Understanding allocation of spectrum for telcos

These days you read a lot about telcos having a war with the Government about allocation of spectrum. So what does it actually mean?

Spectrum is airwaves which carry sound on a given frequency or band. It is scarce because there is limited bandwidth and a major chunk of airwaves is controlled by defense forces in India. There is only a finite spectrum and it is limited – cannot be created. (just like real-estate, which is a limited commodity and is not being created).

For those who want to get very technical: Spectrum is the collection of all frequencies available for the transmission of light, not sound. When the frequency is very high, you get ultraviolet rays. When the frequency is lower, you get optical light, and when the frequency is lower than that you get infra-red light (which also transmits heat and the information between TV remotes and TV sets). Still lower frequencies carry light in the form of radio waves. Cell phones function through the transmission and reception of radio waves.

For example Department of Telecommunication in India has earmarked 100 Mhz on 900 and 1800 Mhz band frequencies for 2G services (GSM/CDMA). It basically means that at 900Mhz to 1000 MhZ and from 1800Mhz to 1900Mhz (assuming total of 200 MhZ) has been allocated for carrying wireless traffic. Each operator gets part of the frequency in geographic locations.

2G basically constitutes of GSM [Global System for Mobile] and CDMA [Code Division Multiple Access] operators. Every GSM player was allocated 6.2 MHz on the 900 and 1800 MHz band frequencies and CDMA players got 5 Mhz in the 900 MHz frequency.

Each Hz can carry “x” number of calls. If the telco wants to take more calls, then, the telco needs additional spectrum. Each operator is asking for additional spectrum in metros so that they can offer more services. More bandwidth requires more Hz as well. Currently, telecom outfits have access to 37 Mhz. This means out of 100MHz, only 37 MHz has been auctioned. In India, the remaining ones are being auctioned. Government is looking at allocating an additional 60-65 MHz to telcos which they will obtain from the defense forces. But the govt wants to allocate additional spectrum provided the telcos invests in setting up additional towers. Currently with 37 MHz India has over 250 million subscribers. The govt plans to raise Rs 25,000 crore [$625 m as of Nov 2007] by auctioning spectrum for 3G.

You cannot use 2G phones on 3G spectrum. 2G phones will continue to operate on historic spectrum. 3G is WCDMA, which is a different technology and voice on 3G requires 3G phones. However, many of the new phones have 2G and 3G technologies built in so that in regions where 3G is not available, it goes back to 2G technology for voice calls. In general 3G protocols will involve faster signals and a 2G phone, which works perfectly well at 1800MHz, will not work at the freqs used for 3G. The freqs for 3G are going to be higher than for 2G for 2 reasons:

(a) the bands in the lower freqs are already full and are in heavy demand, and
(b) signals transmitted at higher frequencies inherently have more bandwidth around them.

The reason for the delay in 3G phone systems is that it takes a while to develop electronics at 3000Mhz or 5000Mhz, and also because international standards for the higher freq applications are not yet established.

To understand (b), think of it this way: if you have a 900MHz signal with a 10MHz band around it, this signal therefore spans from 895MHz to 905MHz. Therefore, the next higher signal has to be centered around 910Mhz, and will span the range 905Mhz to 915MHz. Therefore if you look at a +/-10% range around 900MHz, the total span will be from 810MHz to 990MHz. In this band, you can fit 18 “channels,” each of which is 10MHz wide. If you move the story to the 3G freq of ~3000MHz, you can see that there is a lot more room between, say, 2700MHz and 3300MHz. In fact you can fit in 60 channels, each of which are 10MHz-wide.

The globally used band for WiMAX is 2.5 GHz – 2.7 GHZ, but in India this band is locked for satellite based mobile and broadcast applications such as national emergencies and natural disasters. What is available is the 2.3 GHz- 2.4 GHz and 5.8 GHz that has been allocated to several IPS’s. According to the ISP’s, these bands are good for trials only, but not for city wide and commercial deployment. The key players of WiMAX and even 3G have asked the Indian government to release higher band frequencies so that deployment can be made.

For content contribution thanks to Mahesh.

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