The Hindu Business Line : Spectre of no free frequency in spectrum

Spectrum is a band of colours, a definition that we remember from our school days. But did you know that the word was used to denote what is now called a spectre or a phantom?

HAVING sat through a barrage of news on the auction of spectrum — entry fee for spectrum allocation, TRAI recommending additional spectrum for the CDMA players, DoT suggesting that spectrum be shared according to traffic, Mr Ratan Tata's statement on spectrum as a scarce resource, defence being nudged out of spectrum space, and so on — if you're asking, "What is spectrum?" it's time for a zero base on the word.

Spectrum is a band of colours, a definition that we remember from our school days, when the Physics teacher showed us hues of the rainbow by passing light through a glass prism to explain refraction or the bending of each colour at a different angle owing to difference in wavelength. It was Sir Isaac Newton who first used the word spectrum in 1666 to refer to the celebrated `Phenomenon of Colours', informs http://encyclopedia.laborlawtalk.com.

An electromagnetic spectrum encompasses all possible wavelengths of electromagnetic radiation or EM radiation. Which, in turn, is "a combination (cross product) of oscillating electric and magnetic fields perpendicular to each other, moving through space as a wave, effectively transporting energy and momentum".

And `spectroscopy' is the study of spectra, that is, the dependence of a physical measure to frequency.

If you find these are beyond your comprehension frequency, check out the crisp diagram at http://jan.ucc.nau.edu explaining electromagnetic spectrum. It lists radio waves, microwaves, X-rays, gamma rays and so forth, laid on a wavelength scale. The ones with short wavelength, such as X-rays, have high energies and frequencies, and vice-versa.

You may be aware that Wilhelm Conrad Röntgen discovered X-rays, "a very energetic portion of the electromagnetic spectrum", in 1895, for which he won the first Nobel Prize in Physics.

A speech you'd love to read, especially if interested in the progress of science in X-ray spectroscopy, is that of A. Gullstrand, at http://nobelprize.org. Heinrich Rudolf Hertz, the scientist who discovered electromagnetic waves and after whom the unit of measure of frequency is named had learnt Arabic and Sanskrit, informs the Encyclopaedia. Max Karl Ernst Ludwig Planck is considered the inventor of quantum theory. In 1899, he discovered the Planck's constant, and showed the direct relationship between a photon's frequency and its energy, as http://heasarc.gsfc.nasa.gov explains.

In his equation, E = hv, E is energy, h is Planck's constant with a value of 6.6262 X 10^-34 Joule seconds, and v stands for the frequency. Albert Einstein and Neils Bohr drew insights from the observation that EM radiation travels at the speed of light in vacuum.

While radiation within the visible range of the spectrum is what helps us recognise objects, radio waves, which lie beyond infrared and microwaves are what the current debate on mobile telephony is about. "Originally a spectrum was what is now called a spectre, that is, a phantom or apparition," explains Wikipedia. "Spectral evidence is testimony about what was done by spectres of persons not present physically, or hearsay evidence about what ghosts or apparitions of Satan said."

Something similar happened to many top scientists too who were disillusioned with the war machine using the new knowledge.

For instance, `Atomic Bomb Timeline' on http://hornacek.coa.edu notes the famous comment of Einstein at the Solvay conference in Brussels, in 1927, that God does not throw dice, in response to which Bohr quipped: "Nor is it our business to prescribe to God how He should run the world."

Even as we throw dice on who should get the spectrum here, it would help to know that radio waves aren't new. Explaining `radio waves and health', www.ericsson.com observes that 3G is a development of the mobile telephony that uses the same type of waves as "radio, television, and radio communications used for many years by the police, air traffic, shipping and transport companies." To dispel the myth that radio wave exposure from base stations can be harmful, the site gives the analogy of light from a spotlight.

To look at how spectrum is used by the military, visit www.nato.int where a `basic fact sheet' discusses `Cooperation in Radio Frequency Management': "the 225-400 MHz band is used NATO-wide for: military aircraft communications in general; naval military communications; military satellite communications; tactical air functions such as airborne surveillance and control data transmission and air-to-air communications; tactical ground communications serving as one of the backbone frequency bands for land forces."

Another site, www.yuma.army.mil explains `spectrum management' as the process that allows the maximum number of people to use a very limited resource. "This resource, `Electromagnetic (EM) Spectrum' (EM), is also called the Radio Frequency (RF) Spectrum.

Spectrum management is accomplished by spectrum engineering, spectrum monitoring, and spectrum assignment to ensure pure spectrum availability. Spectrum users may be separated by frequency, location, and/or time."

In your tour of spectrum knowledge, stop by www.itu.int. "Mobile operators use radio spectrum to provide their services. Spectrum is generally considered a scarce resource, and has been allocated as such," explains the site. "At the World Radio Conference (WRC) in 1993, spectrum allocations for 2G mobile were agreed based on expected demand growth at the time." WRC 2000 allowed the use of current 2G spectrum blocks for 3G technology and allocated 3G spectrum to an upper limit of 3GHz (gigahertz). "The spectrum between 400 MHz and 3 GHz is technically suitable for the third generation," states the International Telecommunications Union.

We are familiar with how cellular technology divides the geographical area into cells, "leading to a more efficient use of the radio spectrum" through `frequency reuse'. However, an early approach to handle increased capacity was to chop or divide frequency to add channels.

As a result, bandwidth available to each user was reduced, and service suffered. For instance, in Frequency Division Multiple Access (FDMA) spectrum is sliced into frequencies and assigned to users, closed for others till the call is over.

Time Division Multiple Access (TDMA), a dominant technology of 2G, "improves spectrum capacity by splitting each frequency into time slots"; and Code Division Multiple Access (CDMA) uses the spread-spectrum technology allowing all users to occupy all channels at the same time by transmitting a signal in a bandwidth considerably greater than the frequency content of the original information.

Interestingly, "Frequency-hopped spread spectrum was invented by actress Hedy Lamarr and musician George Antheil," as The Free Encyclopedia informs. They received a patent in 1942 for their `Secret Communications System'.

"This early version of frequency hopping used a piano-roll to change between 88 frequencies, and was intended to make radio-guided torpedoes harder for enemies to detect or to jam."

On spectrum management, two documents worth referring to are the `Report on the Introduction of Economic Criteria in Spectrum Management' from the European Radiocommunications Committee, and the `Report of Spectrum Management Committee' from the Group on Telecommunications (GoT) constituted by the Prime Minister in 1998.

These would give you a background before you launch into the `Recommendations on Spectrum related issues' from TRAI, a 140-page report issued on May 13.

ZeroBase@TheHindu.co.in

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