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CSIRO Demonstrates Fastest Wireless Link Yet
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.
You can pop your microwave popcorn by just holding it up between the router and the TV during the FBI warning.
it's a blue bright blue Saturday hey hey
Sorry, I just don't understand this DVD streaming thing. Can someone translate this into Libraries of Congress per second?
Want to improve your Karma? Instead of "Post Anonymously", try the "Post Humously" option.
I assume that you're speaking in general, but I would like to point out that the CSIRO (Commonwealth Serum and Industrial Research Organisation) is throwing Australian -- not US -- taxpayer's dollars out the window.
Australia's network covers huge areas with a spare population, it uses radio and/or sattelite links to link remote exchanges to the trunk. During the late 90's I had extensive experience with an Australian wide mobile application, back then the radio links had a 2500 baud connection. Arguing about service to the bush is a political constant that hasn't changed in the last few decades.
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
Remember this the Australian Government research organisation that has been defending there early 802.11a/g wireless patents against some mighty companies corps who want to avoid paying there dues http://www.theage.com.au/news/wireless--broadband/ csiro-wins-landmark-legal-battle/2006/11/15/116326 6614119.html.
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.
CSIRO is Australian.
Your country does indeed take this sort of technology, and doesn't like to honour the patents on it either! So stop complaining.
Actually, the reason you won't have that at home is that it operates at 85 GHz, so it's only useful for line of sight communication. Think next-generation microwave towers, not WLAN.
Only to realise that the extremely high frequency is ionizing my head...
Actually, I wouldn't worry about ionizing radiation as those only start at frequencies above visible light.
Opus: the Swiss army knife of audio codec
A "hertz" is a cycle per second, so what they're really saying is that they're getting 2.4 bits per cycle of the carrier. I agree that bits/sec/Hz is a ridiculous term for someone to have made up, but they would probably justify it by pointing out that there's not just one effective "carrier" in a modern modulation scheme.
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).
Dahlmann tightly grips the knife, which he may have no idea how to use, and steps out into the plain.
Multiply the frequency of the channel being transmitted on by 2.4 and you get the bit rate. Supposing you were transmitting on 2.434 GHz you could get about 5.8 Gbit/s one way. at 85GHz thats 204 Gbit/s. Mind you this is not your actual sustainable data rate. You would likely be limited to 1/4th to 1/10th this by noise, packet overhead, latency issues, etc. A this kind of frequency anything getting in the line of site can kill your signal, of course, your signal can likely kill anything staying too long in the beam as well. I don't really even understand how you can encode 2.4 bits per Hz, cause thats a bit much data to be packing into a single oscillation.
Disclaimer: I am not a HAM, or anything approaching an EE, just someone who likes math / science.
No, not the frequency of the channel - the width of the channel.
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.
....that will keep Windows Vista patched in real time!
I might be wrong, radio comms stuff is not a strong area of mine, but I thought the intention of numbers such as these was to provide a view of the efficiency of the system. For example a QAM system gets 4 bits per cycle, 64-QAM gets, well, 64 (I think it's used in DVB broadcasts in the UK, don't know about elsewhere).
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 frequency band to work with, then it is necessary to increase the number of bits/cycle in order to increase the throughput.
It sort of reminds me of the clocks per instruction measure for cpus.
Back in 1989 I had a 48Mb SCSI hard drive on my Atari ST. That loaded files at 350k/sec. That was fast back then.
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!'
I want a list of atrocities done in your name - Recoil
why don't they try using the rest?
Radio comms has been a productive area of reasearch at CSIRO for decades. Politicians who ignore them are the ones who waste MY tax dollars. There are many examples that defend the CSIRO's enviable reputation for genuine science without political "fear or favour", ie a "model public service" (as opposed to the non-existant "perfected public service" or the ever present "public propoganda service").
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.
And did you exchange a walk on part in the war for a lead role in a cage? - Pink Floyd.
God, I wish there were a -5 "Totally Wrong" moderation.
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.
retrorocket.o not found, launch anyway?
"Doesn't the carrier freq needs to be > 2 times the data per Shannon?"
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.
retrorocket.o not found, launch anyway?
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....