by January 31, 2004 0 comments



Today, though GSM phones let you access the Internet through technologies such as GPRS, CSD and HSCSD, the available bandwidth is a limitation. The bandwidth they provide is enough only for Web browsing and e-mail access, but not for 3G applications such as video conferencing, extranet, VPN and collaborative working that require much higher data-transfer rates. 

Enter EDGE (Enhanced Data rates for GSM Evolution) that promises data transfer rates of 384 kbps (and theoretically up to 473.6 kbps) on your mobile phone. We’ll talk more about EDGE later. But, first we’ll look at the other technologies mentioned above: GSM, CSD, HSCSD and
GPRS.

GSM, CSD, HSCSD
GSM (Global System for Mobile communication) is the digital cellular system for providing mobile voice services. In fact, it is the de facto standard for most parts of the world, including India, with mobile service providers, such as Hutch, Airtel, Orange, IDEA, BSNL and Escotel using it. GSM is purely a voice-based service and does not provide any data service. This means that you cannot use it to access the Internet. 

CSD (Circuit Switched Data) is a GSM-based data technique with which you can dial into an ISP to access the Internet. It offers data transfer rates of 9.6-14.4 kbps. But, this technology is not very popular, because to use it you need a separate ISP account as you would in a dial-up setup. Moreover, CSD offers slow speed. You can get better transfer rates, of up to 43.2 kbps, through HSCSD (High Speed CSD), an enhancement to CSD. 

GSM, CSD and HSCSD use circuit-switched techniques, in which the sender and receiver transfer data over a dedicated path between them. But, this leads to inefficient use of the wireless link since the connection needs to be kept open even when no data transfer is taking place. The connection has to be closed explicitly by either of the two ends on completion of data transfer. This limitation is overcome by another technique called packet switching, which is used in GPRS (General Packet Radio Service).

GPRS
GPRS is the first implementation of packet switching within GSM. With GPRS, you can split the information into a number of packets, which are then independently transmitted to the receiving end. Upon receiving the packets, the receiver reassembles them into their original format. In such a case the link is better utilized as data packets travel independently of each other and no dedicated connection between the sender and the receiver is required. GPRS can offer maximum data rates of 171.2 kbps, though in reality you would get about 40-50 kbps depending on your handset and the service provider’s implementation of GPRS. This speed may be good enough for basic Internet access, but not for 3G applications.

EDGE
3G applications such as video conferencing and streaming can now become a reality with EDGE, with the technology offering data transfer rates of 384 kbps (theoretically up to 473.6 kbps). EDGE is an add-on to GPRS and cannot work in isolation.

What it does is that it makes data transfer more efficient and faster on the existing GPRS network by using better modulation and channel-encoding techniques. The existing technology uses a modulation method called Gaussian minimum shift keying. To increase higher bit rates EDGE uses a different technique called 8-phase shift keying which increases the data rates by a factor of three.

GPRS with the EDGE technology is called EGPRS or enhanced GPRS. 

All this may sound exciting, but to avail the advantages of EDGE you will need compatible handsets and services from cellular operators, both of which are still to happen in India.

Anoop Mangla

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