Visions of the 21st Century Communications Is the Shortage of Radio Spectrum for Broadband Networks of the Future a Self Made Problem?
by: Paul Baran, baran@com21.com
Copyright 1994.
INTRODUCTION
John McQuillan:
Visions of the 21st Century Communications Many of us are wondering what is the role for ATM in the next decade and beyond. It's not far away now, and one of the questions we haven't talked about at this Conference, that we want to focus on now, is wireless an whether the spectrum for wireless is really the scarce resource that many of us have been familiar with all our lives or whether it's really an abundant one.
One of the great challenges for the 21st Century, I believe, is to get al the power of broadband networking that we've been talking about, and, at the same time have the convenience and flexibility of wireless communications. This would indeed be the grand unification. ATM isn't the grand unification - - it's wireless ATM that is the gran unification. And what will it take to bring ATM into the home?
But to make perhaps a more personal introduction for a moment, I did my Ph.D. work in Adaptive Routing Algorithms at Harvard twenty years ago. I did my Ph.D. in 1974. At the time I tried to read everything I coul about what had been done in packet networking up until that point and I came across Paul Baran's work at RAND Corporation ten years previous in 1964.
When Paul sat down, and I don't know how he did this, but he wrote series of ten reports describing, analyzing and predicting packet switches, based on hardware, adaptive routing algorithms, wireless links between them and really conceived of the whole way that we're planning to build hardware ATM based systems today. So, Paul sees things before other do.
You know, in fact, one tries to describe people by their time constant Some people think one day at a time. Some people are good at planning month by month or year by year. You know you can't ask someone to do a three year plan in a business if they're a one week kind of a person. You can think of running the military: You've got to have a day at a time foot soldier; you've got to have your logistics people be people who can plan a little bit longer; and then the generals who are planning th theaters of operation have got to be able to see out a year or two.
Well, I've never met anybody with a longer time constant and a more accurate record than Paul Baran... Paul!
PAUL BARAN:
Thank you John!
John entitled this talk Visions of the 21st Century. I am humbled tryin to do justice to such an over-reaching title. I am reminded of tha Wausau Insurance Company TV commercial. An efficiency expert is introduced who is supposed to give a detailed presentation on insurance recommendations. This guy gets up to the podium and says one word, "Wausau". Then he walks off the stage to an awkward silence, until the audience presumably gets the point.
I have to confess that I am tempted to say the three magical letters, ATM (Asynchronous Transfer Mode) and then sit down. ATM pretty well define where the higher level protocol portion of the network evolution is going in the future. At least in the mind of some of we ATM techno-bigots.
PHYSICAL MEDI
We have only a limited number of terrestrial transmission media to consider. Really, only four. For the metropolitan network, the cable TV network appears to be the winner, using a combination of fiber at the top of the tree networks, while the tails are coaxial drop cables to houses and businesses. This two-way path provides a lower cost transmission pip to the home than twisted copper pairs and can even support telephony at a lower cost than in place twisted pairs. This is the position announced by Pac Tel in California. Thus, we expect to see both the telephone and TV cable companies competing using essentially the same technology.
When it comes to transmission over distances greater than about a kilometer, fiber is the clear winner. And the capabilities of fiber suggest continuing significant cost declines and capability increases over time in terms of $/bit-kilometer.
This morning I would like to discuss an issue that limits this possibility of our next generation networks. In brief, I am going to talk about communications policy issue that will determine what we can, and won't be able to do with our emerging networks of the future. Our particular concern is that well meaning government administrators, responsible for control of the radio spectrum space, are making seemingly innocent decisions that could have disastrous unforeseen consequences. It coul even cause our networks of the future to be unnecessarily expensive and less capable than if a wider appreciation of what's really happening was better understood. Of course, any negative consequences of such a resul are totally at variance with the objectives sought by those responsible for telecommunication policy. What appears to be missing from the deliberations is an understanding of some basic technological issues.
THE SHORTAGE
The key point at issue that we will question is the widespread belief that we don't have enough radio spectrum to go around. This is a common, fundamental belief. Since we live in a world of scarcity or natural resources it is almost automatic that we believe that there is a shortag of frequencies. This particular resource is somewhat different.
This morning, let's start by reviewing this presumption of a permanent shortage. Let's consider how, with an application of already known technology, we could create even a surplus of frequencies. What may be going on is an inadvertent shortage created by a regulatory structure which has yet to appreciate the potential capabilities of the new digita signal processing technology as applied to communications.
A LINK IS NOT A SYSTE
When we talk about radio or wireless in the following, we should appreciate that no single communications medium is ideal in ever situations, so we build communication networks by choosing the combination of various media links, optimized as a network. If our link requirement is for long distance transmission, then fiber optics tends to be ideal. If it is for distribution of signals to many users located only hundreds of meters apart from one another, then coax cable or twisted pai is the preferred medium, depending on the data rates. And, in the futur when we deal with increasing numbers of users, wireless could in turn become the preferred medium, particularly for the network tails in a increasing number of instances. Conceptually this remove the constraints of being like the dog whose freedom of action is limited by the length of his leash.
A PARADOX
Of course any suggestion that there is no real shortage of UHF spectrum is at variance with the common wisdom. But, tune a spectrum analyzer across the band of UHF frequencies, and you will encounter a few strong signals, while most of the band at any instant is primarily silence, or very weak signals. (My words this morning are focused on the UHF range, that's the frequencies from 300 to 3,000 megahertz -- the most valuable part of the radio spectrum for communications with high data rate local data devices.)
TABOO FREQUENCIES
SPREAD SPECTRU
NEGROPONTE'S SUGGESTIO
We can save a vast amount of bandwidth by at least starting to off loa applications that hog bandwidth and that could be better served by usin alternative media. For example, TV cable now passes about 96% of the U households and could allow many more TV channels to be delivered to the home than can be supported over the air and could release a vast amount of spectrum space. The use of TV cable started primarily in the US and i also now rapidly growing internationally. Professor Negroponte of MIT oft quoted half facetious words to the effect that the way to solve thi problem is Tthat everything now sent by radio should be sent over wires and everything now sent by wire should be sent by radioU does have som merit. And the transfer need not be 100%. Shorter range rf transceivers connected to fiber could produce a significant improvement - - tremendous improvement, really. Let's talk about the ...
EVOLUTION TO DIGITAL
Digital modulation is the key. It is far more bandwidth efficient than todayUs analog modulation. Digital modulation in lieu of the present analog modulation allows ten times as many TV signals to be sent over an existing TV cable and of better quality. If a TV cable carries 50 analog channels, then the same cable would now carry 500 channels. The 50 channel digital TV cable systems are in early manufacturing stage today. The demand for this capability is not to present 500 different channels of TV, but rather to allow the transmission of pay-per-view movies with multiple start-times to make them more attractive to potential viewers. So, the same program would start on the hour, thirty minutes after the hour, on the next hour... so when you come in, you would be able to see a movie right from the beginning
RANGE REDUCTION
Another direction that promises great improvement in bandwidth efficiency is in the reduction of the transmitted power. In the UHF band the number of geographically dispersed users that can be simultaneously accommodated in a fixed spectrum space varies as the inverse square of distance. Cut the range in half, and the number of users that can be supported is doubled. Cut the range by a factor of ten, and 100 times as many users can be served. Reduce the power further, and essentially any number of users can be fit into the exact same spectrum space presently tied u supporting a few longer distance users. Thus, a mixture of terrestrial links plus shorter range radio links has the effect of increasing b orders and orders of magnitude the amount of frequency spectrum that ca be made available. We speak of inverse square ranges. While true for free space signals, when it comes to the real world, the payoff is even more dramatic. For example, radio signal attenuation within concrete office buildings, such as a building like this one we are in now is closer to the inverse 4Uth power of the transmitted power. Given the attenuation encountered in these type of buildings means that increasing radiated power doesnUt buy much in the way of range, anyway. By authorizing hig power to support a few users to reach slightly longer distances we deprive ourselves of the opportunity to serve the many.
SMART TRANSMITTERS
SOME KINDERGARTEN RULES
Rule #1. Keep away from the big bullies in the playground. (Avoid the strongest signals.)
Rule #2. Share your toys. (Minimize your transmitted power. Use the shortest hop distances feasible. Minimize average power density per Hertz.)
Rule #3. If you have nothing to say, keep quiet.
Rule #5. If you feel you absolutely must beat up somebody, be sure to pick someone smaller than yourself. (Now this is a less obvious one, as weak signals represent far away transmissions; so your signals will likely be attenuated the same amount in the reverse direction and probably not cause significant interference.
Rule #6. DonUt get too close to your neighbor. Even the weakest signals are very strong when they are shouted in your ear.
Rule #7. Lastly, donUt be a cry baby. (If you insist on using obsolete technology that is highly sensitive to interfering signals, donUt expec much sympathy when you complain about interfering signals in a shared band.)
That about summarizes that subject other than to note that this isn't the way we presently handle frequency assignments
The hang-up here today is that our highly institutionalized regulatory structures contain implicit assumptions about technology that once were true; less so today, and probably not at all tomorrow. The regulatory game is run by lawyers, while the issues are primarily technical. Lawyers tend to view the frequency similar to a piece of real estate. If I owned a frequency, then you canUt use my frequency. ItUs mine, all mine. Frequencies today are treated as a property right. Yet, communications engineers know that statistical averaging of larger blocks of frequencies allow far better usage. That's something we all know about. This is the heart of the concept of sharing an ATM network. We all win as each shared user encounters far better economics than if we had to dedicate a separate network to each group of users. We did that in the old days. This concept of sharing is what cellular radio is all about. Of course we finally did get cellular, but over a decade was wasted because of the regulatory lag between the time that technology was feasible until the time that it was implemented. In fairness, newer thinking is increasingly being incorporated in our regulatory decisions. But, from the point of view of a technologist, the process is agonizingly slow. I think we can do better.
WHERE WE ARE
Today the pioneer who proposes to use the radio spectrum in any trul innovative way faces a bureaucratic hoop jumping game, interrupted with interminable delays. Underneath it all is the implicit assumption that there is a God given shortage of frequencies. That being so, the government must dole out the slivers with great care. It does so using a set of rules based on concepts inherited from an earlier era, but now cast in administrative laws. The lawyerUs real estate model of frequencies is but a zero sum game; while the communications engineer views it as a game where many more can win.
ORIGIN OF THE FREQUENCY SHORTAG
Lack of frequencies is not a new problem. Next year, radio is going to be 100 years old counting back from the time Marconi, as a teen teenager, ra his first experiments in his back yard. Yes, we got radio as a byproduc of an experimental hobby activity; not as the result of any major corporation's research department. The first experiments in radio were funded by Marconi's mother as his father refused to come across with th pocket change for such foolishness -- at least until the time radio worked. Then, his father became a great supporter -- with an excess of advice.
The issue of spectrum efficiency has been with us right from the outset, starting with the early question, "Would it ever be possible to allow more than one radio transmitter to operate at one time?" Sharing the channel was one of the first challenge to early radio technology development. Ever since the turn of this Century much of the history of radio technology has focused on living within an over-crowded radio spectrum. Given the limitations of past technology, the shortage of preferred frequencies was real. Very real. And, with an excess of potential users it was mandatory for governments to create the necessary rationin mechanism. National and international regulatory structures evolved, concerned in major measure with the ever present issue of scarcity o bandwidth. And, so it was institutionalized into regulatory policy. And once institutionalized, the basic assumptions that got us there are very rarely ever re-examined. And, when they were, changes tended to occur at glacial speeds. .
CREATING MONOPOLIES
To put things into perspective, let's take a moment to understand how the game was played in the past, leading up to today and consider a likely scenario or two. Early spectrum was acquired by the pioneer user, but with the government use assuming priority. As additional spectrum was awarded, it tended to be granted in response to economic and political power of the applicants. Whatever organization held most power obviously was serving most users. Economists regard regulation as a substitute for competition and preferred its use whenever a natural monopoly exists Whenever a government issues frequency, it creates a monopoly. Become a regulated monopoly, and the government will keep out your competitors
TERMINATING MONOPOLIES
When a better technology comes along that allows the feasibility of multiple suppliers, it invalidates the natural monopoly argument. The en of a monopoly is rarely a swift process and it is never painless -- particularly if it were well run and highly profitable. After long running anti-trust battles the US telephone monopoly, AT&T, was in part fractured into seven local area monopolies and competition was permitted in the long distance telephone and data communications field. This was an extremely controversial move at the time, and was met by all sorts o Chicken Little sky falling predictions. The sky didn't fall. Instead w saw a major increase in effectiveness in long distance services, fostered by the new competition. And this was perceived as being so successful by other countries, that similar long distance services are being deregulate throughout the world, even by those nations with a long history of sole governmental control.
DEREGULATION OF THE REST OF THE SYSTEM
CREATION OF A NEW MONOPOLY
If you spent all your life working in a monopoly and it is going away, it is understandable that you may want to create another one. But, where If the technology is going to be a combination of TV cable technology plus radio tails, a monopoly protection defense line might be the regulate spectrum ownership of the tails of the network. Maintenance of the monopoly then hinges on maintenance of a spectrum shortage. Those that "own" today's frequencies face a diminished value of their asset unless the shortage can be maintained
THE AUCTIONING GAME
The frequencies being auctioned off today (and there's going to be a big sale of these next month) came partially from a give-up of the frequencie reserved by the military and partially from point to point users who are to be assigned alternative frequencies, and who will receive payment for new equipment in the process. While auctioning might seem to be an answer to an unsolved problem, I believe that it will exacerbate the problem and is more likely to lead to the creation of new monopolies. He with the most up-front money gets to lock up frequencies to create an oligopolistic>