iSky.org – Wireless

Step by step the satellite networking is becoming “close to the Earth”, such factors as price, availability and realization, having an increasing impact on the spread of this technology.

One small step for one man but a giant leap for mankind is the technology, which transfers data making its way into open space. Information is no longer tied exclusively to terrestrial networks. Now, thanks to wireless technology, it enters the space and reflect of the constellation of satellites.

Despite the fact that the potential of modern satellite systems is not fully used, they provide independent of the location switched broadband, thanks to which networks and applications are able to reach the most remote corners of the earth – whether it be mountains, deserts or similar places.

FCC gives only basics no recommendations about where you should place a satellite dish, however, these parameters can be considered as well-established. In addition, local rules may include some requirements of buildings owner before you install the satellite system in the place you need. But in general the situation looks quite favorable. This year in February, the World Trade Organization approved the document on how to open the global telecommunications market. Together with the less stringent requirements in the U.S. (thanks to the Telecommunications Act), it should prepare the way for satellite services, as well as for further development and improvement of this technology.

Considering the transfer of network information through space in position of its outlook, please be aware of such factors as price, availability and implementation should be modified accordingly, otherwise this technology is not widespread.

FUNDAMENTALS OF SATELLITE COMMUNICATIONS

The principles of satellite technology is quite simple. Satellite systems transmit signals from ground-based transceivers (receiver / transmitter) on a satellite transponder (receiver / transmitter located on satellites). Transponder receive the signal from a ground station in the microwave range, amplifies it and sends it back to Earth. Transfer to a satellite channel called bottom-up, and from a satellite – top-down.

Parabolic antennas of the ground stations are aimed at the satellite, and compressed signals that contains hundreds of channels comes on the satellite in the form of super-waves. These signals are routed to the remote relay terminals. With the RF modulation and demodulation equipment of radio frequency signal may carry information across the network.

In addition to its usual line (telephony, television, data transmission, etc.) the satellites are using as a backup communications in case of failure of the ground line.

Inevitably?

The catalyst for the development of satellite networking technologies became the Internet and corporate network. Access to the Internet through satellite technology is often much more low than high-speed terrestrial channels. According to the Intranet, the organization of such networks with a help of the land lines is often ineffective because of the constant increase of the volume of files and high delays due to competition for access to the transmitting.

In this satellite network users have high speed access to the Internet and to interactive services. Wireless Access Server operates as an interface between the network Ethernet 10/100 network and satellite components.

Other catalysts used multimedia and entertainment applications for the home. If this market will be sufficiently far-reaching, the satellite is awaiting a real boom.

The development of satellite-based network technologies also stimulates mobile communications. Today, the demand for mobile communications is really high, more than ever, and users will make choices in favor of personal communications and related technologies, this demand will only grow, providing additional pressure on the satellite as a means that providing such services.

P.G. Narayanan is the president of Internet-working Division, indicates one more thing that can increase the development of satellite communications. “Satellite technology is an ideal mechanism for forced circulation, – he explains. – And the technology is in need to be advertising on TV.”

Satellite communication has certain advantages over terrestrial communications systems. With using of wireless technology networks we can reach remote geographical areas, including the countries with poorly developed communications infrastructure. Thanks to its independence from the services of telecommunication companies, satellite communications does not have any intermissions (cable damage during construction work and related confusion does not affects on it).

However, the dignity of satellite technology does not allow to connive at its shortcomings. In particular the satellite network is very expensive and relatively young. And major projects in this area is not so easy to realize (multiple consortia, such as Iridium and Intelsat are trying realize them), in this case company must have substantial financial resources and get approval in several national and international organizations .

From a technical point of view of the potential problem is the blocking of the received satellite signals by buildings and even the leaves of trees, depending on the type of used technology.

The question of information security also requires of its solution: the satellite signal can be received by any unauthorized person. There is no any encryption of satellite channels, but some companies offers software encryption, with the help of which you can protect your traffic from eavesdropping.

TYPES OF SATELLITE

The satellites can be divided into two main categories: GEO and LEO. Among other technologies are the medium orbit satellites and hybrid forms of satellite networks.

For more than 30 years of geostationary satellites provided the only type of commercial communications through space. For one-sided communication, these systems are quite effective, but they have a two-way limited applicability. In fact that demand for power terminals, and significant delays in the transmission signal due to the remoteness of the satellites from the Earth are making them useless for two-way communication, which means that for many high-speed services this technology is not suitable.

This problem is mainly physical. Geostationary satellites revolve around Earth with the same speed as the Earth at the distance of 40 000 km from the planet. On this height the link has the full delay in transmission from the end to end for nearly a quarter of a second. The more time it takes signals to travel there and back, the less bandwidth it can provide.

The determining factor for the magnitude of the delay is the size of buffers for data storage on a temporary basis: the higher the bit rate, the more buffers are overloaded. Restrictions on the buffer size and transfer rate leads to a situation where the system is unable to provide sufficient for some applications bandwidth.

Buffer Size is usually determined by the transfer protocol. For long time experts believed that the buffers impose insurmountable restrictions on the capacity of satellite ATM networks and TCP / IP can support. This year NASA made a series of experiments to determine the effect of buffer size on the rate of transmission. As a result, it was found that TCP / IP via satellite is able to support speeds of up to 622 Mbps.

In addition, the so-called super-geostationary satellites can cover specific areas of the Earth, such as Latin America. These systems are aimed at users who are within a restricted area, so they especially do not need a global service.

If delays in communication of geostationary satellites cause irritation during intercontinental phone calls, so their influence on such type of applications as video conference makes these systems unusable for the network.

Despite its weaknesses, geostationary satellites can provide an effective infrastructure for satellite networks. Many of the shortcomings of technologies are investigated and eliminated step by step.

In spring of 1997 Osicom announced a strategic alliance with ABCN (Asia Broadcasting and Communications Network) in the project based on geostationary satellites. Osicom become the main supplier of technology for high-speed Internet access and interactive services for this project.

ABCN was formed to create a wide base of broadband broadcasting services for Direct Broadcasting Services (DBS), including high speed Internet access and interactive services. Presumably the first geostationary satellite to be launched in late 1997 and the second one in 1998. Each of these systems should provide between 400 and 500 channels for digital DBS services, and provides transmission speeds of 45 Mbps. The satellites will be manufactured by Space Systems / Loral.

Low-Earth orbit are a relatively small constellation of satellites rotating at a lower altitude than geostationary system. These satellites can be divided into two main classes: large and small. First working on frequencies above 1 GHz, and the second one on less than 1 GHz.

Communication through LEO satellites has a small delay and the potential to increase its capacity. However, in the case of low-Earth orbit communications satellites provide a greater number than in the case of geostationary counterparts. Used principles here are really close to the technology used in cellular phones, except that the base stations are located at a distance of hundreds of kilometers from land. This similarity with the telephone services looks very promising.

Teledesic Network, which is scheduled to start operation in 2002, is deployed with the support of Bill Gates and a pioneer in the field of cellular communications Greg MacKay. Presumably, the network will be supported by 840 low-orbit satellite which include data and voice transfer with the typical optical speeds.

Teledesic Network will consist of 840 interconnected low-Earth orbit to provide voice, data and video transfer. Thanks to a global agreement, network will provide digital connections between users of the network, as well as to other customers of other networks through gateways, it are reported, the delay will not exceed the value of similar value in the transmission of an optical cable. Different types of terminals will be available on-demand channel of transmission speeds from 16 Kbps to 2048 Mbps (E-1) and, for special applications up to 1,244 Gbps (OC-24).

As expected, Teledesic Network will support a maximum capacity of 1 million compounds Full E-1. In addition, the availability level of channel would be 99.9% for of the United States. Teledesic intends to provide services to operators, but not to end users.

Another project with the usage of large low-Earth orbit satellites is Iridium. It is implemented by a consortium of organizations such as Lockheed Martin, Motorola, Raytheon and Sprint. Iridium network will consist of 66 satellites and provide a link between them, moreover, calls will be handled directly at the satellite. This technology provides for the use of software, as well as commuting computers on satellites.