FORT LAUDERDALE--Communications firm xG Technology yesterday conducted another wireless line-of-site demonstration of its xMAX solution here, transmitting a 3.5 MB/s data stream a distance of 18 miles using less than 36 milliwatts of power using 10 MHz of unlicensed spectrum in the ISM 900 MHz band.
Last week, xG conducted a similar demonstration transmitting a 3.7 MB/s data stream from its omnidirectional, vertical whip antenna on an 850-foot tower to a patch antenna on a 12-foot mast located 18 miles away using 50 milliwatts of power. However, some press reports expressed skepticism about the demonstration because no one in attendance was allowed on the 850-foot tower to ensure that the transmitting antenna and the power levels cited were those being used.
During yesterday’s demonstration, this reporter and an xG investor were allowed on the tower to view the transmitter—attached to a spectrum analyzer—and confirm that the cabling was attached to xG’s antenna.
Others attending the demonstration remained at the receiver site and—via phone—noted changes in the signal strength as the power level was reduced from 63 mW to 56 mW to 45 mW (calculated by xG based on spectrum-analyzer readings at the tower). Although the signal weakened as power decreased, the signal was clear, and the data rate at the receiver remained stable at 3.676 MB/s at these power levels.
At 35.80 mW, the signal again weakened and the data rate dropped slightly, to 3.571 MB/s. When the power was reduced to 13 mW, the signal was very weak and no data rate registered.
Joe Bobier, xG’s vice president and inventor of the xMAX technology, said the 13 mW signal would have introduced too many errors to be of much use. However, he said the signals at the higher levels—63 mW and 56 mW—probably would have been strong enough to penetrate a building, although this was not demonstrated.
Bobier said xG wanted to transmit video and stereo sound from a DVD playing on the tower to the receiver site 18 miles away, but a series of logistical problems prevented his staff from completing the software to decode the signal for the demonstration. In tests conducted the previous night, the stereo sound was fine, but the video quality still looked like “a bad satellite signal,” he said. The software likely will be ready by the weekend, he said.
The data rates achieved in the demonstration are “as bad as it gets” for xG’s single-cycle waveform technology, Bobier said. No carrier signal—which would have required 6 KHz of dedicated spectrum—was used, reducing the data rate by about 25%, he said. Many common techniques to improve performance were not used in an effort to keep the demonstration as “vanilla” as possible, he said.