A wireless telecommunication technology being tested by a small startup in Ridgeland, Mississippi, could allow mobile operators in developing countries to take advantage of an existing infrastructure with far greater population reach than most cellular networks: television broadcasting systems.
A technology patented by Sigfx LLC could carry voice calls over all or part of the spectrum normally assigned to a TV station, according to the company, which is now using the technology in a small trial in its hometown. The system could be adapted to work on any country's TV system, according to Sigfx Chief Executive Officer Dallas Nash.
In addition to reaching people who now live outside the practical range of mobile cells and wired telephone networks, the technology could open the door to a mobile service significantly less expensive than current wireless offerings, Nash said. That feature could make it an attractive alternative option for consumers in developed countries as well, he added.
In most developing countries, television broadcasts are available much more widely than either mobile or fixed telephone service.
India, for example, which had 2.3 million mobile phones as of November 2000, already had 63 million televisions in 1997, according to U.S. Central Intelligence Agency statistics. Televisions far outnumbered even wired phone lines, which totaled only 27.7 million there in 2000.
The cost of installing phone lines, as well as building a cellular infrastructure, is prohibitive in many developing countries. Rough and mountainous terrain can translate into more cells and higher deployment cost, Nash said. A single TV antenna can serve the same area as 29 cellular antennae in a typical cellular network, he added.
Sigfx's approach could help bring mobile telephony to a large portion of the population in a country such as India or China, according to Shiv Bakhshi, research manager for wireless infrastructure at IDC, in Framingham, Massachusetts. (IDC is a division of International Data Group Inc., the parent company of IDG News Service.) In those countries, there is substantial TV spectrum that the government could order allocated to this use, and the markets are big enough that economies of scale might make up for the cost of developing a special handset, he said.
Nevertheless, much work remains to be done between invention and deployment -- work that Sigfx seems set for, Bakhshi said.
"These are serious people who have thought through and recognized many of these problems," he said.
Sigfx's system uses the existing broadcast antenna for transmission outbound to handsets and an array of smaller antennae on the same tower for receiving signals from the handsets. A rack-mounted return signal processor (RSP) and a control computer are collocated in the building that houses the station's broadcast equipment.
Because a TV signal can reach as far as 70 miles using VHF (Very High Frequency) or 30 miles using UHF (Ultra High Frequency), the operator does not have to build and maintain dozens of cell sites to cover that area, Nash said. However, the system has to find a relatively weak handset signal over a long distance, which could blend in with overall radio "noise." The RSP uses patented Sigfx technology to distinguish those signals from the noise -- a capability that could benefit traditional mobile providers as well, Nash said.
The amount of spectrum normally assigned to one TV station would provide approximately the equivalent of 1.5M bps (bits per second) of network capacity, enough for about 1,000 to 1,500 concurrent calls. That spectrum could be used for telephony full time or shifted over to TV broadcasting during prime viewing hours, such as in the evening.
Carriers could also use just a portion of the TV channel, such as the VBI (vertical blanking interval), a portion of the TV spectrum that in the U.S. is intended for extra services such as closed captioning of TV programs. The VBI on one channel, excluding the portion used for closed captions, would provide a small fraction of a full channel's capacity, enough for about 50 to 60 concurrent calls. However, the VBIs of several stations in a metropolitan area could be combined to provide more capacity, Nash said. Sigfx's experimental service in Ridgeland, in place for about a year, uses the VBI segment of a single channel and can support about 50 concurrent calls, he said.
Where there is unused spectrum like this, telephony makes good business sense for a broadcaster, which could get new revenue out of a collocation deal with a mobile operator, Nash said.
Sigfx initially will build its own RSPs but will license its technology to wireless equipment makers to design and build handsets and other gear. It has had discussions about potential services with some governments in Central America and signed a memorandum of understanding with equipment manufacturers and a government entity in China that are interested in studying the technology, Nash said.
Sigfx last month received an experimental license from the U.S. Federal Communications Commission to continue operating the Ridgeland network for three more years. It had been operating under a series of temporary licenses. That network serves as a demonstration system for interested vendors and broadcasters.
Although such a system would present lower costs than a typical cellular network in terms of equipment and other factors, it's still unclear how well the business case would stack up, according to IDC's Bakhshi.
"A technological breakthrough is a wonderful thing, (but) finding what is technically possible and translating it into an operating business model is a different kettle of fish all together," Bakhshi said.
An operator could use some of its savings on network equipment to subsidize the price of handsets, but it would also face the intangible costs of implementing a new kind of network and hooking it up to an existing broadcasting system, he said.
"You'd save yourself a few million dollars building the network ... but it's not so easy, because there's a lot of trouble these people have to go to," he said.
An added concern is that different handset models would be required for different countries, because not all countries use the same kind of TV network.
Still, in a large country such as China or India, this type of system could make telephony available for the first time to tens of millions of people, introducing economies of scale that might allow a vendor to build the system at an attractive cost and sell the handsets at an affordable price, he added.