An energy-conscious wireless technology

While there has been a lot of hype around WiMax and 3G (third-generation) cellular for delivering high-speed data to laptops and cell phones, the biggest hurdle these technologies face is being able to send loads of data over long distances without zapping the life out of batteries.

The problem is simple. When you increase the capacity or speed of the network, you inevitably have to make a trade-off in distance--the higher the speed the shorter the transmission distance. High speeds over longer distances can be achieved, but it means boosting energy levels, which chews up the battery life of devices on the receiving end.

"Power consumption is the No. 1 issue in any mobile application," said Craig Mathias, a principal at Farpoint Group, a consultancy specializing in wireless and mobile technologies. "The longer you can preserve the battery, the more valuable the technology becomes. Controlling power consumption opens to the door to so many more applications for mobile devices."

The company that developed xMax, xG Technology, has planned a public demonstration of the technology in Miami and Fort Lauderdale, Fla. to prove that it will work. The test bed, which will launch in September, will transmit data at 40mbps over 15 miles, using less than 1 watt of power.

"There is still a lot of skepticism out there, which is appropriate," said Rick Mooers, executive chairman of xG. "These are not incremental improvements we're talking about here. If this catches on, it could be revolutionary."

WiMax, which has been described as Wi-Fi on steroids, has a range of up to 30 miles and can deliver broadband at a theoretical maximum of 75mbps. But today, power consumption is so high on WiMax receivers that they cannot be used in consumer products such as laptops, let alone on handheld devices such as cell phones.

Even though 3G is only now starting to be offered in the United States, mobile operators are already working on Super 3G technology that will allow TV and interactive gaming via mobile devices. Cell phone makers will likely come out with high-resolution LCD screens for handsets to view this content. But these added applications and features will certainly put a strain on power consumption, zapping the life out of standard cell phone batteries.

Mooers said that the technology could help WiMax and next-generation cellular technologies overcome these hurdles.

"xMax doesn't go head-to-head with WiMax or 3G wireless," he said. "It can work with these technologies to significantly lower power consumption. On cell phones, this could mean making talk times comparable to today's standby times. So a battery that lasts a few hours when you're talking a lot could last two to three days before it needs to be recharged."

How does xMax work? Take the energy issue first. xMax uses a modulation technique designed to allow more data to be transmitted on a single sine wave than is required with typical modulation technologies. So instead of using more than 100,000 sine waves to transmit one bit of data, xMax uses a ratio closer to 1:1. This technique would therefore be more efficient and keep energy levels very low, which would mean devices that receive the signals wouldn't consume much power.

To solve the distance problem, xMax uses frequency channels in the sub-gigahertz range, which can penetrate obstacles such as walls or trees. But channels below 1GHz are very narrow, which means it is difficult to pack large amounts of data into them.

To solve this problem Joe Bobier, the inventor of xMax, developed a technique that splits radio transmissions over multiple channels. Narrowband sub-GHz channels could be used to establish and coordinate the sending and receiving of signals. And because power levels are much lower than those permitted by the Federal Communications Commission for unintentional out-of-band signals by normal transmitters, data can be transmitted without any interference over adjacent channels that are already carrying traffic from other devices.

"All transmitters have power energy that goes outside the licensed channel," Mooers said. "The FCC dictates how much it can go over into other spectrums. Our technology is upwards of 100,000 times lower than the allowed power levels, so it's so miniscule that it can't be detected."

Mooers said xG Technology is talking to several companies that may want to license the technology. Intel, which is developing WiMax chips, and Qualcomm, the maker of next-generation cellular technology, could be potential partners, although Mooers could not specifically name them. Neither company was available to comment.

While xMax sounds like it could be a disruptive technology on paper, analysts such as Mathias say it's still in the early days.

"I've never heard of anything like it," he said. "It sounds very promising, but we have to see if actually works as they say it does."