While solar bursts and broken handsets can cause dropped calls, a defunct or congested cell tower -- or too few or no cell towers in the region -- can also cause the phone's signal to fade.

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For SRI International, a research firm best known for demonstrating the first computer mouse, the solution to eliminate some dropped calls is simple: Make cell phones less dependent on cell towers.

"If the cell tower goes down, does my phone work? No," said Peter Marcotullio, director of business development for SRI.

SRI, which has been developing technology in its labs for almost 60 years, has software that when implemented in a wireless handheld device allows the handset to continue working even when the network is down.

SRI's PacketHop software is embedded in the phone. The signal of the device then jumps from handset to handset -– which must also have the software -– until it reaches its final destination. Theoretically, it could work from New York to California if there were enough phones lined up in the right places. Realistically, this would be a solution for short-distance calls.

SRI has tested the software in only 802.11b wireless ethernet local area network radios. But it could see the software implemented in cell phones to improve coverage.

"It tends to make the network more robust," Marcotullio said. "It allows people to communicate directly rather than have to pay for infrastructure."

While there are other companies that use similar routing algorithms to maintain cell-phone coverage, most of the software sits in the cell towers. SRI says mobile phone operators prefer this method to keep track of calls made on the network and to be able to bill customers later on.

One of the advantages SRI boasted of its software is that it would make cell-phone calls cheaper because the carrier wouldn't be able to track calls made to nearby phones.

But carriers and companies dedicated to improving cell-phone coverage say building more cell towers and/or overhauling the present ones is the most efficient way to enhance service.

"A peer-to-peer mobile phone network wouldn't work, anyway, because mobile phones transmit less than a watt of power," said Adam Schwartz, chief technology officer for LGC Wireless, a company that improves cell-phone coverage in congested urban and indoor settings. "You'd have to be close to another mobile phone and have to be close to a base station (in a cell tower) to get that call through."

Marc Goldburg, chief technology officer for ArrayComm, another company that improves on cell-phone coverage, also expressed unease that the quality of cell-phone service would depend on cell-phone users and not the carrier.

"Maybe in the long term some mixture approach is the right approach," he said. "But I don't think (a handset solution) would result in very reliable service."

SRI, which has faced rejection in the past for innovations such as the always-on packet-switch networks that made Japan's "i-mode" mobile Internet service popular, remains confident.

If history proves him right, Marcotullio is convinced a handset solution will be the answer to some of the woes surrounding wireless service.

In 1976, a bread van dressed by SRI was the location of the first Internet transmission. Later on, SRI added a wireless radio component to it, making it the first packet-switch network that would allow the transmission of voice over Internet protocol calls and mobile Internet applications.

In the 1970s, AT&T and Motorola rejected the idea because they were convinced circuit-switch networks -- today's landline infrastructure -- was the wave of the future, said Don Nielson, a scientist who has worked for SRI the last 40 years.

"We were more surprised that no one was interested in it," Nielson said. "Then we were surprised by the enthusiasm."