New Wireless Architecture Would Extend Cell-Phone Coverage to Where It Is Needed Most

HELSINKI, Finland -- A new architecture for next-generation wireless systems for cellular phones proposed by University at Buffalo researchers could provide an efficient and flexible way to extend outdoor coverage, as well as provide indoor coverage, without building additional cellular phone towers.

It also could make it much easier to complete a call on your cell phone, even when cell phone use is heaviest.

Called iCAR, (integrated Cellular Ad hoc Relay), the new system combines conventional cellular technology with Ad hoc Relay Station (ARS) technology, in which the stations relay or reroute calls from the congested cell to an adjacent one that is not congested.

An ARS is a wireless relaying device that receives a signal from a mobile handset or personal digital assistant and transmits it either to another ARS or to a regular cell tower. Unlike cellular towers, which have a range of a few kilometers, ad-hoc relay stations cover a much smaller area, typically only a few hundred meters.

An update on the new system was presented here today (June 12, 2001) at the 2001 IEEE International Conference on Communications. A paper on the system also will be published in an upcoming special issue of IEEE's Journal of Selected Areas of Communication (J-SAC).

The new system addresses what its developers say is the inability of the current cellular-phone system to effectively deal with "hot spots" that arise when demand for cellular phone calls in some areas surges, or when traffic becomes unbalanced among different cells.

That leads to the ironic situation with which most cell phone callers are all too familiar: Calls are most likely to be blocked or dropped under the precise circumstances in which people need to place them the most, such as on a convention floor inside an arena, or in an emergency, such as at a traffic accident or in a natural disaster.

According to the UB researchers, that situation arises because callers located in one "cell" cannot access resources available in neighboring cells.

"The shortcoming of these systems is that even though a neighboring tower may have channels available for use, if you are physically in a busy cell, you cannot place or receive calls," explained Chunming Qiao, Ph.D., UB associate professor of computer science and engineering. Qiao developed the system with Hongyi Wu, UB doctoral candidate in the Department of Computer Science and Engineering and Ozan Tonguz, Ph.D., UB professor of electrical engineering.

"The challenge is to find a cost-effective way to dynamically balance the traffic load among the cells," said Qiao. "With iCAR, this means finding a relay route consisting of Ad-Hoc Relay Stations that will lead from a congested cell to a non-congested cell."

The new system performed well in computer simulations conducted by the UB researchers.

Functionally, Qiao explained, the ARS is very similar to a cell tower, but on a much smaller scale. Cell phone towers have to be tall, he explained, because they need to cover a range of several kilometers. They are usually connected to a wired network using conventional copper or fiber-optic cables, and they must be built according to local zoning regulations with permission from authorities.

On the other hand, Qiao explained, because an ARS can have a far-more-limited range of, say, only several hundred meters, it can be small, perhaps as small as a cell phone, and since it is completely wireless, it also is portable. An ARS could be mounted on top of a vehicle or a building, or even be carried by an individual.

"Either technology by itself, the cell tower or the relay station, will not scale up cost-effectively," he said, "which is why integrating the two of them is such a good idea."

According to Qiao, the iCAR works well because it automatically will find a route, jumping from one ARS to another, until it finds an uncongested cell and it will do so in real time.

"If a route is available, it shouldn't take more than a few tens of milliseconds," said Qiao.

He added that the concept of using a completely separate channel for relaying -- for example, the unregulated 2.5 gigaherz frequency band -- also would apply to the integration of various wireless networks that are or will be available commercially, such as those based on HomeRF, Wireless LAN Bluetooth or even satellite networks.

The research is supported by the National Science Foundation's Information Technology Research program, and by the Nokia Research Center.