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The next step in telephony

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Ajai Sreevatsan and Shyam Ranganathan

3G phone allows simultaneous use of speech and data services

CHENNAI: If a mobile phone is an integral part of your identity, all the recent talk about 3G might have left you a bit lost and confused. The government has earned windfall revenue from the recent 3G spectrum auction, but what does the acronym mean to users hooked to their mobile device?

3G or 3rd Generation is the next step in the evolution of mobile telephony standards. A mobile phone is essentially an extremely sophisticated radio (one which can send and receive a voice message overlapped on top of a carrier signal), and wireless telephony has come a long way since Marconi's first successful trans-Atlantic radio-telegraph message in 1902.

“The significant difference in the functionality offered by a 3G phone is that it allows simultaneous use of speech and data services,” says Bhaskar Ramamurthi, head of the Centre of Excellence in Wireless Technology (CEWiT), IIT-Madras.

Packet Switching

The 3G phone uses a method of data transmission technology called Packet Switching. Data is split into packets that have a unique address. Data can be sent on any path in a network and recombined and inter-connected. Thus data will be transmitted faster than voice calls, though both are routed through the same virtual band of frequencies called the spectrum.

The higher data rate, however, comes at a cost. During the recent spectrum auctions, 5MHz slots were allotted to various telecom players.

Imagine the 2G GSM (Global System for Mobile Communications) standard of 31 carriers of 200KHz to be 31 cycle tracks, says Dr. Ramamurthi, “then the 5MHz 3G spectrum split into four 1.25MHz carrier pathways (as per International Telecommunication Union standards) can be viewed as a highway with traffic in both directions. Voice and data can be accommodated in the same channel, as the carrying capacity is greater. Data transfer rates can go up to several Mbps.”

Services like video calling and on-demand TV essentially tap into this extra space in the air waves. The amount of bandwidth required to explore the full potential of 3G could be as much as 15-20 MHz, a 500-fold increase in the amount of bandwidth required.

The widened spectrum means that an upgrade of both the handset (due to the requirement for a baseband chipset architecture that supports the 3G cellular modem) and the air interfaces of the existing cellular network is required. The dominant 3G air interface technologies are W-CDMA (Wideband Code Division Multiple Access) and CDMA200, which are 'revolutionary' upgrades of GSM and CDMA.

As devices get upgraded, 3G will be at the convergence of computing, communications and consumer devices.

“How many are going to upgrade their handset just to get 3G services” asks J. Shivkumar, Chief Technology Officer of Wi5, a wireless solutions provider. “It is going to be a premium service and will be available only in high density zones like Central Business Districts. Data access speeds will drop outside these zones. In other locations, coverage will be available, but not the required bandwidth to offer fast data access.” A mobile voice call typically consumes only 6-13 kbps.

Pointing out that data usage revenue has already overtaken voice revenue in the U.S., A. Subramanian, Chief General Manager, BSNL Chennai, says: “The focus is now going to be on getting more customers into 2.5G services such as GPRS and EDGE through cheaper rates. Most of the existing handsets can handle GPRS. Once initiated to data services, customers will tend to shift to 3G for better access speeds.”

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