In late 2005, there was a flurry in the technical press about a Florida company, xG Technology, which claimed to have a new wireless technology with performance far surpassing 3G or anyone else’s 4G roadmap. I happened to run into a friend who actually knew something (unfortunately under NDA) about the subject, so I got interested, scanned several patent applications filed by the founder, Joe Bobier, and wrote a blog post, xG Technology — Physics or Snake Oil?
At the time, I concluded that Joe Bobier might be well intentioned, but had no clue about digital communications theory. On the other hand, he might have accidently stumbled on a loop hole in FCC regulations that might allow someone to legally transmit a spread spectrum signal that spreads across the entire spectrum below 3 GHz.
A few weeks ago, Phil Karn, commented on my blog post and pointed me at two excellent papers he’s written on the subject. In xG Technology’s xMax, Phil examines the published information on xG’s November 2005 demonstration, works out the link budget including antenna gains, and taking account of the specified transmitter power and likely receiver performance, concludes:
The xMax demo may impress those who haven’t done the calculations and are unaware of how little power it takes to transmit digital data over a benign line-of-sight path. But the same demonstrated performance could have been easily achieved with just about any conventional digital modulation scheme…
In his second paper, Bobier’s TriState Integer Cycle Modulation, Phil examines one of xG’s recent patents, US 7,003,047 and concludes it’s just frequency shift keying. But Phil goes far beyond the cursory glance I did last year and provides a detailed analysis of this specific patent. Although the title says “Tri-state” what is described is continuous phase, frequency shift keying with biphase coding. Phil’s conclusion is simple and dead on:
… the techniques described in this patent are not novel, having been around for decades. They cannot provide the advantages claimed by the inventor.
What’s more, while I haven’t gone back to scan the other Bobier patent filings, this one has zero chance of spreading the spectrum in any useful fashion. The principal energy is on either side of the chosen carrier frequency — the patent suggests choosing two tones 30 KHz apart — and the resulting spectrum is very, very conventional. So the one thought I had last year, about something neat they might be doing, doesn’t apply.