Fixed Wireless Equipment

Building Big, Invisible Bridges

The wireless Internet is complex and invisible. One company claims its bridges build links where none were possible before.

by Alex Goldman ISP-Planet Associate Editor [February 10, 2004]

Based in beautiful Ashburton, UK, with U.S. offices in Waltham, Mass., Orthogon Systems is a wireless broadband equipment maker you may not have heard of, but it says its equipment does things you may think impossible.

Founded in 2000, the company spent years developing its radios, shipping the first one on June 30, 2003. The R&D team included key members of the wireless center of excellence of Nortel Networks. The company says its technology is the first "true non line of sight" in the business.

So what's different about the OS-Gemini C, Orthogon's product? A lot, says Phil Bolt, Orthogon CEO.

"We started with the best radio, with the best transmitting power and sensitivity," explains Bolt. "The radio is 25 times more powerful than other radios. We have the maximum transmission power allowed by the FCC, and our receivers are more sensitive." It operates in the 5.8 GHz spectrum, which is unlicensed but is usually less crowded than the more popular 2.4 GHz band.

Able to receive at -97 dB, the system is 14 dB better than others. Since dB is a log scale, 14 dB is 25 times greater performance.

Readers may wonder how much power such a radio consumes. Bolt says that on average, it consumes 35 watts, with a maximum of 55 watts.

The cruelty of time
In addition, Bolt says his radio solves a problem we've never heard of before: temporal fading. He says that myriad environmental factors work against any individual signal "like an elephant being attacked by ants." The result is that signals fade in and out over time.

He says the rough engineering rule is to expect a fadeoff of "10 dBs per decade." This means that 90 percent of the time you'll observe performance of 0dB (regular) to -10 db. 9 percent of the time you'll observe performance of -11 dB to -20 dB. 0.9 percent of the time, performance will fall up to -30 dB. And the series continues.

If the fade period is short, the sharp falloffs will not affect the actual IP signal. But in some cases, where the fade period is hours or even days long, that 0.9 percent and 0.09 percent fadeoff is significant. The signal appears to disappear, and because wireless signals are invisible, the problem cannot be traced.

The Orthogon answer to this problem is to use more than one signal in a system the company calls MultiBeam Space Time Coding. Additional signals solve the temporal fading problem but add to problems caused by reflections and interference. "We send them in a de-correlated manner so that each beam behaves differently," Bolt explains.

Receiving multiple signals requires a significant amount of intelligence built into each unit. Being able to interpret multiple reflections and diffractions, these radios avoid the problems of traditional radios, and no longer require a free Fresnel Zone. "The space time coding requires sophisticated mathematics to isolate all the signals we send," says Bolt, not wishing to give away all the company's secrets.

The radios also work over long distances across bodies of water. Water reflects and absorbs radio waves, but Orthogon radios, the company claims, can handle the unique problems of wireless transmission over water.

Using multiple signals enables the OS-Gemini to handle obstructions, even those that are very close to the radio. "That's like talking with your hand right in front of your mouth," says Bolt. This has been particularly important in urban areas. One reference customer, TowerStream, uses it to send signals around buildings in certain dense urban areas.

A key technological advantage is the tech that gives the company its name: Orthogonal Frequency Division Multiplexing (OFDM). Like MultiBeam Space Time Coding, this technology requires that the radio be able to transmit several signals simultaneously, and be able to receive several signals simultaneously.

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