, Big Opportunities. Telecommunications International Edition. Retrieved November 4, 2004 from http://www.telecommagazine.com/default.asp? journalid=2&func=articles&page=0304i09&year=2003&month=4

15. Martin Jarrold.(2004). A+B+C=VSAT. Online Journal of Space Communication. Issue 7, Retrieved November 3, 2004 from www.spacejournal.org

16. Daniel Azaren, William Courtney, Joseph Freitag, Peter Hadinger, Douglas Shannon, Terrence Smigla and Eric Wiswell. (2001) The Multimedia Migration: Transponder Versus Processing Payload VSAT Networks. Space Communications. Issue 17. 24

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18. As 18

19. Luis Adrianzen. (2004). Rural Telephony Solutions: Telerep-Fixed Satellite Telephony in Peru. Online Journal of Space Communication. Issue 7. Retrieved November 2, 2004 from http://satjournal.tcom.ohiou.edu/Issue7/cur_gilattel.html

20. Gilat Delivers Broadband to Brazil(2004). Online Journal of Space Communication. Issue 7. Retrieved October 29, 2004 from http://satjournal.tcom.ohiou/Issue&/cur_gilatcorp.html

21. Frame Relay for Corporate Networks: Satellite Back-up for the United States Postal Service. (2004). Online Journal of Space Communication. Issue 7. Retrieved November 1,2004 from http://satjournal.tcom.ohiou/Issue&/cur_gilatcorp.html

22. Caron Carlson. (December 3, 2001). WorldCom to promote VSAT Service. eWeek. 36

23. Jeong-Hyun Park and Sun-Bae Lim. (September 1998).Key Distribution for Secure VSAT Satellite Communications. IEEE Transactions on BROADCASTING. 274

24. Inter-American Telecommunication Commission (August 1995). Report of the Work Group on the Use of VSATs in the Americas. Retrieved November 2, 2004 from http://www.citel.oas.org/Vsat_report_1.asp

25. Martin Jarrold. (2004). In The Land of the ‘Coffeenet’. Online Journal of Space Communication. Issue 7. Retrieved November 2, 2004 from http://satjournal.tcom.ohiou.edu/Issue7/editor.html

26. Global VSAT Forum. (2004). The VSAT Industry. Retrieved October 23, 2004 from http://www.gvf.org/vsat_industry/issues/index.cfm

27. Denise Pappalardo. (February 4, 2002). VSAT Services Are Finding New Customers. NetworkWorld. 38.

28. Christopher Baugh. Is Content King After All. 24Broadband.

29. Petah Tikva. (March 25, 2004). Gilat Brings VSAT Connection for Russia’s first Distance Education Project. Space Daily, Retrieved November 3, 2004 from http://www.spacedaily.com/news/vsat-04za.html

30. Gilat Satellite Networks Supplies 1,500 VSAT to India (May 2004). India Telecom. 7

31. China Railways to use NSI Voice Module, VSATs. Space News. (March 13, 2000). 10.