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| Shyam Ponappa: Understanding Spectrum | | Telephony and broadband need innovative spectrum management |
| Shyam Ponappa / New Delhi Mar 04, 2010, 00:25 IST |
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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. This electromagnetic radiation (EMR) is primarily from the sun, and secondarily from the stars/cosmos, radioactive elements in soil, rock and gases... .
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).
- 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.)
- 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.
- 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.
- 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.
- 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.
- 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 Telecommunications 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.
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:
- Technology-neutrality: the UK and Norway have not restricted the use of recently auctioned spectrum to any technology.
- 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@gmail.com
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