As the telecom industry gears up to reach billions of potential mobile phone users in developing countries, a Swedish-Indian start-up has developed an innovative piece of equipment: a build-it-yourself radio tower that consumes about as much energy as a light bulb.

For years, telecom operators have been trying to expand into rural areas in Asia, Africa and West Asia a major growth opportunity at a time when urban areas are saturated. Some two billion new subscribers are projected to start using mobile phones in the next five years, and 80% of them live in developing world markets, according to analyst estimates. Yet, wiring villages without reliable electricity, and where residents have little money to spend, requires a technological rethink.

To power mobile networks in remote areas today, telecom operators pair base stations  the tower-top radio transmitters that form the backbone of mobile networks with diesel-powered generators and batteries. These are impractical and expensive: Fuel accounts for 65% of the cost of operating a typical base station.

Vihaan Networks Ltd (VNL), which has headquarters in Gurgaon, outside New Delhi, and Stockholm, has spent the past four years developing a simplified base station that is powered by solar panels and requires just a fraction of the electricity of typical base stations.

But convincing telecom operators to buy a stripped-down base station made by a little-known start-up won't be easy. VNL is among many companies trying to develop mobile phone technologies for poor rural areas. Telecom equipment giants Telefon AB LM Ericsson, Alcatel-Lucent and Motorola Inc. are all looking into how they could tweak existing telecom gear to run on less electricity, or on renewable energy sources.

Ericsson and Alcatel-Lucent have separately installed about 400 solar-powered base stations in African countries, including Senegal and Uganda. In India, Ericsson has installed some 40 base stations that run on biodiesel, essentially recycled cooking oil. Alcatel-Lucent's solar base station requires about 750W to run, while Ericsson's solar base station requires about 600W. The firms wouldn't disclose the costs, but both sets of gear require technical staff to install them over a matter of weeks.

VNL's base station will cost $3,500 (Rs1.5 lakh) and require 100W to run, about the sameas a light bulb. By contrast, the GSM stations most widelyused today can cost anywhere from $40,000 to $100,000.The most energy-efficient models require around 600W; others may need several thousand watts.

"We started with a clean sheet of paper, and told ourselves that we needed to design technology perfectly suited for the rural environment," says VNL chief executiveAnil Raj, a former executiveat Ericsson.

The tower is designed to make it easy for people with little professional training to install. The equipment comes with a pictorial instruction manual similar to those for Ikea's do-it-yourself furniture. It has just one button, used to turn it on. Once the pole is erected, the base station beeps intermittently until the radio antenna is rotated manually to face the direction of the mobile network. When the antenna is perfectly aligned, the sound steadies.

Though tested in labs, VNL's technology is just starting to be tried out on the ground. The start-up recently signed an agreement with Quippo Infrastructure Equipment Ltd, an independent Indian mobile infrastructure company, to test the VNL solar base station in northern India. VNL says it hopes to sign contracts with Indian telecom operators over the next year.

If VNL's base station takes root, it could make it possible for Indian telecom operators such as Vodafone Essar Ltd, in which Vodafone Group Plc. has a majority stake, and Bharti Airtel Ltd to wire more remote villages at a much lower cost and more quickly. That is one of their main objectives, because most people in India's cities already have mobile phones and price competition there is intense. India is expected to have the most rapid growth in new subscribers over the next three years, followed by China, according to Pyramid Research, Cambridge, Massachusetts.

Beyond boosting telecom companies' profits, affordable mobile phone service promises to change everyday life in rural communities worldwide.

As they designed the new base station, VNL officials conducted interviews in and around Deorhi, a village 200km from New Delhi. VNL also asked about its interviewees' skills such as how they repair farm equipment and operate generators information that helped the company design equipment that can be installed without engineers.

Majid Khan, a construction contractor in Deorhi, said his business' productivity has soared since he bought a mobile phone, according to a transcript of VNL's interview with him. Khan can now call workers, rather than driving to their homes when he needs to speak with them.

As VNL chief technology officer Krishna Sirohi and his team started developing the new tower, their goal was to minimize power usage while keeping costs to a minimum.

Computer chips traditionally used for telecom equipment ate up too much power and were too expensive, Sirohi recalls. So VNL decided to buy chips designed for cars and consumer electronics, which are less electricity-hungry. VNL engineers then spent months rewriting the chip software to make it suitable for telecom gear.

VNL decided to produce two versions of the base station one for village centres, where voice traffic would be higher, and another for the surrounding fields, where traffic would be low. Towers in fields could be put in virtual sleep mode to save power when no one was callingon them.