Friday, January 22, 2010

Sand to Silicon By Shivanand Kanavi, Internet Edition-5


“Electrical engineering is of two types: power engineering, which tries to send optimal amount of energy through a line, and communication engineering, which sends a trivial amount of energy through the wire but modulates it to send a meaningful signal”

a technology visionary, dean of MIT and mentor of Claude Shannon.

Death of distance’ is a catchy phrase to express a thought that mankind has had for long—“Oh, I wish I were there”. Travelling in space and time has been right on top of the human fantasy list. It is as if the ‘self’, after becoming aware of itself, immediately wants liberation from the limitations and confines of the body, free to pursue its fancy.

We yearn to travel everywhere in space. Mundane economic reasons may have actually fuelled the transportation revolution: starting with the wheel and progressing to horse carriages, sail ships, steam locomotives, automobiles, bullet trains, airplanes and, finally, manned space exploration. But at the back of every transportation designer’s mind is the dream of speed, the ability to cover vast distances in no time.

In this portion of the book, we will not talk about transportation or the teleportation of science fiction, but about an even more basic urge—the urge to communicate, the urge to reach out and share our thoughts and feelings. This is so basic a desire that it is at the foundation of all civilization and of society itself. Communication is the glue, the bond that builds communities. No communication, no community. Interestingly, the origin of both ‘communicate’ and community’ lies in the Latin word ‘communis’— what is common or shareable. The urge to communicate created language.

The concepts of time and space travel would not have existed if somebody had not created imageries of different times and places—or history and geography. To access knowledge of a different time period we need to have access to archives of stored knowledge about that period, which is where history comes in. But to have access to another place we need quick transportation and instant communication.

Physical transportation has severe limitations imposed by the laws of physics; hence the ancient Indian puranas† talk of the mind’s speed as being the swiftest. But if we can piggyback messages on faster physical carriers then we can achieve speed in communication.

These carriers could be the Athenian runners from Marathon, the poetic clouds in Kalidasa’s Meghadoot,‡ carrier pigeons, or invisible waves of energy, like sound, electricity and light. The development of different carriers to convey our messages underlines the history of communications as a technology.

‘Death of distance’ is a dramatic way of expressing what has been achieved in this technology, but the driving force behind it is the basic urge of the human spirit to reach out.


Voice dominates all human communication. There is a psychological reason for this. Voice and the image of a person add new dimensions to communication. The instrument that decodes the signal, our brain, perceives many more levels in a communication, when voice and image accompany language.

†Ancient Indian mythological texts.
‡Messenger cloud, Sanskrit poetic work by Kalidasa, 4th century AD.

The auditory cortex and the visual cortex of our brain seem to trigger a whole lot of our memories and are able to absorb many more nuances than happens when we merely read a text message in a letter or e-mail, which is processed in the linguistic part of the brain. N. Yegnanarayana of IIT, Madras, who has spent over forty years in signal processing and speech technology, wonders how our brain is able to recognise a friend’s voice on the telephone even if the friend has called after several years.

Data communication came into being with the advent of computers and the need to enhance their usefulness by linking them up. It has less than fifty years of history. Meanwhile digital technology has evolved, which converts even voice and pictures into digital data. This has led to data networks that carry everything—voice, text, music or video. This is called digital convergence.

The economic value of telecommunications services has resulted in large resources being deployed in research and development. This has led to rapid changes, and one of the crowning achievements of science and technology of the twentieth century is modern telecommunications technology.

An attempt to trace the history of telecommunications runs the risk of spinning out of control. There have been several forks and dead ends in the road traversed by communications technology, and these are closely associated with major developments in physics and mathematics.

Some historians have divided the history of telecom into four eras: telegraph and telephone (linked with electromagnetism); wireless (linked with electromagnetic waves); digital technology in signal processing, transmission and switching (linked with electronics); and optical networks (linked with quantum physics). I have employed the historical approach in some parts of this book, which I believe puts things in perspective and strips them of hype. But we will abandon it for a while and try a different tack. Let us start from the present and swing back and forth between the past and the future.


What is the telecommunications revolution all about? Consider these five broad themes:

No man is an island: A personal communication system has come into being with cell phones, which allows us to reach a person rather than a telephone on a desk. With the spread of the mobile phone network over large parts of the urban world, instantaneous communication has become possible. At no point in time or space need one be out of reach. Well, that is a slight exaggeration in the sense that we cannot reach a person anywhere on the globe with an ordinary cell phone. But with global mobile personal communication systems (GMPCS) or satphones for short, we can be in touch with the rest of the world even if we are on Mount Everest. Satphones are not as affordable as mobile phones, so they are used only for special missions: mountaineering expeditions, media coverage of distant wars, on the high seas, etc. A geologist friend of mine, who was part of an Indian expedition to Antarctica, could keep in touch with his family in Baroda via satphone. The tag line in an ad published by a satphone service was: “The end of geography”.

Connecting India: Much before mobile satphones came into being, you could, thanks to communications satellites, use an STD, or subscriber trunk dialling, facility to call Agartala or Imphal in the north-east of India, or Port Blair in the Andaman Islands. Indian stock exchanges have built computer-based share bazaars in which one can sit anywhere in India—in Guwahati,
Bhuj, Jullunder or Kumbhakonam—and do a trade. This is made possible by a network of thousands of VSATs (very small aperture satellite terminals). They can connect their trading terminals to the central computers through a satellite communications system. A network of automated teller machines, or ATMs, have spread around Indian cities in a short period of time, allowing for twenty-four-hour banking. You must have heard of the terrible cyclones that keep hitting the east coast of India, but have you heard of large-scale loss of life due to these cyclones in the last ten to fifteen years? No. The reason is the digital disaster warning system in the villages of the east coast, which is triggered by signals from a satellite. Also, satellites have made it possible for nearly a hundred channels to broadcast news, music, sports, science, wild life, natural wonders and movies in different languages. Twenty-four hours a day of information, entertainment and plain crap. (But that is not a technology issue).

Telephony for the masses: In less than ten years from 1985 we got direct dialling facilities, or STD, to and from all major towns and cities in India and with voice quality greatly improved. The long wait outside a post office to make a ‘trunk’ call was replaced by instant connections at street corner STD booths. This was due to the conversion of the Indian telephone network into a digital system and the development of digital switching at the Centre for Development of Telematics, or C-DOT. The C-DOT class of switches, used in almost all exchanges in India, is one of the most widely used class of switches in the world. Long-distance communications have come to the doorstep of every Indian, despite a relatively small number of telephones per thousand of population.

Global village: A World Wide Web of information and communication has come into being through the Internet, which has levelled the playing field for a student or a researcher in India vis-à-vis their counterparts in the most advanced countries. It has brought the dream of a universal digital library containing millions of books, articles and documents nearer to reality. Internet-related technologies have greatly reduced the cost of communication through e-mail, chat, instant messaging, and voice and video over Internet. They are making global collaboration possible. The Internet is also creating the conditions for a global marketplace for goods and services.

Telecom for all: The cost of a long-distance telephone call has fallen steeply due to the digital communications revolution and rapidly falling bandwidth costs. Optical networking shaped this reality.

We will look at the evolution of the Internet in the next chapter, but let us now see how the other four features of the telecom revolution came into being.


The first major step in the telecom revolution was the digitisation of communications. But the difference it made will not be clear unless we get a broad picture of what existed before digital communications came into being.

It is worth noting that the first successful telecom device of the modern age was the telegraph, which, in essence, was a digital device that relayed a text message in dots and dashes of Morse code. Almost as soon as electromagnetism was discovered in the 1800s, efforts began to apply it to communications. For almost a century from the 1830s the telegraph became the main long-distance communication medium.

The British colonial administration in India was quick to introduce telegraph to India. The first line was laid way back in 1851, between Calcutta and Diamond Harbour. After the 1857 uprising, the colonial government laid out a nationwide network of telegraphy with great alacrity, to facilitate trade, administration and troop movements.

The telegraph was also seen as a major development in international communications. A transatlantic submarine cable was laid way back in 1858. It took sixteen hours to transmit a ninety-word message from Queen Victoria—and then the cable collapsed. Lord Kelvin, an accomplished physicist and engineer (and founder of today’s Cable & Wireless) took great pains to establish a viable transatlantic cable. A line connecting Mumbai and London, and another connecting Calcutta and London, were established in the 1860s.

But telegraph was quickly eclipsed by telephone. The magic of voice communication, pioneered by Alexander Graham Bell’s telephone, was so overpowering that it quickly overwhelmed telegraph. “Watson, come here,” Bell’s humdrum summons to his assistant at the other end of his laboratory, became famous as the first words to be communicated electrically.


Financiers and entrepreneurs quickly saw the opportunity in telephony, and money poured into this service. The use of telephony increased dramatically in a short period of time. This kind of telephony was based on what communications engineers call ‘analog’ technology. What is analog? The word originates from the Greek word analogos, meaning proportionate. The electrical signal generated by your voice in the telephone speaker is proportional to it. As your voice varies continuously the signal also varies continuously and proportionately in voltage.

Several decades of engineering ingenuity led to an excellent voice communication system. As soon as vacuum tubes were invented, repeaters based on vacuum tube amplifiers were built in 1913. By 1915 a long-distance line was laid from the east coast of the US to the west coast— a distance of almost 3,000 miles.

With an increasing number of subscribers, pretty soon it became clear that the telephone company had to create a network. A network is actually a simple concept. We see networks in nature all the time. In our own body we see a network of nerves, a network of blood vessels, a network of air sacs in the lungs, and so on.

When many people have to be connected, connecting each telephone directly to every other would mean weaving a tangled web of cables. For example, to connect a community of 100 telephone users, 4,950 cables would have to be laid between them. The cost of the copper in the cables would make the system prohibitively expensive. An alternative is to create a hub and spoke structure, as in a bicycle wheel, so that all the telephones are connected to an exchange, which can connect the caller to the desired number. Such an arrangement brings down the number of cables needed to a mere hundred.

The system can be designed to optimise it for actual use and hence reduce costs further. Let’s see how. If there are a hundred subscribers in a neighbourhood, then we find that on the average only ten per cent of subscribers use the telephone at one time. In a commercial complex the usage is higher but still far less than a hundred per cent. This fact allows the telephone company to optimise the size of the exchange.


Cutting-edge technologies play a vital role in a mass service like telecommunications. Yet methods of organisation that shrink the service cost play an even more important role. The reach of the service and its economic viability to the service provider depends on managing costs while maintaining an acceptable quality of service.

That is why consumer behaviour studies play a major role in communications. Such studies enable the telephone company to build a network based on statistically verified real-life behaviour rather than a perfect network. “In a fundamental sense statistics play a vital role in the technology and economic viability of telecommunication networks, be they wired or wireless,” says Ashok Jhunjhunwala of IIT, Madras, whose research group is doing innovative work in creating affordable telecom solutions in developing economies.


Switching technologies developed from human switches—called ‘operators’—to electromechanical ones. But problems of quality persisted in long-distance telephony, since the signals had to be amplified at intervals and the amplifiers could not filter out the noise in the signal. To overpower the noise in the signal, speakers would talk loudly during long distance calls.

Today we can whisper into a telephone even when making an international call. We have the digitisation of communications to thank for that. Though vacuum tubes made digitisation technologically possible, the real digital revolution started with the invention of the transistor. Soon transistor circuits were devised to convert voice signals into digital pulses at one end and these pulses back into voice signals at the other end.

The basic idea behind digitising a signal, or what is now known as digital signal processing (DSP), is actually very simple. Suppose you want to send the picture of a smooth curve to a friend, how would you do it? One way would be to trace the curve at one end with an electrical pen, convert the motion of the pen into an electrical signal, which, at the receiver’s end, is used to drive another pen that traces the same curve on a sheet of paper. This is analog communication.

Now think of another way. What if I send only a small number of points representing the position of the pen every tenth of a second. Since the pen is tracing a smooth curve and is not expected to jerk around, I send these positions to the receiving end as coordinates. If the receiver gets these points marked on graph paper, then by connecting them smoothly he can reasonably reproduce the original smooth curve.

Sounds familiar? Children do it all the time. They have these drawing books full of dots, which they have to connect to reproduce the original picture. If children knew it and drawing teachers knew it, then how come communication engineers did not?

The problem was: how many discrete points need to be sent to recover the original signal “faithfully”? To explain, let me extend the curve of the earlier example into a circle. Now, if you transmit the coordinates of four points on the circle, the way I did earlier, you may end up reproducing a quadrilateral rather than a circle at the other end. If you send data on more than four points, there is a good chance you will draw a polygon at the other end. As you send more points, you might approximate the circle quite well, approaching a situation, which mathematicians would explain thus: ‘A polygon with infinite number of sides creates a circle.’

However, as we see time and again, engineering is not about exact results but working results. The crucial issue of how much to compromise and how pragmatic to be is decided by consumer acceptability and product safety. Here subjectivism, perceptions and economics all roll into one and produce successful technology.

Is the user happy with it, is it within his budget, can we give him better satisfaction at the same production cost or the same product with a lower cost of production? These are the questions that industry constantly battles with. The telecommunications industry, like other services, must choose appropriate technology that satisfies customers and does not drive them away by making the service too expensive. As the telecom industry worldwide has got de-monopolised, another issue has been added: can a telephone company give that little bit more in terms of features, quality and price than its rivals?

Let us now return to signal processing. The answer to signal recovery was provided way back in the 1920s by Henry Nyquist, a scientist at Bell Labs. He said that sampling the waveform at double the signal bandwidth would completely recover the signal. This is the first principle that is applied in digitising the voice signal. The voltage in the signal is measured 8,000 times a second, the resulting values are converted into binary zeroes and ones, and these are sent as pulses. In telecom jargon this is called pulse code modulation, or PCM. Pulse code modulation, achieved primarily at Bell Labs in the 1940s, was the first major advance in digital communications.

I did a sleight of hand there. We were discussing recovering the shape of the signal and suddenly brought in frequency components of a curve. The theory of ‘Fourier transforms’ allows us to do that. Jean-Baptiste- Joseph Fourier (1768-1830)—son of a tailor, a brilliant mathematician and an ardent participant in the French Revolution—pondered over complex questions of mathematical physics in the heat of the Egyptian desert while advising Napoleon Bonaparte. Today Fourier’s theory is the bread and butter of communication engineers. And we leave it at that.


Since noise and distortion were major hindrances in long-distance telephony, the application of digital signal processing led to dramatic improvement in quality. With a sufficient number of repeaters one could transmit voice flawlessly.

The next turning point came when the signal could also be transmitted in digital form. Human speech normally ranges in frequency from 300 Hz to 3,300 Hz. Coincidentally copper wires too transmit roughly this range of frequencies most efficiently with the least amount of dissipation and distortion. Of course, if you want to transmit a song by Lata Mangeshkar, the higher frequencies produced by the singer may get chopped. Hi-fi transmission is not possible in this mode but, if we use a very high frequency signal as a carrier and piggyback the voice signal on it, we can transmit a broad range of frequencies—also called bandwidth—thereby achieving even hi-fi transmission. This piggy-riding technology, invented by Major Armstrong, is called frequency modulation, and is similar to a walking commuter riding a high-speed train.

We could go a step further and transmit television signals, which need a thousand times more bandwidth along wires. That is what our neighbourhood cablewallah does. This kind of transmission requires coaxial cables—a copper core surrounded by a hollow, conducting cylinder separated by an insulator. (A simple copper wire will not do.) But high frequency signals are highly dissipated in cables, so how is this possible? This is where solid-state repeaters come into the picture. With their low power consumption, low price and compactness, we can insert as many repeaters as we need even at distances of a couple of miles or so in a cable.


Telephony utilised this approach in a clever way. With the possibility of carrying high frequency signals, which allow a large range of frequencies or large bandwidth to piggyback on, engineers started multiplexing. Multiplexing is nothing but many signals sharing the same cable, like many cars using the same highway.

How do many cars use the same highway? They go behind one another in an orderly fashion (though not on Indian roads). But, on high-speed highways, if drivers try to overtake one another they can cause fatal accidents. In communications, too, there is something similar called ‘data collision’, which proves fatal to the two pieces of data that collide! There is need for lane discipline.

By the way, if you find me using a lot of analogies from transportation to explain concepts in telecommunication, don’t be surprised. At a fundamental level, the two fields share many concepts and mathematical theories. Coming back to efficient ways of transportation, we can have double-decker buses where two single-decker busloads of people can travel at the same time, in the same lane, just by being at different levels. Communication engineers used the double-decker concept too. They sent signals at different frequencies at the same time through the same cable. With the high range of frequencies, or bandwidth, available on coaxial cables, this became eminently possible. Thus, if we have a cable with a bandwidth of 68 KHz, we can send sixteen separate voice channels of 4 KHz each. The remaining bandwidth of 4 KHz would be utilised for various signalling purposes. In engineering jargon this is called frequency division multiple access, or FDMA, which allows different signals to be filtered out at the end of the cable. This technology led to a steep improvement in the efficiency of cables, and it was soon adopted in intercity trunk lines.

Now consider yet another way in which efficiencies were improved. If you reserve a certain part of the available bandwidth—or ‘channel’, as it is also called—for one conversation, then you are being slightly extravagant. After all, even a breathless speaker’s speech has pauses and, since a telephone conversation is usually a dialogue, the speaker at one end has to listen to the other party for roughly half the time. It has been found that a speaker uses the line for less than forty per cent of the time. Telecom engineers wondered if they could utilise the remaining sixty per cent of the time to send another signal, thereby easily doubling the capacity? They found they could, with a clever innovation called time division multiple access, or TDMA.

TDMA involves sending a small piece of signal A for a fixed time, then sending a piece of signal B and then again the next piece of signal A, and so on. The equipment at the other end separates the two streams of signals and feeds them to separate listeners as coherently as the speech of the speakers at the transmitting ends, and without any kind of cross-connection.
Only high-speed electronic circuits can allow engineers to split and transmit signals in this manner. Since our ears cannot discern the millisecond gaps in speech connected in this manner, it works out perfectly fine.

Remember Vishwanathan Anand playing lightning chess with several players simultaneously, an example I used to explain time sharing in mainframe computers in the chapter on computing? Well, TDMA is basically the same kind of thing. The same cable and same bandwidth are used to send several signals together. We could send pulses from one channel for a few microseconds, and then insert the next bunch from another signal, then the third and so on. Only a few milliseconds would have elapsed when we came back to the original signal.

For the last three decades, TDMA has been the preferred technology in telephone networks, but frequency division multiplexing—which had vanished with the disappearance of analog telephony—has come back with a bang in a different avatar. In state-of-the-art optical networks, a technology known as dense wave division multiplexing (DWDM) has allowed terabits of data to be sent down hair-thin optical fibres. With DWDM, laser signals are modulated with the data to be carried and several such signals of different wavelengths are shot down the same fibre. This is nothing but a form of frequency division multiplexing!

Good ideas rarely die; they reappear in a different form at a later date. After all, there are not that many good ideas!

The next thing that was needed was digitisation of the exchange, or the ‘switch’. This could be accomplished with the advent of integrated circuits and microprocessors. Thus the technology for digital communication was more or less ready in the mid-1970s, but to convert the networks to digital took almost twenty more years.


Even today the copper wire between your telephone and the exchange— also called ‘the last mile’ or ‘local loop’—still uses mostly analog technology. Though ingenious new technologies called integrated services digital network (ISDN) and digital subscriber line (DSL) have come into being to make the last mile also digital, they are still to be deployed widely.

That is the reason why, when you need to connect your computer to the Internet, you need a modem. A modem converts the digital signals from the computer into analog signals and pushes them into the telephone line, and converts incoming signals from the Internet service provider into digital mode again so that your computer can process them. Hence the word modem, which stands for modulator-demodulator.

By the way, analog lines are not suited for data transmission; they are fine tuned to carry and reproduce voice well. They do that with devices like echo suppressors and loading coils. Unfortunately, these devices slow down data transmission. These obstacles can be overcome by sending a high frequency signal down the line to begin with.

Remember the screeching sounds that the modem makes when you dial up? They are nothing but signals generated by the modem and sent down the line to facilitate data transmission while simultaneously ‘talking’ to the modem at the other end for identification, or doing a ‘handshake’. A naturalist friend of mine, an ardent bird watcher, used to call them the mating calls of modems!


What are the advantages of digital communications? There are many:

• Signal regeneration is done at every intermediate stage; this allows the system to tolerate a high level of noise, cross talk and distortion. It is rugged and unaffected by fluctuations in the medium.

• We can multiplex speech, data, fax, video, music, etc., all through one ‘pipe’.

• It allows for much higher data rates than does analog.

• One can control the network remotely.

• The signal can be very easily encrypted, allowing for greater privacy.

• The clinching factor: digital communications became more cost effective than analog with full digitisation of signal processing, transmission and switching.


Let us look at some of the innovations in digital technology that have happened behind the scenes. When we, as consumers, see a good picture on the TV set, or get good voice quality on the telephone, we are scarcely aware of the thousands of innovators who have worked in the last fifty years to make these facilities possible.

Interestingly, as with computer science, the communications arena too has had several prominent Indian contributors. One reason for this is that some leading Indian educational institutions like the Indian Institute of Science (IISc), Bangalore, and IIT, Kharagpur, started teaching communication engineering quite early. “In the early 1960s, when digital signal processing was just evolving, IISc was perhaps one of the first institutions in the world to produce PhDs in this subject,” says N. Yegnanarayana of IIT, Madras.

Teachers like B.S. Ramakrishna at IISc and G.S. Sanyal at IIT, Kharagpur, are remembered by hundreds of students who are now at the cutting edge of the telecom industry as researchers and managers. In the US professors, like Amar Bose at MIT, Tom Kailath at Stanford University, Sanjit Mitra at the University of California at Santa Barbara, P P Vaidyanathan at Caltech and Arogyasami Paul Raj at Stanford have carved out a unique place for themselves not only as first-rate researchers but also as excellent teachers.


When we look for individual contributions, we have to be cautious. Says Arun Netravali, chief scientist, Lucent Technologies, “As technologies mature, it is more and more difficult for fully worked out great ideas to come from an individual. Innovations come increasingly from teams, in academia and industry. Teams are replacing the individual because the financial stakes in the communications industry today are high.

“The moment an innovative idea appears somewhere, venture capitalists and large companies are ready to invest millions of dollars into commercialising it. Time-to-market becomes crucial. It does not matter who lit the spark. Large teams are deployed immediately to develop the idea further and to commercialise it. Many Indians have made important contributions in the area of communications as members of large organisations; it is difficult to identify them as single sources of a technology.”

Nevertheless, the contributions of several Indians stand out, and they have received public recognition for their work. Let us look at some of them.


One of the persistent problems in voice communications is echo. The problem could be solved in digital communication as Debasis Mitra, currently vice president, mathematical research, at Bell Labs, and Man Mohan Sondhi, now retired, showed back in the early seventies. Says Sondhi, “The echo cancelling equipment would have cost a prohibitive $1,500. It was only in 1980-81, as IC prices fell, that the echo canceller chip became economical and the telecom industry harnessed the technology. In fact, Donald Duttweiler, who made the chip, was also given the IEEE Award. It was one of the most complex special purpose chips at that time, and it had about 30,000 transistors. Today millions of echo cancelling chips are embedded in the network. In fact, there is a problem of echo in Internet telephony, in cell phones, in speakerphones and in teleconferencing equipment. So the echo cancellers are finding more and more applications.”

The important point to note here is that without the IC revolution the digital communications revolution could not have happened. What has made the advances in communication theory and technology useful to the masses is the semiconductor industry churning out increasingly powerful chips at lower and lower costs, following the famous Moore’s Law.


A major preoccupation of communications engineers is: What is the maximum capacity of a channel, and how much information can we push through it? And what is information itself? These fundamental questions bothered Claude Shannon at Bell Labs in the 1940s. He had joined Bell Labs after his epochal thesis at MIT connecting switching circuits with Boolean logic and laying the basis for digital computers (as we saw in the chapter on computing).

Shannon figured out the answers to his questions in communications theory in the mid-1940s, but he did not publish them till his boss pushed him. The result was the paper, A Mathematical Theory of Communication, published in two instalments in the Bell Lab Technical Journal in 1948.

That was the birth of information theory. Shannon’s paper used mathematics too complex for the communications engineers of those times. It took some time for the impact to sink in; when it did, it was path breaking. A discussion on Shannon’s theory is obviously beyond the scope of this book. Briefly, Shannon showed that communications systems could transmit data with zero error even in the presence of noise as long as the data rate was less than a limit called the channel capacity. The channel capacity, depends on bandwidth and the signal-to-noise ratio. The surprising result was that error-free transmission is possible even through a noisy channel. Though he did not show how to achieve maximum channel capacity, Shannon provided a limit for it.

Shannon’s insights into the nature of information itself led to the whole field of coding theory and compression. Simply put, he argued that real information in any communication is that which is unpredictable. That is, if the receiver can guess what comes next then you need not send it at all! All compression techniques use this insight and see what is redundant. Then communication engineers go to great lengths to compress the signal through complex coding algorithms to push through as much information as possible through a given bandwidth.


Actually this is not very different from what kids do nowadays, with SMS. They are driven by the restriction that they can send a maximum of 160 characters in a message. Thus, for example, when you send an SMS message to your friend: CU L8R F2F HVE GR8 WKND. These words might seem like gobbledegook to the uninitiated. However, your friend knows that you said, “See you later face to face. Have a great weekend”. You have managed to send a 48-character message in 23 characters (including spaces). This is data compression. Millions of people who routinely use SMS may not know it, but they are using Shannon’s information theory every day.

Interestingly, SMS has become so popular with youngsters today that the lingo is fast becoming a new dialect of the English language. The ultimate recognition of this has come from the venerable Concise Oxford English Dictionary itself, which has published a list of various acronyms frequently used in SMS and Internet chats, in its 2002 edition.


The name of the game in communications is optimising the use of bandwidth to reduce costs. One issue that has bothered engineers has been how to compress human speech and manage with much less than the 64 Kbits required for a toll-quality line.

Bishnu Atal found an innovative solution to this problem at Bell Labs in the 1970s. “Those days people did not take me seriously,” recalls Atal. But his work was finally recognised in the ’80s. The question he asked was, “If we know the amplitude in speech in the past few milliseconds, can we reasonably predict its present value?” His answer was affirmative, and his solution became known as linear predictive coding.

Atal used his techniques for voice transmission at 16 Kbps and even 8 Kbps while maintaining a reasonable quality. The US military was immediately interested; as they saw that low bit rate communications was necessary in battlefield conditions. They also saw that with Atal’s digital techniques encryption would become easy for secret communications.

“I did not want to work on secret projects, since that would have restricted my visits to India. So, I told them that I had done the required scientific work for compression and anybody else could work on encryption”, says Atal. A Bell Labs fellow and a fellow of the National
Academy of Engineering, Atal has now retired to teach at the University of Washington in Seattle.

With the advent of cellular telephony, where bandwidth is at a premium, any technique that can send voice or data at low bit rates is manna from heaven. A version of Atal’s technique, called code excited linear prediction, is used in every cell phone today.


While Atal worked to make low bandwidth channels useful for reasonable quality of voice transmission, there were others who were working on pushing high-bandwidth applications like high-quality audio and video through relatively lower bandwidths. Sending a full-motion video signal as it appears in the TV studio requires about 70 Mbps of bandwidth. Yet, amazingly, we can see a videoconference on a webcam or listen to MP3 audio, all on a simple dial-up Internet line of 56 Kbits. How is that? Scientists like Arun Netravali and N Jayant worked on techniques that made this possible.

Jayant and his team’s work at the Signal Processing Research Lab at Bell Labs, related to audio transmission, led to the development of the ‘MPEG Phase 1 Layer 3’ (MP3) standard of audio compression. This technique was later commercialised by the Fraunhoffer Institute of
Germany. Thanks to MP3 compression, we can now store hundreds of songs on an audio CD instead of the mere eight to ten songs we could earlier.

Netravali, currently chief scientist at Lucent Technologies, contributed enormously to digital video in the 1970s and 1980s. His work in video is widely recognised and used in media like DVD, video streaming and digital satellite TV. “In the 1970s and 1980s we had all the algorithms we needed, but the electronics we had was not fast enough to implement them,” says Netravali. Then the microchip brought a sea change. It is good to see some of the technologies we worked on get commercialised.” The Indian government honoured Netravali in 2001 with a Padma Bhushan, and the US government also in 2001, with the National Technology Award—the highest honour for a technologist in America.

Is compression a modern concept? No. That is how people have packed their baggage for centuries. Even your grandmother would say, “Keep the essentials and don’t leave any free space.”


This is not a politically correct sequel to Mel Gibson’s movie, What Women Want, but an example of how perceptual studies have advanced communications. Netravali and Jayant’s work is highly technical, but even laymen can understand some of the ideas used by them. They discovered that human perception, aural and visual, is remarkably inured to certain details. For example, Jayant and his team found that almost ninety per cent of the frequencies in high quality audio can be thrown away without affecting the audio quality, as perceived by listeners, because they get masked by the other ten per cent, and the human ear is none the wiser. This was great news for music companies, as they could now store hi-fi sound in a few megabytes of memory instead of a hundred megabytes.

Netravali also found that just applying coding algorithms would not provide enough compression to transmit full motion video. So he studied the physiology of the human eye and the cognitive powers of the viewer. What he found was this: if we are transmitting, say, the image of a person sitting on a lawn, then clearly we want good pictures of the person’s face and body but not necessarily the details of the grass. Our eye and brain are not interested in the grass.

Similarly, when we transmit a head-and-shoulders shot of a person in motion, the motion makes only a small difference from frame to frame. What we need to do is calculate the speed with which different parts of the body are moving and estimate their position in the next frame, then subtract it from the actual signal to be sent in the next frame and instead send only the difference along with the coding algorithm. If we can do that, then we can achieve a lot of compression. Jayant and Netravali did this. They also studied the reaction of the eye to different colours and used the knowledge in coding colour information. The key factor in their approach was the analysis of perception.

What they did was not entirely new. In another context, Amar Bose, chairman of the Bose Corporation, applied psycho-acoustics to come up with his amazing speakers and audio wave-guides. “After my PhD at MIT in 1956, when I had a month’s time before taking up a year’s assignment in India, I bought a hi-fi set to listen to (I have always been a keen electronics hobbyist since my teens). But, to my horror, I found that despite having the right technical specifications, the equipment did not sound anywhere near high-fidelity,” recounts Bose.

Bose then conducted psycho-acoustic experiments to see what people want when they hear music. He incorporated that information into the design of his equipment. As he continued to teach at MIT from 1958- 2001, his course in psychoacoustics was one of the most popular ones on the campus. Besides using good engineering, mathematics and digital electronics, Bose has continued to use psycho-acoustics as an essential ingredient in his products. The result: Bose is today rated as one of the biggest audio brands in the world.

The moral of the story: for a successful technology or a product, good engineering, mathematics and physics are not enough; we require perceptual inputs as well. We need a healthy mix of hard technology and ‘what people want’!


While all these wonderful things were happening in the developed world, what was the state of telecommunications in India? The less said the better. Until the mid-1980s, the telephone was considered a rich man’s toy, not an essential instrument for improving productivity and the quality of life. Though India produced top class engineers, they were migrating to the Bell Labs of the world, and the government, which had a monopoly over telecommunications, did not invest enough to spread the network and modernise it.

For their own colonialist reasons the British had introduced telegraphy and telephony to India quite early in the day, but independent India did not keep pace with the rest of the world. Even in the 1970s, Indian telegraphy was archaic (telex and teleprinters were just being introduced). The short forms and tricks employed by youngsters today, in SMS messages were then being used to save money by keeping telegrams short.

Curiously, while SMS sends your words faithfully there was no such guarantee with telegraphy. The mistakes made by telegraph employees sometimes caused avoidable heartbreak for job applicants and anxious relatives of seriously sick people.

The telephone service was notoriously bad. Telephones often turned up dead for days. Long distance telephony meant making a trip to the post office, “booking a call” and waiting for an hour or more for the operator to connect you. Often, after hours of waiting, the response would be: “The lines are busy”. If you did get connected, the noise and distortion on the line were so bad that you had to not only shout at the top of your voice, throwing privacy to the winds, but also spend half the time repeating, “Hello, can you hear me?” This was India barely twenty years ago.


Then things began changing. Today there are over eight lakh STD booths (public call offices) all over the country from which anyone can directly dial nearly 30,000 towns and cities in India and a large number of cities in most other countries. The networks have been expanded massively, with many more exchanges and it is so much easier to get a telephone connection. This has not only improved business communications but also communications among ordinary people, be it migrant labourers calling home or people keeping in touch with kith and kin. The poor use long-distance telephony as much as the upper classes and businesses.

Voice quality over telephone lines is excellent today; you don’t have a problem getting a dial tone and the line you desire. The total number of telephones in India has increased from 5.5 million in 1991 to 30 million in 2002. As a result, the long waiting lists for telephones have vanished. You can get a connection practically on demand.

New services such as mobile phones have been introduced, and already the number of mobile subscribers has crossed fifty million in ten years. Mobile phones are no longer associated with businessmen, stockbrokers, film stars and politicians. College students, taxi drivers, plumbers and electricians use them now. For artisans and other self-employed people, mobile phones seem to have become the much-needed contact points with customers.

Over three lakh route-kilometres of optical fibre have been laid in India in the last two decades. Broadband Internet services have become available to offices and homes, and their usage will grow as prices decline. But there is no space for complacency. China has achieved much more progress in telecom than India has, in the same period of time. China, too, had about 5.5 million telephones in 1991. In 2002 China had nearly 200 million mobile phones. China manufactures most of the telecom equipment it needs, including that required for optical networks within the country. We do have lessons to learn from the Chinese experience.

Fortunately, there is now widespread recognition in India that telecom is an essential component of infrastructure for the economic and social life of the country. The deregulation of the sector has led to large investments by many private sector companies. These new entrants are building their networks with state-of-the-art technology and providing the necessary element of competition by bringing in new and better services. Greater competition has resulted in a dramatic reduction in tariffs, expanding the market quickly. Clearly there is a sense of excitement in the air. Gartner Group has predicted that by 2007 there will be seventy million cell phone users in India. It may well surpass that.

If the past two decades have seen dramatic change, then the next twenty years may be hard to describe. The communication landscape of India will not be recognisable.

The achievement, in numbers, in the last twenty years is remarkable, and the progress in quality of service even more so. How did this transformation take place? Thousands of dedicated engineers and managers have endeavoured to change the scene, but there have been two key catalysts: the Indian Space Research Organisation (ISRO) and the Centre for Development of Telematics (C-DOT).


We will begin with communication satellites because they were the first hi-tech area to be developed and deployed to suit Indian requirements. Satellites have connected even the remotest areas of India through long distance telephony and national TV broadcasting. Today’s buzz words such as distance learning, telemedicine and wide area networking of computers were first demonstrated and then implemented through Indian satellite systems in the 1970s.

The famous British science fiction writer, Arthur C Clarke, first mooted the idea of communication satellites. If you read Clarke’s paper, ‘Extra Terrestrial Relays—Can Rocket Stations give World-wide Radio Coverage?’, you would not believe, till you read the dateline, that it was written in 1945. At that time, there were no rockets (except a few leftover German V-2 ballistic missiles); and definitely no artificial satellites or space stations. But Clarke was audacious. He put forward a vision of three geo-stationary artificial satellites (see box on space jargon) hovering 36,000 km above the earth and being used as transmission towers in the sky to provide global communications coverage.

Many sci-fi aficionados believe that science fiction can be serious science, giving Clarke’s satcom (satellite communication) as an example. As it happened, Clarke was a communications engineer who had worked on the radar project in the UK during the Second World War, and his paper is a serious scientific study, not a sci-fi story.


Geostationary orbit

Any object placed in orbit at 36,000 km above the equator will take the same amount of time as Earth does to complete one revolution. This makes it stationary in relation to Earth. A dish antenna receiving signals from the satellite does not need to move to continuously track it, which makes tracking cheaper and less complex.


A communication satellite used for telecom or TV receives the electromagnetic signal from the ground transmitter (uplink). It then retransmits it at a different frequency (downlink) towards Earth. The communication equipment on board a satellite that does the receiving and transmitting of such signals is called a transponder.

Why multi-stage rockets?

The heavier the weight that is carried into space, the larger must be the rocket ferrying it, because of the need for more fuel and power. It costs approximately $30,000 to put one kilo into geostationary orbit. In a multi-stage rocket the burnt out stages are detached one by one and drop to Earth so that less and less weight is actually carried into orbit.

Remote sensing

Observing Earth from a distance and getting information based on the reflective properties of different objects is known as remote sensing. Remote sensing can also be done using aircraft, but satellite remote sensing is far cheaper and more comprehensive.

What is digital direct-to-home broadcasting?

In DTH broadcasting, the signal frequency allows the consumer to receive the broadcast by means of a small dish antenna about a foot in diameter. Digital technology helps compress the signals so that many channels can be broadcast from a single transponder. This technology enables broadcasters to monitor and control usage since the signal can be keyed to individual users, who can then be charged subscription fees. Since it uses digital technology, DTH provides extremely high-quality picture and sound, as on a laser disc or CD. The satellite signals need to be decoded by a set-top box.

Why should we use liquid-fuelled rockets when solid-fuelled rockets are much simpler to make?
Solid-fuelled rockets cannot be turned on or off at will; once lit they burn till the propellant is exhausted. A liquid-fuelled rocket, on the other hand, can be easily controlled like the ignition key and accelerator of a car.

Arthur C. Clarke’s dream of putting man-made satellites in space came true in the 1960s. The first step was the Russian Sputnik in 1957—a technology demonstrator rather than a communications satellite. It proved that a satellite could be injected into an orbit around the earth using rockets. The second big step was the launch of Telstar by AT&T in 1962 for a communications project. John Pierce, then president of Bell Labs, led the experiment. But Sputnik and Telstar were not geostationary satellites. They did not hover over the earth at the same spot, but zipped around every couple of hours. The first geostationary satellite was Syncom-2, launched by Hughes Aircraft Corp of the US in 1963. This made intercontinental TV broadcasting a reality. (It carried a live transmission of the Tokyo Olympics in 1964.)

In 1964, an international agency called Intelsat was created to provide satellite communications services. Intelsat launched the maiden international communications satellite, the Early Bird, in 1965. India was one of the first to join the Intelsat project, and has a place on the board of directors of the company. In fact, Videsh Sanchar Nigam Ltd (VSNL) is one of the largest shareholders in Intelsat, owning about five per cent of its equity. Intelsat has dozens of satellites in orbit over the equator above the Atlantic, Pacific and Indian Ocean regions, providing telephone and TV broadcasting services.

The concept of a communications satellite is actually quite simple. Radio waves have been used to send messages since the turn of the century. The Indian scientist Jagdish Chandra Bose was one of the pioneers in the field; he developed a range of microwave detectors for 12.5-60 GHz, made of iron and mercury. Bose’s microwave coherer played a crucial role in the design of Marconi’s wireless.

Certain ionised layers in the atmosphere reflect radio waves. This fact makes long distance communications, including radio broadcasts, possible. That’s how a whole generation of us could listen to Amin Sayani on Radio Ceylon, and heard the Voice of America broadcasting a live commentary of Neil Armstrong’s first steps on the moon and Radio Peking calling the peasant movement in Naxalbari as “the spring thunder over India”.


TV broadcasting was possible only with much shorter wavelengths since only microwaves had enough bandwidth to carry the signal piggyback. The problem with short wavelength or high frequency waves is that they cover a small portion of the earth surrounding the antenna tower. In engineering terms this is called ‘line of sight’ communication. At any distance greater than sixty to eighty km the receiver will be ‘invisible’ to the antenna due to Earth’s curvature. The only way to increase the reach of broadcast is to increase the height of the TV tower. That is why the tallest towers in the world—be it in Moscow, Toronto, New York or Paris—have TV antennae on them.

If the height of the tower is a vital factor in efficient broadcasting, then why not put the antenna up in the sky? That is the idea behind communications satellites. The only difference is that unlike TV towers, which originate the signal, satellites just relay the signal received from Earth back to Earth.

Earlier, short wave radio was used for intercontinental telephony too, making short waves bounce off the ionised layers surrounding Earth. But these layers constantly and unpredictably shift their characteristics; which is why intercontinental telephony was beset by a lot of noise.
Satellites provided a great advantage since the relaying tower was not a dynamic ionised stratum of the atmosphere, but a reliable stationary satellite. Thus satellites became great platforms for intercontinental telephony as well.

The capacity of a submarine fibre optic cable, like the one connecting India to Dubai to Europe (Southeast Asia-Middle East-Western Europe) is many times that of satellites. Even so, satellites provide a low-cost alternative on certain routes. Over land they eliminate the need to dig trenches and bury expensive cable networks. To talk to Agartala from Mumbai you need a ‘gateway’ near Mumbai, a ‘gateway’ near Agartala and a satellite in the sky—and that’s it. In fact, satellites proved for the first time that distance does not matter.

• A satellite call from Mumbai to Agartala, over 2,000 km away, costs the same as one to Pune, less than 200 km away.

• For nationwide TV broadcasting, instead of setting up a network of microwave towers every 30-50 km all across the landscape of India, which is a very expensive proposition, we can simply park a satellite in space.

• A satellite link can be set up in hours when needed. For example, after the Gujarat earthquake in 2001, the telecom network in Bhuj and nearby districts, including fibre optic cables, was damaged, but ISRO’s satellite technology was immediately pressed into service to aid the administration in the quake-affected areas.

“A large part of basic satellite technology was developed at Comsat Labs in US and later at DCC and Hughes Network Systems,” says Pradman Kaul, corporate senior vice president, Hughes Electronics Corporation and chairman and CEO of Hughes Network Systems. Kaul
himself played a significant role in this.

As soon as satellite communications technology for TV broadcasting and telephony was developed, it became apparent that one of the irreplaceable uses of geostationary satellites would be mobile communications, where the transmitter and receiver are mobile, as in ships. Here, too, short wave radio was used for a long time, but sitcom provided reliable communication for the first time.

An international organisation, Inmarsat, was formed to provide maritime communications services in 1979. India, represented by VSNL is an early investor in Inmarsat, too. “In essence, Inmarsat provided the first global mobile phone service,” says Jai P Singh, who himself played an important role first in ISRO and then in Inmarsat and ICO-Global. “Since the satellite is at a height of about 36,000 km above the earth, the terminal on the ship initially had to be bulky, with considerable transmitting power. However, Inmarsat then came out with a mobile phone that looks like a laptop computer, which can be used anywhere. Some of these instruments have high enough data rates to send pictures or flickering videos. Most journalists have been using this technology for newsgathering and transmission from remote areas of the world.”

Several projects were initiated during the 1990s to make a lightweight satphone, available for telephony anywhere in the world. These included Iridium, with 66 low-orbit satellites, ICO-Global, with 12 medium-orbit satellites, and Globalstar, with 48 low-orbit satellites.

India, through VSNL, became one of the early investors in Iridium and ICO-Global. Both projects have faced financial problems. Iridium, promoted by Motorola, was the only project that was fully commissioned, but the high cost of the project ($7 billion), high user charges ($5-$10 per minute), and finally a very small number of subscribers led it to bankruptcy. Today, Iridium is being used mainly by the US department of defence. Globalstar, and New Ico Global, too, have gone through restructuring after near-bankruptcy. Recently, Globalstar has taken off in some parts of the world.

A geostationary satellite-based system called Thuraya is operating over West Asia. Most journalists in the recent US-led war against Iraq used satphones from Thuraya, which has been promoted by leading telecommunications companies in the UAE and other Arab countries.

The Indian foray into space and satellites started with an audacious dream way back in 1963. The dreamer was Vikram Sarabhai. Like Bhabha, Sarabhai too was a cosmic ray physicist. While Bhabha concentrated on developing Indian competency in nuclear energy, Sarabhai focused on applications of space technology when it was still in its infancy. Today, India has become one of the pre-eminent players in space technology.

The Indian Space Research Organisation has half a dozen advanced communications satellites of the Insat series in space. These were designed and fabricated in India. It has another half a dozen remote sensing satellites (the IRS series), making it part of an exclusive club of commercial remote sensing that counts the US and France among its members. It has its own rocket, the Polar Satellite Launch Vehicle (PSLV), which can launch a one-tonne satellite in a 400-1,000-km orbit for remote sensing purposes, and it is currently developing the Geostationary Satellite Launch Vehicle (GSLV) to launch a two-tonne communication satellite in the 36,000-km orbit above the equator. It has a state-of-the-art launch pad at Sriharikota near Chennai and its own master control facility to control satellites at Hassan in Karnataka. Indian technologists trained at ISRO have also contributed enormously to global satellite companies such as Intelsat, Inmarsat, ICO-Global, Panamsat, Loral and Hughes.

In just four decades, Indian space technology has come a long way at a fraction of the investments made by other countries. For example, the money invested in the entire Indian space programme from 1963 to 1997 was only half of the $2.4 billion Japan invested in developing its H-2 rocket in ten years. Yet the H-2, with a price tag of $150- 180 million per launch, was priced out of the market. Japan invested another $900 million to modify the rocket into H-2A, using all he manufacturing muscle of heavyweights like Mitsubishi, Kawasaki, Nissan and NEC to bring the launch cost to about $80 million. The H-2A has the same payload capacity as ISRO’s GSLV, which is being developed at an additional cost of only $100 million to augment the capabilities of the earlier PSLV. No wonder, the prestigious aerospace magazine, Aviation Weekly and Space Technology, in a cover story in April 1997, hailed the Indian space programme as a “success with a shoestring budget”.


It is hard to believe that it all started with a metre-long rocket a little bigger than a Diwali firecracker. How did ISRO leap to these heights from its humble beginnings? It took men of vision like Sarabhai and Satish Dhawan and thousands of innovative engineers and scientists to learn and improvise on technology that was at times not available through any foreign source at any price.

“It all started in a church where space is worshipped” might sound like a corny ad line or something from a sci-fi story, but it is a fact that the Indian space programme actually started in 1963 in a church and the adjoining bishop’s house. While looking for a site to house the proposed Equatorial Rocket Launching Station, Sarabhai liked the spot, and the local Christian community at Thumba, near Thiruvananthapuram, graciously offered the premises for the cause. Scientists led by Sarabhai worked in the bishop’s house, and the metre-long sounding rockets were actually assembled in the anteroom of the church and fired from a launch pad on the beach.

Pramod Kale, who retired as director of Vikram Sarabhai Space Centre at Thiruvananthapuram, remembers carrying out the traditional countdown for the first launch of a sounding rocket, at Thumba, to study the ionosphere. Today, the church, which has a history dating back to AD 1544, has been turned into the most comprehensive space museum in India, and has thousands of youthful ‘worshippers’ visiting every day.

In the 1960s, it was daydreaming of the highest order to think of an Indian rocket injecting an Indian satellite into orbit. But Sarabhai did just that and audaciously went ahead, realising his dream step by step.

“I was an undergraduate student studying physics when the Soviets launched the Sputnik. I made up my mind to join the space programme, though India did not have one then. Soon after my BSc honours, I went to Ahmedabad and met Dr Sarabhai. He asked me to come to Ahmedabad, finish my post-graduate studies and then join him in the Physical Research
Laboratory,” recalls Kale. He became one of the first to be roped into the space programme.

A characteristic feature of ISRO is its penchant for improvisation with whatever resources were available. Today, Indian remote sensing has come of age and its IRS data and expertise are in demand globally. Remote sensing as a technology was just emerging from the war-torn jungles of Indo-China, where it was deployed by the US to locate camouflaged Vietcong guerrilla positions. In the mid-1960s, when an opportunity came along to learn remote sensing in the US with the Earth Resources Technology Satellite project, Sarabhai grabbed it and sent Kale, P.R. Pisharoty, C. Dakshinamurthy and B. Krishnamurthy for the programme. These men later became well-known experts in the field.

“The first remote sensing experiment we did was driven by a very practical problem,” says Kale. “There was this common scourge called ‘coconut wilt’ affecting coconut trees in Kerala. The disease affects the crown of the tree and cannot be seen from the ground, which means you can’t estimate the damage. So we flew in a helicopter, and took pictures of coconut plantations using a camera with infrared-sensitive film. From that modest experiment, followed by decades of painstaking work, India has today become one of the global leaders in all aspects of remote sensing. This points to a defining characteristic of ISRO’s work: it is driven by decidedly practical problems and inputs from a definite group of end users,” says K. Kasturirangan, ISRO’s former chairman.


Where rocket technology was concerned, the US refused to part with even the most elementary know-how because of the possibility of the technology being used to build missiles. They were only willing to sell their sounding rockets without any technology transfer. The French were more helpful. They sold solid-fuel technology for small sounding rockets. These were a far cry from the rockets required to launch satellites, but ISRO engineers like Brahm Prakash, Vasant Gowarikar and A.P.J. Abdul Kalam (now the president of India) led a focused effort to develop rocket technology.

ISRO went through a series of technology demonstrators like the SLV-3, ASLV and finally the now operational PSLV. The sophisticated, indigenously developed solid propellants in the first stage of the PSLV make it the third most powerful booster rocket in the world.

Solid-fuelled rockets are not enough to build an economical satellite launcher. To launch satellites, you need liquid-fuelled rockets, which are much more sophisticated. In the mid-1970s, France offered to share liquid propulsion technology in exchange for Indian collaboration in further development of the technology. ISRO engineers were to develop the pressure transducers for the Viking liquid engines then under development. While these transducers are hi-tech products, they are only a small component of the liquid-fuel engine. There are so many design complexities that ‘know why’ is absolutely essential to build an engine. The ‘know how’ in terms of drawings are not enough. Why does a component have to be machined to one-micron precision and not two micron? Why does one kind of gasket or ‘O-ring’ have to be used and not any other? Questions like these can make or break a rocket engine after millions of dollars of investment.

The French probably never expected Indians to learn the full technology. The contract was signed at a throwaway price.


A fifty-strong team from ISRO worked in France between 1978 and 1980. It was made up of the cream of young ISRO engineers. Every day they brainstormed and sought solutions to complex design problems in the Viking. When they returned to India they asserted that they could build a sixty-tonne liquid engine. “We asked for only Rs 40 lakh to fund the project,” recounted S Nambinarayanan, who led the team to France. “Prof Dhawan was crazy enough to humour us.”

Two years later, these engineers built a rocket engine model, and in 1984 they built an engine ready for testing. But India did not then have an adequate testing facility (built since then at Mahendragiri in Kerala); so the engine had to be taken all the way to France. The French engineers asked, “Is this your prototype? Do you have a manufacturing programme?” When the answer was in the negative, they could not believe it. According to Nambinarayanan, the French thought that the Indians were crazy.

The engine was tested and, to the jubilation of the Indians and the surprise of the French, it fired beautifully. Today’s Vikas liquid engine used by ISRO is bigger than the French Viking engine and forms one of the essential workhorses of India’s space chariots. Thereby hangs another tale of ISRO’s ingenuity, improvisation and teamwork.


Launching a communications satellite weighing two tonnes or more requires even more powerful cryogenic engines, ones that use liquid oxygen and liquid hydrogen as fuel. The Russians were ready to sell the technology to India, and had even signed an agreement with ISRO in 1992; but the US invoked the Missile Technology Control Regime to bring pressure on Russia to withhold the technology. The Missile Technology Control Regime is an international agreement among ballistic missile owning nations, which aims to prevent missile technology from spreading to other countries.

But nobody on earth would think of using cryogenic engines for missiles since they need days of preparation. US policy did not make any sense, other than to pre-empt the emergence of a commercial rival. After all, launching communication satellites is a lucrative business and with
PSLV, ISRO had already shown that it could build one of the most cost effective rockets in the world.

The technology embargo could only delay ISRO by a few years. The agency bought six engines from Russia without transfer of technology and started building its own cryogenic engine, which would be ready in a few years. ISRO’s track record makes its claim about developing cryogenic engines credible, even though they are an order of magnitude more complex than normal liquid-fuelled rockets. ISRO scientists are busy mastering the cryogenic technology at the Liquid Propulsion Systems Centre at Valiamala, Kerala.


ISRO did not wait to develop a rocket system before mastering satellite technology. Like any ambitious organisation, it did some ‘parallel processing’. The agency grabbed every opportunity that allowed it to gain experience. When the Soviet Union offered to carry an Indian satellite for free, ISRO quickly got down to designing and fabricating the first Indian experimental satellite, Aryabhata, named after the ancient Indian astronomer. The satellite was launched into a low earth orbit on 19 April 1975, and carried a scientific payload to study X-ray astronomy and solar physics.

Then came another generous offer from the Soviet Union to launch two satellites. ISRO designed and built the experimental remote sensing satellites Bhaskara-I and II, named after the ancient Indian mathematician. These were launched in 1979 and 1981, and gave ISRO some valuable experience.

Meanwhile Europe’s Arianespace was trying to popularise its Ariane rocket, and offered to carry an Indian geostationary satellite free on an experimental flight, appropriately called the Ariane Passenger Pay Load Experiment (APPLE). ISRO immediately bit into it. “We worked feverishly to learn comsat technology from scratch,” recalls U.R. Rao, former Chairman, ISRO.

Earlier, an opportunity had come up when the US offered its Application Technology Satellite-6 for an Indian experiment. Sarabhai immediately set his team into action. This led to the pioneering Satellite Instructional Television Experiment (SITE), the largest satellite based distance education experiment ever conducted. Under Yashpal’s leadership, a team of engineers including E. Chitnis, P. Kale, R.M. Vasagam, P. Ramachandran and Kiran Karnik worked hard to make it a reality in 1975-76.

The earlier experience of building a satellite earth station at Arvi for the Overseas Communication Service (now VSNL) helped. Indian engineers also learned how to combine satellite signals with terrestrial low power transmitters to distribute TV in the local area. Eventually, this laid the basis for India’s national TV broadcasting by Doordarshan during the 1982 Asian Games in Delhi.

The moral of the story is: ISRO is a success because of its pragmatic approach, its hunger to internalise new technologies available from others; and to dare to develop it indigenously if the technologies cannot be imported.

One of ISRO’s life-saving innovations is its distributed disaster warning system. This system monitors weather pictures showing the progress of cyclone formations in the Bay of Bengal and broadcasts cyclone warnings via radio, TV and other means, including directly through loudspeakers in the villages on India’s east coast. As a result, the number of cyclone-related deaths has declined since the 1980s.

An important aspect of India’s space programme is its positive attitude towards transferring high technology to private manufacturers, helping them with technical upgradation as well as creating a nascent space industry. U.R. Rao, who took over from Satish Dhawan as chairman of ISRO, worked hard to build a space industry in India by getting industrial vendors to produce components and sub-assemblies.

Today we have several companies such as L&T, Godrej, MTAR and Triveni Structurals as space-age equipment suppliers. After learning to manufacture to ISRO’s extremely tough specifications and quality procedures, many suppliers found ISO 9000 and other such certifications child’s play. As one wag put it, the documentation for a satellite weighs more than the satellite!

ISRO satellites have many other useful features, like search-and-rescue and global positioning. Today, not just long-distance telephony and TV but also ATM networks, stock exchanges, corporate data networks and even lotteries depend on the satellite systems.

G. Madhavan Nair, the current ISRO chairman, now has another audacious dream—that of reaching the moon. It looks like a daydream, but so did India’s initial space programme seem in 1963 when Vikram Sarabhai launched a metre-long scientific rocket from the beaches of Thumba.

I think the point has been made sufficiently strongly that the first harbinger of the telecommunication revolution—in the broad sense of the term—in India was the space programme.


It’s time we switched back to telecommunications. Let us get a glimpse of what happens when we make a telephone call.

When we lift the telephone handset, we almost immediately get a dial tone, then we press the keys on the dial pad to dial a number, and in a couple of seconds we get a ring tone (or a busy tone, in which case we decide to call back later). The person at the other end lifts his handset off the hook, and we talk. We end the call by re-placing the handset on the hook. This process is repeated with every call we make. At the end of the month, we get a bill for all the calls we have made, depending on the number of minutes we spoke for and the location we called (local or long distance).

We take this pattern for granted. We curse the telephone company if we do not get the dial tone, if the voice is not clear, if there are frequent disconnections, if there is cross-talk, or if there are mistakes in billing.

Now let us look inside the telephone network and see what actually happens when we make a call.


1. When the subscriber picks up her telephone, the switch, which scans the subscribers in its area every millionth of a second, detects that service is needed and the dial tone is transferred to that line. The mechanism then waits for the subscriber to dial.

2. The dialled number must now be used to set up a connection. The number is received as a train of frequency pairs from a push-button telephone. These signals cause the equipment to set up a path through the exchange to the appropriate outgoing line.

3. The line connecting the exchange to the receiver might be busy. It is necessary to detect a ‘busy’ (or ‘engaged’) condition and to notify the caller. Similarly, as there are only a limited number of paths through the exchange, the exchange itself may not be capable of making the connection. If the exchange is unable to make a connection, it will pass a busy signal to the caller’s line. In a good network the latter would be a rarity.

4. The receiver’s phone should then ring. Sending a signal down the line that activates the ringer does this.

5. The telephone of the receiving person is now ringing, but when that person answers, the ringing signal should be stopped. If nobody picks up the phone, the exchange may, after a respectable wait, disconnect the call.

6. When the call is successfully established and completed, and both the parties have put their telephones down, the circuit is disconnected, freeing the interconnection paths for other calls.

7. Last, there must be a way of recording the number of calls each subscriber makes and the duration and distance of long distance calls. This data is then used to produce month-end bills.

In the case of a long distance call, several exchanges and the trunk lines connecting them will be involved, and the process is slightly more complicated. But the essential point I am trying to make is that the exchange or the switch is the heart of the telephone network. Thus when a telecom system is to be modernised, one has to look at transmission and switching equipment. If transmission can be compared to the arteries and veins of the telecom body then the switch is clearly the brain.

We talked earlier of why switching is necessary for economical telephone networks; otherwise everybody has to be connected to everybody else. To make this cost saving, the telephone company must invest in building intelligence at the heart of the switching equipment.
In the early days, the most intelligent switches were used—human beings called operators. As telephone traffic increased, human beings proved inadequate to handle the rush, and new electromechanical relays and switches were invented to do the job.

Electromechanical equipment needed frequent maintenance as moving parts wore out very fast. The reliability of such equipment also decreased as traffic increased. Then transistors, and later integrated circuits and microprocessors, arrived on the scene as a deus ex machina.

The marriage of semiconductor technology and computing with telecommunications’ switching needs led to the development of digital switches. These devices were essentially special purpose computers. The initial switches were mini-computers; only large metro exchanges could afford them. As microprocessors came into being and followed Moore’s
Law, the possibility arose of pervasive digital switching. Rapid adoption of digital switching in the 1970s facilitated better quality of service as well as lower costs.

There is another extremely important aspect of digital switching. Since the switch is actually a kind of computer whose capabilities are defined by the software written for it, whenever an upgrade is needed it can be achieved simply by writing new switching software.

In business, investments are not made only on the basis of the cost of equipment but what is called the ‘lifecycle cost of service’. This includes the cost of the equipment, its maintenance, spares, consumables, and upgrading and support costs until the end of its designed life. At times equipment that is cheaper up front could mean larger costs over the life cycle. In the case of digital switching technology, we mainly need to upgrade the software, whereas previously an upgrade in electromechanical switches meant throwing out all the old switches and replacing them with new ones, which was, obviously, a time-consuming and costly process.

For a telecom company, digital electronic switching equipment has another important advantage over its analog predecessor: it uses microchips as its basic building blocks and therefore takes up little space. A large metropolitan switching station for 50,000 phone connections once occupied a six- to ten-floor building and needed hundreds of people to keep it operational. The same capacity can now be housed in one-tenth of the space and requires a staff of perhaps ten people to operate. The only serious drawback with the new technology is that digital switches produce heat and must be air-conditioned to prevent overheating. But that cost is small compared with the other costs that are eliminated.


Sun Microsystems, the famous Silicon Valley computer maker, which sells a range of Internet servers, used to have an ad line a few years ago, which said: “We are the dot in .com”. Obviously, the slogan was meant to advertise Sun’s role in Internet infrastructure. If one were to coin a similar slogan for C-DOT, then it would be: “C-DOT is the com in Indian telecom”.

Until the 1980s, Indian telecom was dominated entirely by electromechanical switches. This was one of the main reasons for bad telephone service. The Indian government was then looking at ways of modernising telecom. An obvious option was to import digital switches from the US, Japan or Europe. While this was the fastest route, there were primarily three drawbacks to it:

• India had meagre foreign exchange resources.

• The switches made by multinational companies were designed to handle a large number of lines (up to 100,000), and hence suited large cities. They did not have small switches that could handle about 100-200 lines, or the intermediate-range ones the country needed to spread telecom to small towns and large villages in India.

• It would have meant no incentive for indigenous R&D.

The question was, could India afford to spend enough money to develop its own switch and manufacture it at a competitive price? Even the most optimistic advocates of indigenous effort were sceptical, and they preferred to take the route of licensed production in agreement with a foreign multinational company. The CEO of a large multinational wrote to Prime Minister Indira Gandhi, cautioning her that his company had invested more than a billion dollars in developing the technology, and implying that it would be foolhardy for India to attempt to re-invent the wheel with its limited resources.

That accepted wisdom needed challenging. And the person who could dare to do so was Sam Pitroda, a Chicago-based telecom engineer from Orissa, who had studied in the US and participated in the development and evolution of digital switching technology. Pitroda had over thirty patents in the technology while working at GTE and later at Rockwell.
As an entrepreneur, he had done very well for himself financially.

In the early 1980s, he heard from a friend that Prime Minister Indira Gandhi had set up a high-level committee to look into the modernization of Indian telecommunications. He thought it was time he paid his dues to his country of origin. Having seen poverty and social discrimination in his childhood in his village, and now having become a participant in the worldwide IT revolution, Pitroda had no doubt that a modern telecom infrastructure would go a long way “in promoting openness, accessibility, accountability, connectivity, democracy, decentralisation—all the ‘soft’ qualities so essential to effective social, economic, and political development,” as he wrote later in the Harvard Business Review.

Pitroda brought along with him his knowledge of technology, a ‘can do’ attitude and an impressive silvery mane he tossed while making a point, but not much else. He brought a breath of fresh air of optimism, aggression, confidence, flamboyance and media savvy into Indian telecom. He offered his services to the Indian government for one rupee a year.
And the offer was taken.

To recap the situation, in 1980, India had fewer than 2.5 million telephones, almost all of them in a handful of urban centres. In fact, seven per cent of the country’s urban population had fifty-five per cent of the nation’s telephones. The country had only twelve thousand public telephones for seven hundred million people, and ninety-seven per cent of India’s six hundred thousand villages had no telephones at all.

“India, like most of the Third World, was using its foreign exchange to buy the West’s abandoned technology and install obsolete equipment that doomed the poor to move like telecom snails where Europeans, Americans and Japanese were beginning to move like information greyhounds,” asserts Pitroda in his characteristic fashion. “The technological disparity was getting bigger, not smaller. India and countries like her were falling farther and farther behind not just in the ability to chat with relatives or call the doctor but, much more critically, in the capacity to coordinate development activities, pursue scientific study, conduct business, operate markets, and participate more fully in the international community. I was perfectly certain that no large country entirely lacking an indigenous electronics industry could hope to compete economically in the coming century. To survive, India had to bring telecommunications to its towns and villages; to thrive, it had to do it with Indian talent and Indian technology”, Pitroda added in his article.

Many discussions over three years, plus flying back and forth between New Delhi and Chicago, led to the establishment of C-DOT, the Centre for Development of Telematics. C-DOT was registered as a non-profit society funded by the government but enjoying complete autonomy. The Indian parliament agreed to allocate $36 million to C-DOT over 36 months to develop a digital switching system suited to the Indian network.

“We found five rooms in a rundown government hotel, and we went to work using beds as desks,” says Pitroda of those early days. “A few months later, in October 1984, Mrs Gandhi was assassinated, and her son Rajiv became prime minister. He and I decided that I should press ahead with the initiative for all it was worth.”

According to Pitroda, C-DOT engineers were conspicuously young, and they never seemed to sleep or rest. “C-DOT was much more than an engineering project. It did, of course, test the technical ability of our young engineers to design a whole family of digital switching systems and associated software suited to India’s peculiar conditions. But it was also an exercise in national self-assurance. Years earlier, India’s space and nuclear programmes had given the country pride in its scientific capability. Now C-DOT had the chance to resurrect that pride.”

By 1987, within the three-year limit, C-DOT had delivered a 128-line rural exchange, a 128-line private automatic branch exchange for businesses, a small central exchange with a capacity of 512 lines, and was working on a 10,000-line exchange. The components for all these exchanges were interchangeable for maximum flexibility in design, installation and repairs, and all of it was being manufactured in India to international standards—a guaranteed maximum of one hour’s downtime in twenty years of service! There was one problem; C-DOT had fallen short on one goal—the large urban exchange was behind schedule—but, overall, it had proved itself a colossal, resounding success.

What about the heat and dust in India and the need for air-conditioned rooms for digital switches? This was a serious issue for the country, large parts of which do not get a continuous supply of electricity. The solution was simple but ingenious. “First, to produce less heat, we used low-power microprocessors and other devices that made the exchanges work just slightly slower. Secondly, we spread out the circuitry to give it a little more opportunity to ‘breathe’. The cabinet had to be sealed against dust, of course, but by making the whole assembly a little larger than necessary, we created an opportunity for heat to rise internally to the cabinet cover and dissipate,” explains Pitroda.

The final product was a metal container about three feet by two feet by three feet, costing about $8,000, that required no air-conditioning and could be installed in a protected space somewhere in a village. It could switch phone calls more or less indefinitely in the heat and dust of an Indian summer as well as through the torrential Indian monsoon.

By November 2002, C-DOT switches equipped over 44,000 exchanges all over India. In the rural areas, ninety-one per cent of the telephone networks use C-DOT switches. Every village has not been covered yet, but we are getting there. Nationwide, 16 million lines, that is, forty per cent of the total operational lines in India, are covered by C-DOT switches.

Pitroda and Rajiv Gandhi also decided to open up the technology to the private sector. So C-DOT rapidly transferred the technology to over 680 manufacturers, who have supplied equipment worth Rs 7,230 crore and created 35,000 jobs in electronics. Seeing the ruggedness of these rural exchanges, many developing countries, such as Bhutan, Bangladesh, Vietnam, Ghana, Costa Rica, Ethiopia, Nepal, Tanzania, Nigeria, Uganda and Yemen decided to try them out.

For any institution, sustaining the initial zeal is hard once the immediate goals are achieved. After C-DOT’s goals were achieved, the Indian telecom sector has gone through, and is still going through, a regulatory and technological upheaval. But that has not deterred C-DOT’s engineers.

“It is creditable that through all this turbulence C-DOT has moved on to produce optical fibre transmission equipment, VSAT equipment, upgrading its switches to ISDN, intelligent networking, and even mobile switching technology. Today C-DOT may not be as high profile as it was in the 1980s, but it continues to provide essential hardware and software for Indian telecom despite intense competition from global vendors,” says Bishnu Pradhan, a telecom expert who was among C-DOT leaders between 1990 and 1996.


Before we move on to other parts of the communications revolution, let us note a characteristically Indian innovation not so much in technology as in management, which led to quantum leap in connectivity. That is the lowly public call office, or PCO, found at every street corner all over India today. These PCOs gave easy access to those who couldn’t afford telephones, and brought subscriber trunk dialling to millions of Indians.

Public call offices are a part of any network anywhere in the world, so what is innovative about India’s PCOs? The innovation lies in privately managed PCOs. As a result, we have over 600,000 small entrepreneurs running these booths and the telecom companies’ income from long distance telephony has multiplied manifold.

The innovation also lies in realising that Indian society is essentially frugal in nature, and is amenable to sharing resources. What Pitroda did was to translate the Indian village and small town experience of sharing newspapers into the telecommunications scenario.


We now come to mobile phones, which have caught the world’s fancy like nothing before. Today’s communications world is divided into wired and wireless, denoting the way signals are exchanged. Wired communications have the great advantage of concentrating energy along a thin cylindrical strand of copper or silica. There is greater clarity in voice communications and much greater capacity to carry data. The disadvantage is obvious; you have to be available at the end of the wire to receive the message!

In wireless communications, the message rides piggyback on electromagnetic waves and leaves them in space (or ether as nineteenth century scientists called it). You can then reach any person, as long as he is in a position to receive those waves. He need not be at an office desk or at any fixed place where a wire can terminate. He can be almost anywhere on earth, provided certain conditions are fulfilled.

The caveats appear because buildings, trees, atmosphere, clouds and other such obstructions absorb electromagnetic waves. For example, you may not be able to receive a cellular call inside certain buildings. Some objects create ‘shadows’ so you may not receive the signal when you are behind them, for example, when you are in a valley or between tall buildings, or urban canyons. Then there is the effect of the earth’s curvature, which compels you to be in the line of sight of a transmitter or repeater. But, despite all these problems, it has become possible for people to talk to one another, regardless of where they are.

The change in the communications culture brought about by wireless cellular phones can be seen by the simple fact that the opening of a conversation is no longer, “Hello, who is this?” but “Hello, where are you?”

The weak link in wireless communications is that the receiver is a tiny point in space whereas the transmitter has to send energy all over the space, wasting most of it. A very small portion of the transmitted energy reaches the receiver. “Most people would be surprised to know that the power of the signals received by a mobile phone is a hundred billionth of a billionth watt!” says Ashok Jhunjhunwala of IIT, Madras.

The amount of ‘information’ that can be sent through a channel depends on the ratio of the signal power to the noise power at the receiver’s end, as shown by Claude Shannon. This creates the engineering challenge of building receivers that are able to detect a very weak signal and separate it from noise. By the way, by ‘noise’ engineers do not mean the audible noise of the bazaar, but random electrical fluctuations in the handset caused by: heat and internal circuitry, background electromagnetic radiation coming from the ionosphere or high tension wires, or even other people’s cell phones near yours. Such electrical noise becomes an audible ‘hiss’ in your radio set, for example.

A brute force method to solve the problem of improving the signal to noise ratio is to make the transmitter as powerful as possible so that a sufficiently strong signal reaches the receiver. But there are limitations to the power pumped by the transmitter, especially when your cell phone itself is a transmitter. These limitations come from two sources: the power and longevity of the battery in a portable set (which should ideally weigh a few grams), and health hazards from the effect of powerful microwaves on the human brain.

It has been suspected that prolonged exposure to powerful microwaves could lead to brain tumours. Even though information in this area is patchy, everyone is aware of the risk. Hence portable handsets held close to the ear are mandated to be of low power – less than a watt. In most cases they actually have about half a watt of power. The sum result: the spreading nature of waves reduces the data rates possible on wireless compared with wired networks.

Incidentally, mobile wireless personal communications are not new. A demonstration of such communications took place in 1898, when Guglielmo Marconi, a flamboyant showman, gave a running commentary of a regatta on the Hudson river in New York while broadcasting from a tug. Another incident, which made wireless communication the talk of the town, was the capture in 1910 of a criminal on board a ship, when the captain of the ship received a secret wireless message. In the 1920s and 1930s experiments were conducted to use radio-telephony in the military, in police departments and fire brigades in the US.

The main issue, one that had to be tackled before commercial wireless communications became possible, was spectrum. To this day, spectrum allocation remains a major challenge.

Spectrum is the most precious societal resource, according to wireless engineers. It is a portion of the electromagnetic spectrum, or band of frequencies, reserved for a particular service. Regulatory agencies internationally and in individual countries allocate spectrum for various uses. For example, if you look at the frequency allocation in India by the wireless planning committee of the department of telecom (see box), you will see that different frequencies are allotted for different services like radio, TV, marine, defence, aeronautics, cell phones, pagers, radar, police, satellite up-linking and down-linking, and so on. The purpose of such allocation is to ensure that one service does not interfere with another.

The recent history of the wireless industry is full of jockeying by different service providers to get as big a chunk of frequencies for themselves as possible. Governments in the US and Europe have also looked at spectrum as a resource to be auctioned, and have earned large sums of money that way. In these countries there is hardly any licence fee for starting a service, but you have to buy the right to use a particular frequency exclusively for your service.

Interestingly, the first real advance in ‘multiplying’ the spectrum has been the multiple input multiple output (MIMO) technology, which uses multiple antennae at both ends of the link. The spectrum is multiplied by the number of antenna pairs! This idea, originally proposed by
Arogyaswami Paulraj of the Information Systems Laboratory at Stanford University, is now a major frontier for enhancing wireless systems.


Electromagnetic waves, first predicted by British scientist James Clerk Maxwell, were later experimentally discovered by H.R. Hertz, to commemorate which, one electromagnetic wave vibration is called a hertz (Hz). A KiloHz is a thousand hertz, a MegaHz(MHz) is a million hertz and a GigaHz (GHz) is a billion hertz.

The part of the spectrum used for communications and broadcasting is known as the radio frequency (RF) spectrum; it extends from about 10 kHz to about 30 GHz. The International Telecom Union, an intergovernmental body, regulates the allocation of different bands for various end uses worldwide.

The following table illustrates the primary use to which different parts of the spectrum are allocated by the wireless planning committee of the Indian government:

Frequency Frequency band Use

500KHz- 1.6 MHz Medium Wave Radio broadcast, All India Radio

2MHz-28 MHz Short Wave (HF) Overseas radio broadcast, defence, diplomatic, corporate, police aviation

30 MHz-300 MHz Very High Frequency(VHF) TV, police, paging, FM radio, aeronautical and maritime coomunications, trunk telecommunications

300 MHz-3 GHz Ultra High Frequency (UHF) TV, defence, aeronautical, railways, cellular mobile, global positioning, WLL, radar

3 GHz-7 GHz C-band and Extended C band Microwave links (DoT), VSAT, INSAT uplink and down link, civil and defence radars

7 GHZ-8.5 GHz X-band Mobile base stations, remote sensing satellites

10 GHz-30 GHz Ku-band Intracity microwave, inter-satellite Communications, direct- to-home (DTH) broadcasting,

20 GHz-30 GHz Ka-band Broadband satellite service

It is the scarcity of available spectrum that has led to all of the major technological developments in wireless over the last fifty years. The idea of cellular telephones emerged from this scarcity. Cellular telephony is actually very simple, and was articulated as far back as the 1940s by scientists at Bell Labs. Let me illustrate it with a simple example (the figures are illustrative, not realistic).

Every voice channel needs a certain bandwidth. Thus, within the allotted spectrum of, say, 10 MHz (850 MHz–860 MHz) only 5,000 calls can be handled at one time, assuming a highly compressed voice channel of only 2 kHz (16 kbit). If, on an average only ten per cent of subscribers use the telephone at any given time, we can conclude that the network can support 50,000 users. This may be fine for a police force or fire brigade but definitely not for a commercial service in a large city.


Cellular technology solves this conundrum by dividing a large city into cells containing, say, a thousand subscribers each. It uses 850-852.5 MHz in one cell, 852.5-855 MHz each in the surrounding six cells, and 855- 857.5 Mhz in the next layer of cells. Using transmitters of the right power, we can ensure that the effect of the first set of frequencies do not reach farther than the cell containing the transmitter and its immediate neighbours, so that the next circle of cells using 855-857.5 MHz do not receive anything from the 850-852.5 MHz transmitters. This assured, we can use the 850-852.5 MHz frequency again in the fourth set of cells safely without any danger of interference.

By planning a sufficiently small and dense cellular structure, we can cover a million subscribers in a city like Mumbai using only 7.5 MHz of spectrum and keeping the remaining 2.5 MHz for emergencies or sudden surges in demand. Making use of the short range of microwaves, cellular architecture allows for the reuse use of the same set of frequencies, thereby increasing capacity.

If the transmitting power of the cell phone is so low, then how does the call reach somebody who is miles away and is moving? First of all each cell has a base station with which the caller communicates. This base station is connected to other base stations and finally to the mobile switching centre. When a mobile caller activates his handset, the base station recognises the subscriber through an automatically generated signal, checks the services he is eligible for and notifies the network that the caller is in this particular cell. Then it sends the message to the switch that he wishes to talk to another subscriber with a number.

The mobile switching centre talks to different base stations, finds out where the receiver is at that moment and connects the caller’s base station with the base station in whose territory the receiver is available. The connection is made. Meanwhile, the caller might move out of the sphere of influence of the first base station and into that of its neighbouring base station. If that happens, the neighbouring station first detects his approach, assigns a new set of frequencies to him (remember, neighbouring base stations use different frequencies) and continues his call without interruption. This is called a hand-off. All this takes place in milliseconds, and neither the caller nor the receiver is aware that a transfer has taken place. When the call is over, the connection is broken and the information is sent to the records for billing purposes.


When you travel to a different city or state which has a different service provider, a ‘roaming’ facility is provided. Under this the local cell phone company in that city acts as a conduit for the calls you are making; you get one single bill as if you were moving through one continuous, ubiquitous network. The accounting and sharing of revenues by the two companies is not visible to the customer.

Historically, several analog cellular services came into being in the US and Europe in the 1970s. In a continent like Europe where travelling a few hundred miles can take you through several countries, the question of a system with a smooth roaming facility became important. A group was set up in the early 1980s to study the issue and prescribe standards. The group, which came out with the new generation of digital cellular standards was called Groupe Speciale Mobile (GSM).

GSM is widely used in India, China, all of Asia (except Japan), Oceania and Europe. A characteristic of this technology is that all the subscriber information is in a smart chip called the SIM card, which is inserted in the handset. If you wish to change your handset, you simply remove the SIM card from the old handset, insert it in your new handset and you are all set to make or receive a call.

While Europe created a standard through consultations among experts and imposed it on everybody, the US took a different route. It has allowed the use of several different technologies, and expected the market to decide which is better. Thus analog (AMPS), PCS, GSM (with a different spectrum than in India) and CDMA coexist in the US. But since the technologies are widely different, it becomes expensive, and at times impossible, to roam all over the US unless your particular network also has its coverage where you currently are.


The US was the first country to deregulate telecom and introduce competition. The process started with the breaking up of AT&T in the early 1980s and has continued to this day. The introduction of competition and the restriction of monopolies have benefited customers in a big way. But this has, at times, led to piquant situations. Companies that understood the technology were not allowed to offer the service and new players were allowed entry even when their sole qualification was that they did not know the technology! Thus, when cellular licences were first released in the US, as an anti-monopoly measure, AT&T, which had pioneered cellular architecture, was not allowed to offer a cellular service. The smaller companies that were allowed were new entrepreneurs who did not have expertise in cellular technology.

This potentially chaotic situation spelt opportunities for some people. One smart Indian wireless engineer who exploited the opportunity was Rajendra Singh. “I had just finished my PhD in wireless technology and started teaching in Kansas; and my wife Neera, a chemical engineer, was doing her Master’s there,” recalls Singh at his beautiful mansion on the banks of the Potomac river in Washington, DC. At that time entrepreneurs who wanted to start a cellular service were supposed to submit their network plan to the Federal Communications Commission (FCC), the telecom regulatory body in the US. But independent experts to file and evaluate the bids were lacking.

“I started helping some of them,” says Singh. “Since Neera knew computer programming, we developed software on a simple IBM PC to work out base station placement to get uniform coverage. We also developed simple equipment that could actually measure the signal at various points in the area and check the theoretical calculations. We sent the plan to a company which had won the licence for the Baltimore area near Washington DC. The company called back and asked how much we wanted to be paid for this. I said we did not want anything. It is just a piece of simple calculation that we did. But the guy said, ‘No, you have to accept some money for this’. I said, ‘OK, I shall charge $1,500’. The company wanted me to immediately shift to Washington and join them. I was told that other consultants had asked for six months’ time and a fee of $80,000 to do what we had done overnight with our software.”

It was not always so luxurious for Singh, who came from a backward village, Kairoo, in Rajasthan, which had neither electricity nor telephones. He lost an eye in a childhood accident due to lack of medical facilities in the village. Singh studied electrical engineering at IIT, Kanpur, went to the US in 1975 for his PhD, and proved to be a smart engineer who built a fortune using appropriate technology. This Indian engineering couple effectively became the architects of most US cellular networks in the 1980s. Later, in the 1990s, their consulting company, LCC, spread its wings to over forty countries.

While optimum use of spectrum became Mr & Mrs Singh’s bread, butter and jam, there was another trend that violated all common sense in wireless engineering. It was called spread spectrum. Its champions said they would use the entire available spectrum to send a message. For wireless engineers weaned from childhood on ‘communication channels’, this was sacrilege. Interestingly, the champion of this technology was a Hollywood actress.


Hedy Lamarr hit the headlines as an actress with a nude swimming scene in the Czech film Ecstasy (1933). She then married a rich pro-Nazi arms merchant, Fritz Mandl. For Mandl, she was a trophy wife, who he took along to parties and dinners to mingle with the high and mighty in Europe’s political, military and business circles. But Hedy was no bimbo. Little did he suspect that beneath the beautiful exterior lay a sharp brain with an aptitude for technology! Lamarr was able to pick up quite a bit of the technical shoptalk of the men around the table.

When the Second World War began, Lamarr, a staunch anti-Nazi escaped to London. There she convinced Louis Mayer of MGM Studios to sign her up. Mayer, having heard of her reputation after Ecstacy, advised her to change her name from Hedwig Eva Marie Kiesler to Hedy Lamarr and to act in “wholesome family movies”, which she promptly agreed to.

As the war progressed and the US joined the UK and the Soviet Union after the Japanese attack on Pearl Harbour, Lamarr informed the US government that she was privy to a considerable amount of Axis war technology and she wanted to help. The defence department had little faith in her claims and advised her, instead, to sell war bonds to rich Americans. But Lamarr was unrelenting. Along with her friend George Antheil, an avant-garde composer and musician, she patented their ‘secret communication system’ and gave the patent rights free to the US military. The patent was about a design for a jamming-free radio guidance system for submarine-launched torpedoes based on the frequency-hopping spread-spectrum technique.

Lamarr’s idea consisted of two identical punched paper rolls. One roll was located in the submarine, and changed the transmission frequency as it was rotated. The other, embedded in the torpedo, also rotated and hopped to the appropriate receiving frequency. The enemy jammer would thus be left guessing about the guiding frequency. The idea, which came to be named frequency hopping, was ingenious but the US navy was not technologically advanced enough to use it!


In the late 1950s, as digital computers appeared on the scene, the US Navy revived its interest in Lamarr’s ideas. With the development of microchips and digital communications, advanced and secure communications systems have been developed for military purposes using spread spectrum techniques. Since this technology can be used for secure communications, which cannot be jammed or intercepted, the US military has done extensive research and development in it since the 1960s.

In the telecom revolution of the 1990s, these techniques have been used to develop civilian applications in cellular phones, wireless in local loop, personal communication systems, and so on. The unlikely inventor showed that if you have a sharp brain, party hopping can lead to frequency hopping!

Spread spectrum technology assures a high level of security and privacy in wireless communication. It came into wide usage in the 1990s as Qualcomm demonstrated its successful application for cellular phones.

Another anti-snooping technique involves signals being mixed with strong doses of ‘noise’, and then transmitted. Only the intended receiver knows the exact characteristics of the ‘noise’ that has been added, and can subtract it from the received signal, thereby recovering the transmitted signal. This technique works best when the added ‘noise’ is very powerful.

Qualcomm used this technique to develop its CDMA technology, which is not only inherently secure but also less prone to a common, ‘multipath’ problem, or fading in and fading out of voice in cell phones. The problem occurs because of the signal getting reflected by natural and man-made structures and reaching the receiver at different times, causing interference and the fading-in and fading-out effect. However, multipath is a frequency-dependent effect; hence it does not affect spread spectrum based systems as the broadcast is made not at one frequency, but a whole bunch of them in a wide band.

In the late 1990s, before their break-up, Hollywood stars Tom Cruise and Nicole Kidman were deeply upset when a man used a commonly available frequency scanner to find out what frequency their cellular phones were using. He then proceeded to snoop into their private conversations, tape them and sell them to an American tabloid. The episode brought to light the lack of privacy in an analog cellular phone call, and stressed the advantage of cell phones using digital spread spectrum technology like CDMA.

Because of their high costs and tariffs, cellular phones were initially popular only among the rich and powerful. In the early 1990s you could see cell phones mainly with a small set of people: senior executives, stock brokers, politicians, film stars, etc. But, as costs drop, they are finding increasing use among ordinary people everywhere.

In a country like India cellular phones are not a luxury, but a necessity for a large section of the middle class and lower middle class population, including the self-employed, be they taxi drivers, carpenters, plumbers, electricians, roadside mechanics, salesmen, medical representatives or couriers. Either their profession makes them continuously mobile or they do not have shops and offices. Even if they do have an office, you might ask, what is the point in having a fixed phone there, when they are out servicing customers? That is why, for many Indians, the telecom revolution translates to STD booths and affordable cell phones.


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