CSIRO Demonstrates Fastest Wireless Link Yet 94
rob101 writes "The CSIRO yesterday demonstrated the world's 'fastest' wireless radio link by transmitting sixteen full quality DVD streams over a 250m link and only using a quarter of the available bandwidth. 'The CSIRO ICT Centre today announced that it has achieved over six gigabits per second over a point to point wireless connection with the highest efficiency (2.4bits/s/Hz) ever achieved for such a system.'" CSIRO hopes to double the speed of this connection in the future, pushing twelve gigabits a second.
Side benefit (Score:5, Funny)
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This technology operates at 85GHz, which is still in the microwave/radar band of the EM spectrum, so it's likely to interfere with radars.
Interferes with Radar? (Score:1)
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Can't wait... (Score:1)
Only to realise that the extremely high frequency is ionizing my head, and to make and receive my calls I use up all of 1 hundredth of its power.
That is progress indeed.
Funny, but misses the point. (Score:5, Informative)
Opps, hic, taxi!!! (Score:2)
Re:Can't wait... (Score:4, Interesting)
Actually, I wouldn't worry about ionizing radiation [wikipedia.org] as those only start at frequencies above visible light.
Terminology (Score:5, Funny)
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In any case, that 10TB number I found seemed a bit small and the page looked sort of old. So it's probably not very accurate - but that wasn't really the point. I hadn't looked at the article yet, either, and decided it'd be more fun to base it almost entirely on the b
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Re: Significant figures (Score:2)
Which is why slide rules ought to be used in introductory science classes, not calculators. Slide rule use does two things: 1) enforces a basic understanding of significant figures, and 2) creates an ability to quickly calculate order of magnitude and therefore to quickly dismiss solutions that cannot possibly be correct.
However, I suspect that the parent posters know all of the above, and that this is ju
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(Sure would be nice if ampersand-mu or ampersand-#956 worked on
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I always wondered why the rate of DVDs / t is used as a way of conveying bandwidth developments to the public. It's kind of a tease, as though there will be some point at which it will be legal to stream DVD-quality video in some way without giving up all your rights or paying more for the righ
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The MPAA may ask that this link be heavily encrypted, but it will make a nice CS hobby project in trying to decrypt it.
Ugh! (Score:1, Interesting)
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Re:Ugh! (Score:4, Interesting)
To give an example of just one "public service": The CSIRO were the first to demonstrate to the world that radiation from atmoshperic testing of nukes was ending up as plutonium and other RA trace elements in childrens bones (MY bones considering the era). They found out by starting with an agricultural study into sheep near an Australian test site run by the Brit's and found the bombs were adding to a rapidly growing planet wide "haze" of radioactive dust.
Obviously they were not popular with the politicians of the day when their extrodinary claim was promptly backed with extrodinary evidence.
Re:Ugh! (Score:5, Informative)
Your country does indeed take this sort of technology, and doesn't like to honour the patents [slashdot.org] on it either! So stop complaining.
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How many tax dollars? (Score:2)
Total Income (including tax $'s): $929M Income from tax $'s: $250M ($12.50 per Aussie) Total expenditure: $947M Total Equity: $1126M
Not everyone is a taxpayer and many taxpayers would rather spend
Rare, example of tech patents working (Score:5, Insightful)
Heartening to know the licence fees are not just going to the lawyers (something they have received some flack for in Aus), but getting invested in more research. More power to them I say.
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A better example of patents working would be if CSIRO said "we're doing this because we think we can make money by patenting it".
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They have been around for nearly a century, they have "lost" heaps by under-selling or giving patents away (particularly in the area of drug research). In the 80's there was a drive to get more "value" from their inventions and they are a bit wiser in that area now. However the CSIRO is still a "public service" (and a good one at that), similar to NASA and other US agencies i
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(2.4bits/s/Hz)? (Score:1)
Re:(2.4bits/s/Hz)? (Score:4, Informative)
In any event 2.4 bits/s/Hz is nothing special, unless it applies to individual subcarriers in an OFDM-like scheme. 802.11g sends 54 MB/sec in a channel about 20 MHz wide, for a bandwidth efficiency of 2.7 bits/second/Hz. Sounds like they basically threw a metric assload of RF bandwidth at the problem (another technical term found in relatively-few EE textbooks).
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As the amount of information per cycle goes up, the risk of noise and corruption increases, since they have a more significant effect on the signal. Seeing as there is usually a fixed freque
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Not so fast, you're forgetting a logarithm (base 2) here: 1 bit gives 2 possible values, 2 bits give 4 distinct combinations etc...
So QAM, using 4 distinct phases of the carrier transmits 2 bits per cycle. 64-QAM requires you to distinguish between 64 different possibilities for each cycle, and that gets you 6 bits. Whether it is actually possible to distinguish the different possibilities depends on the signal-to-noise ratio.
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Look up the Shannon-Hartley theorem on Wikipedia for some context. It establishes the theoretical maximum capacity given the signal to noise ration and the width of the channel.
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No, no, no NO!!!! (Score:5, Informative)
Carrier frequency has nothing to do with how much information a channel can carry. Channel bandwidth (spectrum used on each side of the carrier frequency) is what matters.
For example, a 6 MHz channel at 450 MHz and one at around 800 MHz have the exact same channel capacity (assuming that the SNR at the receiver is the same on each channel.)
To be specific, the formula for maximum channel capacity of a communications channel is given by Shannon's Law:
C = W log (1 + Eb/No), where Eb/No is the signal to noise ratio of the channel and W is the channel bandwidth.
Maximum C for a given SNR and W (or minimum SNR for a given C and W) is not achievable in practice, but recent advances in error control coding techniques such as LDPC and turbo codes have allowed people to get to within just 1 dB of the minimum SNR for a few years. (And yes, this technology is in cell phones. If I recall correctly, turbo codes are used on some cell phone downlinks when transmitting image data that is not latency-sensitive. Unfortunately both turbo codes and LDPC both introduce pretty high latency to a communications system.
2.4 bits/sec/Hz is nothing new. As others have pointed out, plenty of other systems have been doing this for quite some time.
Cable modems - I believe the DOCSIS maximum limit is 36 Mbits/sec over a 6 MHz channel. 6 bits/sec/Hz - the nice thing about cable distribution is that the inverse square law goes bye bye and high SNRs are easily achievable.
ATSC digital television - 8VSB provides 19.2 mbits/sec over a 6 MHz channel. Just over 3 bits/sec/Hz over relatively long free-space distances, although transmitter power is measured in kilowatts.
There isn't really enough information to figure out exactly what they did, but it looks like the CSIRO people just threw a massive amount of channel bandwidth at the problem. 2.4 bits/sec/Hz means their SNR was not that high.
BTW, yes, it IS true that at higher carrier frequencies, there is more free spectrum available to use wider channels, but there is no direct link between carrier frequency and channel capacity as you claim.
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You can't have 2MHz of bandwidth on a 100Hz center frequency. It would be more correct to say in this case that the center frequency is somewhere around 1MHz.
As you increase the information content by modulating the carrier, the channel bandwidth increases. The AM, FM, or phase modulation creates sidebands.
The main reason higher carrier frequencies are used is so that it is easier to create large bandwidths. (I know that thi
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In addition to there being more free spectrum, it's also true that many aspects of transmitter and receiver construction become more difficult as the ratio of bandwidth to carrier frequency increases. i.e. an antenna covering 1 GHz of bandwidth with a 2 GHz carrier
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2.4 bits/sec/Hz is nothing new
Indeed, to digital communications people this is nothing special. Moreover: it is rather meaningless to say how many bits/s/Hz you get without any mention of distance, power or SNR (signal to noise ratio). I don't think the achievement has anything to do with clever modulation techniques, just with the large bandwidth emerging from just one transmitter. Just like a 1000 ton car consuming 1000 liters of fuel per km is no great technological achievement (in terms of theoretica
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If you managed to have a 2.5GHz channel bandwidth at 2.4bits/s/Hz that would be the ~6 gigabit/s they claimed as data throughput. At 85GHz that would be from 83.75GHz - 86.25GHz.
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Perhaps read the first sentence of the article? (six gigabits per second)
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Re:Shannon (Score:5, Informative)
No, that's Nyquist sampling. To sample an analog signal without aliasing, the sampling rate needs to be 2x the bandwidth of the input signal. Doesn't directly apply here, although it does govern how fast a receiver ADC must be for a software defined radio. NOTE: Carrier frequency does not impose any requirements on the ADC, only channel bandwidth. i.e. an ATSC digital television signal needs at least a 12 MHz sampling rate to be properly sampled, as it is approximately 6 MHz wide regardless of channel carrier frequency.
Shannon's Law states:
C = W log (1 + SNR)
C = channel capacity
W = channel bandwidth
SNR = signal to noise ratio of the channel
Thus, achieving 2.4 bits/sec/Hz is easy - just increase your transmit power or your channel gain to increase SNR. This is why cable modems easily achieve 6 bits/sec/Hz (DOCSIS upper limit is 36 Mbits/sec over a 6 MHz channel, any lower speed is an artificial cap from your provider) - when you are transmitting over a cable instead of free space, losses are (comparatively) low and hence high SNRs are not difficult to achieve.
In this case, it appears the CSIRO guys just threw a lot of bandwidth at the problem (large W).
Easier said than done in the real world. Fixed point-to-point links are easy (directional antennas reduce multipath significantly, what multipath does remain does not change rapidly so requires little receiver processing power to estimate and compensate for.) Mobile environments with rapidly changing high amounts of multipath are where the real challenges are, and thanks to Moore's Law, technology is growing by leaps and bounds in this regard. Error correction techniques known since the 1960s but not implementable until recently (such as LDPC) are now in regular use thanks to increased computing power.
Old news! (Score:1)
Unfortunately I missed my only chance of slashdot fame by deciding to drink beer at our staff Christmas party rather than witness the demonstration. Oh well
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Wow, finally a technology.... (Score:3, Funny)
Sometimes you forget to think 'wow!' (Score:3, Insightful)
Now we have data going through the air at 6Gb/sec. It's all too easy to get used to the steady stream of new stuff but every now and then you need to stop, think about how much has changed in the last 15 years or so and think.. 'Wow!'
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Only a quarter of the available bandwidth... (Score:3, Funny)
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Re:Only a quarter of the available bandwidth... (Score:4, Interesting)
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Data Gravity (Score:2)
Does this fiber have to warm up like my old B&W TV?
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In other words, since they say their spectral efficiency is 2.4b/s/Hz and their link rate is 6 Gb/s, their system must use 2.5GHz of RF spectrum to accomplish that. The article says the system operates at 85GHz, so technically it probably emits energy along the entire range from 83.75GHz to 86.25GHz, assuming the bandwidth is centered at 85GHz.
Also, this is wireless technology, not fiber, although that doesn't affect the above.
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Too bad. I'd love to see a physical example of bits per second per second, data acceleration. Especially traveling at the constant speed of light.
Pshaww.... (Score:3, Funny)
A DVD is 4.5GB (say). So 6Gb/s means a DVD can be transferred over the distance (250m) in 6 seconds.
In my backpack, I can put a 100 DVDs (a spindle). Assume I'm not in shape and can't carry more. I can walk the 250m in just over 4 minnutes (at a leisurely pace of 1m/s).
So if I carry my 100 DVDs the distance, I'll cover it in 250 seconds, which works out to a speed of 14.4 Gb/s, more than double of what these boffins are getting.
Never underestimate the bandwidth of a backpack full of DVDs....
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Use a real datarate! (Score:1)
They fixed it (Score:2)
Oops. I think that the marketing people at a networking products company should get this kind of thing, above all else, correct. Especially when transmission speed is the focus of the announcement... :)