UB Researchers Focus on Improving Performance of Cell Phones, Avoiding Busy Signals

BUFFALO, N.Y. -- Cell phones have taken on an added dimension since Sept. 11.

The events of the day underscored the phones' value as wireless lifelines, conveying final messages of a lifetime to loved ones, as well as helping emergency personnel pinpoint the location of victims trapped in demolished buildings and in desperate need of rescue and medical attention.

But for all of the dramatic connections that cell phones facilitated on that fateful day, there no doubt were many others from victims that did not go through, blocked by rubble or because cellular towers covering the area were congested by too many simultaneous calls.

Making sure that cell-phone calls go through, particularly in times of disaster, as well as at times of heaviest use, is the goal of new architecture for next-generation wireless systems for cellular telephones being proposed by researchers at the University at Buffalo.

Described in a paper in the October issue of J-SAC, the Journal of Selected Areas in Communications of the Institute of Electrical and Electronics Engineers, the new system could provide an efficient and flexible way to extend outdoor coverage, as well as provide indoor coverage, without building additional cellular phone towers. The research was previously described -- and released to the media -- in June at the 2001 IEEE International Conference on Communications in Helsinki, Finland.

"My understanding is that just following the attacks, too many people were trying to make cell phone calls at the same time in an area covered by a single tower," said Chunming Qiao, Ph.D., UB associate professor of computer science and engineering. "Our system is designed to alleviate that situation by relaying 'overflow' calls to nearby cell towers."

Qiao developed the system with Hongyi Wu, doctoral candidate in the UB Department of Computer Science and Engineering, and Ozan Tonguz, Ph.D., former UB professor of electrical engineering, now at Carnegie Mellon University. A provisional patent has been filed on the technology.

Called iCAR, (integrated Cellular Ad hoc Relay), the new system combines conventional cellular technology with Ad hoc Relay Station (ARS) technology, in which 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.

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 they most need to place them, such as on a convention floor inside an arena, or in an emergency situation, such as the one caused by the terrorist attacks on the World Trade Center.

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

"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 is performing well in computer simulations conducted by the UB researchers.

This past summer the UB researchers also collaborated with Nokia, one of the sponsors of the research, on developing signaling protocols that allow for the establishment of these relaying routes. In addition, their preliminary results on the so-called "Quality of Coverage" offered by Ad-hoc Relay Stations in the iCAR system were reported in August at the prestigious SIGCOMM (Special Interest Group in Communications) meeting in San Diego.

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, he added, 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.

Swades De and Evsen Yanmaz, both doctoral candidates in the UB Department of Electrical Engineering, and Sumita Mishra, who recently received his doctorate in electrical engineering from UB, also were on the project team.

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