LUIZ SUGIMOTO

Professor Dalton Arantes: article kept in a drawer

Professor Max Costa would never praise himself, even though he arrived at a mathematical result that promises to support profound changes in the telecommunications sector, worldwide. It was up to professor Dalton Soares Arantes, aware of his friend's modesty, to assess the importance of a theoretical work that was published in 1983, but for which, now, applications can be found that should provide technological advances and a lot of money in a market that already moves trillions. of dollars.

An already established application of the formula by Max Henrique Machado Costa, professor at the Department of Communications at the Faculty of Electrical and Computer Engineering (FEEC) is in watermarks to identify the authorship of digital signals (a film or a song, for example ), ensuring legal support for those who suffer from piracy. All future applications are not yet clearly foreseen, but the most impactful would be to multiply the current capacity of the means of communication several times - speaking here of cell phones, transmission of TV signals and the Internet, among other services that already show signs of strangulation.

“What we have is a theory, a resource that can be transformed into practical methods, but which still requires a lot of research. Recent work indicates the practical viability of Max’s theory”, states Dalton Arantes. The fact is that the international scientific community, in relation to watermarks, is already dividing this knowledge between “before and after Costa”, and that his name has been frequently cited lately in other research in the area of ​​telecommunications, including the alongside Claude Shannon. The mathematician Shannon was the one who developed Information Theory, quantifying it with measurements from the bit and offering the basis for the digital revolution we see today.

In his office at FEEC, Max Costa talks about the sleepless night 20 years ago, after days of thinking about the mathematical problem posed in a routine meeting between his advisor and doctoral students like him, at Stanford. “It was already past midnight. It's paradoxical, because I should be tired at that time. There was no way to distract myself, I couldn't talk to other people because they were already asleep. So the only option was to focus on the problem,” he recalls.

Dirty Paper – The professor's excitement at realizing that he had obtained an impactful result lasted until dawn, but faded over 15 years, until in 1998 the first practical applications for his mathematical result were considered. The formula “y = s + i + w” is the beginning of an equation that is unintelligible to laymen, but is detailed in detail in the renowned IEEE Signal Processing magazine, from May this year, in a tutorial article entitled On Dirty-Paper Coding. Dirty Paper). Title similar to that of the article that the researcher published in 1983, Writing on Dirty Paper.

In the article, Max Costa considers a telecommunications system in which part of the transmission noise is known to the encoder. The transmitter can allocate a portion of the available power to partially or completely cancel the known noise component, but this solution is “sub-optimal” as it reduces the system capacity. Instead of trying to cancel the noise, the “optimal” solution consists of building a family of codes, and choosing, among the codes that are compatible with the noise signal, the signals for the messages. Translation: if fate gives you a lemon, make lemonade. Costa showed that with the code family (Dirty Paper coding), the system capacity is the same as if the known noise component were non-existent.

“Really, it's like writing on paper that has already been used. The idea is to impregnate a digital signal (a film, a song) with another signal, the watermark, to establish its ownership. This mark must be indelible, so that no one can eliminate it, and it must also minimally distort the so-called 'host' signal that we want to protect”, explains Max Costa. The watermark can contain a large amount of information, such as the date of creation of the sign, authors, directors, etc., offering irrefutable evidence in favor of the owner before the courts. A specialist in video and image compression, the professor adds that the watermarks we see today on television are easily eliminated: the objective is the immediate identification of the broadcaster, not the protection of the signal's content.

Professor Max Costa: indelible watermark

Cell Phones – If the watermark applied with Dirty Paper coding is indelible and the ability to transmit information is not diminished by the host signal, this means that it is possible to place a new layer of “writing” on top of another on dirty paper. Hence the most recent application of the theory, announced in 2000, when scientists observed that the same operation can be transported to cell phones, reducing the serious interference problem that currently afflicts users, and also allowing the system's capacity to be multiplied.
Max Costa explains that the cellular service is provided from a base radio station (ERB), which can send signals to several mobile users in the same frequency band; the signal sent to the first user interferes with the second user's signal and vice versa. “Using the precoding technique of Dirty Paper, we managed to eliminate the interference of the first in the second”, he assures. The effect is unidirectional, as it does not eliminate the interference of the second in the first. Even so, there is an increase in the capacity of the system as a whole. “If there is no interference in one of the directions, we can place signals in layers, four or five of them, which means many more cell phones in the same frequency band”, he observes.

Economy – Costa is well aware of how much telecommunications on land are limited by frequency bands. Having spent time at NASA's Jet Propulsion Laboratory (JPL) on his CV, he is aware of the opposite situation experienced in space communications, where there is unlimited range and the limitation is power. “It is extremely difficult to place an onboard power into orbit or into interplanetary space. On a ship going to another planet, a reduction of 1 dB (close to 20% power reduction) means savings of around US$60 million. On land, the competition is for spectrum, everyone wants a little band to transmit their signal”, illustrates the researcher. The economic gain from spectrum optimization, made possible by Costa's theory, is estimated by Professor Arantes in an interview on this page.

 

The economic impact Contemporaries from many years at Unicamp, professor Dalton Arantes, also from the FEEC Communications Department, remembers when he received a copy of his work from Max Costa. He found it very interesting and, like other researchers who had access to the mathematical result, he kept the article in a drawer. Now that the first practical applications for the theory are emerging, Arantes takes the initiative to praise his friend's discovery and risk projections about the economic impact it could have on the telecommunications sector. “People are usually dazzled by technological development, but by what it offers in terms of entertainment. For a country like Brazil, it is time to stop seeing technology as a toy, looking for ways to transform it into a source of wealth. The country lacks national, pragmatic and objective projects that bring together good minds, both from universities, research centers and companies. Some Brazilian projects failed due to a lack of synergy and pragmatism, in addition to excessive verticalization, as they depended on small and isolated research niches”, criticizes the professor. Arantes reflects on the value of the entire spectrum in the world for transmitting information. He recalls that only the third generation cell phone system, which will allow high-speed Internet access (it will be possible to watch TV on the phone), had its spectrum in Europe auctioned for an amount approaching US$200 billion . The Internet in the world, the professor estimates, is certainly worth tens of trillions of dollars. “Once applications for Max Costa's theory are made viable, we will also be talking about multiplying the capacity of video transmission systems. Special sessions on dirty paper coding are being planned at many international telecommunications conferences”, notes the professor. He recommends consulting Google.com, using these keywords, to check the large number of references to this technology and the potential of its applications. “In a short time, up to 90% of the Internet will be used for video transmission. There will be a sharp drop in costs, such as high-resolution monitors, and we will be able to observe an extremely realistic image of an interlocutor anywhere in the world, as if they were in front of us”, predicts Arantes. The researcher imagines himself doing virtual tourism, visiting Tibet, the Walls of China and the museums of Europe, as if he were there, revealing the phase of amazement that affects enthusiastic users. Dalton Arantes, finishing, remembers that the frequency spectrum is increasingly congested. Existing technology, with just one antenna on the receiver, offers a certain capacity. But based on the first work with multiple antennas (in the transmitter and receiver), scientists estimate that it is possible to increase this capacity by up to 10 times. According to the professor, Anatel, today, would have great difficulty in allocating channels for the implementation of digital television in the city of São Paulo. It will take a lot of creativity and efficiency to increase capacity. “Max Costa’s work could contribute to this.”