New Technology Could Kill WiMax?

GolygyddMax writes "Techworld reports that a Florida-based start-up, xG, has developed a technology that's a 1000 times more efficient than WiMax and which could, in theory, lead to wireless LANs being powered by watch batteries. It is still in early development, but this technology could allow anyone to set up as an ISP. This could kill WiMax before it even gets off the ground." From the article: "At the demonstration with other reporters, we were able to verify that the signals were being sent wirelessly, and checked the distance by GPS, but had to take the 50mW base station - and its omnidirectional antenna - on trust, since it was at the top of an 850ft mast. The demonstration will be repeated for the US press next week. The system carried 7.4 Mbit/s per MHz per Watt, said Professor Schwartz. By comparison, GSM would have around 0.0058, and CDMA/EV-DO about 0.0085 Mbit/s per MHz per Watt. "

Comments

Re:How can they DO that?

[jonesboy_damnit]

From TFA:

"xMax is unconventional," said Stuart Schwartz, professor of electrical engineering at Princeton Universithy, who has scrutinised xG's demonstration set-up, speaking at the xMax demonstration. "It is clever and innovative, but it is not magic. It uses single cycle modulation, and needs much less power than other technologies."
Single-cycle modulation is the invention of xG's chief technology officer Joe Bobier, with backing from Mooers Branton, a merchant bank, whose founder Rick Mooers also serves as xG's chief executive. The modulation scheme alters the frequency of individual cycles of the carrier wave, which has the effect of introducing very low power side-bands to the signal.

My take is that they're using the difference in frequency between the carrier frequency and the generated sideband frequency to represent a value (ie. +10kHz = 0001; +15kHz = 0010; etc.). This seems awfully similar to the SSB modulation commonly used in shortwave radiocommunications to me.

Since they're operating in the license-free 900mHz ISM band, it also *must* implement some sort of frequency-hopping (or direct sequence, I suppose) spread spectrum stuff in order to be legal. Could be kind of an interesting technology. I'd like to play with a couple of the radios and a good spectrum analyzer to see what it looks like.

In the interests of full disclosure, IANARE (but I played one at a job once for awhile).

-Matt

Re:How can they DO that?

[jonesboy_damnit]

Actually, increasing the transmit power *can* buy you greater data rates, as long as your data rate is limited by signal-to-noise ratio.

For example, let us build (in our minds) a transmitter/receiver pair which can encode/decode one symbol every second. OK? Every second we send one symbol (effectively a magic combination of waves which means something to a demodulator) from the transmitter, and every second we decode one symbol at the receiver.

If we have lousy SNR, we might only be able to differentiate between the most distinct two states of the transmitter (one bit per symbol: either 1 or 0), since all the noise impinging on our signal looks an awful lot like the more subtle states (or even worse, completely obstructs all states, making decoding impossible). This gives us a data rate of 1bps.

If we can increase the signal level at the receiver, thus increasing SNR (assuming we're not distorting the living hell out of our transmission, natch) but increasing our transmitter's output, we might be able to encode *two* bits per symbol (00, 01, 10 or 11) by adding two more symbols to the constellation. By doing this, we haven't increased our symbol rate (still only one symbol every second), but we *have* doubled our throughput.

Make sense?

-Matt