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?"

Comments

Raw stats on movies...

[strredwolf]

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?

Huh?

[div_B]

Didn't Tesla predict infinite bandwidth in the wireless spectrum by combining frequencies in certain combinations? ..

Isn't the range of frequencies available for combination itself the bandwidth?
Wider band of frequencies => sharper pulses can be formed by fourier synthesis => more 1s and 0s transmitted in a given time-frame?

Re:Huh?

[_defiant_]

OFDM(orthogonal frequency division multiplexing) is a spread-spectrum technique meaning it spreads its energy(the data) out over a wide range of carrier frequencies -- the total power output required is actually less than by using a single carrier.

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)

Re:When can we can a whiff of this speed in the US

[emmons]

Because your cable company still has to pay off the bonds it issued in the 80s to put the cable in the ground in the first place.

Cisco did this 6-7 years ago

[dangermen]

I remember Cisco offering a product six or seven years ago that did vectored orthogonal frequency division multiplexing. It could do 45mbps non-line of sight as point-to-point or as a unidirectional 28 channel T1'looking setup al la Cisco 2600 WIC Cards. I wonder how this is different.

OFDM is old technology

[Bored Huge Krill]

This article seems to imply that OFDM (used in 802.11a and 802.11g) is somehow a "new" technology. It isn't. It turns out to be quite hard to find the oldest use of OFDM, because it appears to have been used in military systems which were classified long before it became publicly known. However, the oldest published document I know of is a patent for orthogonal frequency multiplexing, filed in 1966 (granted in 1970) by Robert W. Chang of Bell Labs. I don't remember the patent number off the top of my head. :-) The real change to get enormous data rate with increased spectral efficiency (which you'll really need...) over a useful range is MIMO (multiple input multiple output) which uses spatial diversity to effectively create many spatially diverse (mostly) independent communication channels simultaneously on the same frequency channel. Methods combining OFDM and MIMO make up all of the front running proposals for the future 802.11n standard currently in the works.

Re:ofdm vs. cdma

[Wesley Felter]

OFDM is a modulation technique (i.e. it turns 1s and 0s into radio waves) and CMDA is a multiple-access technique (i.e. it lets multiple radios share a channel), so they're really orthogonal.

radio pollution and the shannon limit

[j1m 5n0w]

Well, Claude Shannon showed that, with a perfect modulation and error correction scheme, you could only push so much data over a given communications media, with a given amount of bandwidth and SNR. If you want more, you have to either

• use more spectrum (aka bandwidth)
• increase signal strength
• decrease noise

Since background noise is not controllable, they would have to be doing one of the first two (effectively increasing radio pollution), or overcoming inefficiencies in a previous modulation scheme.

Anyone know how close the various 802.11 standards are to the shannon limit?

-jim

Re:radio pollution and the shannon limit

[Anonymous Coward]

Well, the shannon limit only aplies to single input single output (SISO) channels. Future high data rate wireless systems will use multiple input multiple output (MIMO) which exploits multipath channels. Using multiple transmit and receive antennas you can increase data rates without using any more spectrum. I think you can effectively get *N speed up where N is the number of transmit or receive antennas. It works because the channels created by separating the antennas in space by a certain multiple of wavelengths are uncorrelated. Through special coding techniques you can use these like they are separate channels but still use the same frequency bandwidth.

Here's a cool link: http://www.linuxjournal.com/article.php?sid=7386

which talks about how a research group at a company in New Zealand is using Linux to help in development of space-time systems. I think the future 802.11n standard will use MIMO to get the high data rates people desire, without increase spectrum usage.

Re:radio pollution and the shannon limit

[femto]

You've missed out an option:

• Increase spatial diversity

This is the spatial equivalent to the time/frequency option of 'use more spectrum'. Achieving spatial diversity is typically done by adding more antennas (and RF gear) to the receiver and transmitter.

As an example, a special (simple) case of spatial diversity is using an array of antennas to do beamforming. Making the antenna occupy more space increases the antenna gain (directivity) allowing multiple data streams to reuse the same frequency.

In its most general form, spatial diversity allows multiple streams of data to be transmitted and received on the same antenna array, thus allowing capacity to be boosted over what you would expect from the wikipedia version of Shannon's equation.

In actual fact, the 'W' in wikipedia's equation should be a matrix involving spatial terms. This fact was discovered a decade or two ago and forms the basis of the hot topic of MIMO or space-time coding. An update to the 802.X standard, based on these techniques, is in the pipeline.

It's an ongoing topic of research to discover what the 'real' Shannon limit is when spatial diversity is taken into account. It looks (by my understanding) to be a function of the available frequency bandwidth and the available volume of space measured in wavelengths.

Re:radio pollution and the shannon limit

[Anonymous Coward]

Increasing signal cannot and would not provide you with more bandwidth. It might help you overcome noise thus maximizing your current maximum capacity. But increasing signal also increases the possiblity of reflections which in turn increases noise.

Wrong. The most effective modulation you can use depends on the SNR. With a given noise level, increasing the signal power allows using a more efficient modulation scheme (packing more bits per baud). The more bits per baud, the highest the SNR required.
This is of course a simplification. As other said increasing power is not a magic solution. But is usually helps.

Re:radio pollution and the shannon limit

[sploxx]

OMG. +5 Insightful. I have to do something about it.

Increasing signal cannot and would not provide you with more bandwidth. It might help you overcome noise thus maximizing your current maximum capacity. But increasing signal also increases the possiblity of reflections which in turn increases noise.

No. And yes for the last part. But this is not the whole truth.

Did you know that Maxwell's equations were *linear*? I.e. if you increase the output power by a certain factor, you increase the received power by the same factor if all else parameters (location etc.) are constant. Interference patterns (your described noise) don't change their form. The signal increases and also the amount of noise *caused by scattering*. All else noise powers stay the same (noise in the receiver electronics, noise from electric switches/lightnings etc). So the overall SNR gets better -> the datarate gets better.
Of course, there are limiting factors. I.e. too strong sources may overshine weaker ones in a WLAN setting our you may just see all the nodes of every WLAN in a city (thereby decreasing bandwidth). There's an optimum. Directional antennas help in this case.

Or do you want to say that you have to take non-linearity in vacuum or materials (i.e. air/concrete) into the equation? Hello?! We're not talking about 511keV photons creating electrons/positrons or polarising frequency multiplier crystals with lasers or similar stuff.

Re:Nice troll

[B2382F29]

You had neither the first satellite in orbit nor the first man in space, nor did you create the first modern rocket.

You did not discover Fission neither did you understand the theory behind it.

Oh, and you didn't invent computers.

Now, you sure are proud of being the first nation creating the Nuclear Bomb and USING it.

OFDM is already used for high bandwidth streaming!

[Goth Biker Babe]

Last night, as I sat in bed, I channel hopped and ended up watching BBC 3 on my bedroom TV which receives it's signal through a small set top antenna. In fact that TV can pick up over seventy TV and Radio channels through that antenna.

Why? Because DVB-T, the terrestrial form of the DVB digital television standard uses OFDM to ensure signal reliability. There are roughly eight TV channels per multiplex at PAL resolution which is quite a bandwidth. So how is this new?

Re:ofdm vs. cdma

[femto]

Actually, OFDM is a special case of CDMA.

CDMA is simply a way of superimposing multiple data streams (users) which have been encoded in some way (typically by mutiplying by a code sequence). This is a very general technique. Choose the CDMA codes to be a set of orthogonal sine waves and the result is OFDM.

Ultimately CDMA and OFDM have the same performance (they are the same thing) but the special case of OFDM is typically easier to implement. The symmetry of the OFDM code set allows an FFT to be used to separate data streams.

A typical wireless LAN assigns all codes (carriers) to a single user but that doesn't have to be the case.

As a further example, chose the codes to be a set of orthogoal pulses and CDMA becomes TDMA.

CDMA is really just another name for 'superposition', that is, construction a linear combination of a set of sequences. The sequences don't even have to be orthogonal.