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Sci Tech
CorDECT occupies pride of place
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Thanks to corDECT technology that offers a wireless last mile connection, many neglected smaller towns would soon find a place in the telecom map of India.
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Indigenously developed technology would provide consumers voice and data connectivity.
THE TIDE has turned and the waiting is over. The corDECT wireless in local loop (WLL) technology has been chosen to connect 5.77 lakh consumers spread across the country by Bharat Sanchar Nigam Limited (BSNL). With this the biggest dream of Ashok Jhunjhunwala, Professor of Electrical Engineering Department of IIT, Madras to telecom network the neglected smaller towns is coming true. It has also vindicated his claim that corDECT is a less expensive and superior technology for the smaller towns and rural areas.
The corDECT technology developed indigenously provides the last mile wireless connection between the telephone exchange and end consumer. Conventionally copper wires achieved this.
This is not the first time that corDECT technology has been chosen by the government. In 2001 the Department of Telecommunications opted for this technology to network 24 cities. However, the number of lines was limited to 25,000.
The good news is that many major telecom players who have entered the fray to provide basic telephone services are seriously looking at using corDECT. The Chennai based Internet service provider Satyam Infoway Ltd (Sify) has not ruled out the possibility of using it to connect its `i ways' (cyber cafés) in smaller towns.
Its relevance is not restricted to rural areas alone. For the urban areas where the telephone penetration is better the use of corDECT will go a long way in meeting the specific requirement of providing faster Internet connectivity.
The corDECT technology provides 70 kilo bits per second (kbps) connectivity speed. This drops to 35 kbps when Internet and phone are used simultaneously.
Now compare it with 40-50 kbps speed when Internet is accessed using a dial up line within one km radius from the telephone exchange and 25-38 kbps when more than one km radius. Smaller towns have speeds anywhere between 14.4-19.6 kbps and rural areas have pitiable speeds of 4.8-9.6 kbps.
Though access speed seems comparable in the urban areas, it is common knowledge that the access speed reduces when more subscribers log on to the Net in the case of dial up lines. But this is not the case with corDECT as the speed remains constant. "This is because dedicated pipelines are provided to each customer that are not shared with other subscribers," explained Shirish B. Purohit, Director of Midas Communication Technologies Pvt Ltd, Chennai.
Bandwidth sharing is not unique to dial up connection — both GSM (Global Service for Mobile communication) and CDMA (Code Division Multiple Access) based WLL technology use the same principle. GSM and CDMA are primarily designed to support only voice and not data (Internet). But the use of certain technologies makes it possible for GSM and CDMA to transfer data. But this data transfer is typically for transactional applications and cannot meet the requirements of a typical home user looking at sustained browsing. Even data transfer in spurts suffers from slow speed due to bandwidth sharing.
This is not the case with CorDECT as it works on the principle of reusing spectrum very often by using microcellular architecture. The use of multiple smaller cell sites enables a wise utilisation of bandwidth. The technology does not require frequency planning. "It is designed to allow multiple operators to use the same spectrum in the same area without having to coordinate on spectrum division," Mr. Purohit explained.
The corDECT combines 20 frequencies and 10 time slots to make available 120 channels in every sector at any given point of time. The subscriber terminal continuously scans for channels and chooses the quietest channel and a base station delivering the strongest signal. These channels according to Mr. Purohit can be reused and are limited only by the number of installed base stations.
But will a situation not arise when there are more subscribers in a given area posing a challenge to availability of channels and hence the assurance of `dedicated pipelines?' "We solve this by first increasing the number of base stations. By doing this we are effectively reducing the number of subscribers per cell site," Mr. Purohit elucidated. "Alternatively we could use special antennas or network planning to overcome capacity saturation." A cell site in urban area can serve customers in a 2 km radius and this can go up to 10 km radius in rural areas.
Several special antennas with narrow beam width can be mounted in different directions on a single base station. This way the antennas essentially divide the area served many fold by using a single base station.
Ironically, the government's decision to use corDECT technology on a large-scale vis-à-vis other competing technologies like CDMA's WLL comes long after it has been accepted and deployed in other countries. "Contrast this with the way the U.S. banned GSM technology (being used in Europe) for nine long years to help its industry develop a competing technology. And here we have people who would go to any length to promote a foreign technology," lamented Prof Jhunjhunwala. Alas, the old tale that the `Made in India' label (stigma) takes a long time to sell not just outside but also within the country still holds good!
R. Prasad
in Chennai
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