Friday, March 5, 2010

Understanding Spectrum

Telephony and broadband need innovative spectrum management


Shyam Ponappa / New Delhi March 4, 2010

Twenty years ago, “spectrum” implied the colours of the rainbow. Now, we understand that spectrum also relates to mobile phones. We encounter spectrum daily, in TV remote controls, microwave ovens, even sunlight. So, what exactly is spectrum, and how do government and commercial decisions on this scientific phenomenon affect public facilities and costs?

“Spectrum” is short for “electromagnetic spectrum”, the range of radiated energies that envelop the Earth and extend through space. This electromagnetic radiation (EMR) is primarily from the sun, and secondarily from the stars/cosmos, radioactive elements in soil, rock and gases.  

[Added later - May 26, 2013:
For more details on what spectrum is, please see the footnote.1  The rest of the article is on the uses of spectrum.]

One section of EMR is visible light; another is radio frequency (RF) spectrum. There are many other “wavelengths” in EMR with different characteristics and effects, such as infrared and ultraviolet rays. All countries have the same RF spectrum in equivalent areas.

How is spectrum used?

The length of a wave, its associated frequency (“wavelengths” or “cycles” per second) and energy determine its usage (see Figure 1).

Figure 1: The Electromagnetic Spectrum


Source:
http://galileo.phys.virginia.edu/classes/USEM/SciImg/home_files/introduction_files/EMSpec.gif
  1. Radio waves are relatively long, with wavelengths from 1,000 metres (1 km) to 10 cms, and frequencies from 3 kilohertz (3,000 cycles per second) to 3 gigahertz (GHz) or 3 billion cycles per second for the shortest, sometimes also called microwaves. (There are longer waves, e.g., electric power, of several km.)
  2. Microwaves in the centimetre and millimetre range can have frequencies up to 300 GHz. There is an overlap in terminology depending on use; microwaves for cooking use several hundred watts of electricity at RF wavelengths of about 32 cms (915 MHz) and 12 cms (2.45 GHz). Microwaves from low-powered devices of a few watts at these frequencies are used for communications, and emit insignificant heat.
  3. Infrared waves are smaller, and are felt as heat, e.g., from lamps and infrared grills used for cooking. Higher infrared bands used for communications in remote control devices and for imaging/night vision have no heating effect.
  4. Wavelengths between 700 and 400 nanometres (about 430 to 750 terahertz or THz) form the visible spectrum from red to violet, combining to form white light. For example, we perceive wavelengths of about 635-700 nm (430-480 THz) as the colour red.
  5. Shorter wavelengths form ultraviolet rays, of which those around 380-280 nm cause sunburn. Sunlight at sea level comprises about 53 per cent infrared, 44 per cent visible light, and 3 per cent ultraviolet rays.
  6. Yet smaller waves are classified as X-rays, and the smallest as gamma rays, both used in medical and industrial imaging.

The sweet spot in the RF spectrum for telephony and the Internet

For telephony and broadband, lower frequencies (700-900 MHz) are most cost-effective, as they traverse long distances without attenuation, penetrating walls and foliage. Radio waves in the atmosphere are affected by water vapour and ionisation, as well as events such as solar flares with bursts of X-rays. Depending on temperature, moisture, etc., radio waves may be absorbed, refracted, or reflected in the atmosphere, and by hills or other obstacles. Low frequency waves penetrate buildings and trees, and curve over slopes. Higher frequencies are more absorbed or reflected by the atmosphere; they are also more attenuated by distance and rain. Networks at lower frequencies require fewer towers than at higher frequencies.

What are 2G and 3G?

These signify different stages of technological development, starting with 1st Generation (1G) analog wireless in the 1980s, e.g., in car phones. 2G (2nd Generation) began in the 1990s with the digital wireless GSM standard for mobiles, extending to other standards, e.g., CDMA. 3G (3rd Generation) has faster data speed and greater network capacity.

What is 2G/3G spectrum?

There is no difference in the spectrum; only the convention of government regulations and harmonisation between countries by the International Telecommunication Union (ITU) earmark wavelengths for different applications. Both 2G and 3G can and do work at 800-900 and 1800-1900 MHz.

Combined with the advantages of prices dropping as volumes rise, one estimate puts 3G coverage with 900 MHz at 50-70 per cent lower cost than at the designated 2.1 GHz. 3G networks using 900 MHz (“2G spectrum”) exist in Finland, Iceland, Australia, New Zealand, Thailand, Venezuela, Denmark and Sweden, and countries like France encourage 2G networks to upgrade to 3G services.

Spectrum allocated for 2G and 3G by various countries is at Figure 2; the current and proposed allocation in India is shown below.


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* Existing # Proposed BWA: Broadband Wireless Access
[For details on 2G GSM & CDMA in November 2009, see: http://mobile.broadbandindia.com/2009/11/complete-2g-spectrum-allocation-info.html.

For proposed 3G and BWA auction bands, see:
For National Frequency Allocation Plan 2008: (Care - ~ 67 MB!)

This shows India’s dearth of spectrum for public use because of government and defence allocations. We need innovative methods to maximise capacity given our needs, limited landline networks, and the relative costs. (For details on the chart, please see: http://www.umtsworld.com/technology/frequencies.htm)

For example, China has allocated 250 MHz in the 800/1800 MHz bands. By not charging auction fees and spectrum charges, ubiquitous networks were built at lower cost with high capacity. These result in lower costs for users and higher productivity. With its focused approach, China also developed its own standard (TD-SCDMA).

India’s spectrum allocation is burdened with short-term revenue collection for the government, and a shortage mentality. There is apparently insufficient clarity on spectrum usage for ubiquitous broadband/telephony as in other countries, let alone more ambitious targets, such as developing an Indian standard.

Our policies could address the requirement for enhanced coverage/capacity at low cost to make services available everywhere at reasonable prices. Innovative approaches to spectrum management could help get these, through:
  1. Technology-neutrality: the UK and Norway have not restricted the use of recently auctioned spectrum to any technology.
  2. A focused strategy for service delivery at low cost, as in China.
This needs a combination of methods, e.g., along with technology-neutrality, (a) data-base driven, shared spectrum usage, under trial in the US, (b) “Cognitive Radio”, whereby smart devices sense available channels for dynamic, non-conflicting use in unlicensed spectrum bands, (c) incentives for rural broadband delivery, e.g., by subvention of fees and government charges, with (d) subsidies.

                                                      shyamponappa at gmail dot com


Footnote - Added later: May 26, 2013

1 What is Spectrum?



A more detailed explanation requires an understanding of the interrelated concepts of energy, work, and force, which are explained below.  Those who are not interested in technical details are advised to skip the box below to the paragraph with the diagram.

Energy, Work, & Force

Energy is the capacity to do work.  More precisely, it is the state or property of a system that enables it to perform work.  Work is defined as the change in position of an object, or of the state of an object or another system in motion or at rest through a transfer of energy to it, e.g., its temperature, which is a measure of the random motion of the particles comprising that system, or of the amount of light (i.e., radiant energy) or chemical energy in it, or its state of motion or rest.

Work is done through the application of force, the expending of any form of energy.  The major forms of energy are: electromagnetic radiation -- including RF spectrum, light, gamma rays, x rays, and so on; electrical energy; thermal energy or heat; mechanical energy; chemical energy; nuclear energy; sound energy; and gravitational energy.  Force is any influence that produces change in an object's or system’s state of motion or rest, or in its internal state.  Force has both direction and magnitude.  There are four known “fundamental forces” or “interactions” in physics:

- Gravitation, which affects all objects with mass.  Every object exerts a gravitational force on all other objects.  It is the weakest interaction, operates over infinite distances, and governs the structure of the universe. 

- Weak interaction, which affects all particles, and operates only at very short range.  It acts at the subatomic scale of atomic nucleii.

- Electromagnetic interaction, which affects all particles, has infinite range like gravity, and is much stronger than both gravity and weak interaction.  This form of interaction is responsible for the attractive or repulsive forces between electrical charges.

- Strong interaction, which affects subatomic particles called hadrons, which are themselves made up of quarks.  This type of interaction binds the nucleons in the nucleus of all atoms with the strongest force, operating at very short range.

These interactions hold particles together and organize them into complex objects (http://keyhole.web.cern.ch/keyhole/theory/main-5.html).  For details on the fundamental forces, see http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html; for more about electric and magnetic charges and fields, see http://en.wikipedia.org/wiki/Electric_charge.




Electromagnetic radiation is pure energy without mass, and consists of waves of electrical and magnetic energy (see diagram below). 





These waves consist of a stream of photons, which are packets of energy that can be thought to behave like waves.  The energy in a stream of photons determines what kind of wave it is, i.e., whether they are light waves that we see as visible light, or radio waves or X-rays that are invisible.  This energy also determines the effect the photons have when they come into contact (interact) with particles of matter.

What Gives Rise To EMR?

All matter consists of atoms, which consist of mostly empty space.  Atoms are made up of negatively charged electrons revolving around a nucleus at the centre, which comprises positively charged protons and neutrons with no charge.  For example, a hydrogen atom has one proton and one neutron in its nucleus, and one electron in orbit.  The atom is 100,000 times the size of the proton.  This means if the nucleus of the atom were enlarged to the size of a tennis ball (6.5 cm), its electron would be at a distance of 6.5 km away; hence the mostly empty space. 

When energy is absorbed by an atom, one or more of its electrons shifts to a more distant, higher-energy orbit around the nucleus.  When the electron returns to its original level of orbit, energy is released as EMR and/or in some other form/s.  Depending on the material of the atom and the amount of energy released, the energy takes the form of heat, light, EMR, or other radiation such as X-rays or gamma rays.

SP
May 26, 2013

1 comment:

Reba Som said...

very lucid explanation