xG shows off two-way radio

Remember our Floridian pals xG, with their ground-breaking voice over IP wireless system? Remember that they said recently that anyone who was a journalist or analyst could pop down to see them and check out their test installation?
Written by Rupert Goodwins, Contributor

Remember our Floridian pals xG, with their ground-breaking voice over IP wireless system? Remember that they said recently that anyone who was a journalist or analyst could pop down to see them and check out their test installation?

RIch Tehrani, "VoIP industry expert, visionary, author and columnist", and owner of TMCnet took xG up on its offer. He was driven around Fort Lauderdale between a set of six base stations, talking into a phone hooked up to a laptop, and reports that the voice quality was fine. After a while, the phone overheated and shut down.

Which as first demonstrations go, is fair enough. For fans of xG, though, that's all it showed. It doesn't qualify the headline on the piece that "xG Technology xMax Works As Advertised" (remember the thousand square kilometers from a single base station? the "fastest roll-out in history" promised in 2006? Between its launch in 1991, and 1993, GSM put on a million customers) nor to justify any comparisons with LTE and WiMAX. Nor, to be honest, with bog standard 1991 vintage GSM.

All it demonstrates that you can have a conversation within a few square miles on one handset, if you surround it with six base stations. There was a hand-over demonstrated, but as you can see from the various videos connected with the article, not much more. It would be brutal of me to say I could demonstrate much the same with a couple of 5 watt VHF/UHF walkie-talkies: brutal, but quite accurate.

The article, unfortunately, doesn't go into technicalities. Tehrani didn't ask, and xG didn't offer to say, whether the system used xG's proprietary xG Flash Signal single-cycle modulation.

There were some interesting snippets, such as each base station being able to handle 252 handsets, 14 in each of 18 channels. (GSM has around 500 channels, depending on bands available, each supporting up to 16 calls).

The handsets are able to change channel, base station or whatever, thirty three times a second - which is a very high rate, much higher than other systems, and one that may be dictated by the need to keep dodging interference in the 900 MHz unlicensed band that xG is designed to use - and commercialise on, because operators who use xG's equipment don't pay any auction or licence fees. (There is no such band in Europe, by the way, nor any equivalent that could support xG).

900MHz is full of interference - baby alarms, cordless phones, video links and so on. How call density will vary with interference hasn't been stated, as being able to hop to another channel within 30 milliseconds isn't much good if all the other channels are also being interfered with, or have conversations on. Wiith just one handset on the system, then as long as one of eighteen frequencies was clear the demonstration would have worked. And whether interference in one channel can knock out all 14 calls there - again, not specified.

There was no explanation given for the handset getting so hot it shut down - or rather, "it was charging" and "there's no power management" didn't really add up. Early stuff does get hot; this handset, though is their second and has been in development for years.

One of the few technical details to have escaped from xG to date is that there's a very high peak power transmitted from the handsets, which would cause a lot of heat and not a lot of battery life. Without any more information, it's not clear - or indeed even guessable - how battery life will pan out, or how the system would work under a more moderate power regime.

The published specifications for the base station suggest that it transmits one watt per channel for a total of eighteen watts, but consumes 1350 watts in doing so. That's interesting efficiency.

The company has added a flip antenna to their TX-60 handset, which makes sense - 900 MHz has a reasonably long wavelength of around 35 cm, and many early GSM handsets which worked on the same frequencies had external antennas. Although GSM outside America still uses 900MHz, modern handsets have dispensed with external antennas due to improvements in receiver circuitry and overall system design.

Other things not mentioned? Security, authentication, billing systems, bandwidth for data, international use or maximum cell coverage area (one cell was quoted as "6 to 8 miles, bigger than their GSM equipment", although GSM is specified to work at up to 22 miles).

If we get answers to that lot, then we may be able to say what xG is really up to and whether it has a commercial chance. The company may have to move fast, though; its latest half-yearly financial report (PDF) does not bode well for the long term.

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