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Germans Reach 360 Mbps in Mobile Network Tests
povvell writes "German telecomms giant Siemens has managed to hit speeds of an astonishing 360 Mbps in field tests in the centre of Munich using 'orthogonal frequency division multiplexing (OFDM) and the so-called multi-hop technology'. This is not the only demonstration of OFDM producing super fast wireless speeds, as other companies are also working on variants of the technology. It surely can't be long now before we're all streaming the latest blockbuster movies to our laptops on the commuter train home?"
Distribute full length David Hasselhoff movies in mere seconds! Fear!
360mbps seems like alot for wireless, considering the mess 108mbps (by using 2 different spectrums) created, what would a multiple dynamic frequency wireless setup leave us...what happens when you have 50+ different networks together?
Okay, let's get some raw movie stats. Assume plain RGB pixmap flipping at 24 frames per sec, movie size. That's 720x480, three bytes per pixel.
That's about 1 Megabyte a second, or 8 Megabit. Add another 256 Kilobits/sec for audio (Mp3, Vorbis, or AAC, anyone?) and that's 10 Megabit and change.
Isn't Divx compression good?
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# Canmephians for a better Linux Kernel
$Stalag99{"URL"}="http://stalag99.net";
Certain statements in this release, other than statements of historical fact, may include forward-looking information that involves various risks and uncertainties. These may include, without limitation, statements based on current expectations involving a number of risks and uncertainties related to all aspects of the wireless communications industry.
. . . you can be pretty confident that you are reading a press release. This was written by the company that owns the equipment used in the test. This is essentially an advertisement.
http://www.busyweather.com/
Since almost all servers are not connected to better than 100Mbps (I haven't been on that side of the eq since 1998 so I'm making assumptions, 'scuze me if I'm wrong) , network congestion, etc, I never see the full bandwidth of my 4Mbps line used on one task. 360Mbps might make for an impressive show of ability, but that has limitations at other bottle necks.
The only immediate application I can think of for is setting up temporary offices where you don't want the expense of cabling, but even then you quickly fill the RF bandwidth.
Bacardi + slashdot = negative karma.
It's even smarter than that! Your little rect in time domain is an inf. sinc in the frequency domain. Of course, after a certain length it dies down to a negligible strength (call this point B). If you wanted to modulate another pulse, to guarantee they will both be exactly recoverable you need to modulate the new pulse up to 2B.
OFDM basically take advantage of the fact that the signal is digital. Instead of modulating the next pulse at 2B, you modulate it so that the next pulse is centered over the first zero crossing of the first pulse. Normally, this would cause horrible aliasing, but since you know the shape of your input data, all you care about are the values at the origin and the zero crossing. You don't care about recovering the two original signals exactly, the value at the origin and the first zero crossing give you enough information to reconstruct them. Aliasing be damned!
This takes advantage of the fact that simpler data is more resistant to noise. If you know what you're sending is a 1 or 0, then the waveform can be horribly degraded before it makes a difference. Contrast this with simple voice data, where a deformation in the wave can't be repaired (you don't know what it should look like). In this case, your encoding scheme introduces noise it knows doesn't matter in order to save bandwidth.
Of course, this is also a form of quadrature multiplexing, which lets you send two signals at the same carrier frequency but differentiate them based on the phase. So that gives you twice the transfer amount you'd normally get above.
(yes, I'm in a communications theory course right now)