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| Apr 06, 2007 12:53 pm |
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re: re: re: How much can you put in a 5 pound bag? |
| Tom Foale
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There are theoretical limits and, similarly to Moore's Law, the boundaries of what is achievable keep getting pushed back. I was at a conference last week where I was shown a graph similar to a log chart of Moores Law, but for radio. It had four parallel lines - one for wide area mobile, one for metropolitan networks, one for LANs and one for PANs (personal), with very short range having the highest rates. Each of these is still increasing at a relatively stable rate. We were also shown some research and standards development work on Gigabit WiMAX, which would hit the next spot on the MAN line if it is delivered on time.
New technologies keep adding to the capabilities of wireless, like OFDM and MIMO, and there are more areas for improvement. The efficiency of our WiMAX network is about 3.5bits/Hz and with further development WiMAX should be capable of delivering 4.5bits/Hz. This means that with a 10MHz channel we can deliver around 20Mbps of customer data from a single sector, exclusive of overheads.
The way that all radio technology works is by modulation of an RF carrier by an IF (intermediate frequency) signal. This results in two identical sidebands either side of the carrier frequency, one of which is filtered out to give a band of frequencies from which the signal can be recovered by a receiver. This makes spectrum a scarce resource because two different users of a band can interfere with each other, so spectrum tends to be allocated in non-overlapping bands to single users - or at least to non-interfering users. Although modern technologies such as WiFi can share the same spectrum quite effectively, they do so by avoiding transmitting at the same time.
There is one company with an intriguing new idea. What if, instead of one RF carrier and an IF modulator, we used a large number of harmonic RF carriers and switch them precisely at a common zero crossing point? In theory you should see a series of precise intermittent single frequencies which to most receivers would register as a small amount of noise. This couldn't have been done before now because the RF section was always the most expensive part of the radio, but modern chipsets have reduced that. It could allow many operators to co-exist in a small amount of spectrum, reducing the scarcity of spectrum. It can also transmit data at the same rate as the carrier or higher (depending only on the number of RF frequencies used) - meaning much higher data bandwidths at lower frequencies.
The company is XG and the technology is XMAX - there are patents available which can be found under the name bobier. I think the company is commercially unsound, but the technology looks interesting - if it works. It still lacks the surrounding standards necessary to create something like WiMAX or 3G. It took Qualcomm 10 years to get its CDMA technology accepted by the mobile world, so XG have taken a different route, but I don't think they will have much success with it for a number of reasons. It takes more than a good idea to make a good business.Private Reply to Tom Foale (new win) |
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