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BBC White Paper Claims HD Over Low Bandwidth Signal

Zonk posted more than 7 years ago | from the quite-a-feat dept.

Television 88

Kelten Miynos writes "According to CNet, the BBC has written a white paper in which they claim it's possible to double the available Freeview TV bandwidth by using some clever technologies. 'Doubling the space would mean we could easily have HD channels on Freeview, although everyone would need to buy a new receiver and aerial to pick them up. The key to all this is something called MIMO, which stands for multiple-input multiple-output. MIMO works using two transmitters, and two receivers. The two transmitters mean the two sets of data — sent on the same frequency — will arrive at the receivers at different times. Different arrival times are what allow the receiver to differentiate between the two separate signals and subsequently decode them.' These procedures could then be transplanted abroad to other countries with similar services."

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Great (-1, Troll)

Anonymous Coward | more than 7 years ago | (#18913809)

Now we can hear about nappy headed ho's in higher res

Usage (2, Interesting)

DaAdder (124139) | more than 7 years ago | (#18913815)

Even with two transmitters, it doesn't sound too prone to break downs, this could be a not-too-costly winner.

MIMO isn't exactly news though, but it's of course interesting to see it being used in this context.

I wonder how long this new found bandwidth will be enough, as we tend to expand usage right along side available resources at a disturbingly linear rate.

Fascinating technology, but useless for Freeview (4, Interesting)

Andy_R (114137) | more than 7 years ago | (#18913827)

This wouldn't just require new equipment to view the new transmissions, it would also require throwing out all the freeview kit that the BBC and the digital alliance have spent years convincing the public to buy. This idea could only really be implemented in an unused frequency band - the space vacated by the analogue switch-off seems ideal for it to me, if only the UK government can be prevented from selling it for some other use.

As the article says, a far simpler solution to the badwidth issues of freeview would be to ditch the huge number of junk channels and use the bandwidth to provide a HD signal for the ones that people actually watch.

Re:Fascinating technology, but useless for Freevie (1)

LiquidCoooled (634315) | more than 7 years ago | (#18913863)

My take on this is that standard def freeview will continue, but if you want a HD version you need 2 boxes?

Re:Fascinating technology, but useless for Freevie (0)

Hatta (162192) | more than 7 years ago | (#18914035)

This wouldn't just require new equipment to view the new transmissions, it would also require throwing out all the freeview kit that the BBC and the digital alliance have spent years convincing the public to buy.

Anyone care to tell us yanks wtf freeview is?

Re:Fascinating technology, but useless for Freevie (1)

hedwards (940851) | more than 7 years ago | (#18914079)

Well, I'm also a yank, but I have been following it. Freeview is digital tv over the airwaves. Basically all tv in the UK will be digital, starting a while back in limited areas. Anybody that isn't getting their signal through cable or satellite would have to use freeview. Which of course requires a different tuner than tvs already have.
http://www.freeview.co.uk/home [freeview.co.uk]

Re:Fascinating technology, but useless for Freevie (1)

FinestLittleSpace (719663) | more than 7 years ago | (#18919087)

I wouldn't put it down too much. Freeview is extremely successful in the UK due to some shops managing to cut the prices of boxes to 20-30 pounds these days - plus, all new tvs have had the boxes built in for a long time. It's a very promising transition.

Re:Fascinating technology, but useless for Freevie (1, Insightful)

OverlordQ (264228) | more than 7 years ago | (#18914089)

Judging by your UID, you're not new here. Might try clicking the link IN THE FUCKING SUMMARY that links to the Freeview wikipedia article . . . . . it might explain some things.

Re:Fascinating technology, but useless for Freevie (1)

Hal_Porter (817932) | more than 7 years ago | (#18916563)

People with UIDs that low don't just not read the article, they don't read the summary either. The longer you're here in fact, the less you read. The limiting case is the editors who can't read anything anymore, not even the warning labels on stuff. Which explains the high turnaround of editors we see.

I'm not sure I should even bother to type this, since your UID is much lower than mine.

If you read this far in fact, I'll reward you with this top tip: Avoid the "hard to open" jars in the cabinet in your bathroom. They are not candy.

Mod parent up (-1, Offtopic)

Anonymous Coward | more than 7 years ago | (#18917655)

Mod parent funny or insightful. I can't decide which. I wish I had mod points....

Re:Fascinating technology, but useless for Freevie (1)

Alex (342) | more than 7 years ago | (#18917805)

thats not a low user id......

Re:Fascinating technology, but useless for Freevie (5, Informative)

meringuoid (568297) | more than 7 years ago | (#18914109)

Anyone care to tell us yanks wtf freeview is?

Digital TV via an aerial. [wikipedia.org]

Previously there'd been two competing digital TV providers: Sky, selling digital via satellite, and ITV Digital, selling digital via aerial. Although both carried the same basic menu of free-to-air channels, they were basically pay-TV providers trying to push subscription services, and didn't really achieve much. Sky Digital inherited the viewers from Murdoch's existing satellite operation, but didn't really expand the market AFAIK, and ITV Digital did very poorly, being a second-best offering as a pay-TV platform, and again failing to win over the majority who aren't really interested in pay-TV. ITV Digital folded after a while.

At this point a BBC-led group established the Freeview standard, which is based around a set-top box made as cheap and simple as possible, and which provides a comparatively small number of free-to-air channels. There's an expansion that allows encrypted pay-TV channels, but few exist and hardly anyone bothers. Because the box was very cheap and it was a one-off expense - no subscriptions, no registration - it became the standard very quickly. These days it's being built in to most new TV sets as standard, and supposedly we're on course to be able to switch off the old analogue broadcasts on schedule.

Re:Fascinating technology, but useless for Freevie (1)

EnglishTim (9662) | more than 7 years ago | (#18914455)

Quick nit-pick: you forgot Digital Cable in your list of Digital TV providers in the UK...

Re:Fascinating technology, but useless for Freevie (1)

EvilGrin666 (457869) | more than 7 years ago | (#18914983)

Indeed, however as it stands atm. UK Digital Cable = Virgin Media [wikipedia.org]

Re:Fascinating technology, but useless for Freevie (0)

Anonymous Coward | more than 7 years ago | (#18917359)

One of the interesting points aboutthe ITV digital debacle was the fate of the World origami championships. ITV Digital di have the rights but they folded. It was left to Sky to put it on paper view.

Re:Fascinating technology, but useless for Freevie (0, Troll)

cortana (588495) | more than 7 years ago | (#18914397)

Freeview is an initiative that aims to discourage us from watching television, specifically by making it really annoying to channel-hop. Let me explain. With our existing, analogue equipment, changing channels is nice and fast; it takes perhaps half a second. But the analogue transmitters are going to be shut off in a few years time. Once that happens, the only way to recieve television signals will be with a cable or sky box, or a Freeview box, each of which takes between two and five seconds to do whatever it is that they do to change channels. The result is that I abandon television out of frustration.

It's because there's more than 9 channels... (3, Informative)

rklrkl (554527) | more than 7 years ago | (#18914505)

The "2 to 5 seconds" to change the channels on Freeview is nothing to do with decoding times or slow processors in the Freeview set-top boxes. Nope, it's simply because there's more than 9 channels and the channels can indeed be numbered up to 999, which means that up to 3 digits have to be pressed to change channel.

As anyone with a cable or satellite remote control already knows, multi-digit channel numbering means that if you want to hop non-sequentially between channels and the channel numbers are only one or two digits, then the set-top box will pause for a second or so to see if you are adding the second or third digit. If you don't, then it assume that the digits entered so far are the complete channel number and then jump to it.

This is why many Freeview remotes have a "channel plus" and "channel minus" button to get around this problem for channel surfers - just press that to cycle sequentially through the Freeview channels with no digit-delays. I find channel changing to be about one second on the Freeview and IDTV sets using the +/- buttons on the remote, which is OK (but I could believe slower boxes might take 2 seconds, but certainly not 5).

Channels not nicely numbered to allow such +/- surfing? Again, many Freeview boxes/sets allow you to reorder the channel numbering to your preference (e.g. I can only get Welsh Freeview, which insists on putting S4C on channel 4 and English Channel 4 on channel 8, so I swap those over!) and, even better, let you delete channels completely, which I do for all the pay channels, shopping channels etc.

Re:It's because there's more than 9 channels... (1)

OverlordQ (264228) | more than 7 years ago | (#18915231)

Does it not let you hit, say, 005?

Re:It's because there's more than 9 channels... (1)

jez9999 (618189) | more than 7 years ago | (#18918127)

The "2 to 5 seconds" to change the channels on Freeview is nothing to do with decoding times or slow processors in the Freeview set-top boxes. Nope, it's simply because there's more than 9 channels and the channels can indeed be numbered up to 999, which means that up to 3 digits have to be pressed to change channel.

Actually, the GP may just have been referring to the fact that pretty much all Freeview boxes apparently have crappy firmware/hardware (at least I haven't found one that doesn't), and changing channel actually DOES take a few seconds whilst it 'does stuff'; analogue TV didn't require that slow firmware and changing channels was pretty much instant.

As an aside, Freeview isn't free, you pay a licence fee. I abhor the misleading name.

Re:It's because there's more than 9 channels... (0)

Anonymous Coward | more than 7 years ago | (#18925499)

Freeview is free in the sense that you pay no more for it than you do for analogue TV. If TV were soap powder, Freeview would be the 25% extra 'free' bit. You still have to pay for the powder, but the extra bit is free. - Dan

Re:It's because there's more than 9 channels... (0)

Anonymous Coward | more than 7 years ago | (#18925517)

Considering that all modern video codecs compress multiple frames together, so that only a small fraction of the frames are self-contained and others are coded as changes from previous (and even following) frames, zero delay is not reachable. Not unless you have multiple decoders working in parallels on all channels, and this won't happen any time soon. It will happen once sufficient computing power is dirt cheap, but that won't happen for at least a decade.

Re:Fascinating technology, but useless for Freevie (1)

zippthorne (748122) | more than 7 years ago | (#18914651)

There's a really simple solution to this that isn't very elegant:

Take one HD channel to transmit scaled down versions of all available channels for some given area. Keep one tuner constantly on this channel. When switching, briefly show the scaled down version while the main tuner switches over.

I'm sure this isn't the best solution however.

Re:Fascinating technology, but useless for Freevie (1)

smithmc (451373) | more than 7 years ago | (#18919277)


  Take one HD channel to transmit scaled down versions of all available channels for some given area. Keep one tuner constantly on this channel. When switching, briefly show the scaled down version while the main tuner switches over.

Hey, maybe you could also use that channel as a video channel guide - simultaneously see all available channels, tiled onto one screen in low-res, then pick the one you want...

Re:Fascinating technology, but useless for Freevie (1)

LordSnooty (853791) | more than 7 years ago | (#18915239)

OT: There's another downer with these new type of entertainment boxes - something touched on in Dragons' Den recently. Many of these Freeview boxes eat 100% or near of their max power take even in standby. It got me thinking, why is that? These are effectively small computers decoding over-the-air MPEG - they need to boot up, test & calibrate, and many don't appear to have sufficient component sleep ability. Once again, it's a trade-off - a few seconds of boot-up time coming out of standby vs sucking more power than it needs. They went for the latter. The other digiboxes are not doubt the same, I know that if I crash my cable box I can knock it into standby and the display merrily goes on & off but the box remains crashed. The 'standby' appears to operate the front display and nothing more.

Re:Fascinating technology, but useless for Freevie (1)

drsquare (530038) | more than 7 years ago | (#18914721)

As the article says, a far simpler solution to the badwidth issues of freeview would be to ditch the huge number of junk channels and use the bandwidth to provide a HD signal for the ones that people actually watch.
And who decides what the 'junk' channels are? Not everyone wants to watch mainstream reality-TV and soaps. If I was watching some obscure sci-fi programme or documentary I wouldn't want it cancelled so they could show Washed-Up Celebrities Dancing and Singing Badly on Ice in HD.

Re:Fascinating technology, but useless for Freevie (1)

steevc (54110) | more than 7 years ago | (#18917115)

Yeah, get rid of the shopping channels (never watch then) and the +1 channels (who needs to watch Friends an hour late?) and the there should be enough space for some HD.

Of course we will have to buy new boxes to watch HD anyway.

Re:Fascinating technology, but useless for Freevie (1)

mlk (18543) | more than 7 years ago | (#18917747)

No, don't get rid of the +1 channels. I can not get the standard channels, and have to watch +1. :(

Indoor aerials suck.

Re:Fascinating technology, but useless for Freevie (1)

mpe (36238) | more than 7 years ago | (#18917917)

Yeah, get rid of the shopping channels (never watch then)

Thing is that these along with the quiz (lottery) channels are likely to cost nothing to the broadcaster, possibly they even pay to be broadcast...

Re:Fascinating technology, but useless for Freevie (1)

jez9999 (618189) | more than 7 years ago | (#18918115)

As the article says, a far simpler solution to the badwidth issues of freeview would be to ditch the huge number of junk channels and use the bandwidth to provide a HD signal for the ones that people actually watch.

Quite right. Why do I have to put up with that BBC1/2/3/4, ITV1/2/3, Channel4 and Five junk when I never watch it?

Re:Fascinating technology, but useless for Freevie (1)

funkatron (912521) | more than 7 years ago | (#18918585)

As the article says, a far simpler solution to the badwidth issues of freeview would be to ditch the huge number of junk channels and use the bandwidth to provide a HD signal for the ones that people actually watch.

We could start by only having one channel that plays friends and scrubs all day, instead of three.

Re:Fascinating technology, but useless for Freevie (1)

unitron (5733) | more than 7 years ago | (#18923331)

We could start by only having one channel that plays friends and scrubs all day, instead of three.

Which would free up a channel for all the various flavors of "Law and Order" and another for "CSI-wherever", and I could program out both.

Of course what I really want is for anything to do with Donald Trump (and I mean anything, including any mention of him by others) to be confined to one particular channel, and then I can install a notch filter right where the cable hits the grounding block at the demarcation point.

The upgrade cost means it will never happen (4, Informative)

AmiMoJo (196126) | more than 7 years ago | (#18913839)

In the UK, we are moving over to digital TV region by region, starting next year. Already, people have had to go out and buy Freeview boxes, and in many cases new ariels (I needed one). Somehow, I doubt anyone will go for buying a new box and ariel just for the lucky minority to have HDTV.

Anyway, if you are going to have a new box, why not move to MPEG4 as well? That would double the number of available channels again.

Re:The upgrade cost means it will never happen (4, Interesting)

evilviper (135110) | more than 7 years ago | (#18913913)

Somehow, I doubt anyone will go for buying a new box and ariel just for the lucky minority to have HDTV.

You aren't being forced to switch all frequencies to MIMO. You could just as well leave half the spectrum in-place for standard definition, and just broadcast MIMO on the other half.

Anyway, if you are going to have a new box, why not move to MPEG4 as well?

The PDF mentioned this test was done using h.264.

Re:The upgrade cost means it will never happen (1)

Dogtanian (588974) | more than 7 years ago | (#18919499)

Remember that by the time this gets going, the traditional analogue stations in the area will likely have been switched off.

Re:The upgrade cost means it will never happen (1)

bryan1945 (301828) | more than 7 years ago | (#18923941)

Sorry for the ignorance, but is there any cable TV over there?

In other news... (5, Funny)

Anonymous Coward | more than 7 years ago | (#18913861)

The BBC announced the world premier broadcast of Finding MIMO

Who cares? (1)

swab79 (842256) | more than 7 years ago | (#18913923)

But who cares when we are going to get free HD via satellite [theherald.co.uk] ?

Because we can't all install satellite dishes (1)

goldcd (587052) | more than 7 years ago | (#18914873)

(or would want to). I've got a flat in a listed building in the middle of a town.
Being in a town is great as I can get my Freeview reception and speedy ADSL2 - unfortunately I'm not allowed to slap a satellite dish on the outside of my building and as even the f'in pavement outside is listed, it was considered too expensive to lay cable. If I'm ever to get HDTV it's going to be using MIMO, after switchover, or IPTV.
Now I know I'm probably in a somewhat rare position, but loads of people find they can't receive stuff for all manner of reasons - more methods of getting HDTV into my house the better and competition is always nice.

Re:Because we can't all install satellite dishes (1)

in5ane (961406) | more than 7 years ago | (#18917579)

I live in an apartment which means I get no say in satellite placement or cable installation etc. However, don't give up! Sky have a special team that will talk to the freehold owner/management company of your building if you don't have Sky. With various hidden/camouflaged dishes available and some distribution meaning only one dish required for the whole complex, I'm sure you could arrange something.

Sky HD isn't up to much at the moment, so don't feel like you're missing out :) A couple of HD movie channels and a half-baked 'anytime' service do not constitute a decent HD service. Even BBC HD is lame.

Re:Because we can't all install satellite dishes (0)

Anonymous Coward | more than 7 years ago | (#18918297)

That's not too bad. Like you, we can't slap up a dish due to the building being listed.

However, we can't get freeview as it's not available for some reason. The only logical explaination I have is that the analogue repeaters haven't been updated yet. Cable not an option as we live in Cornwall and the TV signal's are going to be switched off in our area in 2008.

According to Freeveiw though "When your area goes digital, you should be able to see the Freeview channels." - Yeah, like I really expect that to happen.

Re:Because we can't all install satellite dishes (1)

anominous (803001) | more than 7 years ago | (#18924395)

Can't you run a length of Cat5 to Goonhilly? ;)

What is MIMO (4, Informative)

markov_chain (202465) | more than 7 years ago | (#18913931)

MIMO is an intriguing technology but unfortunately the acronym is used loosely to refer to many unrelated things.

The most exciting MIMO technology is also known as "space multiplexing," which lets a system with N transmit and N receive antennas transfer data at N times the rate of a system with just 1 transmit and receive antenna. The marketing departments like to use MIMO to refer to any old system with multiple antennas, because technically the definition is correct. However, most of the time those systems can't get this kind of performance gain. I believe most of the pre-n hardware out there just does fancy antenna selection; the language is usually careful to say that "802.11n supports space multiplexing," even though it is optional, and there are no performance numbers yet. Someone please correct me if I'm wrong, which I'd love to be!

The way space multiplexing works is counterintuitive: each transmit antenna sends an independent stream of data on the same frequency. The "magic" that makes it work is the fact that multiple receiving antennas observe the combined signal at different times (the article summary got it surprisingly right here); specifically, the phase offsets observed at different RX antennas should be random. This can happen when the signals bounce off a lot of objects like walls indoors, or buildings etc. outdoors.

Here is a simplified example that illustrates how this can work. Suppose we have 2 transmit antennas. Suppose at a given time we send two signals a and b. If we only had one receive antenna, we would observe (a+b), and there would be no way to extract the individual signals. However, if we have a second antenna, AND the phase offset happens to be such that the other antenna gets (a-b), we can clearly extract the original signals.

There are environments such as open outdoor fields with line-of-sight, where the received phase offsets are not random and don't happen to be "nice" like in the above example; in that case MIMO performance falls back to 1x1, or a little better if the phase offsets have some degree of randomness.

Re:What is MIMO (5, Informative)

ModelX (182441) | more than 7 years ago | (#18914029)

If you read the BBC paper you will notice that they cheat a little - their MIMO system relies on two polarizations (vertical and horizontal) insted of spatial separation of the two antennas. Satellite TV has been using polarizations for a long time, though not in MIMO mode.

The correct summary would be "BBC White Paper Claims HD By Efficient Use of Existing Bandwidth".

Re:What is MIMO (1)

markov_chain (202465) | more than 7 years ago | (#18914349)

It's interesting that they observed better performance *with* line-of-sight. I guess either that's when there is the least distortion of crosspolarization, or there is also less path-loss; in papers like "MIMO measurements in Manhattan" where the BLAST guys observed better performance *without* line-of-sight, they normalized the capacity calculations to factor our the path-loss. So even if the effect of MIMO might be greater when there are a bunch of buildings in the middle to randomize the signal phases, the increased path loss might not be worth it.

Re:What is MIMO (3, Informative)

Andy Dodd (701) | more than 7 years ago | (#18914553)

Pretty close, but not quite. MIMO doesn't rely in observing the combined signal at different times, but on the fact that in a multipath environment, there is some independence between an antenna at one location and one located a small distance (on the order of only one wavelength or less) away.

A good example - When listening to an old analog FM radio station in your car, you stop at a traffic light or a traffic jam and the station basically fades out to the point that it is static. For whatever reason, you move your car a few feet, and the station is now coming in strong. (Or when driving along the road, the signal quality "flutters" rapidly). What is happening here is that the signal between the radio station and your antenna isn't necessarily traveling in a straight line - more likely the signal is being reflected off of objects near the radio station or near you. In some cases, the path lenghs of these signals are such that they all add in-phase (constructive interference) and the signal is strong. In other cases, they are out of phase and cancel each other (destructive interference) and you get static.

Now imagine that your car had two antennas with some physical distance between them. Then your radio could choose the signal with the strongest signal, with two antennas there is a significantly reduced probability that BOTH will be experiencing multipath fade at once. This is generally called receive diversity. Some companies now call this MIMO even though it really isn't. Some diversity systems user fancier combining algorithms, but most just use selection diversity. It is also possible to have transmit diversity, although it is somewhat more difficult. Usually the transmit modulation scheme and the transmitters themselves need to be modified to do this, unless the transmitter is aware of the path from it to a receiver (i.e. a point-to-point link with some sort of feedback channel from the receiver back to the transmitter). For a scheme that works without knowledge of the channel, search Google of Wikipedia for Alamouti space-time multiplexing. Such systems provide no benefit in line-of-sight situations, but reduce penalty in multipath situations.

Also, a car with two or more receive antennas could instead combine the signals in such a way as to form a single virtual antenna that was directional, rejecting some of the paths causing interference. Such techniques are known as a phased array antenna. Phased arrays can be fixed (directionality governed by wiring harnesses), and steerable (directionality controlled by configurable phase shifters and configurable delays), and this category can be either manually steered (operator steers the antenna) or adaptively steered (receiver guesses the best way to steer the antenna to maximize the received signal.) Again, some companies now call this MIMO. For example, the "MIMO" system used by Ruckus Wireless (and licensed to Netgear of their RangeMax WPN824) is just an adaptive phased array system. (Not that this is necessarily bad - it's the best way to improve performance with "legacy" endpoints that don't understand true MIMO techniques, but can't achieve the full capacity of a true MIMO system.) Phased array systems provide a Log(N) improvement in capacity in line-of-sight situations, and also a reduction in multipath penalties.

A true MIMO system can analyze the paths between all transmit and receive antennas, and effectively transmit different data on each path. In reality, most such systems do it in a more abstract manner - a matrix is formed in which there is one row for each transmit antenna, and one column for each receive antenna, and each element of the matrix is the gain between the transmit and receive antennas associated with that row/column, the singular value decomposition of this matrix is calculated, and the singular values (which are related to the matrix's eigenvalues by the way) represent the gains of the possible "virtual" channels formed by the MIMO system. (I have a link on my work machine to a VERY good description of the mathematics behind MIMO, but not here, and my Google-Fu seems rather weak tonight.) Such a system actually works BETTER in a multipath environment, providing up to min(Nt,Nr) (or is it Nt+Nr) improvement in capacity, while only providing log(Nt+Nr) improvement in a line-of-sight situation. Note that for optimal performance, both transmitter and receiver need to be aware of this matrix (i.e. does not work in a broadcast situation, only for point-to-point communications). Some MIMO variants can provide benefits in situations without full channel knowledge though. (Unfortunately I can't provide any details without the aforementioned link. It was to a set of lectures from some graduate course on wireless comms - Maybe from University of Texas???????)

According to other comments (TFA seems broken for me at the moment), BBC's system relies on cross polarization instead of actual MIMO. Cross polarization for seperation of two signals can double capacity in a line of sight situation (but no more) but will usually break rapidly in a non-LOS situation. (Although it may use some real MIMO techniques to reduce this penalty).

Re:What is MIMO (2, Interesting)

markov_chain (202465) | more than 7 years ago | (#18915437)

Pretty close, but not quite. MIMO doesn't rely in observing the combined signal at different times, but on the fact that in a multipath environment, there is some independence between an antenna at one location and one located a small distance (on the order of only one wavelength or less) away.
Yes, quite. The independence between antenna pairs arises from delay spread, caused by signals traveling different distances.

In some cases, the path lenghs of these signals are such that they all add in-phase (constructive interference) and the signal is strong. In other cases, they are out of phase and cancel each other (destructive interference) and you get static.
So they do arrive at different times. In your two examples they arrive either in-phase, or one half cycle apart in time. ;)

and each element of the matrix is the gain between the transmit and receive antennas
Usually the coefficients are complex, which means they represent both gain (or should I say attenuation) and phase distortion.

A true MIMO system can analyze the paths between all transmit and receive antennas, and effectively transmit different data on each path.
Not quite. This would imply that in a NxM system, we could transmit different data on N*M paths, which is not the case. Upper bound is min(N,M).

Re:What is MIMO (1)

Andy Dodd (701) | more than 7 years ago | (#18915449)

bleh, got so owned there. That teaches me to write detailed explanations after 2/3 a bottle of wine!

Re:What is MIMO (1)

unitron (5733) | more than 7 years ago | (#18923435)

That fluttering when driving is known as "picket fencing".

Early television receivers suffered something similar when airplanes flew overhead and bounced back the signal, which arrived at the antenna slightly later than that which was coming straight from the transmitter.

True MIMO 802.11n exists (1)

mcg1969 (237263) | more than 7 years ago | (#18915713)

I am absolutely certain that any of the 802.11-pren and 802.11-draftn implementations that use the Airgo Networks (now Qualcomm) chipsets do true spatial multiplexing with multiple input and output antennas (MIMO), NOT just "fancy antenna selection" as you put it. I know because I contributed to the design of their first-gen RX implementation. They've never NOT done it. Of course, the chip also supports non-MIMO modes for back-compatability with older access points.

I am almost as certain that other implementations use MIMO as well. But of course since I wasn't on the inside I cannot say. Still, it's pretty much the only way to get more than 54mbps over 802.11 without channel bonding.

Same frequency? (0)

Anonymous Coward | more than 7 years ago | (#18913961)

Just a little question:
Same frequency, different signals does equal noise, doesn't it?
Different frequencys for different signals (frequency multiplexing) would do the job, but if you send two or more different signals on the same frequency you get inter symbol interferences and high chance for errors while decoding (as in 'actual watching tv') the signal.
This white paper sound like BBC-made BS or the description here is faulty ...

btw: part of my course of study is transmission technology and multiplexing for radio and fiber optics ... so i know at least a little bit about it ...

Re:Same frequency? (1)

ChrisMaple (607946) | more than 7 years ago | (#18914351)

With n receiving antennas properly positioned you can null out n-1 transmitting antennas properly positioned, technology that has been in use at least since 1970. MIMO seems to be a bit different, but presumably a similar technique applies. I'll bet that this technology is going to have a lot of trouble with reflections from moving things except in close line-of-sight situations.

Re:Same frequency? (0)

Anonymous Coward | more than 7 years ago | (#18915191)

It's all digital working on phase difference instead of nulling out antennas, and VHF is line of sight, so yeah, you put the ariels on the roof and there you go. The only problems might be airplanes.

Fuck DVB-T (0)

Anonymous Coward | more than 7 years ago | (#18913965)

Freeview and all the rest have pitfull quality compared to a good analog signal...
How could they not, seeing as the image is DVD-resolution and framerate (and coding, MPEG2) but at something like 1/4 to 1/8 of the bitrate..

It's pathetic.

The new digital television technologies are a net _loss_ for consumers. Power-hungry settop boxes, lower quality, possibility for DRM. What's to like?

A decent CRT displaying a decent analog signal beats the pants of an LCD displaying DVB-T any day.

Re:Fuck DVB-T (1)

Proud like a god (656928) | more than 7 years ago | (#18914257)

I know, don't feed the Trolls, but..

Wouldn't better/DVD quality at the same framerate at a lower bitrate simply meant a more efficient compression scheme is being used, meaning lower signal frequency and thus power usage for the same decompressed results?

And what makes you think a digital signal means you can't use an analog display, like all TVs and CRTs have been for years while playing back DVDs and PC content?

Re:Fuck DVB-T (3, Insightful)

Mprx (82435) | more than 7 years ago | (#18914283)

No, they use the same old MPEG2, only at far too low a bitrate, which is why it looks like shit regardless of what display you use.

Re:Fuck DVB-T (1, Interesting)

Anonymous Coward | more than 7 years ago | (#18914373)

You can't blame DVB-T for picture quality issues unless you've got problems with radio interference. DVB-C/T/S is just the medium.

DVB-T in Australia transmits the SD TV (non-HD) channels at a rate of about 3 Gbyte/hour, which should provide a picture at least as good as your average DVD.

Assuming the realtime MPEG-2 encoders at the TV stations aren't junk.

Re:Fuck DVB-T (1)

Jimbookis (517778) | more than 7 years ago | (#18914515)

The encoders _are_ junk. I don't know how anyone can justify paying big bucks for a large SD or HD flat screen these days for use with digital channels. Live TV looks like blocky crap (see what happens when camera flashes go off on the news or a fast pan on during the footy) and I have noticed more and more on the common but lo-fi programming (like that missing persons program on ch9) that whole sections of the image swim and float around on their own. Digital TV is great because I no longer get speckle, herring bones and ghosts but you end up with another set of image problems that stem from crap MPEG encoders and are just as annoying.

Re:Fuck DVB-T (1)

cheekyboy (598084) | more than 7 years ago | (#18915541)

Maybe its just CH9, they are a cheap ass station that puts barely any effort into high quality, all they care is maximum profits.

Yes, I too hate pixelization, but the decode box should really have options to smooth that out/filter process it.

One thing they could do is perhaps offer a SD-HI mode on the HD channel like 7 does. If there is no HD content, then just offer
a 576p SD version at HD bandwidth rates on the HD channel, rathern than just upscaling an SD signal to HD format.

They should also do proper HD formated titles/logos too in HD mode, but they usually are SD level.

Re:Fuck DVB-T (0)

Anonymous Coward | more than 7 years ago | (#18917525)

let me get this right, 7 is broadcasting high bitrate SD when no HD source is available? I can't seem to get it, maybe its because my STB is a SD only STB or its that Canberra Prime is not doing the same. -AC

Re:Fuck DVB-T (0)

Anonymous Coward | more than 7 years ago | (#18914421)

Go down the pub and have a beer, mate - sounds like you need one.

Cable companies did something similar (1)

Richthofen80 (412488) | more than 7 years ago | (#18913979)

To increase bandwidth, cable companies used to have dual channel setups over analog cable (before digital). They used to have 'A/B' switches on the boxes and you could access double the amount of channels.

Re:Cable companies did something similar (1)

taniwha (70410) | more than 7 years ago | (#18914171)

Satellite companies do exactly this today - supporting multiple dishes for multiple satellites (or elliptical dishes with multiple LNBs) and switching between them on the fly as you switch channels - both DiSH and DirectTV do this. Just like the old cable TV plants used to have limited bandwidth (500MHz before they upgraded the current plant to 900MHz) satellite companies are limited to bandwidth per orbital slot (what freqs they can use and where) which they also work on with multiple spot beams on the same freqs - 2 transponders on the same freq but one aimed at the east coast with east coast local stations, the other at the midwest with their locals - while a 3rd transponder might send HBO and ESPN to everyone

Re:Cable companies did something similar (1)

biobogonics (513416) | more than 7 years ago | (#18915879)

To increase bandwidth, cable companies used to have dual channel setups over analog cable (before digital). They used to have 'A/B' switches on the boxes and you could access double the amount of channels.

When I lived in the Comcast service area, they actually had two coax wires entering the house. Without a cable box you would get one channel line up on A and a different line up on B. Both wires went into the cable box. The cable box assigned these signals to a different set of cable channels. IIRC I sometimes had to set a separate A/B switch on the cable box to select alternate channels from the cable line up as well. For example NASA was on one of the alternate channels.

Using just 2 is not all we could do (1)

DumbSwede (521261) | more than 7 years ago | (#18914033)

Two is actually pretty small. There was a system proposed back in 2002 by the acronym BLAST (Bell Lab Layered Space Time) that used up to 8 transmitters. As was noted in another reply if we go with a new transmission method we might as well go for a different encoding scheme like MPEG4 as well and double the available bandwidth again. We might as well go with more than 2 transmitters as well to more than double the bandwidth. This stuff does require A LOT of horse power in signal processing to tease the signals apart especially when you factor in multpath reflection (which is considered somewhat of a plus by BLAST as it make the signals easier to discriminate).

Broadcast antennas have to be in far-flung locations, but receiving antennas need only be directional and can be put virtually on top of one another. To speculate on increasing the bandwidth more we could polarize the signal as well. Throw in a little time-shifted redundancy to the error checking and you could have a very robust system even with electrical noise and lightning, though this would take some SERIOUS horsepower to decode the signals. But Moore has shown bandwidth is precious and processing power will increase. I suspect we could easily pack full 1080P 60fps in 1 MHz channels now, it would just be expensive initially. Remember bandwidth and signal to noise ratios are just competing tradeoffs. With a strong enough signal now you could do HDTV in 1 MHz with no changes to transmission method. Multi Antenna Multi Receiver adds a new dimension to multiplexing the signal in. AM multiplexes one dimensionally in amplitude, FM one dimensionally in frequency, digital uses both for two dimensions. Now we can add spatial multiplexing and to go even more over the top with polarization (though multipath makes polarization crazy hard to decode).

Complete Rubbish (1)

vk2tds (175334) | more than 7 years ago | (#18914169)

This is COMPLETE RUBBISH.

Basically once you add a second transmitter on the same frrequency the noise floor increases. Basically the first transmitter adds noise to the second transmitter, and vice vera. Some people will argue that if you know what the first signal is then you can subtract it to find out the second signal. Things do not work like this since the first signal is distorted in the ether, meaning that you cannot properly subtract it.

If there was the bandwidth available to have the two different transmitters on the same frequency (such as with CDMA), according to Shannon you could then just use the original transmitter and double the amount of data you are sending from it. This might mean doubling the power to get the same energy transmitter per bit, or it may mean that there is already enough power being transmitted thanks to error detection and correction.

This scheme is NOT MIMO. I think you would call it MISO or SIMO.

With MULTIPLE FREQUENCIES this COULD work. It is not that hard. On the receieve side you have two receivers and two buffers, maybe up to 1/2 second long. The data being receieved comes in inside packets. What you then do is split things at the transmit side so that each transmitter is sending half the signal.

But this is where things get fun. Each half of the signal need to be able to generate an OK signal by themselves. Think 128K MP3's Vs 64K MP3's. The 64K ones dound crap, but the 128K sound good. The trick is to define an algorithm to generate the 64's so that they can be combined to create a 128K that sounds good. Using Discrete Cosine Transforms this should not be too much trouble, for instance interleaving the data between the two output paths so that if only one is receieved you still have a picture....

Darryl...

Re:Complete Rubbish (2, Informative)

DumbSwede (521261) | more than 7 years ago | (#18914271)

Lets take a very trivial example of a two-antenna setup doubling bandwidth. If you have one transmission tower to your south and one to your north and you have directional antennas pointed at both you have multiplexed your signal spatially and nearly doubled your transmission rate in the same bandwidth. Multipath makes this harder too tease out, but that's what signal processing is for. Are you really telling me someone with two directional antennas can't tease out two different stations in two different directions? And that is with NO signal processing.

I'm pretty sure the people that made the BLAST demo system back in 2002 know more about this than you do. Yes there is a higher noise to signal ratio, but as long as our multiplexing multiples rise faster than this ratio then we are getting more information. Shannon's laws only apply to single channels, spatial multiplexing adds more channels as would polarization.

Re:Complete Rubbish (3, Interesting)

DrMindWarp (663427) | more than 7 years ago | (#18914275)

The BBC paper isn't rubbish. The Slashdot summary mangles things as usual so you need to go to the original source (dated December 2006 incidently). Even the paper itself says that this isn't news. The same frequency is used for two transmissions at but at different polarizations. So the noise floor is not raised to the levels that you might suggest (although originally orthogonal, reflections and refraction will cause some problems). Theoretically there are two independent channels and experimentally it works.

And if it breaks... (0)

Anonymous Coward | more than 7 years ago | (#18914635)

And if it breaks, you can easily fix it by reversing the polarity.

Re:Complete Rubbish (1)

newandyh-r (724533) | more than 7 years ago | (#18916275)

>> experimentally it works

Does it still work in marginal reception areas (like on the borders of 3 regions) and in unfavorable weather (either heavy rain reducing signal levels or high pressure allowing interference from very long ranges)?

Present Freeview has problems in places not 30 miles from the centre of London - especially
on the ITV channels that use the higher symbol rate.

Andy
(Rayleigh, Essex - on the fringes of London, Meridian, and Anglia areas)

Re:Complete Rubbish (1)

coastwalker (307620) | more than 7 years ago | (#18917213)

Orthogonal polarization of radio signals to increase the bandwidth works very well in the data transmission business that I work in.

Cue "socialism in action" neocon vitriol (-1, Troll)

Anonymous Coward | more than 7 years ago | (#18914219)

Every time the BBC is mentioned on slashdot, there it is.

Rupert Murdoch loves you guys, enjoy your Fox news! [outfoxed.org]

I've seen MIMO before... (1)

daybot (911557) | more than 7 years ago | (#18914261)

I had a MIMO Netgear wireless card and router once. They claimed it doubled the bandwidth and range of your WLAN on the same principle. I thought using two signals was kind of cheating, but it worked.

Here's one of the routers [netgear.com] .

Just like The BS of BluRay or HDDVD (4, Interesting)

Lumpy (12016) | more than 7 years ago | (#18914709)

Almost ALL indie makers are using divx on standard DVD for Hd content distribution. Hell they even MAKE set top dvd players that play DivxHD DVD's and they look fan-fricking-tastic. People like to toute you need insane bitrates for clean HD yet I see every day incredible looking HD content at DVD bitrates played off of DVD discs onto a 1080i projector to a 102 inch screen for customer demos in shop. WE demo HDDVD as well but the custom cant tell the difference.

You can get HD content on standard HD discs. a dual layer standard DVD can hold incredible 1080i content that looks fantastic on all HD displays available, but then it does not have DRM up the wazoo and is not making several companies morbidly rich with royalties.

This seems like something simple I half remember.. (1)

yellowalienbaby (897469) | more than 7 years ago | (#18914947)

If this sticks to adding a second signal at the same frequency at a different time offset, doesn't that make it time division multiplexing? Correct me.. I'm trying to remember like 15 years ago ;P

Re:This seems like something simple I half remembe (0)

Anonymous Coward | more than 7 years ago | (#18915111)

No, because TDM would mean the two data streams were transmitted sequentially in allocated frames in one signal. MIMO transmits two signals simultaneously, and the receivers have the job of using phase information to separate them out.

They have 8 MHz! (1)

TheSync (5291) | more than 7 years ago | (#18915179)

So I don't get the issue - DVB-T in the UK has 8 MHz channels. They have access to 22 Mbps using COFDM even at the most reliable QAM level.

Here in the U.S. we have 6 MHz channels for our terrestrial 8VSB DTV, we have 19 Mbps, and HD works just fine, thanks.

My understanding is that Freeview was SD only because the set-top-boxes had to be cheap.

Re:They have 8 MHz! (0)

Anonymous Coward | more than 7 years ago | (#18916517)

The difference is they'd like to have HD _AND_ be able to stuff 5 channels on the same frequency.

Why not use more channels per station ..... duh (1)

cheekyboy (598084) | more than 7 years ago | (#18915217)

There are more than 60 channels available in the spectrum, but there are NOT ever 60 TV stations.

Give every tv station 3 channels each so they can have a HD channel, SD channel, Repeat Channel. Along with that there are sub channels for each of those, but
thats like a much easier solution, which costs zero dollars.

But I forget, in this world, no one likes solutions that cost $0, because then no one can feed of the system and make more money out of it.

Re:Why not use more channels per station ..... duh (0)

Anonymous Coward | more than 7 years ago | (#18918369)

It's great that there are 60 analog channels in the US. However, the BBC's paper is neither about the US, nor analog TV. If you have a quick look at the wikipedia article on the Freeview service in the UK [wikipedia.org] , you'll realize that there are already about 50 digital TV channnels and dozens of radio stations crammed into the available multiplexes, which happens to be close to the maximum that DVB-T allows to fit into the spectrum currently available.

You comparison with 60 analog channels also fails, because with analog TV, no two adjacent transmitters can use the same frequency (plus some additional safety margin), or they will interfere with their signal, even if they transmit essentially the same signal, while DVB-T is designed as a Same Frequency Network that actually improves reception by using the same frequency for a given multiplex everywhere in the country. Have a quick look at the spectral efficiency [wikipedia.org] , any you'll note that DVB-T is already quite efficient. Can somebody supply the sprectral efficiency data for ATSC?

This technology exists today (1)

theoneknuckles (608389) | more than 7 years ago | (#18915637)

http://www.tv2me.com/ [tv2me.com]

They already sell boxes that tansfer HD signals from 1 location to another. Yes, the context is different but the technology is already on sale.

MIMO (1)

Nom du Keyboard (633989) | more than 7 years ago | (#18916127)

MIMO, sounds too much like GIGO.

Re:MIMO (1)

Hal_Porter (817932) | more than 7 years ago | (#18916617)

Your sig

> If Vista has such great scheduling and other improvements under its hood,
> why does it run slower than XP?

Because it's bigger, and so it swaps more unless you have loads of Ram.

Pity the consumer... (4, Insightful)

cardpuncher (713057) | more than 7 years ago | (#18917499)

Although there's been a relatively high take-up of Digital TV in the UK (about 19 million homes roughly split 45%/45%/10% DVB-S/DVB-T/DVB-C depending on whose figures you believe) there have been two distinct driving factors for this - one is consumer demand for a wider choice of channels and the other is government determination to shut down analogue terrestrial TV in order to make money from the spectrum space by auctioning it.

To a first approximation, the technologies are each presently operated by a separate single supplier: DVB-S by Murdoch's Sky TV, DVB-C by Virgin Media (formerly NTL/Telewest) and DVB-T by Freeview (a consortium in which the BBC is a main player).

The principle advantage of "Freeview" is that it provides a very simple marketing message: you buy a £30 box which plugs into your existing aerial (mostly) and TV and that's it. In exchange you get both a wider range of channels and protection against the "analogue switch-off".

That message is getting progressively less simple, though. Freeview has subscription channels (entertainment and sport) as a result of the legacy of the collapsed On-Digital/ITV Digital service that preceded it (needs box with a card slot). There is also some limited PPV (mainly porn) which interestingly requires no card but an access code obtained by telephone.

Furthermore, there is a significant demand from broadcasters for additional Freeview slots - recently there have been auctions for broadcast rights which have reached millions of pounds per channel. In order to prevent interference to analogue signals, the number and power of DVB-T channels is artificially limited at present leading to a seriously-constrained supply of channels. Partly this has been addressed by improving the encoding and stat-muxing process, partly by compromising on quality (some services average below 2MBit/sec video rate) but basically the available spectrum is full. Sky TV (which is also a content provider as well as operating a DVB-S platform) has 3 channels on Freeview which it has contemplated pulling and replacing with 4 MPEG-4 channels which existing Freeview hardware cannot receive in order to increase the number of channels it can provide on DVB-T.

So, despite the current constraints, DVB-T has been a success. The danger is that the capacity constraints will cause the platform to fragment as different content-providers try to deal with this and the consequent increasing costs by invoking a range of incompatible technical solutions and payment mechanisms.

It was originally believed that the closure of analogue TV would enable a significant increase in the coverage and capacity of Freeview, but the government has since made it very clear that it intends to auction off the spectrum space rather than simply re-allocate it to Freeview as it becomes available. Consequently, the future expansion of Freeview is in doubt and the BBC in particular is concerned that it might only be able to provide HD programmes on DVB-T by sacrificing other channels.

This technical research by the BBC is very much a desperate bid to retain the future viability of DVB-T, in which it now has a significant stake, in the face of current government policy. So don't assume it's the BBC's preferred option: the recent DVB-T HD trials used rather more mundane and easily-deployable technology.

At the same time, there are consultations on switching off FM radio (about which there is a serious outcry as the DAB alternative is also seriously constrained by limited spectrum space meaning that the audio quality of FM is actually better; one possible consequence of which is that FM is switched off and DAB is enhanced incompatibly with current receivers) and trials replacing AM radio with DRM (that's Digital Radio Mondiale in this context!).

In almost 90 years of public broadcasting there has historically been only one major technology shift in Europe that has obsoleted consumer equipment - the move to colour TV (which led, after a decent interval, to the shutting down of incompatible black & white services using other than 625 lines/50Hz systems). Suddenly, we're not only contemplating switching off analogue TV and analogue Radio but also undermining the digital platforms that are supposed to replace them (DAB and DVB-T) before there's even a mature marketplace for the new technology.

At a time when consumers are turning away from traditional media, it hardly seems like an intelligent approach.

Re:Pity the consumer... (1)

Dan100 (1003855) | more than 7 years ago | (#18921517)

You forget to mention the role of the regulator, Ofcom. They have already made it clear that they will not let the current success of Freeview be undermined by alternative technologies - they have effectively told Sky that their MPEG4 plans will be blocked.

The BBC and ITV recently announced Freesat, beginning next year, that will deliver their channels in HD via satellite. Looks like a good solution for those happy to pay a premium for HD.

Personally I believe the government will have to rething their plans to sell the analogue spectrum to mobile phone companies - they over-bid for the 3G licenses and are struggling to turn a profit with that technology; I do not see them keen to buy more bandwidth. But the government will hang on to the dream to the last - they want the money, bad.

As an aside, one downside of the UK's early lead in digital broadcasting is that we got saddled with MPEG2, as MPEG4 wasn't mature at the time the spec was developed.

Move to digital is bad enough (1)

gilesjuk (604902) | more than 7 years ago | (#18918355)

The move from analogue to digital has been bad enough. Many people have had to change their aerial, TV and purchase a box. I doubt many people will be willing to do this again anytime soon.

The tech savvy people might be willing to do so, therefore if this happens it should be in parallel to the existing system.

HD will be good news, but only if they don't compress it too much. The compression needs to deal with motion well too for sports events.

Er... (1)

VoidCrow (836595) | more than 7 years ago | (#18918401)

Isn't this called *multiplexing*?

Re:Er... (0)

Anonymous Coward | more than 7 years ago | (#18925179)

No, they aren't mingling two different programs in the same signal. They're actually sending different signals from separate antennas, with a receiver that can extract the signals (even though they're at the same frequency) because they travel via different paths and reach the receiver's separate antennas in different phase relationships.

Multiple-input multiple-output communications [wikipedia.org]

Oh Brother, I can see it now... (1)

bratwiz (635601) | more than 7 years ago | (#18924121)

Harold: Hurry up Martha, the cricket game is coming on the tellie

Martha: Oh Blimey Harold, you and your matches are gonna be the death of me.

Harold: Edwina, darling, are you ready for the game?

Edwina: Yes, Father, just climbing into position now.

Harold: Okay Martha, a little farther up and to the left..

Martha: (Mutters something unintelligible)

Harold: Now Edwina, my little flower, if you'll hold your antenna straight and turn ever so slightly towards the south, that would be lovely.

Edwina: Certainly Papa.

Harold: Martha! You old cow, I thought I told you to hold that bloody antenna still!

Martha: That's it Harold, I've had it. If you want anything more to do with this bleedin NEMO-- MINI-- NINI or whatever it is business, you're going to have to get up off your bloody arse and do it yourself!

Harold: How many times do I have to tell you, its MIMO!
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