Not much will screw it up, in comparison with
2.4GHz products, such as the current range of wavelans or bluetooth.
Firstly, at 2.4GHz there is a lot of stuff as the band is unlicensed. Microwave ovens emit in the same band. So there is a high probability of interference with any of the 2.4GHz products, that will only get worse as BlueTooth starts to be accepted. In comparison the 5GHz bands are licensed for use with WLAN products, with similar bands licensed worldwide. This basically means that the 5GHz products have to play fair with each other.
Secondly, there is a lot of bandwidth available at 5GHz, especially in the US and Europe (Japanese have a lot less), for WLAN applications. Given that the amount of data you can carry is pretty much proportional to your bandwidth (ignoring noise for the moment) this gives potentially enormous resources. For instance the American natioanl infrastructure bands are 5.15GHz to 5.35GHz and 5.725 to 5.825GHz, giving a total of 12x20MHz channels each capable of 54Mb/s. In Europe you have 19x20MHz bands. All of this bandwidth is liscensed NOW worldwide for this style of product.
Then you have to consider the type of coding used on these 5GHz systems. They are all OFDM.. Effectively, this means that those 20MHz bands are
split up in 64 seperate channel (some used for guardbands) and each of the 64 channels is modulated seperately. So all those horrible indoor propagation effects that cause channel fading are less importance. In a traditional single carrier system multipath can kill the channel, but with OFDM you lose a couple of channels which are then recovered with error correction
All in all, I'd prefer one of these 5GHz systems over anything in the 2.4GHz band.
summarised all of the research into biological effects of mobile phones. The conclusion was that the studies have been going long enough to measure the risk of increased cancer from mobile phone use. However, the stated that given the current data it must be less that 2 times increase and maybe no effect whatsoever. Quoting the article
The epidemiological results, so far, are certainly inconsistent with any large increase in risk (a doubling or more) of brain cancer from use of cell phones
Now your LAN systems are shorter range, thus lower power, and you're not going to hold your LAN card against your head while its in use. So I think we can safely say the risks from WaveLAN cards are minimal
Yeah and what about 802.11a, or it european equivalent HIPERLAN/2, or japenese equivalent MMAC HiSWAN. Chips are starting to come back from the fab for first testing. 54Mb/s at the air interface!!!!! Look for them to appear is about a year.
The big advantage of the 802.11a type systems is that they use the 5GHz frequency band and not the 2.4GHz ISM band that current wavelen systems use. The 2.4GHz band is pretty full, and also has pretty bad interference from your microwaves ovens. But the 5GHz bands that have recently been allocated to wireless lan systems are complete empty.
As for BlueTooth (ie. 802.15.1), BlueTooth II is also specified but not in production yet, and the 802.15 standard commitee is currently even considering 802.15.3 a 20Mb/s version of BlueTooth which will probably appear in about 3 or 4 years.
HomeRF's market is different than 802.11b. 802.11b is aimed at the Office, and as the name say HomeRF is aimed at the Home. Business are willing to pay more than personal customers, and so HomeRF cuts corners on the specs of the components to squeeze the cost down. I.E. Noisy RF, slower ADC's, differential modulation to similify the syncronisation.
Given the choice between HomeRF and 802.11b, I'd choose 802.11b, but the cost difference my sway me.
Tesla himself thought of this one. However, he achieved fairly poor efficiencies. The modern version of the idea is the "Rectenna". Which is basically an array of antennas connected by diodes. You can get a large DC voltage at the edges of the array. For example check
Were they are talking about 50Vdc from a simple patch array. I've also heard the Koreans are pretty interested in this stuff. At a conference I was at recently they talked about a 100kW system
that they'd had a demonstrator of!!!!
A good reference is
W. C. Brown The history of power transmission by radiowaves, IEEE Trans MTT, Vol MTT-32, No 9, Sept 1984
Smart sys admins set their BIOS to "Boot: C only". Thus no way to boot from a floppy. If they also have linux installed they give lilo the "single-key" option so you can't give the installed kernel boot options to use the floppy as the root image.
In any case if they wanted security they wouldn't have an M$ product installed in the first place:-)
D.
Just the KT term from Boltzmanns constant gives you a value of -174dBm/Hz. Assuming their 10KHz bandwidth, required C/I of 4.9dB as they state at their website and ignoring implementation losses and receiever impartments, we therefore have an
ideal receiever sensivity of -129.1dBm. After taking into account losses in filters before the LNA and implementation loss and the noise figure of the receiver is is more likely to be -120dBm.
Taking your 270dB S/N gives a received power requirement of 150dBm. Take a path loss from the
receiver to transmit of a very lower 30dB and we
need to transmit 180dbm or 1e15 watts of RF!!!!
Star wars eat your heart out!!!!
I've read the article and even visited the referenced websites and read the documentation there too. On the page
http://www.vmskglobal.com/engineer.html
they stated that if they modulate their carrier with a modulation depth of less that 0.25radians they effectively have a pure spectral line. I can't this as anything but a bit a black magic.
We can write the modulated signal as
v(t) = A * exp(j * m * (d(t) - 0.5))
where d(t) is a binary data signal. If m=Pi/2 then we have a BPSK style modulation. Make m small and we get a VMSK signal. This small value of m is what gives them a proportionally smaller occupation of the spectrum for the bit rate.
NoW consider the constellation of this modulation in the complex plane, we have two points representing the bits 0 and 1. For BPSK they are seperated by Pi radians, while with VMSK they are much closer together. VMSK is therefore clearly more vunerable to noise than a BPSK scheme. At the above website they clearly state that the noise resistance (C/I) is significantly better with VMSK!!!
It seems clear that there is a basic fault in their reasoning, and they can't beat Shannon in this manner.
D.
There been a lot of recent investigation of Plasma Antennas mostly for military applications. Consider that anything that radiates also has a large radar cross-section, then consider how many independent communications systems are currently used by the military and you understand why. Plasma antennas allow you to effectively have your antenna disappear when you aren't using its, thus reducing that chance that an enemy can see you.
A couple of interesting references are this article where they basically experiment with using a household fluroscent tube as an HF antenna. Or page where a few more references are given.
I have to ask myself with all of this though, what the point of having an radar invisible antenna, that is optically highly visible. I have visions of fluro lit battlefields... D.
QNX support is in XFree 3.3.6 and I believe it is now also in 3.9.18. So why pay for a QNX Xserver that is only X11R5 when you can have X11R6.3 with XFree 3.3.6 and X11R6.4 with XFree 3.9.18
D.
IBM logo 6 atoms high in 1989 with an STM.
on
Nano Logo
·
· Score: 1
The IBM logo was first written with a Scanning Tunnel Microscope a few atoms high in 1989. The case that everyone here is mentioning 5 years ago was the first time they wrote the IBM logo at room temperature with an STM. Prior to that the jitter due to thermal effects caused the atoms in the logo to be misplaced, so the samples had to be cooled done to -270c (liquid nitrogen). You can check the IBM press release here.
I also just looked up that Heinrich Rohrer and Gerd Karl Binnig won the Nobel Prize for Physics in 1986 for the invention of the STM. They were working for the IBM research labs in germany at the time.
Yup, that was them. Two of their researchers won the Nobel prize for the invention of the Scanning Tunnel Microsope, which also allowed individual atoms to be moved about. They then had the bad taste to use their invention to write the name "IBM" in what looked like ancient dot matrix print, but which was in fact individual atoms. If I remember correctly it was 6 atoms high. This sure beat 6 microns!
Slashdot Mirror
Firstly, at 2.4GHz there is a lot of stuff as the band is unlicensed. Microwave ovens emit in the same band. So there is a high probability of interference with any of the 2.4GHz products, that will only get worse as BlueTooth starts to be accepted. In comparison the 5GHz bands are licensed for use with WLAN products, with similar bands licensed worldwide. This basically means that the 5GHz products have to play fair with each other.
Secondly, there is a lot of bandwidth available at 5GHz, especially in the US and Europe (Japanese have a lot less), for WLAN applications. Given that the amount of data you can carry is pretty much proportional to your bandwidth (ignoring noise for the moment) this gives potentially enormous resources. For instance the American natioanl infrastructure bands are 5.15GHz to 5.35GHz and 5.725 to 5.825GHz, giving a total of 12x20MHz channels each capable of 54Mb/s. In Europe you have 19x20MHz bands. All of this bandwidth is liscensed NOW worldwide for this style of product.
Then you have to consider the type of coding used on these 5GHz systems. They are all OFDM.. Effectively, this means that those 20MHz bands are split up in 64 seperate channel (some used for guardbands) and each of the 64 channels is modulated seperately. So all those horrible indoor propagation effects that cause channel fading are less importance. In a traditional single carrier system multipath can kill the channel, but with OFDM you lose a couple of channels which are then recovered with error correction
All in all, I'd prefer one of these 5GHz systems over anything in the 2.4GHz band.
D.
Are Mobile Phones Safe?
summarised all of the research into biological effects of mobile phones. The conclusion was that the studies have been going long enough to measure the risk of increased cancer from mobile phone use. However, the stated that given the current data it must be less that 2 times increase and maybe no effect whatsoever. Quoting the article
The epidemiological results, so far, are certainly inconsistent with any large increase in risk (a doubling or more) of brain cancer from use of cell phones
Now your LAN systems are shorter range, thus lower power, and you're not going to hold your LAN card against your head while its in use. So I think we can safely say the risks from WaveLAN cards are minimal
D.
The big advantage of the 802.11a type systems is that they use the 5GHz frequency band and not the 2.4GHz ISM band that current wavelen systems use. The 2.4GHz band is pretty full, and also has pretty bad interference from your microwaves ovens. But the 5GHz bands that have recently been allocated to wireless lan systems are complete empty.
As for BlueTooth (ie. 802.15.1), BlueTooth II is also specified but not in production yet, and the 802.15 standard commitee is currently even considering 802.15.3 a 20Mb/s version of BlueTooth which will probably appear in about 3 or 4 years.
D.
Given the choice between HomeRF and 802.11b, I'd choose 802.11b, but the cost difference my sway me.
D.
http://www.nasatech.com/Briefs/ Aug 00/NPO20641.html
Were they are talking about 50Vdc from a simple patch array. I've also heard the Koreans are pretty interested in this stuff. At a conference I was at recently they talked about a 100kW system that they'd had a demonstrator of!!!!
A good reference is
W. C. Brown The history of power transmission by radiowaves, IEEE Trans MTT, Vol MTT-32, No 9, Sept 1984
Cheers
D.
Germans care what happens in Germany :-)
D.
Smart sys admins set their BIOS to "Boot: C only". Thus no way to boot from a floppy. If they also have linux installed they give lilo the "single-key" option so you can't give the installed kernel boot options to use the floppy as the root image. In any case if they wanted security they wouldn't have an M$ product installed in the first place :-)
D.
Receiver Sensitivity (dBm) = Required C/I (dB) + Implementation Loss (dB) + KT (dBm/Hz) + 10log(Bandwidth Hz) + Receiver Noise Figure (dB)
Just the KT term from Boltzmanns constant gives you a value of -174dBm/Hz. Assuming their 10KHz bandwidth, required C/I of 4.9dB as they state at their website and ignoring implementation losses and receiever impartments, we therefore have an ideal receiever sensivity of -129.1dBm. After taking into account losses in filters before the LNA and implementation loss and the noise figure of the receiver is is more likely to be -120dBm.
Taking your 270dB S/N gives a received power requirement of 150dBm. Take a path loss from the receiver to transmit of a very lower 30dB and we need to transmit 180dbm or 1e15 watts of RF!!!! Star wars eat your heart out!!!!
D.
We can write the modulated signal as
v(t) = A * exp(j * m * (d(t) - 0.5))
where d(t) is a binary data signal. If m=Pi/2 then we have a BPSK style modulation. Make m small and we get a VMSK signal. This small value of m is what gives them a proportionally smaller occupation of the spectrum for the bit rate.
NoW consider the constellation of this modulation in the complex plane, we have two points representing the bits 0 and 1. For BPSK they are seperated by Pi radians, while with VMSK they are much closer together. VMSK is therefore clearly more vunerable to noise than a BPSK scheme. At the above website they clearly state that the noise resistance (C/I) is significantly better with VMSK!!!
It seems clear that there is a basic fault in their reasoning, and they can't beat Shannon in this manner. D.
A couple of interesting references are this article where they basically experiment with using a household fluroscent tube as an HF antenna. Or page where a few more references are given.
I have to ask myself with all of this though, what the point of having an radar invisible antenna, that is optically highly visible. I have visions of fluro lit battlefields... D.
QNX support is in XFree 3.3.6 and I believe it is now also in 3.9.18. So why pay for a QNX Xserver that is only X11R5 when you can have X11R6.3 with XFree 3.3.6 and X11R6.4 with XFree 3.9.18
D.
I also just looked up that Heinrich Rohrer and Gerd Karl Binnig won the Nobel Prize for Physics in 1986 for the invention of the STM. They were working for the IBM research labs in germany at the time.
Yup, that was them. Two of their researchers won the Nobel prize for the invention of the Scanning Tunnel Microsope, which also allowed individual atoms to be moved about. They then had the bad taste to use their invention to write the name "IBM" in what looked like ancient dot matrix print, but which was in fact individual atoms. If I remember correctly it was 6 atoms high. This sure beat 6 microns!