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Teledesic: The Orbiting InternetTeledesic: The Orbiting Internet


Teledesic Corp.Teledesic was formed in June of 1990 with the objective of creating a means of providing affordable access to advanced network connections to all those parts of the world that will never get such advanced capabilities though existing technologies.

Information is becoming increasingly essential to all those things we associate with quality of life: economic opportunity, education, health care, and public services. Yet, most people and places in the world do not now have access even to basic telephone service. Even those who do have access to basic phone service get it through 100 year old technology - analog copper wire networks, that for the overwhelming part will never be upgraded to an advanced digital capability. Even in the developed countries, there is a risk that whole areas and populations will be denied access to the powerful digital technologies that are changing the world.

Teledesic InternetThe digital revolution is just as fundamental as the industrial revolution and the agricultural revolution before that. It will change all aspects of our societies. Those previous changes took place over many generations, indeed in parts of the world they are still ongoing today. Driven by advances in microelectronics technologies, where product generations are measured in months, the digital revolution is taking place at a breathtaking pace. The digital technologies that grow more powerful every day in our notebook computers will soon be exploding out through network connections. Yet, outside of the most advanced urban areas, most of the world will never get access to these technologies through conventional wireline means.

While there is a lot of fiber out there in the world, and the number of places is growing, it is used primarily to connect countries and telephone company central offices. Even in Europe, little of that fiber will be extended for local access to individual offices and homes, which represents 80 percent of the cost of a network. In most of the world, fiber deployment likely never will happen.

This is a big problem for all of our societies. If these powerful technologies are available only in advanced urban areas, people will be forced to migrate to those areas in search of economic opportunity and to fulfill other needs and desires. Society now is organised around the economics of infrastructure. With the agricultural revolution, technology tied people to the land and brought them together in towns and villages. With the industrial revolution, people came together in increasingly congested urban areas, all organised around the economics of industrial infrastructure - wires, rails, highways, pipes, machinery. To the extent the digital revolution is tied to wires, it is just an extension of the industrial age paradigm. Like the highways and the railways before that, wires are rigidly dedicated to particular locations. If you live along side the main line you prosper. If you live a few miles distant, you are left behind.

To date, Teledesic has received most of its funding from Bill Gates, the founder of Microsoft, the world's largest computer software company and Craig McCaw who founded McCaw Cellular, the world's largest cellular communications service provider before its sale to AT&T in 1994. Their investment is symbolic, as well as financial.

Moore's Law, which says that a microprocessor will do twice as much for the same cost every 18 months, has correctly predicted the exponential growth of the computer industry for over 20 years. However, while computers today are thousands of times faster than those available a decade or two ago, networking has shown only linear growth. Improvements in networking performance, which have required the digging up of the streets and replacement of the antiquated copper with modern fiber optic technology, have not come close to keeping pace.

The solution is wireless access to advanced network connections. Unlike wireline technologies, the cost of wireless access is largely indifferent to location. But to get the bandwidth required for fiber like service through wireless means, it is necessary to move way up in to the millimeter wave frequencies in the 20 to 30 GHz range (the Ka band). But, sending signals horizontally, over the land, in those frequencies is problematic. They are subject to rain attenuation and blocking by terrain, foliage, and buildings. The solution adopted was simple. Send the signals vertically. This leads to a satellite based solution.

To ensure seamless compatibility with those fiber networks, it is important that the satellite network have the same essential characteristics as fiber. Those characteristics include: broadband channels, low error rates, and low delay.

The advanced digital broadband networks will be packet switched networks in which voice, video, and data are all just packets of digitised bits. In these networks you cannot separate out the applications that can tolerate delay from those that can't. People will not want to maintain two networks: one for delay sensitive applications and another for applications that can tolerate delay. Traditional geostationary orbit (GSO) satellites will never be able to provide fiber like quality of service.

Teledesic SatelliteThis leads to a low Earth orbit (LEO) network. To put this in perspective, the space shuttle orbits at about 250 kilometers above Earth's surface. There is only one geostationary orbit, and that is over the equator at 36,000 kilometers almost 150 times further out than the space shuttle. By contrast, Teledesic's satellites would orbit at about 700 kilometers, 50 times closer to Earth than geostationary satellites.

With the combination of a very high minimum vertical angle to the satellite to overcome the blocking and attenuation problems associated with the Ka band and the low altitude, geometry takes over, and a constellation of hundreds of satellites is required to cover Earth. The large number of satellites also allows economies of scale in manufacturing and creates a system with very large capacity which allows a low cost of service.

The concept of a network consisting of hundreds of satellites may seem like a radical concept when compared to traditional geostationary satellites but it is less radical when compared with the evolution of networks on the ground. Computer networks have evolved from centralised systems built around a single mainframe computer to distributed networks of interconnected PCs. Similarly, satellite networks (for switched network connections) are evolving from centralised systems built around a single geostationary satellite to distributed networks of interconnected LEO satellites. The evolution in both cases is being driven by some of the same forces.

A decentralised network offers other advantages: A distributed topology provides greater reliability. Redundancy and reliability can be built more economically into the network rather than the individual unit. Also, because a LEO satellite has a smaller footprint within which frequencies can be reused, it is inherently more efficient in its use of spectrum resources. Geostationary satellites will continue to have an important role to play, particularly for broadcast applications where their large footprint is advantageous. But increasingly, geostationary satellites will coexist with non-geostationary orbit (NGSO) satellite networks.

This evolution toward NGSO systems has resulted in three LEO system types, each focused on a different service segment and using a different portion of the radio frequency spectrum. The best way of distinguishing between these three LEO system types is by reference to their corresponding terrestrial services:

The so-called little LEOs, like OrbComm, are the satellite equivalent of paging. They operate below 1 GHz, and provide simple store and forward messaging. These systems offer low data rates but can provide valuable services in a wide range of settings, such as remote monitoring and vehicle tracking.

The so-called big LEOs like Iridium, Globalstar and ICO, have received the most attention. They are the satellite equivalent of cellular phone service, and operate between 1 and 3 GHz.

Teledesic is the first proposed broadband LEO. It will provide the satellite equivalent to optical fiber. Because it will operate in the Ka band, essentially line of sight from the user terminal to the satellite is required, which makes it more appropriate for fixed applications, or mobile applications like maritime and aviation use, where line of sight is not an issue. It will provide the advanced, digital broadband network connections to all those parts of the world that are not likely to get those capabilities through wireline means.

When Teledesic was first publicised in early 1994, most people seemed to have difficulty comprehending the services that the Teledesic Network would provide. It is not cellular like hand-held phones, like Iridium and Globalstar, and it is not broadcast video delivery, like Hughes's DirecTV.

Since then, the emergence of the World Wide Web and network-centric computing have provided a compelling model for a different kind of telecommunications: switched, broadband services. Peer to peer networking, based on the ubiquity and exponential improvements of personal computing, is transforming the way individuals live and businesses create value. Switched connections communicate from anyone to anyone, and broadband allows the transmission of all forms of digital information, voice, data, videoconferencing, and interactive multimedia.

The Internet today is still at a relatively primitive stage of development, comparable to the first personal computers in the late 1970s. At that time, it was difficult to imagine the pervasiveness and range of applications of personal computing today. By contrast, the World Wide Web already provides a revealing glimpse of the promise of the Internet, with tens of thousands of companies and millions of individuals exploring, publishing and developing on this new medium. Any and all information can and will be digitised, uploaded, and transmitted anywhere.

Well, not quite anywhere. The promise of the information age is constrained by the lack of access to switched, broadband services in most of the developed and virtually all of the developing world. The Teledesic Network will provide a means to help extend these switched, broadband connections on demand anywhere on Earth.

There is an important aspect of these non-geostationary satellite systems that is worth noting. There have been many studies, many of them by the ITU, that show a direct correlation between economic prosperity and teledensity. In the absence of a high level of economic development, however, a country is not likely to attract the investment required for an advanced information infrastructure. NGSO systems like Teledesic can help developing countries overcome this problem in telecommunications development.

Once you come out of a geostationary orbit, then by definition, satellites move in relation to Earth. With an NGSO system, continuous coverage of any point requires, in effect, global coverage. In order to provide service to the advanced markets, the same quality and quantity of capacity has to be provided to the developing markets, including those areas to which no one would provide that kind of capacity for its own sake. In this sense, NGSO satellite systems represent an inherently egalitarian technology that promises to radically transform the economics of telecommunications infrastructure. It is a form of cross-subsidy from the advanced markets to the developing world, but one that does not have to be enforced by regulation but rather is inherent in the technology.

Even at the speed of light, round trip communications through a geostationary satellite entail a minimum transmission latency end to end delay of approximately half a second. This latency causes the annoying delay in many intercontinental phone calls, impeding understanding and distorting the personal nuances of speech. What can be an inconvenience for analogue voice transmissions, however, can be untenable for videoconferencing and many data applications.

Excessive latency causes otherwise high bandwidth connections to communicate at a fraction of their capacity. And these issues arise not with obscure data protocols or obsolete hardware, but with almost all implementations of the only data protocol with which most people are familiar, TCP/IP, which connects the global Internet and is the standard for corporate networking.

Teledesic Internet OrbitFor all lossless protocols that guarantee the integrity of the data transmission, latency is a constraining factor on the usable bandwidth. Since a data packet may be lost in transmission, a copy of it must be kept in a buffer on the sending computer until receipt of an acknowledgment from the computer at the other end that the packet arrived successfully. Most common data protocols operate on this principle. The data packet's trip over the geostationary connection takes 250 milliseconds at best, and the acknowledgment packet takes another 250 milliseconds to get back, so the copy of the data packet cannot be removed from the buffer for at least 500 milliseconds. Since packets cannot be transmitted unless they are stored in the buffer, and the buffer can only hold a limited number of packets, no new packets can be transmitted until old ones are removed when their acknowledgments are received.

Specifically, the default buffer size in the reference implementation of TCP/IP is 4 kilobytes, which is 32 kilobits. This means that at any given moment, only 32 kilobits can be in transit and awaiting acknowledgment. No matter how many bits the channel theoretically can transmit, it still takes at least half a second for any 32 bits to be acknowledged. So, the maximum data throughput rate is 32 kilobits per half second, or 64 kilobits per second.

To put this in perspective, if you take off the shelf hardware and software, hook up a broadband geostationary link, and order a T1 line (1.544 megabits per second), you expect to be able to transmit about a T1 line worth of data. In fact, any connection via a geostationary satellite is constrained to only 64 kilobits per second, which is 4 percent of the purchased capacity.

Changing protocols is not a feasible solution to this situation. The trend in data networking is toward a single pipe carrying many types of data (including voice and other real-time data). It is therefore likely to be neither useful nor economical to transmit specific kinds of data using custom, proprietary protocols. In theory, the implementations of standard protocols, such as TCP/IP, can be modified to support higher buffer sizes. But these modifications are rarely simple or convenient, as computers on both sides of any connection need to be upgraded. Moreover, the maximum buffer size possible in TCP/IP is 64 kilobytes, which still only provides 1.024 megabits per second, or 67 percent of a T1 line over a geostationary link.

Even worse, if the geostationary link is not at one of the endpoints of the data transmission but is instead an intermediate connection, there is no method to notify the transmitting computer to use a larger buffer size. Thus, while data packets can seamlessly traverse multiple fiber and fiber like networks (such as Teledesic), geostationary links are unsuitable for seamless intermediate connections.

The interplay of latency and buffer sizes does not affect all data transmissions, only lossless ones. For real time data, such as voice and video, where it is not essential that all data be transmitted, lossy protocols can transmit higher data rates with less overhead. Unfortunately, real time applications, such as voice telephony and videoconferencing, are precisely the applications most susceptible to unacceptable quality degradation as a result of high latency.

Instead of attempting to modify the entire installed base of network equipment with which one might want to communicate, receiving seamless compatibility with existing terrestrial networks becomes increasingly attractive. As both bandwidth requirements and the use of real time data accelerate, the benefits of the fiber like service that Teledesic offers are only growing in importance.

What all of this discussion makes clear is that no one single technology or satellite system type is going to be appropriate for all communications needs in all settings. The capabilities of fiber cannot be matched for very dense traffic. For basic telephone service, the economics of terrestrial cellular systems are compelling, particularly where no wireline infrastructure exists. Geostationary satellites will continue to play an important role, particularly for video distribution and other broadcast applications, where latency is not an issue and a large footprint is desirable. And each of the LEO system types has an important role to play.

For the past 30 years of satellite communications, geostationary satellites have been virtually the entire relevant universe and the international satellite spectrum allocations and associated regulations reflect that. Geostationary satellites currently enjoy general priority status in all fixed satellite service frequency bands. This subjects NGSO satellite systems to unbounded regulatory uncertainty, as their operation would be vulnerable to preemption by any and all geostationary satellites, even those deployed long after the NGSO systems. For someone like Teledesic who proposes a non geostationary satellite system, special accommodation is required, by contrast, someone proposing a geostationary satellite system need only file the appropriate paperwork with the ITU.

In bands such as the C and Ku bands that already are congested with geostationary satellite systems, it would not be appropriate to change this regime. To allow for the future development of both satellite system types, however, designated sub bands in which non geostationary systems would have priority status need to be established in the satellite service expansion bands.

Of course, the value of systems like Teledesic or any technology ultimately is measured by their ability to enhance the quality and meaning of our lives. The benefits to be derived from the advanced information services they enable are as vast as the areas of need to which they can extend.

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