Is XMax a Breakthrough in Wireless Communications?

The FCC granted xG Technology LLC permission to begin over-the-air testing of its xMax technology. xMax promises high-data rate transmission using a narrow-band carrier with data transmitted in sidebands 60 to 100 dB below the carrier amplitude. The low power of the sidebands complies with FCC part 15 emission limits.
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The FCC granted xG Technology LLC permission to begin over-the-air testing of its xMax technology. xMax promises high-data rate transmission using a narrow-band carrier with data transmitted in sidebands 60 to 100 dB below the carrier amplitude. The low power of the sidebands complies with FCC part 15 emission limits. The xG Technology Web site offers little technical information about exactly how xMax works, but said, "In addition to its advanced modulation technology, xMax uses a unique encoding system that dramatically reduces sideband emissions while multiplying the data throughput rate. This technique is called Index-N."

The heading on one of the spectrum analyzer plots shows a data rate of 6.24 Mbps at a narrow-band carrier frequency of 102.6 MHz. The FAQ page states the technology does not break Shannon's law. With more bandwidth, higher speeds should be possible. The FAQ lists "Wireless ATM Circuit (622 Mbs)" as one of the potential applications.

Due to its narrow-band carrier, xMax can use sub-GHz (VHF and UHF) frequencies to carry multi-megabit per second data rates in its low amplitude sidebands, which it refers to as the xG Flash Signal, xG Technology reports.

In May, xG Technology conducted a long-range field test of the technology. It used a VHF paging channel to transmit data over a one mile, non-line-of-sight path using a power of 0.0005 watts and ground level antennas. While the data rate wasn't specified, the news release compared xMax to a WiFi 802.11 hot spot, which it said requires 1 watt of transmit power to go 300 feet under non-line-of-sight conditions.

Demonstrating that broadband wireless communications can occur at such micro-power levels in the presence of interfering signals overturns long-held industry ideas. What is really exciting, however, is that xMax's unique signal profile is a perfect fit for low frequency channels that have been previously unsuitable for wireless broadband," said Joe Bobier, President of XG Technology LLC and inventor of the technology, commenting on the tests.

"xG technology can deliver broadband speeds with a remarkably efficient use of the radio spectrum. It is technology that has the potential for a major impact on the area of wireless communications," said Dr. Stuart Schwartz, Princeton University engineering professor and IEEE fellow.

Could this technology be used for data transmission on low-VHF TV channels? Without concrete data on how xMax performs in the presence of impulse noise, it is difficult to answer that question. xG Technology's comments filed in the access broadband-over-power line (BPL) proceeding are encouraging. "Rigorous testing at xGT's facilities in Key West, Fla. has shown that the technology is capable of performing up to its design specifications even in the presence of real-world electrical noise and multipath interference," according to the comments. The xG Technology filing provided additional information on xMax, saying the narrow-band carrier "appears on the spectrum as an unmodulated carrier" and "Sideband energy, consisting of integer cycles (single cycles) of RF energy in quite specific spectrum locations relative to the carrier, is not detectable by normal means." When used in the 100 KHz to 30 MHz BPL spectrum, the filing said data speeds in excess of 14 Mbps are achievable for In-House systems while speeds closer to 2-3 Mbps "are foreseen for Access systems."

xMax can be operated in an OFDM mode to allow interleaving of multiple signals, according to xG Technology's BPL comments, but they do not explain in detail how the xG Flash Signal is created.