All about band spectrum

The concept

In physics, spectrum refers to a range of frequencies at which electromagnetic waves can be transmitted. Such waves—radio waves, infrared and ultraviolet radiation, microwaves and visible light—abound in nature and travel at various frequencies. Ever since scientists learned to generate artificial electromagnetic waves, these have been used to transmit data for various service—cellular telephony, broadcasting, satellite communications and navigation systems.

Interference
If all these services operated on the same frequency, there would be interference and confusion. “To give an example, humans can hear sound waves between 20 Hz and 20,000 Hz (cycles per second). Since each one of us has a differently pitched voice and uses different inflections, we are able to hear one another even in a crowded place. But if two people were to shout at the same pitch or frequency, they wouldn’t be able,”

Bands...

To minimise interference, the International Telecommunication Union has guidelines to divide spectrum into sections called bands, which are then allocated for particular uses according to each country’s National Frequency Allocation Plan. In India, the Wireless Planning and Coordination wing of the Department of Telecommunications is the regulator. Most of the 88-108 MHz band is for FM broadcast; parts of the 800-900 MHz and the 1,700-2,000 MHz bands are for cellular communication by GSM and CDMA service providers. These are licensed; bands reserved for amateur radio, Wi-Fi and Bluetooth are free to use.

Think of spectrum as a multi-lane highway with curbs in between. Each lane carries a specific type of vehicle; a curb prevents a car from bumping into a bike. Leaving a small margin between bands and installing filters are some preventions against interference.

It doesn’t always work, though. If your microwave or cordless phone causes your Wi-Fi router to act funny, it’s because the devices work on similar frequencies.

...And sub-bands

Spectrum, while naturally occurring, is limited — at least the part we can utilise. “You cannot create additional spectrum. Higher frequencies can scatter the propagation of a wave,” . Existing “efficient” bands are broken into sub-bands and allocated to newer technologies that did not exist at the time of the original allocation.

In India, the 585-806 MHz band is broadly used for broadcasting services including mobile TV, but within it the sub-band 746-806 MHz is for public protection and disaster relief, along with 806-824 and 851-869 MHz.

The S-Band (2-4-GHz) is traditionally allotted for satellite communications but is increasingly being used for other services the world over. In the Indian Space Research Organisation’s deal with Devas, the spectrum to be allotted was part of this band.

Monitoring equipment is in place to prevent hacking into frequencies not allocated to a given service.

Band names

The S-Band is now being used for services such as WiFi, satellite and instructional TV in the US, apart from satellite communications. The C-Band is usually allotted for commercial and educational satellite TV transmission, the X-Band for military and government satellite communication, and the Ku-K-Ka range for satellite broadcast and point-to-point communication. (Illustration shows broad frequency ranges and services)

Gold mine

spectrum is invisible real estate. Last year, the government auctioned 15 MHz of S-Band frequencies for Rs. 67,719 crore towards 3G mobile services. This figure has frequently been compared to the “Rs 1,000 crore for 70 MHz” in the ISRO-Devas deal.The value of a spectrum depends on the demand and possible uses. The demand for a band widely used across the world for a certain service, such as 3G, is bound to be high as it makes it easier for manufacturers and service providers if they can follow the world frequency standards.

India and the world

In India, 2G spectrum has traditionally been offered on a first-come-first-served basis, instead of being market-linked as in other countries. The 3G and WMA auctions last year were a competitive diversion, bringing in sizeable revenues for the government by linking spectrum to market prices. Now the Telecom Ministry has said 2G operators will have to pay market-determined prices for spectrum beyond the 6.2 MHz allotted to them.

In most countries, spectrum usage and allocation are well-planned out according to a predetermined roadmap. India, on the other hand, is struggling to free up spectrum for various services.

2G, 3G, 4G

2G technology heralded an era of digital telephony; 3G will usher in the age of mobile data transfer and multimedia consumption. As 2G technology evolved, it spawned a new generation of devices compatible with what are called 2.5G systems. These devices could connect to the Internet using GPRS, which basically used the 2G bandwidth of 200 KHz per carrier frequency to offer data services at 64 kilobits per second or higher.

The data-oriented 3G system, which uses High Speed Packet Access (HSPA), offers connection speeds up to 3 Mbps. Only recently deployed in India, 3G offers possibilities of live streaming, video calls and Internet telephony. Meanwhile, a new term has cropped up with the advent of devices that can support 7.2 Mbps and more: 3.5G or 3G+ devices.

Last year, the government auctioned the 2.3 GHz spectrum for Rs. 38,000 crore towards broadband wireless access services. This spectrum may be used to deploy 4G technologies like WiMax and Long-Term Evolution, already in use in some countries. 4G, which uses a single line for voice and data, is capable of speeds upwards of 100 Mbps.